Voltage Constant?

[LazyMan]

I am looking at specs for a servo which say voltage constant is 15.71V/100rpm. What does that actually mean?

[Al_The_Man]

It means that it generates 15.71 v at 100 rpm, from this you can calculate the voltage required to operate up to max rpm.
If the rpm of the motor is 2000, then if you supply 315vdc it will operate at 2000rpm,
Al.

[LazyMan]

That is what I initially thought but when I read these specs for a servo motor it made me confused. So with with the rated voltage constant I can only get roughly 450rpm at 72 volts? With a maximum RPM of 4200 for this servo something just seems wrong with the specs. Any explanations?

* skewed rotor design
* continuous torque: 170 oz/in
* peak torque: 850 oz/in
* terminal voltage: 72 VDC
* continuous current: 8.5A
* peak current: 38A
* inertia: 3.39 kg.cm^
* maximum operating speed: 4200 rpm
* torque constant (KT): .1757 N. m/am
* voltage constant (KE): 15.71 volts/100 rpm
* resistance: 85 ohm
* inductance: 2.35 mH
* weight: 8.8 lbs
* 7 inches

[Mariss Freimanis]

The specification is in error. It should be 15.71 Volts/1,000 RPM. Proof:

Kt (in-oz/A) is always 1.351 Ke (V/KRPM). If Kv = 157.1 then Kt would be 212 in-oz per Amp or 1.5 N-m. This is almost 10 times higher than the published 0.1757 N-m.

Mariss

[LazyMan]

Now it all makes sense. Thanks guys!