Greetings,
Is it possible to measure or approximate torque put out from DC-motor (not stepper, not DC-motor+servo-feedback) by only looking at I-V values?
For example if I'm able to control voltage to DC-motor and able to measure the current drawn by DC-motor, may I approximate the load encountered by DC-motor without knowing RPM? Or should I do a scan from e.g. 10V to 12V and see the derivatives, for example delta current?
Thanks,
No. What matters is the torque delivered to the load.
You would be able to estimate the torque from voltage and current, after you have done some kind of experimental calibration of your motor, measuring the torque somehow. You could then use that calibration later, to estimate the torque from the current when you have put the motor into your robot or whatever.
Torque depends only on the current, nothing to do with the voltage, for a permanent magnet DC
motor. That current has to provide torque that overcomes friction in the bearings (depends on
speed) and in the brushes (usually large and fairly constant), and what's left over gets to the load.
Guessing is easy - 12
...R
You could determine the torque empirically, but that would take a long time.
Normally you would measure the force at a given distance from the axis, either by using
string round a drum or directly measuring the force at the end of a level arm. This
gives the static torque. Dynamic torque is much harder to measure unless you can measure
the torque the motor exerts on its mounting.
I know there are power conversion formula's for motors that allow you to calculate torque from rpm and a few other variables.
But that's for a running motor, you might be able to get a close estimate by calculating the startup torque.
Unfortunately its been well over a year sense I did any kind of motors lab and I don't have the notes with me right now.
I'm sure most of the math is on-line somewhere.
with k being the DC motor constant:
T = kI torque = k times current
E = kw backEMF = k times angular velocity
k has units Nm/A or Vs/rad
You can model the winding resistance R:
V = IR+E, therefore V = IR + kw