Motor Control Issue

It sounds to me that you still have a bad commander.

John you have helped me on many issues. I wish I could help. Sorry to say the holder of the answer is way above my pay grade. I am confident that you will figure it out and your posted solution will benefit all of us, which again, is no help at all now. 

Assuming this is a Pullmor open-frame motor, have you checked the end play and vertical motion of the armature?  The amount of motion of the armature depends upon both the direction and the loading.  Light or no load on the bench may not show a problem if the brush holders are dragging when the armature rises up under load.

Unless I'm missing it, I don't see the step you took by simply switching the motor wires.  That would quickly narrow it down to the chassis or the board.

Use a 4.7uf NP 50v cap across the motor, remove the 10 ohm series resistors.  If this fails,  try adding a 0.1uf 50v ceramic cap on the Mini output before the "steering" diodes to the motor.   Connect the caps right across the 2 pin connector on the board on the HC1 and HC2 outputs.

If this still does not work, a new Mini commander is in order.

I forgot to mention that, I swapped the two plugs on the MB thus changing the driver that was driving the motor.  Yes, I have also swapped the two leads going to the motor as well, the problem always stays with the unit going forward.

I have the cap across the motor, that was my first step. I figured this was probably some sort of noise coming back from the motor, odd that I didn't see it before on other similar installations.  I had already removed the resistors, they were just as a test to try to add filtering from the motor noise, obviously not successful.

I'll try the .1 caps directly on the board, I didn't do that. 

I see a cap that is directly across each of the outputs, but it's not labeled.  What value is that cap?

I take back my previous comment!  Clearly, though earlier I was swapping motor leads, I didn't do it when it was all together it appears.  So, when I swapped them and ran it, it ran forward like a champ, and it stutters in reverse.  However, by the headlight indications, it thinks it's in forward, so it appears it's always the HC1 output that has the problem.

I put the .1 caps on, there was no change in operation.  I also swapped to my other MiniCommander (ENG) board, that board exhibits exactly the same issue.  Both of these boards were purchased at the same time, which may be a factor.

One additional observation.  When it's running smoothly (using the drive from the HC2 output), it ramps up as you'd expect, and with the Legacy controller you can hear the motor start to hum at first, but until you get to about 5 in TMCC steps, it doesn't move.  This is similar to my two other motorized units that also have the same board.

When it's going in the problem direction (using drive from the HC1 output), it starts to move much sooner, and typically at 2 or three it's rolling at a pretty fast (but very jerky) clip.  Obviously, the control is not linear for the problem direction, it appears that some electrical noise somewhere is scrambling the logic.  Once you get to a higher speed, say 9-10, it smooths out and seems to run almost as well as the other direction.  However, on the bench, you can still hear the motor making more noise in that direction, presumably because it's still seeing noise and making sudden changes in current.

Conclusions

Since I now know it runs smoothly in either direction using one output from the board, and won't run smoothly in either direction using the "problem" output, I think I can eliminate the motor and mechanics from the picture.  It appears that for some reason, the environment of the speeder has an effect on the electronics of the MiniCommander board.  What is causing it to act this way is a mystery. 

Although I hate to do it, I think I'll rip one of my working motorized units apart and try that board in this unit.

MYSTERY SOLVED! 

Obviously ERR got a bad batch of boards, or they were corrupted during programming!My old board from another unit runs like a champ, I wish I'd taken that out and tested it earlier.  About four hours down the drain.   So much for having a "spare" board to verify it wasn't a board issue!

Now I just need to get replacements and hope the problem has been corrected in the latest batch.

The Cap is a 0.01 100V.

What diodes (part number) do you have  going to the motor? 

I will have a boards tested here at the office tomorrow. 

Some theory of operation: The Triacs are fired into the 0.01uf caps to turn on; then the resultant (chopped) AC waveform is rectified and used to drive the motor.  The Triacs may be within spec and not firing as expected. This is why I asked you to add the 0.1 cap to see if this helps the firing angle.  In any case, after I try a few tests tomorrow, I will post my results. 

NOTE: it is premature to think a bad batch of boards exists, or *extremely* unlikely a programming error occurred.   The Last purchase of Mini Commanders was 4 years ago (we buy in BULK) and the boards all are in the same batch.