Blogs

Very nice work by Ioannis Kedros here. It's an APM-compatible PDB that allows for all sorts of copter configurations, from X and + to Tri and even "spider". Here's more (via Hackaday):

I’ve start building multicopters (or drones if you like it better) five months ago! My first one was a scratch build tricopter based on a KK2.1.5 flight controller and three DT750 motors. Everything was made out of plywood and pinewood! It held excellent if you consider that I was a newbie pilot (still I am) and I had something like 3-4 crash reports per flight!

Two moths ago I decided to go a step further and make my second multicopter. This time it will look a little bit more professional than my previous one! To begin with it will be a quad copter, carry a better flight controller, reuse parts of the previous build (in order to lower the cost) and it will be able to stay above the ground longer.

And if you wondering how my first attempt to build a multicopter looked like, I am planning on making an article about that but you can have a sneak peak on the picture below

Yeah! It looked ugly but it worked far better that I was expecting! So, going back to the quadcopter now! Somehow I should address the key points that I’ve set above. First the looks of it!

In order to do that you can buy one of the multiple available frames out there. They come in different sizes, build materials, strength levels, colors etc. The only thing you have to do is to assemble the frame, add the components you want and you are ready to go. But there is a weakness point on them and this is not the price. Yes, you can find really expensive ones but they can go as low as $40 (without shipping).

The weakness point is the replacement components! After a crash (that you will have no matter how much experience you have), the replacement components are not available or the cost of them is high – compared to the full original frame. And you should stick to one shopping source as some frames are designed specifically for them, making the replacement parts only available by them!

Together with that, the design and making process by your own is way more enjoyable than just assembling some stuffs that came on the mail. And yes, I decided to design and make my own frame. Basically this is the point (or at least one of them) of the hobby! To design, make and learn out of this process!

I’ve cut some pieces of used A4 papers to the size of the electronics components I am going to use (I will get back to those latter). I even marked the position of the connectors to some of them. Then on a cutting matt I’ve translated what it was on my brain on a quick draw. Place all the papers inside to figure out if I have to increase a dimension or make something different that will accommodate my needs better.

After multiple design changes, moving around drill holes and measuring booms and different components I ended to something like this one

The main body of the frame will be made out of PCB material (like my electronic projects). The GPS module will be raised above the mane frame and the will be hold together with the plate drawn on the left side of the picture.

The booms will again made of 12mm pinewood (like my previous tricopter build) because of three things. They can handle the vibrations perfectly, I can cut them easily in different lengths making the quad more stable (or more agile) and most of all I can find replacements in any hardware store around me super cheap! No more ordering from abroad components thats fitting my needs 100%, waiting for backorders and paying expensive shipping and handling fees!

Having the first drawing on the cutting mat, I load the CAD program on my PC and start making the design a reality

It took something like an hour to design exactly what I needed (from start to finish). You should pay attention on the details if you want something good and that’s exactly what I did! I’ve print the file couple of times, then cut it with scissors and stick the two ends on top of the other to have a better understanding of what I was doing. Yes, an actual 3D item is way better than a 2D on your screen

I even placed spacers to the actual height I needed in order to imagine the finish product and exploit mistakes that will propagate on the building process

Then again fixing the mistakes, redrawing, printing, cutting and looking again all around everything. Even the Mobius camera position changed multiple times trying to figure the best placement

You can find multiple CAD drawing programs and some of them are really sophisticated. But as this is a simple PCB you can use just regular electronic design tools. Some of them are free as well like the PCBWeb. I’ve used this one couple of times with very good results so far!

Before to create the gerber files and send them for production I’ve also cut some paper strips that will play the role of the wooden booms. Together with that I’ve also used some water bottle cups in order to have a better understanding of the different multicopter configurations. With the PCB frame I was designing you can build an X quad or a “spider quad” or even a tricopter.

And now its time for the electronics! As I said above, I’ve used a KK2.1.5 flight controller before and I was really satisfied. Now I will go to something more sophisticated. An APM controller! This can accept missions, has various flight modes, autopilot, robustness and in general is order of magnitudes better than the simple KK.

You can buy one directly from 3DRobotics (they have an awesome company) or their distributors but this will come with a large price tag. And to able to unlock the entire APM features you also need peripheral components like GPS receiver, power module, telemetry module etc. If you consider the cost of all of those then the project will be a no go (at least for me)!

Since the APM is an open source project there are various “clones” out there. Some of them are super cheap with fake sensor ICs that and basically worthless while some others are professionally made and are contributing to the actual project too! One of them is this combo pack from HobbyKing

Basically it includes everything you need. The APM 2.7 flight controller with tis case, the 433MHz telemetry modules (there is also a version for 915MHz for the USA market), the Power Module, theOSD (on screen display), all the cables and finally good quality plastic cases

All the components are individual packed in smaller boxes and antistatic bags. A very good shipping method that will protect all the individual pieces from damages during the shipping. But the most critical component of all is the actual flight controller itself! And this is this one below

Some assembly required, as it comes in different pieces, that wouldn’t take more than 4 minutes. You will get five servo cables as well in the box. Something that will be handy latter when I will connect my 2.4MHz receiver with the flight controller.

Before you secure the case with the four included Philips screws remember to add the reset button. Sometimes is a good idea to add and a cotton paper above the pressure sensor as it is sensitive to light and wind. Regular you don’t have to do that if you are using a case but is always better be secure! This sensor will calculate the altitude my measuring air pressure differences.

And before the actual assembly process of the quadcopter I’ve did some proof of concept by fitting on the components! Donning that, hopefully I will identify errors the soonest possible and I won’t have to take everything apart. On top of that you can find the best possible routes for the cabling by doing something like this

This process took a while but after that I was ready to proceed with the final assembly. First I’ve cut the booms in length. I chose them to be 35mm long. This length will give the copter a good balance between stability and agility. And since they are made of wood I can cut them smaller easily – if I wanted latter

Then I’ve marked the positions of the holes in the booms with a pencil and a ruler and drill them with my old Proxon tool

Having the booms ready it time for the PCB frame. In the internal side where then booms met, I’ve placed the power pad. I am going to add all the red cables here. I flood the pad with some solder. Doing that I will be able to solder the cables easily and will help with the currents as well. The pad itself can handle easily high currents by itself. But as I told before, its better to be safe than sorry!

Then I add the cables that will go to the ESCs together with an extra cable for the LEDs and other peripheral components

Next a small piece of double-sided tape will hold the 433MHz Telemetry Module without any problem on the internal side of the frame. Using this module (supports the MAVLink protocol) you can have live feed of telemetry data on your laptop of your Android phone/tablet. Together with that you can set missions and upload them while the copter is flying

Next in line is the Power Module. This can handle up to a 10S LiPo battery, with a maximum current set to 90A, and give back result of voltage and current at any specific time. Together with that gives the proper power to the APM. It comes like in a not very useful setup for my configuration but the build quality is perfect

I’ve cut the protective plastic heat tube and the remove the power cable from both ends leaving exposed only the actual module itself

Then, I used my own cables in the length that I wanted and added the power module at the center of my frame. To protect it even further, a few turns of electricians tape used. A new heat shrink tube will be better idea but I was out of luck when ordering the components I needed

Four spacers around the PCB frame, some bolts to hold the booms together, a few cables and ten minutes later the frame was almost ready! I’ve placed internally the cables of the telemetry module as well as the ones for the power module and the OSD

I’ve also made a small low pass filter for measuring RSSI from the FrSky X8R receiver output. This is nothing more than a RC topology but helps a lot with the results

Going forward, a few bits and pieces placed together, some wire harnesses added to the frame and overall the process was going great without any bad surprises. Something that I was hopefully expecting because I’ve paid so much time in advance, designing the frame and selecting the appropriate components

Next, the four ESCs. Those are the F-20A from HobbyKing. As the name identifies they are capable of continuous 20A current. I don’t need anything close to that but I haven’t got any other better alternative

The wire ends are coming without any 3.5mm bullet connectors. You have to add them by yourself and that’s what I did (including the wires I’ve previously add the to frame itself)

The GPS module I’ve order is not coming with an embedded compass IC, a must have component for a multicopter based on the APM platform. The problem solved easily by using a compass module of mine. Its using the I2C protocol for communication between the sensor and the APM. You don’t have to change any of the code of the APM or do any hardware hacking at all! Its 100% compatible out of the box, plugs to the regular compass port and works exactly the same like using any other external compass

From a previous project I was working on I had some spare led strips. I thought that it would be a good idea to add some of those on the front booms. The original thought was that those would help me a lot with the orientation of the copter.

Those strips are super bright but outdoors in day light and few meters apart from me are just like there is nothing there! On the other hand those are wonderful in night flying!

There are a couple of free output ports on the APM flight controller and I decided to make a small circuit to control the lights. Nothing fancy! Just On/Off! I’ve used a mosfet and a 10K resistor from the gate to the ground and add them in a small prototyping board

After the testing phase I add some hot glue to make the circuit more strong and then place it inside a small heat shrink tube.

I am going to use this quadcopter as an FPV platform as well (have a look here for my FPV setup). Despite that there will be a Mobius camera on board I will use a second camera just for the FPV. The reasons are mainly two. The small board camera can handle the light variations way better than the Mobius and there is no latency problem as well!

The second camera is the Sony Super HAD CCD from securitycamera2000. I am very satisfied with this one and it’s the one that has the best reviews from the FPV community

There is a small lip around the camera for mounting purposes. I’ve removed it using a plier and then add the camera to a plastic enclosure for better protection during crashes. It adds a few grams in weight but its not important for now

To do that you should first remove the lens and the lens holder and then insert the camera inside the case

Its a good idea to secure the crystal oscillator as well. There is some bad feedback on the net about this one. Just solder again the pads with a soldering iron and then add some hot glue or even a few drops of epoxy (but I am not recommending it)

The plastic enclosure comes together with this metallic base. I am going to place the camera lower in the PCB frame (between the two PCB plates) and that’s why I should do a few cuts to it!

Then, two cable ties will hold the camera securely in the frame. During a crash the cable ties will brake protecting the component.

In general, cable ties are a must have if you are building a multicopter. They are offering great durability and also are adding a weak point at the place you want in the copter. Doing so, the weak points will break first – absorbing mush of the crash force and saving the expensive components!

Before place the ESCs on their final position and secure everything in place I should change the firmware of the Atmel chip inside the ESCs. I am going to use the SimonK one that offers greater refresh rates and better stability over the default firmware

To do this upgrade, just cut the plastic of the ESC like the following photo, add some solder and place six flying wires

You can also make a probe like tool but I thought that this is a useless step for my needs. The actual programming tool is the USBasp AVR Programming Device (the stick at the lower end of the photo) and you can find it in the previous link. This is not only useful for just those ESC but for Atmel microcontrollers in general!

After the completion of the firmware upgrades and the overall assembly I’ve add some landing feet close to the tips of the booms. Those are made from old antistatic DIP IC tubes!

Finally depending of your transmitter, you should follow the calibration procedure for the ESCs and then program the APM with the latest copter software. There are so many options in there that this post alone couldn’t even scratch the surface. But there is a full explanatory web page here that will answer your entire question about setting up your APM

And yes! My first quad copter is ready to fly!!!

As you can see, the quad is in the “spider” or “dead cat” arrangement. This is helpful when you are using cameras, especially if those are having wide-angle lenses. The booms of the copter are out of the viewing angle making a more immersive experience of flying. The negative side of those are that you have to spend some more time configuring the PID values for better stability

But as I said above, the frame plates are design to accept easily quadcopters in the regular X configuration, together with tricopters as well! The only thing you have to do is to change the position of the booms!

And you can go from a “spider” (or “dead cat” if you like) quad

to a super agile with great yaw authority tricopter

all the way to a regular X type multicopter

And yes, I am super excited about this project! It flies well and has all the wow factors of the APM flight controller, like the return to launch, waypoints, autopilot, super stability etc

 

After a few fun flights with the copter I desired to move the front booms to the regular X style. And in case you want a few second of low altitude loiter flight with it then enjoy the next video! I am going to add more info about this copter soon! Stay tuned!

 
 

More photos os the project here

For any other info, suggestion or anything else that you want (even if you just want to say hello) drop me a mail at: john_kedros@hotmail.com

I have a few spare PCB frames and in case you want to have one of them and make your own scratch build multicopter then have a look on the Surplus section