On Thu, 11 Feb 2016 17:40:20 -0600, Jon Elson
wrote:

wrote:


The handwheels turn an encoder that makes a servo motor turn a
leadscrew. I want to monitor the servo current draw and use it to put
a drag on the handwheel. So more work for the servo makes the
handwheels harder to turn.
What you want is a small servo motor controlled by a servo amplifier. The
torque is proportional to motor current. Just take the current monitor
signal from the servo amp, amplify and apply to the handwheel motor.

Trying to do this with clutches or brakes will lead to great frustration.
Only the most exotic clutches and brakes are very smooth, and otherwise
would put a lot of stick-slip friction into a systemw here you really DON'T
want that.

If the main motor is a DC brush servo, it is possible that a resistor can be
put in series with it, and the handwheel motor connected across that
resistor. Then you would not require a separate small servo amplifier.

Jon
Greetings Jon,
The brakes and clutches I have seriously considered are non-contact
devices so the stick-slip problem is one I wouldn't need to deal with.
I thought about using a small motor as the brake but n oit the way
you describe. The main servos are DC brush servos and will be using 20
amps max for about 4 minutes max, with maybe a 7 second period of a 4
amp draw and then 20 amps again and so on. There will be peaks of much
higher current draws, maybe 80 amps, but these peaks will be quite
short and the servo amps can handle the loads. Can you explain a
little about how the resistor in series with the main servo and the
handwheel servo, which supplies the drag, connected in parallel with
the resistor, would work?
Thanks,
Eric