In article ,
Jon Elson wrote:

Ignoramus7096 wrote:
One encoder on Y axis installed. Y was the most accessible axis and I
already opened up the encoder box on it, so it was an easy choice. I
will from now on test with Y axis, as opposed to X axis. I will try to
make it a one axis CNC machine.

Might want to disconnect the timing belt to keep myself safer.

Well, you can, but don't try to tune the servo response with no load,
you will
end up having to re-do it later. Just start out with the P gain low.
First, with
servo amps off, move the motor by hand and make sure EMC's DRO reading
changes in the right direction. If not, invert the sign of INPUT_SCALE in
the .ini file for that axis. Once you have the direction of motion
right, you
can then enable the servo amps. They may run away if the output direction
is wrong, so be prepared to E-stop. If it does run away, then either
reverse the
motor wires or invert the sign of OUTPUT_SCALE. Now, it should hold
position.
You can start making jog moves to see how well it performs. At this point
you want to read
http://wiki.linuxcnc.org/cgi-bin/emc...rvo_Amplifiers

This was written for the PWM servo system, but almost all of it is
applicable to
the PPMC and velocity servo amps, too. One complication is if the velocity
servo amps are not well-tuned, you have to figure out which bobbles are due
to the servo amp and which are due to EMC's PID tuning. You can contact me
for hints on how to decipher that.

I would add one thing - initially, reduce the power-supply voltage available to
drive the motors, or put a big power resistor in series with the motor, enough
to slow things down and reduce the forces when it gets away.

Joe Gwinn