Help! Slave Engine being Drug

@Paul Lytle posted:

One thing that I did find however is that when I would slow the B&O lead units motor that has the tack reader, or press down on the frame to slow the tack reader motor then the other motors would power and then turn and work properly.

That is relatively normal and expected operation. The controller is giving ALL motors the exact same voltage (PWM to be more exact). The tach reader motor is giving feedback to the controller loop. When you slow the tach reader- the controller gives MORE voltage(PWM) to all motors until the tach motor achieves the target rpm.

What it means is- your other motors either have more friction or more load and your tach motor wheel set and gears are extremely free - but ALSO may not have good traction.

Again, this is somewhat expected- the system is working as intended. You either have a traction limited situation (clean your track, ensure your wheels have good clean fresh traction tires) or reduce the load (drag or number of cars).

Again, the way this system works, in the lead unit, the controller is sensing only 1 speed- the tach motor, and that sets the overall voltage to BOTH motors in that unit. If the tach reader truck slips- then the other truck may grip, but then also not be given more voltage unless the throttle is raised even higher. Not ideal but just how it works.

When you have a trailing slave board unit in PS2- that is an "analog" board- so called because the signals it's getting from the lead unit are direct motor and light outputs and then just "buffered" by the board. The slave unit board has more or less a similar circuit as the lead motor drive unit using a relay and 2 FETs. This way, when it duplicates the lead unit PWM, the resulting PWM or voltage to the trailing engine motors is identical to the lead unit. In practice, I find that the trailing powered unit actually has slightly less pull with the slave board- but that is just how the system works.

But again, ALL of this is ONLY effective when the lead unit tachometer motor and truck is NOT slipping!!! Again, the system only really works when the most important truck and motor- the one with the tach, is not slipping.

This same problem can be found in countless locos- Example the MTH Turbotrain. On that engine, due to the shell and clearance, the rear truck in that only has one drive axle and traction tires and is known for slipping, meanwhile the front truck is a powered 4 wheel truck.

I don’t know if this will help but I had the same issue with my B&O F7 ABA set and even ended up sending it to GGG who tested the board and sent it back saying nothing was wrong with it. He did suggest a friction issue so I pulled both motors in both units and lightly greased the gears and carefully reassembled and the problem went away. George said that it was most likely that one of the motors was slightly misaligned, maybe your issue could be something that simple as well.

@terryd73 posted:

I don’t know if this will help but I had the same issue with my B&O F7 ABA set and even ended up sending it to GGG who tested the board and sent it back saying nothing was wrong with it. He did suggest a friction issue so I pulled both motors in both units and lightly greased the gears and carefully reassembled and the problem went away. George said that it was most likely that one of the motors was slightly misaligned, maybe your issue could be something that simple as well.

Correct, again, the limitation of the system is only 1 motor is sensed for RPM feedback. The assumption is, all the other trucks and motors are free, not binding, and thus the same voltage (PWM) makes them spin with the same RPM as the sensed motor. That's only valid as long as none of them are fighting friction and losses within the truck and gearing.

Some of these unit have gear lash issues and since the slave is delayed sending voltage if a motor hangs up and the gears get bound (slave is moving in reverse) they can't turn.  So checking trucks, cleaning motors, can help with this.  When running for testing have shells off so you can watch motors.  One may be turning and another not, or both, etc...