Raspberry pi based Drone Quadricopter

Base assembled. (upside down)

Side view of base (upside down)

Add on battery holder.

Cardboard squares are then glued onto remaining struts for support.

We first bent thick wire into a U shape and inserted into the quadcopter frame. We chose to use hot glue for this due to its thickness. If you choose to bend the ends up like we did, ensure that the ends have plenty of clearance so they don’t collide with the props.

Use double sided tape/ anti vibration tape to mount the control board to the top of the frame.

Take each section of thick, high amperage wire and use a razor blade to carefully strip five sections of about an 2 cm that are about 2.5 cm apart down the wire.

Strip the end of each wire about 1 cm and tin them both.

Make a jig by drilling holes to match the sizes of the battery connectors, so that the battery connectors plug into it nicely and don’t move around. This video shows the process well. http://www.youtube.com/watch?v=MnldHRtjre8

Tin the cups of the connectors by melting solder into them until they are almost full or solder.

Let the battery connectors cool for a little while after they have been tinned.

Melt the solder in the battery connectors a second time and insert the end of the battery wire into the molten solder.

Remove the soldering iron and hold the wire motionless for about a minute or until the solder is completely re-hardened.

Heat shrink over these joints so that you won’t be able to short the battery.

Tin the other exposed sections of wire carefully with your soldering iron set on high heat.

Tin the ends of the motor speed controller and BEC wires that you will be connecting to the main power wire.

Wrap the ends of the motor speed controller wires around the stripped and tined sections of the high amperage wire using pliers.

Solder the two wires together ensuring that a good connection is made.

Place heat shrink over this new joint and shrink it so that the new joint is insulated and protected.

Solder the next motor speed controller to the power distribution wire and heat shrink it. Repeat this until all of the motor speed controllers and the BEC are soldered to both the power and ground wires and heat shrinked.

Heat Shrink over the ends of both wires that do not contain the connectors so that these ends do not short.

Thread the electronic speed controllers through the holes.

Secure the power distributor to the bottom of the copter. This can be as simple as a piece of tape.

Thread the output from the ESCs through the wire routing holes and connect to motors.

Label the propellers according to their spin direction.

Solder the electrical components onto a perf board according to the schematic for the Schmitt trigger.

We used an oscilloscope to test the switch. We sent up an output signal from the raspberry pi to something like 1.7ms pulse and then use the RC controller to toggle back and forth. You should see the signal instantly change.

Use the servo connector female female cables to connect the switch, the RC receiver, and the flight controller.

We decided to use Rasbian, a distribution that is relatively easy to set up and meant for the pi. We decided to not install X for performance reasons, but got up a basic c++ tool chain, wifi connections using wicd, and ssh. We then installed many libraries, including OpenCV, and servoblaster. Due to the speed of the raspberry pi, this process is quite slow and takes many hours.

Always write code on a computer. Due to the number of libraries we are using and the speed of the Raspberry Pi compile times are quite painful to debug with. In general, all code can be written on the computer, tested on the computer, and then uploaded to the Pi. Another more extreme option to minimize recompiles is to place all of the configuration values in an external file that can be changed at runtime.

As with all programming, start small and test. At least in our experience, the code can get quite complex very quickly and it helped a lot to make small tests.

Test your code! When writing image based autonomous code, its generally a good idea to run automated tests on your code. These tests take your code, and would run them in various virtual environments on a simulated quadcopter that behaves like the actual one. For our project we where not doing very complicated autonomy so we opted not to create this simulated environment. If your plan is to add more, we would strongly recommend creating a testing environment such as this.

If you want a starting point, see our code: Our codebase is located at https://github.com/lukemetz/PiQuopter-Vision.

The first thing we did when we got out flight controller was to reprogram it to use the kapteinkuk xcopter kk firmware. To do this, we used the kkMulticopter Flashtool. We went with the xwing configuration because we have a camera on board. The camera look forward if it is placed between two arms and not have to look through propeller blades.

To finish setting up the flight controller, follow the kk Quad x setup guide located at RCExplorer. This guide walks you through testing and configuring the ESC and the flight controller.

We used the anti-vibration mounting tape to secure the remaining electronics, but anything will do. Finally secure the camera to the forward side of the quadcopter.

Because there are many different kinds of receivers and transmitters, reference the manual to learn how to do this.

Tunning our quad copter was quite difficult for us. To begin with, we neutral the potentiometers. Move the first and third pot to 50% and the second pot to 0%. In the firmware we are using the second pot is unused. To begin with, we tied down our quadcopter such that it could not fly away. We then used the RC controllers trim values to trim it level. This step takes a lot of time and tinkering with controls.

Once the copter is more or less level, use the first pot to adjust roll and pitch gains and then tune the 3rd pot until the copter flies straight.

Once you have configured your quadcopter, you are going to want to scope the output of the RC receiver such that you can emulate the tunning in the autonomous code.

While doing this step, we strongly recommend you tie down your quadcopter to prevent it from getting out of control. Never turn off the controller while the battery is plugged in, as the default mode for the control board is all motors full on.