The blades started spinning yesterday for the first time, so I thought I’d show what I’ve been up to after the turtle. Although the blades are spinning, it’s not left the ground yet. There’s a lot of work to simply get takeoff, and then have it level out without hitting something in the room (i.e. me!). Currently it’s a drone – control is all within the Python script integrating the I2C PWM and motion detectors. I have plans to add a second RPi as a controller, but currently I just rlogin to kick off the blades. A ctrl-C on the python shuts them off pronto!
The body itself is a DJI Flamewheel 450 – the kit provides the body, motors, cabling and ESCs, leaving it to me to provide the control parts.
The Spy in the title comes from the RPi camera it will carry when available.
P.S. An ESC is an electronic speed controller. It takes a PWM input, with a carrier frequency of up to 400Hz, and in each 2.5ms cycle, the signal is high for 1 – 2ms. The ESC then takes this signal, converts it to a 3 phase equivalent (120o separation), feeds the result into 3 H-bridges which control how long the 30A, 11.1V power is fed into each motor stator per cycle. Note the current through the coils is always at maximum, but it is the time it is fed which controls the overall power and hence blade spin speed. The ESC gets inductive feedback through the same cables driving the motors allowing it to fine turn the power it applies.
In my original whitterings about doing a quadcopter, I though the ESC could be replaced by Pis – ignorance is bliss! Having learnt the above, I’ll leave the ESCs to the people that know how and leave the Pi to do PWM, acceleromer and operator control function!