The "home made" driver will allow us to drive and control the 4 brushless motors that will propel the UAV.
The controller will require not only a precise control of the motors, but also to know their speed at t time. These two things are impossible with simple trade drivers. We use a microcontoller and a H-bridge structure to drive the 3 phases of a brushless motor.
The developped board will use a dsPIC30F4011 and 3 MCP14628 MOSFET drivers. Power MOSFETs are IRFR3710 supporting a continuous current of 42A
To design this board, we used a Microchip application note (AN901) named Using the dsPIC30F for Sensorless BLDC Control. However, we made an improvement relieving us of the use of 3 analog inputs on the dsPIC.
After multiple problems, we have finally a working brushless driver board. We had to make these modifications :
- adding resistors between the outputs of the drivers and the gates of the MOSFETs
- adding high capacitors on 5V drivers power supply, because of huge pic of current
- adding a very high capacitor near the power part (MOSFETs) able to provide the energy required when feeding a phase, but also to recover the energy from the inductor during the opening of the transistors.
Despite of the higly inductive effect of the motor, freewheel diodes in the transistors are sufficient to limit over-voltage. The addition of other diodes, even fast diodes, nearly do not change the signal.
We are currently working on the synchronization algorithm for generating control signals with the engine.