Re: [CAD_CAM_EDM_DRO] Re: Power Supply for Gecko 320 and servo motors for 3 axis router

caudlet wrote:

> On Servos you need to adhere to
>the nameplate voltage specs.
>

Not always. In the special case when a current-limiting servo amp is
used, yuou don't have to adhere to the voltage ratings in the normal way
you'd expect. For instance, the very common Camtronics motor by
Ametek are rated at 36 (or 38) VDC at 900 RPM. This is actually
the back EMF generated at 900 RPM, not a voltage limit.

If you built a system with a 36 V power supply and expected to get
900 RPM under load, you'd be disappointed. It will produce no torque
at 900 RPM because the back EMF fully matches the power supply
voltage, and no current can flow.

The motors are rated at 12A peak, but the resistance of the samples I
measured were around 4 Ohms. If you apply 36 V to a 4 Ohm resistor,
only 9 amps will flow. So, you can't even REACH peak current with a
36 V supply. At 450 RPM, the back EMF would be 18 V, so only 4.5
Amps could flow.

>
>Servo motor torque ratings are much more realistic since they are
>taken at higher working RPM instead of at stall like steppers. A 360
>oz/in servo will have that torque across a wider range of its RPM
>than a similar rated stepper.
>

On brush motors, the torque is almost precisely proportional to armature
current. The RATING may decline as other heat sources come into play,
but the actual torque produced per amp can be taken as a straight line.

Jon