Unfortunately the replacement Ardunuo board took longer than expected to arrive which delayed getting the ultrasonic sensor working considerably. Once assembled the sensor worked very well, however it was observed that when it is powered from the 5v out from the PI the values unusable, this is likely because the PI did not have enough power for the sensor and the Ardunio board, However the sensor works fine when powered from an ESC.
Additionally the control board for the quadcopter has been replaced with a smaller version which does not have a barometer, However this is not a problem as the barometer is not accurate enough the keep the quadcopter as a certain height at low altitude.
For this test the Raspberry PI is controlling just throttle and attempting to keep the copter at 30cm from the ground where as the rest of the movement is controlled manually. The test is using a simple bang-bang controller so once it reaches a certain height it lowers the throttle and once is under it increases the throttle. This creates extreme oscillations in flight, which is unsuitable for a sustainable flight. However considering the obvious problems the flight was very successful in the sense of the PI being able to control the quadcopter.
The next stage is to implement a PID controller that will generate an error value which will be used to increase or decrease the throttle, hopefully creating a smooth movement.
Currently the Raspberry PI is putting a considerable amount of load on one the ESC’s which is getting pretty hot, Additionally the PI has had poor performance when connected to copter which has made it hard to test. For this reason the next step is to replace 5v power from the ESCs (Powering the control boards) with an independent BEC (battery eliminator circuit) providing higher power.