"From The Ground Up" : One persons experience with DIY drones and ArduPilot - Part One


This is a Blog I decided to start chronicling my experience in the hopes that I might make it easier for newcomers to get involved with these amazing machines we call UAVs!


First let me tell you a little about myself. I live in the Adirondack Mountains of upstate New York, in the United States. I'm shown above with my new Senior Telemaster. (Anyone who has followed any of my posts knows the lengths I have gone to to obtain this plane. That's another story!) I am a Network Administrator with a Composites Manufacturer providing Manufacturing capabilities to medical, industrial, and recreational vendors. I have a background in CAD, and CNC Machining. I have had a lifelong love of aviation since I was a small boy growing up in the suburbs of Boston Massachusetts I have always had an interest in electronics, computer programming, and model aviation. First came Radio Control.in about 1989 I started flying a Great Planes PT-40 I purchased at the local hobby shop. Next came an introduction to robotics about 2 years ago with a kit my son got of the Parallax BOE-BOT. This led me to the Arduino platform. Then last January my brother-in-law (a really good guy) gave me a gift certificate to Sparkfun for my birthday! When browsing Sparkfun's web store I came across the ArduPilot, the rest is my experience chronicled here.


First lets talk about my choice of airframe. I wanted a large, stable platform, with a large interior. My "mission" was aerial photography/videography, OK lets face it really I just want to have fun! Anyway , you need to look at what you want to do with your project when deciding on the proper plane to purchase. If you are looking to burn holes in the sky, then a high wing trainer isn't a good choice; if however you want a gentle stable flyer to take aerial photos (as I did) then a high wing trainer is a good choice Many people here like the Multiplex Easystar. The choice is yours but take some time and decide what your "mission profile" is and then seek the advice of others if you aren't familiar with a particular model. While I'm talking about the airframe let me make a basic recommendation, when we all learned to ride a bike, we didn't hope on a 10 speed and just take off down the street never looking back. Rather we started with a beginners bike, and training wheels.If you haven't flown Radio Control before, do yourself a favor and contact your local club and find yourself an instructor. You'll be glad you did!



Shown in the picture above are the two main boards of the ArduPilot system. On the left is the ArduPilot board on the left, and the ArduIMU+ V2. The ArduPilot is the "brain" of the system that integrates all the sensor data, from sensors such as the ArduIMU, and what output is necessary to obtain the desired performance from the aircraft. The IMU is an option as opposed to using thermopiles. Both systems monitor the attitude of the aircraft by sensing the aircraft' orientation in space. The sense I got was that the IMU provided better stability than the thermopiles in mountainous terrain (such as where I live).




. Shown here to the left is the uBlox GPS module.

This module has proven to be very popular, and in my experience very easy to work with. If you've spent any

time reading threads around here you'll probably realize

it does have a few weak points, the antenna connection

is very fragile; so care must be taken to make sure to protect it. The connector on the back of the module is

also very fragile so care should be taken with it as well.

You can see the uBlox adapter, sold at the DIY drones

store, hidden behind the uBlox module. I would suggest using some hot-glue to hold the two parts firmly

together.


Crash protection is highly recommended with this very fragile item. I have heard several methods of protection, including shrink wrapping the parts together, However I have also heard reports of reduced numbers of satellites

obtaining a lock as the temperature rises, so it's important now to insulate it too well.


There are a several supported brands and communications protocols to choose from. With a wide range of features and a wide range of price as well Another important thing to consider is sampling rate, most GPS units come with sampling rates in the 1Hz to 10Hz range. At the low end 1Hz, a slow moving RC car might be able to use a sampling rate this low, but it's not very practical for a plane, at the 10Hz end you could have good data for a fast moving plane. For me 4Hz was great for a slow flying high wing trainer. The choice yours.



No matter what hardware you have, you'll need to consider how to mount them in your airframe. I wanted to have a system I could adjust.

The ArduIMU needs to be parallel to the ground in level flight. Unfortunately it's not easy to calculate exactly where that will be without some actual flight testing. Most planes will fly at a slightly positive AoA (Angle of Attack), therefore the ArduIMU would need to be mounted at an equivalent NEGATIVE angle in order to be parallel to the ground.


The picture on the left shows the installation of my mounting system in my Senior Telemaster. At the back you can see a long strip of Velcro, this acts as a hinge for the plate to pivot on. The 4 Velcro tabs are to attach the removable AP system panel from the mounting plate. The socket head cap screw at the front of the mounting board allows the adjustment of the pitch, positive or negative, of the mount.


While not necessary to make an adjustable mount I think it will allow me some greater degree of precision. If you are using something like a Multiplex EasyStar, it wouldn't make sense to go with something this elaborate.





This picture above shows how I protected my uBlox module with a foam cradle. Notice the cable connected to the uBlox adapter, it goes AFT to the main payload bay where it is connected to the ArduIMU.

The picture below shows the assembly after it was slid in place between the battery tunnel and the fuselage side.




This picture shows the battery monitor adapter, and associated cable I made to attach to the battery monitor on the Ardu Shield V2. If your not going to use the optional telemetry you can ignore this item, as it's unnecessary.


Because I am using a 6s1p LiPo battery pack whose nominal pack voltage is 22.2 volts, well over the 15 volt maximum input to the Ardu Shield V2 board, I needed a way to modify reduce the voltage "seen" by the analog input (AN5).


The battery monitor circuit on the Ardu Shield V2, uses a voltage divider to drop the voltage down to a value AN5 can read without causing damage to the board. Using the formula: Vout = (R1 / (R2 + R1 + "X") * Vin, I was able to determine the value of "X" necessary to bring the voltage down to 5 volts. For me that was 164k ohms. This is only necessary if you are using a voltage greater than 15 volts at full charge. Always calculate based on the full maximum charge, not the nominal rated voltage.



In this picture I've added the Ardu Shield V2. This enables us to add the differential pressure sensor (black box in the middle on the left) for airspeed sensing, and the battery monitoring capability with the voltage divider. It simply rests atop the ArduPilot board. I haven't installed the pitot tubes yet, but the will go out on the wing at least one prop diameter out on the wing. It's important to note here that you should install both the active and the static tubes outside the airframe, and out of the disturbed airflow behind the prop. If you are using a pusher such as with the Multiplex EasyStar you can simply install these in the nose of the aircraft.


Many people using fast moving airframes with IMUs don't bother using the airspeed sensor, however in slow moving airframes, or airframes that fly near stall speed, the Ardu Shield is recommended.



Here in the picture on the left you can see the ArduIMU on the left, the ArduPilot (red board) on the right, and the Ardu Shield on top of the ArduPilot.


They are all isolated from vibration using two different types of foam. You can see a 1/4" thick layer of neoprene foam on the bottom, and a 3/4" pocketed closed cell blue packing foam.


The idea is that the different foam densities protect the electronics from vibration at different frequencies.That's the idea at least, we'll see how well it works in practice.


At the top of the payload bay you can see the battery monitor cable coming from the forward compartment visible at the top of the photograph. Towards the front on the right hand side, you can see where the momentary push-button reset switch is installed through the fuselage side.










This picture shows how the adjustable mount is used to level the cradle the IMU is mounted in. First I check to see that the wing saddle is
level, then I move the level to the cradle, and adjust the mount to
bring the mount level with the wing saddle.



Well, that's it for now! In Part Two, I'll install the pitot tube in the wing, load the code, run through some ground tests, and finally begin some flight testing!


Good luck with all your projects,


Nathaniel






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Views: 2004

Comment by Josh Villbrandt on August 15, 2010 at 8:25pm
Solid installation! The Senior Telemaster sure does provide a lot of extra space.
Comment by John Prince on August 15, 2010 at 9:44pm
I hope that is a non-conductive foam! I'd had to see any of that equipment short out!
Comment by Theodoric Hrodeber Roland Alia on August 15, 2010 at 10:03pm
Where can i get some of that foam?

Moderator
Comment by Alex on August 15, 2010 at 11:19pm
A good read, looking forward 2 the next one. And seems like a realy good and easy way to mount the components in the foam :)
Comment by James Turner on August 16, 2010 at 2:49am
A great turotial. Looking forward to part two.
Comment by Troy Reabe on August 16, 2010 at 5:23am
Nice,
I know we used "Hard Disk Drive Anti-Vibration Screws" to mount the IMU and that worked for us.
Comment by Albert Lorincz on August 16, 2010 at 5:33am
Nice write-up. Thanks for taking the time.
Comment by Tom Hastie on August 16, 2010 at 5:51am
If I didn't know better, I'd say that the first picture looks like the NEAT fair grounds near Downsville N.Y?

Ever been to NEAT?

Tom
Comment by Ho-Chung Chang on August 16, 2010 at 8:01am
The pictures you put provides good ideals to place the AP and how to wire in order. Nice job.
Comment by Rana on August 16, 2010 at 10:09am
Wonderful work done, Caner !
I really liked the way you are achieving the neutral in horizontal and vertical axis by means of spirit levels !

Keep it up !

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