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Topic: Anglular precision with brushless motors (Read 1 time) previous topic - next topic

iamdenis

Feb 14, 2013, 02:53 am Last Edit: Feb 14, 2013, 03:10 am by iamdenis Reason: 1
Hello everyone,

I was wondering if someone could give me some advice on how I can approach controlling a brushless motor to specified angles. I am trying to build a camera gimbal with using an imu as the gyro/accelerometer. Is there anyway to do this without using a Hall Effect sensor?

I want to use an ESC, so there will only be 1 PWM signal coming from the board to the motor.

Thank you for your help,
Denis

retrolefty

Sounds like a very difficult requirement to meet to me. First the ESC has no way to know what position the motor shaft is at any specific time, even if stopped. So an absolute encoder or a quadrature encoder + a once a revolution reference sensor would be required mounted to the motor shaft. And depending on the speed the motor is operating at this could be very demanding. I'm not even sure you can command a ESC to stop with any precision such that you could easily make it stop at a specific position even with the position feedback measurement available, there is a lot of momentum involved with a turning motor that would have to be dealt with. All in all I think this is something your going to have to see if anyone else has had the same requirement and how they solved it.

Lefty

iamdenis

this is currently a project from russia:
http://forum.rcdesign.ru/blogs/97312/blog15240.html

Using google translate i get this for the control part:

The required angle vystalyaetsya from the panel. Next PID-controller detects an error in each axis and gives a signal to the motor. Controller output - "Electrical angle" (see operating principle bezkollektornikov). Further, the angle is converted to three sine shifted by 120 degrees., And is served by three PWM-generators for power switches - (half-bridge for each phase). Thus, the vector magnetic field in the stator windings rotated to the desired angle, and the rotor tends to follow him, correcting the error.

Can anyone make sense of this?
bezkollektornikov might mean piezoelectric?

Thank you

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