Hi All,
I have been doing hardware/software (asm & C) development for 30 years so not totally useless but have never done this, or stepper motor control.
I have a project which needs basically 0-13rpm coming out on a 1/4" shaft. There is a whole pile of axial-style motors and planetary gearboxes e.g. this
Few do a 1/4" shaft (6mm is the nearest) but that is another problem :)
The total length has to be 80mm (excl. the shaft).
There are many brush motor solutions, but none are OK because the brushes wear out and this has to run for a very long time - years, in a very high reliability application. No real torque is involved though.
Brushless motors are the way to go and there are ones with built-in controllers which take a 0-10V control voltage, plus a logic level to set the direction.
The 2232BX4SC
But nobody does a suitable assembly which is short enough. To get the max length I have to go to a bare brushless motor (no controller) and mount the controller separately.
The problem is lack of anywhere to put any off the shelf brushless controller... so I have to build my own PCB.
What I know is that the controller uses PWM to synthesise the 3 phase waveform. Obviously the frequency will be the desired RPM and I assume that the "rms" voltage will also be varied - the higher the rpm the more volts. I guess they feed the raw PWM to the motor directly, in the conventional way (I have designed loads of DC brush-servomotor PWM controllers). Is there any standard approach to this, or preferably some proved designs/chips?
The other way is to buy a controller for a model aeroplane. The most expensive ones are $100 which is OK but they don't take a control voltage; they take a 1-2ms pulse whose width is the desired speed and whose repetition rate is fixed at about 50/sec. So I would need to build a voltage to pulse width converter.
But many of these model controllers are crap. My son blows them up all the time...
And I would quite like some kind of closed loop motor speed control. Even though the torque is small, the application needs the speed to be within about 10%. This can be done with back-EMF; should not need a tacho.
A different option is to use a stepper directly, 0-13rpm, no gearbox. This might do but a failure of the electronics could make it go round very fast, whereas a motor+gearbox cannot go beyond a certain point which is perhaps 2x max rpm. Brush motors are inherently speed limited but I can't use one... This application cannot deal with a runaway motor.
Can anyone suggest an easy way to do this? I don't fancy programming up a microcontroller to do the 3-phase synthesis - a wheel which must have been invented by so many people......
I found this
Doesn't anybody make a single chip solution?
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