411 Full power without motion <resolved>

[rjtechserv]

I seem to have habitual bad luck with DC servos motor upgrades possibly damaging the AllInOneDC. I’m wondering if the procedure upgrading the encoder on 29/40in lb servos without cleaning the brush dust may contribute! Normally upgrading the servos that have laid horizontally their entire life allows brush dust to collect on the “bottom”. When installing new encoders servos get flipped every direction possibly causing some commutator shorts? Never gave it a thought until now trying to get this new system installed; so, I’m curious to hear any other contributing feedback from those with experience.

My understanding that the power FET’s on the ALLInOneDC will balance the power to maintain position. So what I’m seeing in the negative direction on the x and y servos is the servo will sometimes very slowly on it’s own have the current meter rise until it trips. Or if I reset the servo and hold tension on the servo in the CCW direction the servo seems content but, if I relax or rotate the servo CW the “411 Full power without motion” to trip out the contactor. To me sounds like the AllInOneDC has a bad FET on axis 1 and 2. The axis3 Z works fine. All work was done the same.

These servos prior to worked fine on the old Bridegport; this was to be just an upgrade update electronics. I’ll attached the report and videos if allowed. Being a one direction problem, I don’t think the problem would be the servo but more likely bad FET’s for some reason?
I increased the voltage from 120v to 160v after the problem was noticed in an effort to reduce the current. Left the current limits set to 12A before the problem. Later set to 15A because they are 40in motors. Ballscrews rotate nicely no force. Whatever thoughts and suggestions you Centroids guys may have would be great!

videos sent through wetransfer https://wetransfer.com/downloads/5ecd2b ... 349/f314f9

[eng199]

Did you do the motor checks in TB155? In particular, turning the motor shaft with windings shorted?
https://www.centroidcnc.com/dealersuppo ... ds/155.pdf
This test will reveal bad commutator segments through rough motion as the shaft is turned.
I would expect this test to show any difference in CW and CCW directions. On a servo motor, I don't know why one direction would be favored over the other. On some motors the brush holders may work better one direction or the commutator may have timing advance. That should not apply to servo motors.

MOSETs typically fail shorted. You can check the row of MOSFETs with the power off. None of the 3 pins should cause a continuity meter beep when checked against each other. Sometimes a motor can take off one direction when power is applied if 2 FETs are shorted. If one FET shorts, normally the paired FET will soon turn on and be destroyed by "shoot through". In this case, the fuse will blow.

MOSFETs rarely fail open. If they do, the part is usually visibly blown to pieces. If one or two FETs are open, it is plausible that there would be no torque at all in one direction.

The bus voltage does not affect the current under normal conditions. The drive controls current (torque) in a closed loop. It will only apply what is required for a given move. Voltage can increase top speed per the voltage gradient (v/kRPM) of the motor.

[rjtechserv]

I didn't catch the TB155. I'll certainly do that. Turns smooth but I'll check it shorted later today.
The +/- checks to ground I think I was seeing 3.5-3.7M ohm on the AllinOneDC. I'll check the FET's in more detail later as well.

Great pointers! Thank You! I'll be back late tonight to report.

[rjtechserv]

I did perform the TB155 as suggested. All appeared to be fine as the TB described. After cleaning the motors and trying again we had the same result. We tried the working axis3 servo on axis 1 and 2 and the same result. We can jog one direction only and fault out going the opposite direction. I'll see if we can do an RMA and have it checked. No shorted FET's and the fuses tested good on the ALLinOneDC.

[rjtechserv]

I did want to report back on this for others; the Centroid board was fine. The problem was my forgetfulness that YOU CAN'T USE normally open limits on the AllInOneDC. This caused my problem to thinking there was a board issue and there wasn't. The 411 Full power without motion was the resulting error in this case. I should have noticed the LED error display telling me such. Yes, that was silly but on me! Hopefully this helps someone in the future!