PWM a DC Motor
PWM a DC Motor
(OP)
I am working on a project in which I need to PWM a small DC permenant magnet motor. Is there a way to calculate the optimum frequency to get a decent torque out of it. I need to be able to fine tune it's angular positon. I am having trouble with the torque at low rpm's. Motor's spec's are .5mH @ 1Khz and 1.3 ohms.
Thanks,
Steve
Thanks,
Steve





RE: PWM a DC Motor
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: PWM a DC Motor
RE: PWM a DC Motor
Sometimes the PWM rate is dropped much lower to provide a bumping like a dither to overcome static friction. This can also create other problems.
RE: PWM a DC Motor
The only source that I can find on the web that seems to be a good source is the Seattle robotics club. They metioned about the time constant also. I was hoping that there would be a better way as I am limited to 10KHz max. I tried @ 9KHz but I had to get the duty cycle up to overcome the static fricion. A low duty cycle @ 150 Hz seems to work ok but I cannot get a fine control. We may need to backup and take another look at our design. Thanks again.
RE: PWM a DC Motor
To get more torque you need to up the current in windings which means upping the average voltage. But, as mentioned earlier, if the motor is not designed for low rpm [like most dc motors], it would still be hard to get fine control. You'll need gear reduction to scale down the "linear range" of the motor. As a ficticious example, a DC motor may be controllable between say 2000 rpm to 4000 rpm but outside this window it would not be linear with voltage.
Alternative might be a brushless dc motor but controller would be more complex.
RE: PWM a DC Motor
Mike Halloran
Pembroke Pines, FL, USA
RE: PWM a DC Motor
RE: PWM a DC Motor
They seem to have gotten quieter in recent decades.
Mike Halloran
Pembroke Pines, FL, USA
RE: PWM a DC Motor
I was hoping to be able to slow the motor as I reached the targeted position to prevent overshoot. Then maintaining the position I may have to bump the motor one direction or the other. A gear reduction may be the best way to go.
RE: PWM a DC Motor
Mike Halloran
Pembroke Pines, FL, USA
RE: PWM a DC Motor
RE: PWM a DC Motor
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: PWM a DC Motor
Should have read your post closer.
Maybe there is a software solution. This will make the design guys happy. I hadn't thought about going to that extreme.
Steve
RE: PWM a DC Motor
Know what you mean. There's nothing as hard as software...
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: PWM a DC Motor
RE: PWM a DC Motor
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: PWM a DC Motor
Is there a lot of friction-stiction in the system you are driving?