Balancing power to PS3 trucks, help.

I see that a lot when the engine is on it's side. I did try to cure it once by actually moving the tach to the other truck. It wasn't worth it and I expect it would be tough for you to try that here as well.

 Sometimes brand new trucks just need a break in period and the low speed performance will smooth out. If the engines on the track do you notice one truck dragging the other or the engine stumbling at very low speeds?

Normal operation, the truck with the tach will get enough power to run at the command speed, the other truck just gets the same voltage and very often doesn't start running at low settings.  It has no effect when you're actually running on the rails.

You can clean motor commutator area with electric motor cleaner. Make sure no issues with gears and lubricate.  If still off or does this when coupled to track, replace motor. G

That is what I wanted to know. So, there is no means to balance voltage to the trucks.  I have since taken the motors apart and lubricated the bearings and I found some bumps on the fitting of the mating housing and since I did that, the motors have come closer to the same speed, starting and stopping equally, but the two speeds are slightly off.  I would be nice to be able to tune the two trucks to the same rpm.  Thank you very much for this response. Bob.

It's a rare locomotive that will run the two trucks at the same speed with the wheels turning freely.  It takes very little energy to turn the wheels with no contact, and the slightest difference in the drivetrain friction or the motor characteristics will make one run faster than the other.  With them both running, you can very easily stop the drive motor that doesn't have the speed sensor.

IMO you're trying to answer a question that probably should be asked unless you see actual operational issues while running under load on the track.

I am listening to you guys, so I have yet to get this loco on the tracks under actual loads.  I will update everyone once that happens. Thanks again for all of your input, I appreciate it. Bob.

I think you'll see when it's on the tracks, you won't see that.

Note that there is a potential traction issue with virtually all twin motor locomotives that have tach based speed control.  If the speed controlled motor loses traction and starts spinning, it will have it's voltage dropped to maintain the set speed (in the air), and the other motor will have minimal voltage as well.  I see this happen on the entry to poorly designed grades, or even a dip in the track.  We had one module on our club layout that had a dip, and several locomotives would lose traction there and just stop with the one truck spinning.  Yes, we fixed the module.

OK, I am just dreaming now, but since I am a multi engine pilot, synchronizing engines is a matter of independent throttle control.  What if an additional tach. was put on the other truck and just measured rpm and not power so that one could see the relative rpm's of both trucks and then be able to independently control that one to match the other.  If that was possible, the traction would be greatly improved, because once one of the trucks is not pulling the same as the other, the efficiency is greatly reduced.  Once one truck is trying to go faster or slower, the effectiveness of the other truck is greatly effected.  Am I wrong?, I know sometimes I think too much. Bob.

I notice this when I clean wheels, its just like JRJ said,  normal without load. All my MTH O gauge diesels do this.

machiningfool posted:

OK, I am just dreaming now, but since I am a multi engine pilot, synchronizing engines is a matter of independent throttle control.

Funny thing, so am I.

machiningfool posted:

What if an additional tach. was put on the other truck and just measured rpm and not power so that one could see the relative rpm's of both trucks and then be able to independently control that one to match the other. 

That's quite possible, and it wouldn't be all that hard to do, just another sensor and obviously some additional software.  However, I have never seen or heard of a case where that's been done on a model train.

Yes, I think it is possible and I also think that battery time would be increased quite alot.  I might also try just running one powered truck and see how that works.  I would probably have to add some weight on top of the truck, I might just try it.  I am trying to imagine what happens when one truck is not pulling the same as the other.  If it is slower, it is putting drag on the one with the tach.  If it is faster, it might just be spinning and therefore exceeding the traction point and then also causing more drag.  I don't really know, but I am thinking about it. Bob.

It really balances out when they're on the rails.  I can tell you with some personal experience, having a single powered truck is not as effective as having both powered trucks.

You're looking for problems where none exist.

My asking questions is for the express purpose of finding out something that I don't know. So, what you are saying is that the voltages and the traction point happens automatically when in operation as if it already has synchronizing ability even though differences in voltage applied, differences in bearing friction, will result in the two trucks turning at the same rpm.  If they are not turning at the same rpm, one would be pushing or pulling the other, wouldn't it?  So I guess what you are saying is that even if it is not turning at the same speed, even though  one might be slipping, it still offers more push than it does drag? Is that correct?  Bob.

GGG posted:

You can clean motor commutator area with electric motor cleaner. Make sure no issues with gears and lubricate.  If still off or does this when coupled to track, replace motor. G

Above advice is sound. CRC has a brushed motor cleaner. I use as shown:

Air dry after application. All my engines (ps3 and ps2) are smooth at scale 2smph and 1smph most of the time.

Thank you very much, I appreciate it. Bob.

machiningfool posted:

So I guess what you are saying is that even if it is not turning at the same speed, even though  one might be slipping, it still offers more push than it does drag? Is that correct?  Bob.

Actually, what I'm saying is the forces equalize when there is a load on both trucks.  Neither truck spins or slips unless it loses traction with the rails.  All the major makers use the same scheme for cruise, one motor is speed controlled, the other truck gets the same motor voltage.

machiningfool posted:

... even though differences in voltage applied, differences in bearing friction, will result in the two trucks turning at the same rpm.  If they are not turning at the same rpm, one would be pushing or pulling the other, wouldn't it? ...

But the voltage applied is the same.  The motors have published speed-torque curves for a given applied voltage.  At one end of the curve is the stall torque (maximum torque at 0 speed).  At the other end is the no-load torque (0 torque at full speed).  From manufacturing variation, motors of same model have slightly different speed-torque curves giving rise to the observed scenario - in other words different speeds for the same applied voltage.

In normal operation, and helped by rubber traction tires, both wheel trucks are spinning at the same rate.  This means both motors are spinning at the same rate.  Since the same voltage is being applied to both motors this means that the two motors are generating slightly different amounts of torque.  But it is still more torque than one motor by itself with the same applied voltage. 

The "fun" comes when you think through the various scenarios...and why they converge to the case of BOTH motor trucks spinning at the same rate on the track.  For example:

Engine stopped. Now commanded to some speed.  The motor with the tach (call it A) starts to spin first.  The gear transmits the torque to the track and the traction tires transfers "all" of it to the track.  But the engine does not move because the other truck (call it motor B) is still locked because its motor is providing no torque.  So the motor control increases voltage to BOTH motors A and B.  At some point either the A motor's torque will be able to start dragging the B truck and/or the B truck will start to spin and the control voltage can be lowered.

The key is A and B can be delivering different amounts of torque and yet spin at the same RPM.  I don't know of a simple analogy but two people, say an adult and a child can be pushing a disabled car and be providing different amounts of force.   Even if the child is not pushing as hard, the force provided still helps.  Or a tandem bicycle still benefits even if one person is pedaling harder. 

Well, that's my view of the situation anyway.  There is a related but separate discussion on electro-mechanical efficiency (e.g., Horsepowers of pulling power output vs. Watts of electrical power input).  At first glance you'd think efficiency is maximized if A and B are perfectly matched and operating at identical points of their speed-torque curves.  But that's at first glance.  Then you go down the rabbit-hole of MU consists with mis-matched engines, etc. etc.

 All I can add to this conversation is what I see more of when upgrading other brands of G scale to MTH command. At very slow speeds (1 or 2 MPH), one truck does seem to drag the other. The engine will make a jerky motion attempting to move. If you advance the speed from 1 or 2 MPH to say 5 MPH, they seem to smooth right out. Then I'd agree with the example of both spinning and maybe one is doing slightly more work than the other, but it's not noticeable to the eye watching the engine's movement.

 It was so pronounced on a particular engine I converted, that I removed traction tired wheels and replaced them with solid metal ones. By adding weight, the traction is good enough yet allows one truck to slip and equalize any low speed differentials. I don't like tires on engines with cheaply made plastic gears anyways (weaker, less quality).

This is a common concern, it's natural to check out the loco unloaded, or 2 locos running light a few apart to see how they match.

Under actual conditions of pulling a train, the motor running faster will be more highly loaded and slow down a bit and equalize with the other motor.

So, unfortunately the natural tesst for how a loco runs is probably the least representative of the actual running conditions.

Oh, and by the way there are DCC decoders that monitor the rpm and bemf of multiple motors in a loco. Better control if there is a severe mismatch. They do it electronically without a tach.

Greg