Re: [CAD_CAM_EDM_DRO] measuring motor torque

ryan_kittredge wrote:

>I purchased some brush dc motors 24VDC. Now that I've got them I'm
>trying to come up with a way to get an idea of how much torque they
>produce.
>
>Has anyone ever made some type of simple dyno to test small electric
>motors?
>
>

You don't need a dyno. A dyno measures power at some speed. A static
measurement will be fine for a DC brush servo. All you need is a way to
control the motor current. A variable voltage DC supply, or a big rheostat
and a fixed-voltage supply will do. Put a drum of some sort on the motor
shaft, and attach a string to it. Put a known weight on the string. If
your
drum is 2" in diameter, this rig will read out directly in In-Oz (or In-Lb,
depending on the weight). Increase motor current until it starts to wind
up the string as it lifts the weight. measure the motor current at that
time. The torque constant is Kt = weight/amps (assuming the 2" diameter).
So, if the weight is 13 Oz, and the current is 0.5 A, then the Kt =
13/0.5 =
26 Oz-In/Amp.

If you have no idea what the continuous or peak current rating of the
motor is, then you have a quandary. The only real way to establish
this is by destructive testing. High peak currents can demagnetize the
permanent magnets. Excessive current over some period of time can
overheat the armature and cause eventual failure.

Jon