MachineKit BLDC Driver
See: Circuit Development, Code Development, and Education
Status
New boards are in, waiting for time...
Next Steps
- stuff one board
- re-hash code for different pinouts, with updated libraries
- try speed control with IQ-less FOC (simple sine commutation)
- if this is not satisfactory (field lag due to inductance), use 6-step comm
- implement speed control network command
- re-hash documentation
- use to control a spindle in a machine
What
The MMKBLDC Project is my attempt at building a decent controller for Brushless Motors. BLDCs are excellent sources of mechatronic actuation: they're power dense and serve the motion control justice present in most state of the art robotics. However, controlling them is non-trivial, and requires the combination of some EE expertise, some control expertise, and some hardware know-how.
Why
This project is largely a follow-on to my Teensy-Powered Brushless Motor Controller, and with this new work, may the TESC project RIP. A moment of silence.
TESC, April 2016 - August 2016
As the world turns,
so did those motors.
Once around is never enough
Eulagies aside, I am still motivated to do this. Brushless motors are the go-to motive force for electromechanical systems. By that I mean that just about any time you see a robot-like thing, or machine, moving about, there's a big likelihood that the thing doing-the-moving has a brushless motor in it's guts - or some variant thereof (stepper motors count as BLDCs in my books). See this characterization of actuators to get a sense for why.
How
We use an ATSAMD51 microcontroller to drive phase voltages through a gate driver, through half-bridge drivers, through motor phases. An encoder reads motor position back to the uc, and we use shunt resistors to measure current flowing through the motor coils. With this information, we can use maths to determine where the motor's magnetic field is, and control that to drive position and torque outputs.
This controller runs with the assumtion you're using the mkxmods infrastructure for controls. Over the network (see link) you will be able1 to issue commands like:
Speed Control
- use key 129, int32_t speed in rpm
- does closed loop PID control to set RPM for spindle control, mostly 'Dumb' Torque Control
- use key 130, int32_t torque val/(2^32) pwm duty
- applies this pwm value to the motor, under simple sinusoid control, to apply closed loop commutation to motor 'Smart' Torque Control
- will require some search for FOC implementation, and should reply with available torques, bandwidths, etc... here be dragons
Building MKBLDC
Mostly, contact me and I'll get you set and ready to programme and use the circuit to control bldc motors.
In the circuit dev page you'll find doc on the BOM for the MKBLDC, and in the embedded dev page you'll find documentation and source code for the firmware to run it as (along with networking code to send messages over the mkxmods network). This is all under development.
Footnotes
- working on it