Control torque of DC motor

Discussion in 'General Electronics Chat' started by Tera-Scale, Jun 27, 2012.

  1. Tera-Scale

    Thread Starter Active Member

    Jan 1, 2011
    I need some points to help me expand in the main principles of DC motor control where current is related to torque while voltage to speed.

    What are the methods used in practice for controlling torque of a DC motor?
  2. WBahn


    Mar 31, 2012
    You control the current.

    But watch out, because demons lie there. You need to be sure that there is a feedback mechanism to prevent runaway. When I was an undergrad I made a gizmo that had three DC motors that had small flat mirrors stuck on the end of the shafts with gummy clay and by bouncing a laser off them you could display Lissajous patterns (the third mirror gave a cool expand contract effect) on the wall. But it was hard to get them stable and so they would always drift. Knowing just enough to be dangerous, I decided to run the motor under current control thinking that a stable current would result in a more stable speed. I didn't know about the relationship between current and torque, yet. Fortunately, having spent my share of time working jet fighters, I at least had the automatic habit of staying out of the plane of rotation whenever possible. So I moved the current control up slowly and the results were completely predictable. The torgue had to build up enough to overcome the static friction. Once it started turning, however, the torque needed to maintain speed was less. So the motor rapidly accelerated and within three seconds the mirror grenaded. I read up on motors that evening and saw almost immediately what had transpired.
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    The torque will also pulse based on commutation. I'm not sure if that will be an issue here.