Positional control with Hall Sensors

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Joined: 10 Feb 2016, 10:21

Positional control with Hall Sensors

Postby wdaehn » 10 Feb 2016, 11:16

I like the positional control a lot including all its use cases but I believe it is heading into the wrong direction currently. Not sure if I got everything though, so please correct me.

The use case for positional control are servo motors and the such, e.g. for a CNC application. Granted. But these have geared motors with huge ratios. Hence the goal is less to turn the motor by 10° but rather make 100 revolutions to move the axis by 1/10th of a mm.

So my point is, while having the option to turn the motor like a servo is fun, this is highly inefficient and it is not what brushless motors are meant for. Hence I would like to enter a value of 50.5 in the position field and that means the motor turns 50 and a half times.

Of course I could as well enter 50.5 * 360° there, to achieve the same. But the scale is just an indication of what it is meant for. Servo versus Geared Drive.
Since I can't get the positional control to work, I assume it requires an encoder. Hall sensor of the motor is not sufficient. Correct?

In my case with the cable cam, I want the cable cam to drive 100m forward, that is 100'000 revolutions. The Hall sensors would tell you where you are. In fact there is a second set of hall sensors (2 only) on one of the running wheels to compensate slippage of the motor. Hence the ultimate solution would be to use the Hall sensor port for the motor control only and connect another port to the STM32F4's 32bit Quad-Encoder to keep track of the current absolute position.

But positioning the motor at 100'000 revolutions with speed ramp would be sufficient already.


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