Unknown DC Motor Specifications

[zer0c123]

I was rummaging through one of my colleges labs looking for usable parts for my groups product design course. I found this medium size motor that weighed about 2-3 pounds. The problem is that there were no stickers at all that indicated its specifications. There were a few numerical engravings, but without words it was hopeless. We hooked it up to a 12 V power source and it powered up fine. Does anyone know of an easy apparatus we can set up to test for its specifications?

I thought maybe hooking the motor up to an arm and having the arm depress a scale would give me the torque output. However I'm not seeing how I would be able to obtain the rpm.

 

[ivymike]

...strobe light and wheel-with-a-line?

 

[Artisi]

A hand held tachometer might be a good way to test rpm

 

[zer0c123]

Thanks for the responses. I'll check with my schools machine shop and see if they have any of the suggested items to check out.

 

[zekeman]

If it is a DC motor, you can get the specs by measuring input voltage, stall torque and current. You don't need to measure RPM. The equations are:
1) V=k1*S+Ir
2) T=k2*I
T= torque, in-lb
S= speed in radians/sec
r= armature resistance
k1 and k2 are motor constants
k1 and k2 are related as follows
multiply 1) by I and 2) by S
V*I=k1*I*S+I^2r
and since this is in watts we use a conversion factor, C from in-lb/sec to watts applied to
T*S=k2*I*S
yielding
3)T*S*C=k2*C*S
Now the first equation shows the electrical power into the motor equals the mechanical power + the I^2*r heating loss.
Therefore, the mechanical power term is k1*I*S which is the same as the RHS of eq 3). Hence , we have
k2*C*I*S=k1*I*S
Therefore k1=k2*C.
And k2 is obtainable from eq 2) under stall conditions.

So all of the DC parameters are available without the speed test, only the voltage, stall torque, current test .