finding mechanical time constant

[faisaldin]

i have to use dc gear motor for position control. Is it can possible that by simply couple potentiometer with motor and by taking the voltage response of potentiometer on the oscillograph I can find the mechanical time constant of that motor?
If not, than, whats the issue?

 

[BobM3]

Do you want just the "mechanical" time constant? Or the "total" time constant (electrical + magnetic + mechanical)?

 

[sreid]

The approximate answer is "Yes" but use a tachometer. Apply a step voltage to the motor and record where the velocity is 63% of the final value.

Approximate since, as BobM3 points out, there will be a delay in current rise due to the electrical time constant (L/R). But this is often less than 10% of the mechanical time constant.

Also, the final velocity will be lower than the friction free velocity. But once again, is likely to be within 10% of the theoritical final velocity.

Both these error can be accounted for with siome simple math. But for a lot of real engineering an approximate solution is "Good Enough."

 

[faisaldin]

Thanks alot sreid.