The quadcopter part 2 : specifications and first manufacturing

So, as you can see there, we had a beginning of stabilization at the end for our first prototype. Still, we were not able to correct the yaw axis, making the drone really hard if not impossible to control. We decided last weekend to build from scratch a new version of the drone. We established the following requierements for this V2 :

- The drone must be built from carbon tubes and balsa wood (that solution seems to be the easiest way to have something very light and robust). To ensure a perfect aligment of the 4 motor axes, we'll double the carbon tubes  for each arm.

- We'll use the following sensors :

  • A gyroscope L3G4200D and an accelerometer ADXL345 to capture the rotation angles of the drone
  • A magnetometer to capture the absolute rotation around the yaw axis (actually, we found a thesis paper showing how a magnetometer, a gyroscope and an accelerometer can work together to give a very precise angle for each axis, so it will do more than only give us the cap)
  • A GPS to capture the absolute position in the 3D space
  • A telemeter (basically a sonar) to capture preciselly the altitude of the drone between 0m and 5m.

Here is a little description of the elements we ordered (unfortunately, we didn't receive the shipment this weekend)

 

3 axis magnetometer "HMC5843"
SiRF StarIII™ based GPS module
SRF02 telemeter

 

 

 

 

 

 

 

 

You can find pictures of the accelerometer and the gyroscope in the previous article. if you want to know more, here are the links to the datasheets

As you can see, all the devices are controlled by numerical interfaces : I²C , SPI or serial bus. This is very convenient to use thanks to the existing Arduino's libraries.

We tried after this to build a 3d model of what the drone will look like

 

Very basic modelisation, but still usefull to check if everything's OK.

Actually, this modelisation will be also used to machine the different parts. Indeed, we made a CNC a few years ago (may be will come an other series of articles to describe this awesome project). To generate the toolpaths, I use Mastercam , and the software used to control the mill machine itself is Mach3.

The toolpath used for machining 4 motor mounts

For now, I made a little video of the machining of a motor mount.

 

[youtube]http://www.youtube.com/watch?v=L6pmeJbbn9Q[/youtube]

 

Gluing the landing gear.

 

 

 

To assemble the parts, we massively use epoxy glue (made of 2 components : a resin and a hardener) so there is no possibility for the vibrations to disassemble it.

 

 

 

 

Here is the result. So far, so good : the 4 motors are perfectly aligned, and we should avoid any excessive yaw-drift problems.