How to optimize the choice of your UAV's radio frequencies

1. Introduction

As we make our UAV fly we use multiple radio frequency bands for different uses : RC control of the craft, eventual telemetry band, eventual video downlink band (FPV or camera monitoring), GPS.

An issue we have all already encountered are interferences between used radio frequencies.

So how could we try to optimize, in a simple manner, the choice of our UAV's various radio frequencies (rc control, telem, FPV, ...) ?

2. Basic radio wave principles background

Radio waves are sinusoidal signals or a combination thereof. Any radio signal can be reconstructed by an addition of sine waves of various amplitudes and frequencies. Alternatively there are mathematical functions we can use to decompose (analyze) an apparently very complex signal in a number of pure sine waves (of various amplitudes and frequencies), so as for example to extract from the lot those who have the largest amplitude. 

The point is that a radio signal is never a pure sine wave propagating on a unique single frequency.

Here come the "harmonics".

Every radio emission does not only emit on its base frequency but also on a number of "harmonics". Harmonics are radio waves propagating at a multiple frequency of the base frequency. The following figure, copied from the amateur radio wiki, illustrates what harmonics are:

(if you'd like more info google "radio frequency harmonics" to find the radio amateur's wiki site)

The issue with harmonics is that they are not on your mind when you decide to use channel 5 of your FPV transmitter. You selected channel 5 on your FPV Tx because it seems to be apparently far enough from all the other frequencies you have on your drone; so it should be right ? guess what : not good enough.

Because of the "upstream" harmonics you might still suffer from interferences that will impact your RC control range, disturb your GPS reception (bad HDOP) and or create lines and interferences in your video downlink.

The most annoying harmonics are mostly the ones resulting from the emission of a lower base frequency having an impact on higher base frequencies. An "impact" means that an harmonic's frequency is too close to another base frequency we want to use.

3. And so what ?

So it becomes quite a burden in practice to define for example which FPV Tx channel should I best use, because thanks to these harmonics we can't simply compare the base frequencies of rc control, telemetry, FPV, GPS. We must also consider all of their harmonics !

Don't worry, except if you're a genius,  you should normally not be able to compute which FPV channel is best, just like that, on top of your head.

So we need either to write down on paper all of the upstream harmonics of all the base frequencies and then compare all of these values manually to find what is the optimum frequency combination.

The best combination is the set of (base) frequencies that maximize the frequency distances (in mhz) between not only these base frequencies themselves but also all of their (upstream) harmonics.

You might ask : up to which harmonics should we compute ? 3rd ? 4th ? 5th ? Well that depends on your base frequencies. For example, if you use very high frequencies such as a FPV 5.8Ghz band, then you will have to compute the harmonics of your 900Mhz telemetry link up to the 8th order.

4. A tentative tool

I tried tonight to produce a simple excel calculation tool (there was nothing on TV) that will automate the computation of which is the best choice for your FPV channel, in function of your defined RC control, telemetry and GPS base frequencies.

I chose the FPV channel as the variable to optimize in the equation, because in practice this is the only radio component on your drone for which you can choose different channels (GPS is fixed, Telemetry is quasi fixed, RC control is fixed in its frequency hopping band).

This is a screenshot of the excel tool :

You enter your own frequeny data in function of your configuration : the yellow cells are the cells where you enter your data.  All frequencies are expressed in Mhz.

You get the ability to enter up to 10 frequencies to analyze (to choose from).

The "Results" frame shows you a color coded computation result for each of the 10 frequencies :

-Green means the best frequencies,

-Orange means it is ok but not optimal (there are other frequencies which are better to use),

-Red means a bad frequency to use because it interferes with another radio component on your UAV.

Optional parameters allow you to define two things:

-Minimimum wished frequency distance (in Mhz) : this is the minimum amount of frequency distance between two frequencies that is required to avoid interferences (100 mhz by default).

-Max capping value for distance calculation : this is an internal computation parameter, just leave it at 100.

I tried this method (manually until this tool) for myself to choose my FPV freq among the 9 available channels and could observe indeed a clear improvement on my GPS HDOP stability (I often had an issue that my 1.3Ghz band FPV would disturb the GPS HDOP). I am curious if this method/tool could also improve your own setup; in any case let the community know what your improvement results are !

You can download the excel tool here: HDFreqoptimisationV1.zip

Any suggestion for improvements welcome,

Hope it will help,

Cheers,

Hugues

How-to guide: Pixhawk auto camera trigger (without CHDK)

1. Introduction:

If, like me, you are not using a canon camera, you then do not have access to the CHDK canon firmware which provides advanced automation scripts to automate your camera trigger on your UAV.

There exist on the market other great alternatives for all camera brands (some of them are functionally richer and simpler to use than CHDK). As an example in this guide, I will use the "Stratosnapper V2". This is a little smart thing that allows you to trigger any camera brand (Sony, Canon, Nikon, etc) by many ways : infrared, cable, LANC, etc.

If you'd like more details on this little marvel read here.

I personally prefer the "IR trigger mode" the best because it does not require an extra cable connected to your camera, which is a must when you are using a brushless gimbal. It supposes of course your camera supports an IR trigger function; I thus assume the use of a Sony NEX5 in this guide, widely used for aerial photography among UAV'iers.

Then there is another obstacle for many of us : how does Pixhawk work to trigger such a triggering device in auto mission ? There is a lot of posts on diydrones.com about how to do this with APM, but not much yet on the recent Pixhawk. Therefore this guide will try to document it.

I will end the guide with a practical auto photo taking mission example (making sure it really works!).

2. Parts and hardware connections:

Let's start by a general hardware scheme showing all the required parts and general cabling:

The parts are:

2.1 Pixhawk board

One or more of the 6 AUX ports can be used on Pixhawk (AUX1=RC9, AUX2=RC10, AUX3=RC11, etc.):

In this guide I chose port 2 which corresponds to AUX2 as is illustrated in this detailed view :

By default, only the three first AUX ports can be used (1 to 3, or RC9 to RC11).

To trigger the IR device, we need a servo output (PWM signal), not a relay signal. We will see later what parameters configuration is required in mission planner screens (we can for example also configure 6 AUX ports as PWM outputs ; more details later - let's finish the hw description first).

2.2 IR trigger device

Here an illustration of "stratosnapper" with its inputs/outputs:

You may notice two servo leads are connected on the input side of stratosnapper.

This is one of the most important point in this guide : a servo lead must be used to power the IR device from a BEC (5V in this case); the power provided by the second servo lead coming from Pixhawk AUX2 port DOES NOT provide enough power to make it work !!!

Either you have powered the Pixhawk ouputs rail with a BEC and you are fine, either you must provide a separate BEC power to the IR device. This is also true for any other type of device you will connect on Pixhawk : DOT NOT expect pixhawk to power these devices (and certainly not servos as we already knew in the context of the previous generation flight controller, APM2.x).

Stratosnapper works with a servo lead on one of its 4 servo inputs (yes, you may control stratosnapper from 4 different inputs, isn't that great ?). The servo inputs may be various things : push-button, stick, two way switch, three way switch, etc (all configured by a GUI configuration utility from your PC via usb).

And it ouputs on a IR cable to trigger a IR led that must be placed in front of your camera IR sensor:

2.3 IR Led positionning and camera gimbal

The IR led works perfectly, even under a bright sun (verified on the field); it works even quite faraway from the sensor (no problem 5 inches away of the Sony NEX5 sensor) and works fine in any orientation versus the sensor.

Shown here is a picture of X8 Mr Grey (formerly known as Mr Red when was used with APM; my wife had only grey flower pots I could snatch to cover the new Pixhawk & electronics). The Sony NEX5 is held in a 2-axis stabilized brushless gimbal (NEX5 not shown...used to take this picture).

Here below a zoomed view of the IR LED positionning and gimbal:

Gardeners & farmers are notoriously UAV friendly; after getting a flower pot to protect your electronics, snatch also some green gardening wire which is very handy to shape your IR LED cable, so it is correctly positionned in front of the camera's IR sensor.

3. Software and parameters configuration:

3.1 Mission planner:

We need to configure Pixhawk to output a servo command on AUX2 (RC10) to trigger stratosnapper which will in turn trigger the IR LED which will in turn trigger the camera. And this needs to happen automatically during an auto mission.

How do we do this ? By using the CAM_TRIGG_DIST function or by using a programmed DO_DIGICAM_CONTROL command. In this guide we will only document the CAM_TRIGG_DIST function.

The CAM_TRIGG_DIST function will command your UAV to take picture everytime it has moved a certain distance (in meters). This is very useful to take pictures at precise distance intervals during geomapping missions or photogrammetry missions.

To configure CAM_TRIGG_DIST, go in mission planner, click on config/tuning to open the full parameters list. In this list you will find three parameters to configure:

-CAM_TRIGG_DIST : defines in meters the distance between two camera triggers. For an auto mission, leave value at zero. It will be changed automatically during the mission by a DO_SET command, to avoid taking pictures before and after the useful parts of your auto mission.

-CAM_TRIG_TYPE : defines if you want the Pixhawk AUX output used to control a relay or to ouput a PWM signal. In the case of an IR device we need a PWM servo signal, so we set it to a value of zero.

-CH7_OPT: internal firmware parameter. In this case, it does NOT correspond to the CH7 of your receiver. You must set it to a value of 9 to indicate the firmware that it must do a camera trigger to the AUX ouput (which will be defined in the camera gimbal setup screen).

Next, we need to define to which AUX ouput we want this servo/PWM signal produced. To do this, open "Initial setup", then "Optional Hardware", then "Camera Gimbal":

In the shutter drop down list, select which AUX port you'd like to use (RC10 = AUX2 in my example).

Then do not forget to adapt the "pushed" and "not pushed" PWM values that will trigger your IR device (stratosnapper in my example). Tune also the duration to the required button pressure duration to trigger your camera (for a Sony NEX5, I set it to 10 = equivalent of 1 second button pressure).

3.2 IR device configuration (stratosnapper V2):

Every IR device comes with its own configuration method. Stratosnapper comes with an ultra easy GUI interface to define which PWM values will trigger what port. It is explained in this video:

(http://player.vimeo.com/video/67660032)

4. Concrete application : test auto mission, applying all of the above

Finally lets' apply all of the above in a true auto mission on the field,

I configured this test auto mission as an example:

To create this auto mission, we can use a very convenient "SURVEY" function of mission planner. You start by drawing a polygon of the zone you'd like to photograph.

Then you right click on the map to select "Survey(Grid)":

It will then show you a configuration screen that will allow you to define which camera make/model you are using and other rather self explanatory parameters (like how much overlap you want between pictures, lens size, etc). The tool will then automatically define for you which is the best CAM_TRIGG_DIST parameter! :

After clicking on "Accept", you will get automatically a list of waypoints starting with a "DO_SET_CAM_TRIGG_DIST" command that will set the distance in meters between two camera triggers during your mission. It ends with another "DO_SET_CAM_TRIGG_DIST" to set the parameter back to zero (stops the shooting).

DO NOT forget to add at least a waypoint (take -off) before and another waypoint (land or RTL) after the last waypoint.

After this is done, after you have passed through your checklist, after you have got all of the authorizations, etc, -> you are then ready to arm, flick the auto switch and off you go!

The above test auto mission lead to this result below. It is a stiched panorama of about 15 pictures; shown here as a reduced thumbnail image (because the full size image is too large at about 107 Mbytes). Click on image for better resolution:

I hope this will help you in your own auto-photo-shoot missions!

Cheers,

Hugues

Hi,

1. Introduction:

Pixhawk 3DR kit is delivered by default with a 4S maximum power module. For those wanting to use 5S or 6S or higher voltage batteries there is currently, to my best knowledge, no “how-to” guide for the Pixhawk board. I therefore decided to document it for others who might need it too.

For those who would like the same “how-to guide” for APM 2.x , here is a link I wrote a while ago:

http://www.diydrones.com/profiles/blogs/powering-your-apm-drone-or-how-not-to-shutdown-apm-like-the-us

Pixhawk comes standard with three (redundant) ways to powered it up:

1-USB : not used to fly obviously; just useful on the ground for connection on a ground station software.

2-The power module port accepting a maximum input voltage of 5.7volts (and will not get destroyed up to 20 Volts input)

3-The RC input pins. Will accept a maximum voltage of 5.7volts also (and is also protected up to 20 Volts)

This guide assumes a use of Pixhawk’s power module port which provides not only a way to power the board but also the pins to measure current and voltage values of the main battery.

This guide assumes a use of a 6S battery in combination with a Attopilot current & Voltage sensor board. This Attopilot “power module” replaces the 3DR 4S limited power module. The Attopilot board comes in three flavors: 45 amps, 90 amps or 180 amps.

The choice of the right Attopilot board (45A, 90A or 180 A) will depend on your motor/props combination: take the Attopilot version that has the smallest amps capacity above your max multicopter current consumption. However we will introduce in this guide a way to use the 90 amps Attopilot board to measure up to 150 amps, still using Pixhawk’s power module port.

2. Attopilot description:

An Attopilot board provides three wire soldering pads to solder : a current measurement wire, a voltage measurement wire and a ground wire. See picture below:

Attopilot 90A support up to 50Volts for a maximum of 90A. However the resistor specifications exceed the 90A limitation which makes it possible to use it for measuring 150 amps (we will take this as a assumed max current as our example for the rest of the explanation).

The datasheet of Attopilot specifies that the Voltage measurement wire outputs an analog voltage of 63,69 milliVolt per Volt. Similarly the current measurement wire outputs an analog voltage of 36,60 milliVolt per Volt.

So for a 6S battery the maximum analog voltage values will be:

-For voltage measurement: [min 0V -  max 1.6V]

-For current measurement: [min 0V – max 3,3 V]

3. Pixhawk power port description (pinout):

Reusing the excellent pixhawk infographics published in the wiki, the image shows circled in yellow where the power port is on the pixhawk board.

The power port is a so-called DF13 connector with 6 pins.

The six pins of this connector are assigned in the following order, starting by the red wire on the leftmost pin:

Power Port Pinout Description:

• 1- Vcc (5V input)
• 2- Vcc (5V input)
• 3- I (Battery current measurement analog voltage input)
• 4- V (Battery voltage measurement analog voltage input)
• 5- Ground
• 6- Ground

4. Wiring Case 1 : to measure up to a maximum of 90 amps

The connections between Attopilot and Pixhawk are shown in the illustration below:

We have added an optional BEC in the illustration that would be connected to the Vcc and Ground wires of the power module. It is optional as Pixhawk could alternatively be powered via the RC inputs.

4. Wiring Case 2 : to measure up to a maximum of 150 amps

The connections between Attopilot and Pixhawk will integrate resistors to be able to measure up to 150 amps.

Indeed the ADC of this power port on Pixhawk has a range of 0-3.3V. This means that for the maximum true current of 150 amps, we want the current analog wire of Attopilot to output maximum 3.3Volts (as it is the case in case1 for 90 amps max without additional resistors).

Note : this part has been updated with a resistor scheme simplification (only one resistor to add in parallel rather than the originally classical R1, R2 resistors divider) thanks to a contribution of Bo, a diydrones member who analyzed in depth the Attopilot circuitry.

So we will build a small resistors divider on wire 3 (current measurement) & wire 5 or 6 (Ground) as follows:

The Attopilot current measurement output masks a circuit that contains an existing output resistor called Rl. According to the Attopilot datasheet, the following equation links to measured current I (called MeasuredCurrent in the equation), the output analog voltage for current measurement Vout, and an existing Rs resistor in Attopilot:

 What we want is to get Vout = 3,3 when Current =150 amps. To do this we will add a new external resisto (Rx) in parallel with the existing Attopilot Rl resistor, so that the new resulting Rl resistor (called Rl’) must be (knowing that Rs = 0.5Mohm as per Attopilot specs):

Therefore we can calculate the Rx resistor value we need to add in parallel as follows:

So, Rx must be ~ 110kohm to have a Vout at 3.3V when the measured current is 150 amps.

You can choose another max amp output (but I would not advise higher than 150 amps with the 90 amps Attopilot, otherwise use the 180 amps version instead) and calculate the resulting Rx resistor

As a result, when the current is 150amps, Vout will have value of 3.3Volts.

5. Mission planner / parameters configuration in battery monitor screen:

In the battery monitor parameters screen, you can manually select which current and voltage sensor you are using. In the present case, you will select the power module and modify the following parameters to make the mission planner voltage and current display match the real values (measured using a wattmeter for example). The explanation below is an extract from the Arducopter parameters list.

Battery monitoring (BATT_MONITOR)

Controls enabling monitoring of the battery’s voltage and current

Battery Voltage sensing pin (BATT_VOLT_PIN)

Setting this to 0 ~ 13 will enable battery current sensing on pins A0 ~ A13. For the 3DR power brick on APM2.5 it should be set to 13. On the PX4 it should be set to 100. On the Pixhawk powered from the PM connector it should be set to 2.

Battery Current sensing pin (BATT_CURR_PIN)

Setting this to 0 ~ 13 will enable battery current sensing on pins A0 ~ A13. For the 3DR power brick on APM2.5 it should be set to 12. On the PX4 it should be set to 101. On the Pixhawk powered from the PM connector it should be set to 3.

Voltage Multiplier (BATT_VOLT_MULT)

Used to convert the voltage of the voltage sensing pin (BATT_VOLT_PIN) to the actual battery’s voltage (pin_voltage * VOLT_MULT). For the 3DR Power brick on APM2 or Pixhawk, this should be set to 10.1. For the Pixhawk with the 3DR 4in1 ESC this should be 12.02. For the PX4 using the PX4IO power supply this should be set to 1.

This is a parameter to adjust to match the real Voltage value with the displayed mission planner value.

Amps per volt (BATT_AMP_PERVOLT)

Number of amps that a 1V reading on the current sensor corresponds to. On the APM2 or Pixhawk using the 3DR Power brick this should be set to 17. For the Pixhawk with the 3DR 4in1 ESC this should be 17. Units: A/V.

This is a parameter to adjust to match the real Voltage value with the displayed mission planner value.

There you go! I hope this will help you configure your pixhawk with higher than 4S batteries.

Cheers,

Hugues

(For those who'd like to read PART 1, it is here )

Pixhawk params were tuned (but strangely enough I do not find anymore the Low_Volt param I had previously on APM. I only find a way to enter this parameter via the battery monitor GUI - weird), ESCs were calibrated, the FPV POD was bench tested succesfully, the Accel, compass calibrations are done.

I still need now attach propellers , then run a compassmot, calibrate current & voltage and I will be good to go !

Stay tuned for maiden flight...

As a follow up of my first tentative to build a suspended FPV quad , here come design Mark II. It uses mostly wood instead of aluminium. The whole blog consists of pictures with integrated comments on them. Enjoy...

End of part1... Next will come the assembly of the propellers protection system and of course the maiden flight. Stay tuned...

Hi,

Here is a short build log of a new quad frame design. I had three objectives:

1-Reduce vibrations. We are all striving to reduce vibrations in our multicopters especially if we want to use ardupilot and make nice stable FPV, pictures or movies.

2-Make it light, but strong enough to embark fpv and small AP cameras,

3-I am tired of the classic sandwich center plates design we find in all multicopters, consisting of two center plates holding the arms by compression. Not only this compression design is heavy but it also transmits vibrations by design to the plates carrying electronics and cameras/gimbals.

I also liked the idea Forrest Frantz used in his light tube construction, where there are no center plates, just two carbon booms crossing.

I did not have any carbon tubes in my basement but I had U shaped aluminium booms. Then came this design idea : let's avoid the center plates by crossing the two U shapes booms. This is done simply by sawing four slots that are as wide as the U side's thickness and half the U side's height in length.In such a way the two booms "merge together" as shown in the picture, as if I had an aluminium cross in one single piece.

To reinforce the cross I added a screw and bolt at the center.

The result is a perfectly rectanguler cross, very rigid and light.

Next : to prepare where the motors will be placed. The objective is to make a platform up to 10 inch propellers that will not blow on the suspended electronics platform. Therefore I hired my son to cut 10 inches disks:

I did not have a carbon fiber plate so I reused what I had, a piece of birch wood, 5 mm thick. This is light enough and rigid enough for my need. I will later replace this birch wood plate by either a carbon fiber plate or a laminated balsa plate.

The paper cut disks allowed me to match the propeller space with the suspended plate to be cut in the birch wood piece:

After positionning the paper disks, I drew the shape of the center plate carefully, checking everything is squared. An X quadcopter is assumed here.

Afterwards, the center shape was cut and put aside. No holes were yet drilled as first the suspension system had to be designed and placed on the aluminium booms.

I used anti-vibration dampers from Secraft. They are very nicely designed as have silicon rings in two perpendicular directions (unlike the expensive cinestar similar system).

 The challenge here is to hang these Secraft dampers so that the plate will be leveled. However with the way I mounted the two booms, I had the issue of having two flat arm sides facing down and two arms with the U opening facing down. To solve this I cut a piece of boom (at least the length of the Secraft damper, about 7 cm) and screw it upside down as shown in picture below:

And it looks like this once everything is screwed on:

At this stage the birch plate, as seen on picture, is cut.

We place the plate beneath the cross to mark the holes that need to be drilled. This way we are sure to get it right (by measurement you are always off due to errors and/or imprecisions during the build)

Here is the final result:

This system provides an isolated mount plate to carry everything :  APM, cameras and all of the electronics in total isolation from the vibrations sources (motors/arms).

It gives enough rigidity not to confuse APM's sensors but provides still enough dampening. I was surprised how the dampening is not too soft. If needed there is even the possibility to replace the red soft silicon rings by the harder black ones from Secraft.

Thus far the total weight is:

=537grams. So adding 150g of APM+electronics, 80 grams of ESCs, 400 grams of motors and props, I should be around 1kg without battery,  for a 40 cm motor-to-motor quadcopter, with I expect excellent vibrations dampening results.

I must now order some motors and ESCs after a few simulations on eCalc.

Any suggestions for a 40 cm quadcopter motor/props combination ? (max prop 10/11 inch). I could use the classic 3DRobotics 800KV/10 inch APC. But It would be nice to use maybe lower RPM if the weight is low enough.

Some of you might remember a previous blog post last summer about my trainer 3DR quad going into the trees.

As a result I broke the 433Mhz telemetry module and antenna, as you can see on the picture above (SMA connector was ripped off the board).

This module was in my drawer since then. At the price of such a module I really did not want to throw it away.

On the other hand I wanted to try using bluetooth to connect my Nexus 7 tablet (with Droidplanner, thx Arthur!) to my X8 Octo. I use it for AP and I want to have my tablet and my TX radio together (not possible to frame a picture with a laptop and control the drone at the same time).

So here was an idea : Build a new antenna for the broken 3DR module, then connecting a bluetooth module to this 3DR module.

1-Let's start with the antenna built :

Due to the damage of the 3DR module, it was not possible to solder a new SMA connector. Plus I do not like very much the standard 433Mhz duck antennas. In these duck antennas we have a quarter wave antenna.

I decided to build a half-wave dipole antenna. Here are the parts to build it:

-A a regular servo lead (>200 mm long). Any other wire will do. it must be thin enough to be inserted in a plastic antenna protective tubing

-A 300 mm long (or longer) antenna plastic tubing like these:

-Solder & iron

-Hot glue

-a Ruler (>30 cm)

Start cutting a 300mm long plastic tube. Mark its middle. Use a hot solder iron to melt a hole in the middle. This hole will be used to pass the servo wires through each half of the tube.

As it is diffciult to pass soft servo wires in such a tube, you can use a small rigid iron wire (take the one your wife uses to attach the roses in the garden...) on which end you solder the tip of the servo lead. Then pull the servo wire through the tube.

It should look like this afterwars:

At this stage the two servo wires are extending out the tube.

We now need to cut each servo wire to measure exactly a quarter of a wavelength (i.e. total dipole length is a half wavelength):

Based on this relation between the speed of light (c), the radio wave frequency (v) , the wavelength is:

So for a radio wave of 433Mhz, the lambda calculation gives (in MKSA standard units, sorry for inchies):

So we have theoritically to cut the servo wires to have a total length of 34,62 cm.

HOWEVER, there is a bit of wire length extending outside the tube (to the 3DR module) AND

the plastic tubing contains carbon. Carbon is an electricity conductor. Therefore carbon based plastics have an impact on radio wave frequency tuning. A rule of thumb : the more plastic (carbon), the more the theoritical length should be shortened. I went for an horizontal length of 30 cm (+ about 1cm of wire outside of the tube, so a total length of 31 cm). 

Thus, take your ruler and measure 15 cm on each side of the hole (300 mm total length) and trim both ends.

Final step : solder the two wires on the 3DR module. At this stage we have to solder one servo lead (half of the antenna) to the ground, and the other servo lead (the other antenna half) to the antenna port of the module.

Be careful when soldering that the wires should never touch!

On the picture, the red servo lead is soldered on the ground port of the 3DR module. The white servo lead is soldered on the antenna port.

Now it is time to check is this home made antenna is worth something. I compared two configurations as follows:

1-the 3DR module with its default duck (quarter wavelength) antenna (and a FTDI cable to the computer on which I'm running mission planner).

2-the 3DR module with this home made dipole (and a FTDI cable to the computer on which I'm running mission planner)

Of course the physical setup/relative positionning between the telemetry modules & antennas remains identical in both cases.

1-Chart with standard duck antenna: RSSI measured between [170-190]

2-Chart with home made dipole (half-wavelength) : RSSI measured  >=200

 The home made dipole wins !

(The second part on the bluetooth connection follows below)

Hello,

AMAZING and THX GUYMCCALDIN ! Guy is the guy, a member of this community, who built a 3D printable APM suspension system. As you see on the hover graph above, for my large X8 octo, I get vibrations between -0.03g and +0.03g (to compare with the vibrations I got just using zeal tape +0.15g and -0.15g ).

So this is a factor x5 improvement on vibrations reduction !

Here attached a picture to show the details on how I mounted APM on this suspension system. You can get it at shapeways; I have no personal interest in shapeways, nor in the business of Guy but I think we should encourage people like him who build such perfect tools for our hobby:

here : http://www.shapeways.com/model/1388904/omnimac-apm-mount-v1-5.html?li=search-results&materialId=6

Until now I had an ugly piece of paper taped on the side of my T9X radio to remember the flight modes configured on the 3 position F.mode in combination with the position of the Ail switch. Not only was this ugly but it was not quick enough to read when you needed to switch modes (especially when you 're looking in panic to find the right switch combination to RTL...)

I saw a great customization trick in one of the 3DRobotics IRIS video where they had customized a sticker around those two switches to indicate the various flight modes.

I decided to reproduce this sticker and give the SVG file to the community so you can print your own (and change text/colors). To edit the SVG you can use the "INKSCAPE" program which is completely free and very easy to use:

This is how my custom sticker looks on my T9X:

Once printed, use an exacto knife to cut the holes, that's it !

Attached the SVG file, have fun!

Hi,

It is very hard to tune a brushless gimbal. Even the best tutorial found on the internet are hard to replicate because we all have different setups : cameras are different, hardware is different, Voltage input to the alexmos board is different, etc.

Let's share our PID settings to constitute an as big library of settings that works as we can. Either you will have the same configuration as someone and you can just copy the settings, either you are close to a published setup and then you can start from there to tune your particular gimbal.

Please post:

-Gimbal hardware : make or model

-Camera : make and model (specify also if you have particular lenses as the weight changes with differetn lenses)

-Brushless motors : make and model, number of turns

-Power , P, I, D for pitch and roll axis

-an eventual youtube video to show your best results with these settings

My turn:

-Gimbal from kamkop.de

-Camera : NEX5R with 16-50 lens

-Brushless motors : GMB 5010 - 150 turns (copies of RCtimers I think)

-Battery to alexmos board : 4S

-ROLL : Power : 120, P : 20, I : 0.17, D : 18

-PITCH : Power 50, P : 17, I : 0.15, D : 15

Result video: https://www.youtube.com/watch?v=fw7Z-iPGiKQ

Your turn now !

Figure 1: general wiring diagram for an 8 motors
& APM drone

Practical build blog: powering your APM drone (or don’t  brownout an APM like the US gov would):

Hi,

1.      Foreword & Introduction:

I would like to introduce a build blog on a critical aspect of a drone’s assembly: how to power your drone & APM. The objective of such a build blog is to be practical. Wherever possible in this blog links will be provided to get the described components. This blog is merely a synthesis of gathered advices I received from many helpful people within this drone community (particular thanks to Randy, Bill, Forrest and many others who taught me lots and are still teaching me lots of stuff)

As a topic I chose “Powering the APM” as it is in my opinion one of the most critical aspect you should care for in assembling your drone. I’d probably be not too far from the truth if I said a majority of drone incidents & crashes are related to power issues or bad wiring/testing (brownouts, wiring mistakes, ground loops, wrong voltage/amps dimensioning, etc.).

Experienced members in this community will find this blog obvious. The blog does target people at early stages of drone build’s learning, like the state I was in a few months ago. It was very hard to find all bits and pieces of information to get a global detailed picture. Let’s hope this blog can help others in their build.

This blog will be written in successive posts as it is a fairly long subject and my time is quite limited. It will also allow others to interact and add complementary input between my posts; to be enriched progressively.

2.      Powering an APM Drone:  Objectives and Constraints?

Cf. figure 1 above illustrates a general wiring diagram for powering a typical drone. It illustrates 8 motors and ESCs but would remain applicable for fewer motors (battery voltage would probably go down to 3S or 4S for quad motors).

First, what are the objectives ?

-As illustrated in figure 1, a first objective is to power ESCs and associated motors with a high power source in terms of amps/volts, able to sustain the maximum throttle consumption and voltage required by the motors and propellers configuration (with a margin is even better). A good way to dimension this for your own setup is to either measure real values on a test bench (not so practical because it implies you would already know what to do and what pieces to buy), or more practically to use an online tool which is not so bad to give rough estimates here : http://www.ecalc.ch/xcoptercalc.htm?ecalc&lang=en

Another good information source about motor testing is an excel sheet with test bench measurements done by Forrest. Forrest, if your read this, could you post your excel sheet please ? Thx.

The eCalc tool asks you to enter your number of motors, the all up weight of your model, the battery type, the ESC capacity in amps, the motor’s brand and model, propeller’s type and model. You then click on calculate and the tool displays at the bottom 5 results columns. The most interesting columns for our exercise are “Motor@maximum” and “Motor@Hover”, because it will give you the consumed amps at maximum and at hover, the voltage and throttle % to hover (ideally should be at 50%). If you are under dimensioned or over dimensioned (under optimized), the tool will display some warning messages. The tool allows you thus to check that all the parts are dimensioned correctly to function together. For example, assume the tool tells you that your hover power consumption is X. However your motor’s maximum power specification is Y. Verify that X < Y. If not change the motors or use smaller props or lower pitch props (same verifications to do with max amps, max volts, max RPM, etc).

I have used this tool to produce a table for a particular motor brand, RC tiger motors here: http://www.diydrones.com/group/arducopterusergroup/forum/topics/tiger-motors-propellers-combinations-for-an-heavy-lift-octocopter?xg_source=activity

-A second objective is to power all other components that are not part of the high power gear, namely APM and all other bits and pieces around it: a receiver, a telemetry unit, a GPS/compass module, etc. Optional servos that are require to power for gimbals for example ARE NOT low powered items; they CANNOT be powered through APM but must be powered directly from the high power source (via UBECs). As far as electronics is concerned, the objective is to feed a very stable and reliable power source at 5 volts (there may be other specific FPV/OSD components that require other voltages such as 12v or 7v but I exclude these components from this blog for now). This second objective seems apparently easy to reach but it is actually a very sensitive and tricky one as we will see in more details later.

Second, what are the constraints ?

We want to reach above described objectives within constraints:

-The power chains must be reliable and as light as possible (typically if we can use the main battery for everything, it will be lighter than if you need a separate battery for every component).

-There is better one main battery as the power source for everything (which avoids different ground references, avoids potential ground loops, makes your build lighter). So we have a constraint to split the power chains to different voltages/amps (main voltage for ESCs and motors, and 5V for APM and associated electronics). These LIPOs are power monsters people should be aware of: they are capable of delivering very high amperage (e.g.: more than 100 amps in my X8 drone application) at a set voltage between 3S (11.1V) and 6S (22.2V) for most drones. If you make the math, we speak here of order of magnitudes of between 1 to a few kilowatts of power!

There is a link you may consult about batteries common brands discussion here: http://www.diydrones.com/group/arducopterusergroup/forum/topics/6s-battery-comparison-on-some-most-common-brands-turnigy-zippy?xg_source=activity

-The main power source must feed high amps and high voltage to the ESCs+motors. We have a constraint to measure both amps and voltage fed to the whole drone as it is a critical piece of information you want to check continuously on your GCS (or goggles) while flying. It would be insane to fly without such real time information, as you do not want to let your copter fall out of the sky once your battery becomes empty.

An assembly constraint is thus to wire every bits and pieces in such a manner that your current and voltage sensors measure the TOTAL (SUM) of all amps consumption. If you use two batteries , do obviously not connect your sensors after one of the two batteries. Another classical mistake is to connect items pumping current and voltage from the sensors wires!

Avoid connecting items in such a way you create ground loops. Connect everything in a STAR topology, with the center of the star connected right after the current/voltage sensor on the high power leads/wires. As it is difficult to visualize your wiring in the practice, make a wiring diagram of your connections and check it out (like I did on figure 1 for example)!

As you will notice on figure 1, I kept a ground loop with the ground wire of the Attopilot module, but it is impossible to connect otherwise. It is one of the weak point of Attopilot sensor usage, unfortunately. Some posts have been done about this here : http://www.diydrones.com/forum/topics/attopilot-volt-current-sensor-significant-parasitic-ground

-At the same time the main power source must be derived to feed a set of sensitive electronics at 5 volts. APM has a constraint to be fed at a voltage between 4.6V minimum and 5.25V maximum. If you are below the minimum voltage, your APM will brownout. If you are above you will fry APM. However it is not so easy to get a stable 5V source as the load varies. Take a look at the picture below that illustrates how unstable an APM 5V power source could be (and there is even worse):

Figure 2 : Bad Vcc illustration

Figure 2 shows a 5V power source from a switching BEC regulator. The measured voltage on this BEC was 5.14V unconnected. We observe from this log picture that once connected the voltage immediately drops down to 4.9V which is not good. Further a strong variability of the voltage between 4.6V and 4.9V is observed. This brings the voltage close to the power limit of APM’s power requirements with a risk of brownout. We will see later in this blog how this problem was solved.

3.      Tested solutions to fulfill powering objectives and constraints:

3.1-Battery solution:

For the main battery, I chose a dual battery setup to reduce total cost of ownership (and increase max amp capacity). In an objective to increase flight duration to the maximum I looked initially at high capacity batteries such as maxamp 12.000 mah or equivalent from other brands. In a 6S voltage these batteries are awfully expensive (sometimes more expensive than a complete 3DR RTF kit!). Therefore, I found best for me to use two smaller 6000mah batteries. It weighs the same or even less than a 12.000 mah battery, it costs a third or a fourth of the price if you get a turnigy nanotech or zippy brand. There comes a physical challenge to install multiple batteries on a drone without ruining your possibilities to attach a camera gimbal underneath, and without ruining your possibility to use a protective dome for electronics on top. So for my octoquad, I’ve custom cut a dual battery holder CF plate that screws on the center plate, providing two side platforms left/right to fix the two batteries (thx VulcanUAV for their help!):

It looks like this once assembled on the drone’s frame:

After choosing the battery , we need to think about how to wirre in a STAR TOPOLOGY.
I found the easiest way to do this was to use a power distribution board, like this:

I personally chose to use a 250 amps capacity power distribution board from VulcanUAV here : http://www.vulcanuav.com/accessories.html

 It is much better and safer than using cable solutions, for example like this:

3.2-Power distribution board

I will now start to detail this power distribution board, based on figure3:

Figure 3 : Power distribution board placement assembly

More to follow (digest this first:)...

UPDATE Oct 28th : Parts 2 and 3 were added on page 1 and 2 of this blog.

As the third and last episode of these summer flights in France, I played around with a great little quad, from Walkera, the Ladybird. It looks like a toy really but it is a full fledged quadcopter with amazing compacity:

-the controller board integrates all of the electronics  : ESCs, Radio receiver, Accelerometers (6-axis), etc

-in a tiny form factor: the board's size is a little bit more than 1,5 inch WxL:

This is truly amazing. You can program it in the equivalent of our APM "Stabilize" mode or "Acro" mode.

In Acro mode you can do flips and rolls! (i broke quite a lot of shells => foresee replacement parts).

The idea of completing your quadcopter/hexa/octo existing arsenbal with such a small addition is obvious for me: you get the best training platform, ultra resistant to shocks, and much better than a simulator. It really behaves like a real quad int he flying sensations (very sporty one). With this I learned to fly my more expensive and serious drones in different orientations, something I would never had tried with "expensive" material. (and I do not like the artificial simulators to train). Further it is half the price of a software simulator !!!

It flies and sounds like a drone (you'd think a big insect is flying near you) : when we will have killed all of the bees, we should have some robotics substitutes... The attached video shows some fun with it.

I have made a test of a NEX5 brushless gimbal used on my X8 Arducopter platform.

The video is raw and has not been post-processed.

For the more technical among you:

-Arducopter APM2.5 platform, firmware V3.0.1

-2-axis (tilt/roll) Brushless gimbal for Sony NEX5 from altigator.com (it is in fact a (re)labeled RC timer aluminium gimbal), using white labeled GBM5010 brushless motors (150 turns, able to hold 500gr cameras) 

-Sony NEX5R with 16-50mm objective. This big sensor compact camera delivers 50 frames/sec video and 16 mios pixels pictures. It can be radio remote controlled through APM and a IR trigger (i used stratosnapper)

It is a second episode of the X8 series of Summer Flights in France and will soon be continued with a third...

This is a summer flight video of my "Mr. Red" Arducopter, configured as an X8.

Although the arducopter X8 setup is the least efficient in terms of number of motors/lifting power ratio, it is a super stable platform for aerial photography and aerial filming.

For the more technical:

-APM 2.5 running v3.0.1

-Tiger motors 3110-17 (700Kv)

-3DR 20 amps ESCs

-Smaller props on top motors: 11x4,7

-Bigger props on bottom motors : 12x3,8

-Frame built based on 3DR, VulcanUAV and other home built/exotic parts

I will soon post a second episode showing filming results you can get with this platform together with a brushless gimbal embarking a NEX5 camera.

Menu of the day:

A quadcopter's failed auto mission as our apetizer, followed by our main course the flyaway of the chef, & our special search and rescue mission for dessert.

The auto mission was more simple as that you could die:

1-take off to altitude 40 meters

2-loiter undefinitely (waypoint 2 was never reached, the gremlins attacked before)

Specs of trainer quad (thank god that was not my main aerial platform): APM 2.5    firmware 3.0.1 custom 3DR based frame 880Kv motors, 11x4.7 props, 4S 4500 mah

My god they reproduce

Is it bad doctor ?

Hello,

In the DIY series, I built a Boxrover on the basis of a plastic food container, APM2.5 with GPS and telemetry, 2S Battery and a HK cheapo frame for the body (monster beatle, it comes with a 25 amps ESC and a brushless motor:

I removed the ugly HK cover to replace it with a plastic box. It is a nice soft plastic, resistant to shocks and easy to drill with a dremel like tool.

A small keychain HD camera is fixed with velcro. The box itself is fixed with dremellized holes, hot glue and a velcro band all around the frame.

One of the point to pay attention to is the parameters in the ardurover that govern the accelerations and speed. Indeed with thesse cheapo frame from HK, the spur gear is in nylon and can easily be shredded (like I did after the first ten minutes...buy replacement parts immediately)

I used version 2.42 of the ardurover firmware.

I tried a simple auto mission with one waypoint and that does not work well because the autopilot must probably calculate the trajectory based on B-splines (although I did not check the code) : instead of going in a straight line to the waypoint , it makes all sorts of arabesques.

However, as expected from bi-splines, when adding lots of waypoints, it goes all right.

I have a very bad video of my first auto Boxrover mission (sorry for the bad video quality, using a phone in the hands of my son, and he is not equipped with a brushless gimbal, yet :)

Hello,

I am trying out different DIY, cheap approaches to be used as alternatives to expensive carbon plates. When you need strong, rigid plates that are light enough for a Quad, you're stuck with either fiberglass which is not so light and has the unconvenience of being  not so rigid (except in higher thickness wich is than even heavier), either with carbon plates that have other disadvantages : price, it is a conductor material and therefore gets in the path of radio waves. They are also difficicult to shape, cut and drill (plus their dust is toxic).

Therefore, I was wondering how we could find alternate materials, which would replace the above described GF/CF plates by having a good compromise on these criteria : to remain light, strong and rigid, to be cheap, to be able to home build them with basis off-the-shelve components, to not interfere as much with radio waves as full carbon plates.

I experimented previously succesfuly with a DIY plate, baptised Hugues'plate in the following excellent post of Frantz :

Frantz post about building copter with tubes

The result was this:

In this first version I used two thin balsa plates, with in the middle a sandwich of epoxy, and a cotton fabric (cotton provides very strong fibers in all directions, therefore reinforcing the linear fiber pattern of balsa wood). It gave pretty good results.

However the fact of having the external sides of the plate as balsa wood was not a good idea, because we all know in the boom theory and practice that the most external layers of a boom support the tension of the load. Therefore to obtain a more rigid plate, you need the most external layers of the plate to be stiffer and stronger than the inner core.

Solution is easy : reverse the sandwich.

This is what I tried herebelow but experimening other materials. I used still a 1.5mm balsa plate as the inner core. Then on both sides I applied first some UHU epoxy:

This is slow cure epoxy. Very messy but very strong. Even stronger when you heat it up during the drying phase. What is also a good trick to apply such epoxy in thin layers on a plate : mix well the two components in a heat resistant cup. Then take the air dryer of your wife (I already took her cotton fabric so she's getting used to my experiments) and blow hot air on the mix. You will get a very liquid exposy that you can apply with a paint brush quite easily on large surfaces.

Secondly, I applied kind of pultruded carbon "fabric", it is less than one mm thick and comes in rolls covered by a plastic sheet, very convenient to apply in laminated construction, without the epoxy coming through on your fingers:

The result is a balsa plate covered with this carbon laminated thing. Problem is that these are fibers aligned in one direction and it is very brittle if you flex it perpendicular to the fiber's direction.

Therefore I applied a second layer of a kind of very light cotton fabric that we call here "Japan paper"; it looks like this:

As I did not have anymore epoxy, I reverted as a second choice to wood glue to apply this fabric. I used that one:

I like this wood gllue because it is very fast set and quite strong. Much more than the usual white wood glue.

The plate was then put under pressure for a night.

The final result looks like this (close up of the sandwich):

Now some numbers:

Dimensions are : 2,9mm thick - 13 cm by 14,5 cm.

Mass is 26 grams.

Volumetric mass (Density) is thus : 0,47 grams per cubic centimeter.

Rigidity is excellent and I will use it as an attachment plate between my X8 and my brushless gimbal.

Here is a short build log of how I converted my APM2.5 Quad to a X8 Octo quad.

First I dismounted everything which is always a pain, especially when you have to disconnect these little bastard DF13 connectors. By doing so a few times already (it is my fourth build with same APM...), I had finally to replace the telemetry cable by a new one. Oh well not too bad...

I could scrap the base 3DR power distribution board which was not meant for 8 ESCs and I got instead a vulcanUAV PDB which allows for (way too) many ESCs and 250 amps as seen on this picture.

I soldered also a 3DR power module and connected a Y battery splitter to be able to connect two batteries in parallel.

I prepared the motors. These are 3110-17 (700Kv) tiger motors. I love 'em. As you notice on the picture, I took my lessons from the first builds : every part is now tagged, either with a number, either with a color sticker, in order to know what motors goes on which arm and which cable connects to which ESCs (and so to keep the correct spin direction).

These motor cables are quite long so I decided to braid them, giving an extra EMI improvement and shortening them a bit:

By dismounting the quad, I noticed that the four screws holding the motors to their motor plate came a little bit loose, due to vibrations. I do not want on these parts to use blue loctite because it is a a nightmare to unscrew (for my next fifth build...). I used instead some hot glue as seen there:

(yeah, I know, I had to mix different screws, not pretty but who cares, nobody sees the bottom motor plate anyway...)

Then I laid on the floor the bottom plate, passed the braided motor cables in the arms, connected all the motor cables to the ESCs (thanks to the color stickers), placed the cables as neatly as possible. I shortened the ESCs power cables to the minimum in order to gain a clean placement. I soldered directly the ESCs to the PDB (no risk of bad connectors). By the way, a lesson I've learnt when you solder so much on a board : get a very high power solder iron otherwise the heat latency of the board gets unmanageable (and gets worse for every ESCs that is added).

I decided to keep only one BEC power cable from one of the ESCs. The other are snugged under the PDB (No, I did not cut them, you never know what will be needed in a next build)

Then it was time to work on the APM itself and all of its accesories : receiver, beeper, telemetry, GPS, etc. In order to get vibrations as low as possible, I tried what you see on the picture : APM is mounted on a small plate about 3cm above the center plate, with rubber dampers-white nylon spacer-silicon damper (what you see between the two metal washers).

This carbon fiber plate is thus never in direct contact with the rest of the frame. APM itself is placed on four corners of moongel (I put a balse plate between the carbon plate and APM to raise it a bit so that APM does not touch the metallic washers).

APM is pressed gently on the moongel with two rubber bands. Later on, after I attached the GPS, I also improved a bit the vibrations levels by adding moongel between the GPS on top of APM and the APM case, so that the APM is sandwiched between two layers of moongel.

 This is how the Electronics look once finalized and all cabled.

Then I took the beast out for a short maiden flight as seen in the video herebelow:

Hello,

In a search to film with a HD camera I made different tentatives with all kinds of materials and devices to avoid the famous "Jello" effect. I tried moongel, I tried elastics with foam, I tried rubber grommets...everything lead to Jello!

I though I would be unable to get rid of it until I got the following idea, inspired from military strategy: not to try to block an ennemy wave at first defence. Rather, build successive defences in cascade : a bit of the attacking wave goes through the first line of defence to the second line; a bit of the bit of the wave goes through the third line, a bit of the bit of the bit of the wave dies on the third line, etc. These cascding lines of defence will utimately get rid of most of the vibrations to the camera. That was the idea, so how to apply this on a quadcopter ?

First decision was to attach the camera gimbal on the bottom plate because I think intuitively that is the best place to start with less vibrations (alternative was to use the sonar mount between two arms, but then I am way to close to the vibrations sources).

First line of defence, the bottom plate

Thus the bottom plate had to be the first anti-vibe line of defence. As shown in the picture below I decoupled this bottom plate from the rest of the frame with 8 M3x20 rubber dampeners (instead of screws):

Second line of defence, transversal booms to hold the camera gimbal:

I purchased a one meter U shape aluminium boom (10mm x 10mm) that I cut in two pieces of the length of the bottom plate plus a few extra inches to hold a camera plate (will be shown in next picture). These two booms are attached in parallel to each other and screwed on the bottom plate with two M3x10 rubber dampeners.

Third line of defence, the camera plate:

The camera gimbal is suspended on a aluminium plate using the two parallel booms. This aluminium plate is attached to the booms with four M3x15 rubber dampeners as shown below,

The extra trick is to keep an extra rigid link between the camera gimbal and the frame. For that I reused an idea that was posted previously on this forum and bought at servocity the famous servo blocks. This is not ideal to avoid jitter of servos in mouvement but this is the best I found until now. Because now the best would be brushless gimbal and that shall be my next project (waiting to do the investment, it is not cheap).

So with all that I did a quick test flight that you can see in this youtube video. This video was not corrected nor transformed. You will see that except mouvements of the gimbal (i flew in stabilize with lots of pitch/roll corrections), the video is absolutely without any Jello.

Mission accomplished.

By the way, the music of the video is a credit for Jake Wells who inspired me.

CU,

Hugues