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Sensing Brushless motor RPM

Posted by David Browne on January 23, 2011 at 1:51pm

Hi everyone.

 

I have recently been designing a PID controller to maintain the speed of the Brushless motor under a range of load torques. The motor is driven by an ESC.

 

I have been reading through old forum posts on similar topics and I cannot seem to get a clear answer on whether an ESC can feedback any velocity feedback to the user or just internally. 

 

Can any one shed any light on this?

 

I am using both a Gaui Brushless motor and ESC.

 

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Replies

  • TaranisAttack March 2, 2011 at 1:46pm
    I doubt there would be a function for this in most controllers as its its not very useful for most users. However, you can determine torque load mathematically as torque is a function of current and magnetic flux IIRC. The velocity of the motor can be measured either using a hall effect sensor, or you can measure the how many times voltage is passed across the wires in a time period, as the voltage is switched on and off across different wires in a sequence. You'll need to look up the details but this should point you in the right direction.
  • Developer
    Doug Weibel January 23, 2011 at 3:47pm
    There are very few, if any, esc's that are set up to give you feedback on the motor rpm.

    There are external loggers that determine the rpm by monitoring the voltage on one of the three motor wires. With the appropriate conversion considering number of poles in the motor, etc, you can convert pulses per second to rpm.

    Also, you may not know there are many of the better esc's that have internal governor programming which includes a PID controller to hold a constant rpm under varying loads. They are designed for helicopters doing aggressive aerobatics, and some do a remarkable job.
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