Re: Pittman Servomotor

Jon,

Actually it's very simple to get Kt once you know Kv. Kt is 1.351
times Kv.

Mariss

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> Mike Haughton wrote:
>
> > I have some Pittman servos taken from a HP7475 pen plotter. Can
anybody
> > supply details of these servomotors? I can't find them on the
Pittman
> > website.
> > Details from the motor
> > 9413D319
> > 3140-0665 rev H
> > 19.1 VDC
> > 1-7-87
>
> It is pretty easy to determine the basic motor constants. Kv is
how many volts it
> takes to get 1000 RPM. You can use a disc with a slot in it and a
photo-sensor,
> and count with an oscilloscope, if you have one. You can also use
a neon bulb
> with a 100 K Ohm resistor and rectifier, all in series. This bulb
will blink 60 times
> a second (at least in the US) and can be held next to a disc with
a wide stripe
> marked on it. Connect the motor to a variable DC power supply, and
adjust for
> 16.67 pulses per second on the oscilloscope for 1000 RPM, and read
voltage.
> Or, set such that the disc only shows one stripe standing still
(with the neon stroboscope)
> and you should be at either 1800 or 3600 RPM. If you increase
voltage to get two
> stripes standing still, that would be 7200 RPM, but that might be
tough on the motor.
> Anyway, at 3600 RPM, divide the voltage by 3.6 and you have your Kv.
>
> For Kt (the torque constant), mount a spool of some sort on the
motor. A thread
> spool might be perfect. Wind some heavy thread or light string on
the drum a few
> turns, and put some modest weight on the string. You might want to
put a power resistor
> of something like 1 - 10 Ohms in series with the power supply, and
hook a DVM
> in series to measure current. Adjust the voltage of the power
supply until it just
> starts to lift the weight. At this point, read the current. Kt is
torque per amp.
> So, knowing the radius of the drum and the weight, you can figure
out the torque
> to lift it in whatever units of measure you like. If the radius of
the drum was one
> inch, and the weight was 10 Oz, then lifting the weight required
torque of 10 Oz-In.
> If it took 1.5 Amps to do that, the Kt of the motor is 10/1.5 =
6.667 Oz-In/Amp.
>
> >
> > The encoder is made by HP and I would appreciate connection
details (4 lead
> > AMP flat cable). The encoder wheel is mylar with two tracks.
>
> If you can find a part # on the encoder or read head (may look like
HEDS-9000
> or some similar) we can be more help.
>
> Jon