Re: [CAD_CAM_EDM_DRO] How to determine Torque from these motor numbers?

Earl wrote:

>Howdy all again.. hope everyone is having a great holiday.
>
>I have some Ametek DC motora here with a few more specs. How do i
>derive the Torque from these numbers, or is more data needed?
>So far I have found out:
>
>Resistance is about 1.7 Ohm, useing the following readings when
>applying the following to the motor with the shaft locked:
>
>10.5V drew 6.5A = 1.6 Ohm
>16.5V drew 9A = 1.8 Ohm
>(my meters wont go above 10A reading)
>
>"30VDC nominal" is printed on the motor, but seems to want to run at
>higher voltages.. it is OK to run it above 30VDC?
>

Yes, the voltage rating is pretty flexible in servo controlled applications.
The motor will only see more than that voltage when required to meet
the commanded speed and torque demands.

>No load resulted in these numbers:
>
>30V .58A = 720 RPM
>50V .67A = 1260 RPM
>60V .73A = 1500 RPM
>
>

See, nothing happened to the motor, and you've already doubled the rating!
Now, if starting the motor from stopped, with 60 V applied directly from
a stiff power source, the current could exceed the peak current limit. But,
a servo amp should be set to not do that.

>Like I said, Id like to know the Torque of these motors, as well as
>if they are a good canidate for a small/medium CNC mill project
>useing Geckos. Ball screws are yet to be obtained.
>
>

Well, the Kv of the motors seems to be about 40 V/KRPM, so the Kt
should be 54 Oz-In/Amp. So, you get 54 Oz-In for each amp of armature
current. But, that gives us no help in figuring out the continuous or peak
current ratings of the motor. The continuous rating can be determined
by how hot you think the motor should be allowed to get. But, the
peak rating is pretty hard to arrive by, except by comparing to similar
motors. (Or, you can do like the manufacturer does, and test one to
destruction.)

Jon