Axes not moving correct distance

Something else you can try. Mark your motor sprocket position. Then command a move that should make exactly 1 revolution. Does it make exactly 1 revolution. Now do a move that would be 10 revolutions. Does it still come out right? Also do 10 single rev. moves in one direction, Does it give the same result as the one 10 rev move?

Double check your sprocket tooth counts to make sure you received what you thought you ordered.

Your acceleration rates are rather high, and if the machine has the power to achieve them, mechanical slippage at a motor or pulley coupling both on acceleration and deceleration could be very possible.

The only time I've found the actual measured distances to differ significantly from the calculated ones (like you're seeing), was when either I made a mistake in the calculations, or there was a mechanical or other issue like missed steps or a configuration problem.

Hey Todd,
thanks for the suggestions. I thought I had a 3:1 reduction drive but the manufacturer sent me 22 tooth timing gears instead of 20 tooth, so I really have a 2.7:1 ratio. That explains why my calculated scale factor was so far off. I corrected the math in my .ini and the moves are obviously much closer. Unfortunately I still have the "drift" problem. There is no slippage in the system, the drive system is tight and has almost no backlash. I also adjusted the acceleration way down but that had no effect on this.

Say I home the machine, then command it to move to X5. It will move very close to X5. Then if I command it back to X1, it actually moves to X1- a few thou. Then back to X5, it goes to X5- a few thou... Bouncing back and forth between X1 and X5, the X1 eventually lands near X0. I describe this behavior as drift because that 4" move drifts to the left.

I still have to do the tests you suggested where I send a # of steps and see how far the motor turns. Can you think of any other config that could affect this drift phenomenon? Is this a PID tuning thing?

Thanks again,
Jamie

That kind of result is almost always a mechanical problem or missing steps. Either a shaft coupling, sprocket or pinion gear is slipping on the shaft.

The position and step count between the Linuxcnc motion planner and the stepgenerator (software or hardware) is a closed loop system and should not loose position. If position is being lost it is after the steps are generated, either the drive isn't seeing all the step pulses for some reason, the motor isn't making all the steps sent to it, or something is slipping somewhere.