nnChipmunk - 800mm
Part 6 - How to Design DTFB Planes
This is my latest project that I wanted to take on just for fun. I was curious to see how well a quadcopter could perform as a mobile rocket launch platform, so I decided to build one and test it out. This is a scratch build quadcopter with a motor-to-motor of about 900 mm. I wanted it to be big and heavy so that I could have inertia, if anything, to combat the forces from the rocket launch. However, I also wanted it to be durable in the event of a crash. The end result is an insanely overbuilt quadcopter that works surprisingly well for launching rockets.
A full build log as well as a parts list can also be found at:
I began the build by laying out all the components for the quadcopter. In the picture below you can see the frame, motors, propellors, ESC's, batteries and miscellaneous hardware for assembling the frame.
The motors were AX-2810 750KV motors rated for about 400 watts on a 4s battery. I chose to use them with 12" propellors and that seemed to be an ideal configuration for this build.
The batteries I used were the 2200 4s Zippy Compact series. They were rated at 25C discharge and were relatively inexpensive compared to the other 2200's on the market.
The center plates were designed by a friend of mine (PolakiumEngineering) and then lasercut from 3 mm plywood. The small rectangular tabs beside the center plate were motor mounts also lasercut from 3 mm plywood.
For the arms on this quadcopter I chose to use 1" square poplar wood. Each section was 36" (900 mm) long and I used the entire 36" section for the arm.
I began the build by notching the two arms so that they could slot together in the center. To ensure the notches were of equal dimensions, I lined up the two arms and then drew some parallel lines on the surface to use as a guide for cutting.
I used a small saw to cut half way through the wood and create the notch on both arms.
Once the nothces were made, I used some sand paper to even out the edges and obtain a nice square fit.
I clamped the two arms together and added a small bit of wood glue in the middle to make produce the strongest bond possible.
Next, I began drilling out the arms for mounting the motors. I used the rectangular motor mount tabs as a guide to do this. I placed one tab on top of the arm and one tab on the bottom and then passed my drill through bothof them to get as straight a hole as possible.
This is what the arms looked like once the holes had been drilled out.
I secured the motors onto the arms using 35 mm long M3 bolts. I also attached the propellors onto the motor to give me a good estimation of how much room I had to work with on the upper surface of the quadcopter.
This is what the bottom of each of the arms looked like once I had mounted the motors using the M3 bolts and the motor mount tabs.
I then moved on to securing the center plates and repeated the same drilling/guide process I used for the motors. The bolts for the center plates were M5 so the holes needed to be slightly larger.
Once the holes were drilled, I passed the M5 bolts through the top side.
I then secured them to the underside of the quadcopter using M5 locknuts.
This is what the top of the center plate looked like oncer all the bolts had been secured in place.
And this is what the overall quadcopter looked like at this stage in the build. Having the propellors on allowed me to visualize where I could mount any extra equipment like cameras and microphones.
I then moved on to soldering on all of the bullet connectors to the motors.
I soldered all 12 of them on and the added heat shrink.
I used zipties to secure the bullets to the underside of the arm so that I could keep it out of the way of the rocket blast.
I added a few more zip ties here and there to clean up the wiring.
Next, I moved on to preparing the ESC's for the build. I chose to use the HobbyKing F-30A ESC's for this quad because they were cheap and readily available.
I stripped off all the heat shrink and began desoldering the signal wires.
Once all the wires were desoldered I took this opportunity to flash the ESC's with SimonK's latest firmware.
I then cut my own 9" long sections of wire to traverse the lenght of arm between the motors and the center plates.
I soldered bullets and added heat shrink to all 12 of these wires as well.
I then soldered all these wires to the ESC's.
And I finished of the ESC's by sealing them up with some black heat shrink.
Next, I went ahead and connected the bullets between the ESC's and the motors. In order to consolidate the mess of wires, I used a staple gun to secure the signal wires to the underside of the arm.
Several staples down the length of the amr did just the trick and held everything in place nicely.
Once the wires were all stapled down, I mounted the ESC's onto the center plates and secured them with zipties.
This is what the top of the center plate looked like once the ESC was mounted. Again, I was trying to keep the top side as sparse as possible to minimize the damage caused by the rocket exhaust.
This is what the arms of the quadcopter looked like once the ESC and wires had all been mounted.
And this is what the whole underside of the quadcopter looked like at this stage in the build.
The next major step for me was configuring a power distribution. Usually I would just clump the wires together and solder them that way but for this build I needed to keep the center of the quadcopter as empty as possible to allow room for the controller board.
To solve this problem, I came up with the idea of using thin power rails to distribute the power from the batteries.
Initially I was going to use these copper bus bars as the rails and secure them to the underside of the center plate with M2 screws. However, it soon became apparent to me that soldering to such a large copper surface is very difficult withouth excessive amounts of heat. Because of this I decided to switch to using thin strips of copper-clad PCB which were cut to the same dimensions as the bus bars.
Once I had cut the copper-clad PCB, I covered one strip on black heat shrink for ground and the other in red heat shrink for power.
I then went ahead and started soldering the ESC's to the power rails. This was actually very easy, as all it involved was cutting away a small patch of heat srhink and then soldering the cables onto the PCB.
This is what it looked like once all the ESC's were soldered into place.
Next, I moved onto preparing the flight controller for mounting. For this build I chose to use the CC3D because it is highly configurable and I happened to have one on me at the time. I used some 35 mm M3 bolts and some nylon spacers for mounting it to the quadcopter.
The bolts went in easily and held very well. As you can see, having the power rails as opposed to a large solder joint saved me a lot of space between the CC3D and the center plate.
The next step was soldering on leads for the batteries. For this I just created to XT60 pigtails (two because I would be running two batteries in parallel).
I cut out some notches in the power rails and tinned them with some solder.
I then went ahead and soldered both my pigtails onto the power rails in a parallel configuration.
Then, just to clean up the wiring a little bit, I wrapped the ESC's BEC wires around the power and ground connections.
Once that was complete, this is what the underside of the quadcopter looked like.
And a little bit closer.
Also here are few last things which I didn't get a chance to document with picutres. I added a relay system to the quadcopter which I used to trigger the rocket launch. It wasn't anything fancy, just $5 relay I ordered from HobbyKing. It was triggered by a spare channel on my transmitter and opened up a connection to the 16 V battery lines which is what triggered the fuse inside the rocket engine. Also, due to the fact that everything was on the underside of the quadcopter, I needed some landing gear to prevent all my electronics from getting squished. You can see the landing gear in the picture below. They were just a quick and simple design I threw together and were 3D printed by a friend of mine. They simply screwed into the side of arms using small M2 screws. The last addition I made was a circular steel plate on the top side of the center plate so that the rocket exhaust wouldn't burn through the plywood.
And that was pretty much it! After all that work, the quadcopter flew surprisingly well and succesfully performed 8 rocket launches without issue or failure. If you have any questions or comments please feel free to leave comment and I'll try my best to answer as quickly as possible. Thanks for looking, hope you enjoyed!