Railking GP7 - jackrabbit stop

Joe,

If you purchased the engine used, it's possible that the previous owner used DCS to set the engine's deceleration rate very high. Anyone with a DCS set can reset it for you to factory settings.

Gee Barry,does that apply in conventional? How would he change things if he dont have DCS?

Dale H

Dale,   That's the problem with GP7's and 9's.   The body is narrow.    This particular GP7 is packed.   The capacitors sound good, but man I don't see how they'd fit.

Barry, This was a new engine.  But it is DCS.   And I guess the vendor could have demo'd the engine, and messed with the settings.   Hope not, because I don't have DCS.

see if there is room to attach it (back to back 1000uf condensers) to either or both motors,that is how k-Line did it. Secure with electrical tape around the motor(s). You could also get single 470 or 1000uf 35V NP ones from and electrical supply,they would be a bit smaller.

I do not see how DCS is a factor. When you hit the direction button,you are basically removing power to the motors and the PWM circuit. I do not think there is residual capacitance in the boards to drive motors but I could be wrong.

Dale H

If you are not running DCS (you didn't say), I tend to agree with Dale.  If your layout is set up for conventional so that pressing the direction button cuts all power to the track, the only momentum will be the flywheel.  DCS wouldn't affect it because there is no power to be cut gradually.  If you're running DCS, on the remote there is a way to change the deceleration rate.

Shouldn't the fly-wheel be enough to bring the engine to gradual stop without derailing the cars?  Cruise should be on by default, whether that helps or not I don't know.

The flywheels are not very heavy. Train makers are considering conventional operators less and less although a lot of people still run that way.

Dale H

I am surprised that the loco stops that quickly.  I winder if its mechanism is tight  While the flywheels aren't much, they do slow the deceleration down a bit.  I have an old Lionel RS3 with no flywheels, & it does stop short

Joe,

If the engine is new, you could just return it for one that behaves properly. If you have a store, club or friend that has DCS, you could have the setting changed by them.

Bob,

DCS wouldn't affect it because there is no power to be cut gradually

Not true.

I ran my PS2 engines conventionally before I had DCS and they would coast a bit when power was momentarily cut, as when changing direction.

Depends on how long one holds down the button.

Dale,

As I stated above...

"I ran my PS2 engines conventionally before I had DCS and they would coast a bit when power was momentarily cut, as when changing direction."

I had flywheel-equipped can-motored locos before DCS was invented, and they did coast more than the ancient Lionel.  Derailing cars was never an issue.  Sounds to me like this loco may be binding internally.  I would call MTH tech support.

If power is cut and kept off, I don't see why a DCS-equipped loco would coast any better than a non-DCS-equipped, can-motored loco.  I can't see how there could be enough capacitance in a DCS component that could make a noticeable difference in coasting.

JoeMack, does it do this if you turn power off and leave it off, or do you give the button a push and release?  This would narrow the possibilities.

Robert,

If power is cut and kept off, I don't see why a DCS-equipped loco would coast any better than a non-DCS-equipped, can-motored loco

Agreed!

I think the battery must come into play else the engine would be changing direction at the slightest power interruption... Command or Conventional.  The only engines I had that came to an abrupt stop were early Williams with no fly-wheels

Maybe the engine needs a good  lube job.

I wonder if anyone tried to glue on a piece of lead, flattened into the disc shape of the flywheel and secured it on to the existing flywheel. That would increase flywheel mass and perhaps increase coasting. Looking at my Williams engines, flywheels do not all seem to be the same material. Perhaps MTH wheels are not all the same weight,depending on supply of parts.

Dale H

Absolutely.  If you "do the math" and calculate the energy stored in a typical can motor flywheel spinning at 1000 RPM or whatever, the Joules will be equivalent to a ginormous capacitor placed on the electronics side.  Joules for Joule, the mechanical reservoir is more efficient as it is in the desired form whereas the electrical energy must be converted to mechanical work via the motor which is inherently inefficient.

Whether or not there's headroom to add to the flywheel (or space to add capacitors for that matter) is a problem left to the student...

I doubt that one could add enough weight to make a significant difference.  Sounds to me like binding, as I said, and it should be addressed before motor burnout.

Does it abruptly stop the same way going in forward and reverse?

I think you have a problem engine since I don't think you should be derailing cars.  That said, if you actually want to tinker with it (rather than just send it in for repair) I would attempt to isolate it to an electrical or mechanical issue.

It sounds like you have the shell off.  Can you run the engine up on wood blocks (or whatever) and attach 2 alligator clip cables to apply track power?  One would clip to a center roller, the other to the chassis frame.  Then run the engine and see if it violently brakes when power is removed at different starting speeds.  By lifting the chassis off the track you break the mechanical linkage between the two trucks.  If BOTH motors abruptly stop then it could be an electrical issue since both motors are electrically tied together.  If ONE motor abruptly stops then you could have a mechanical binding in that truck as others have suggested.

In what may fall in the "don't try this at home" category I suppose you could attempt a "clean and jerk" lift of a moving chassis off the track to kill track power allowing the trucks to operate independently.  You'd have to grab the engine just right and in the split second after the lift observe what those flywheels are doing.  Just food for thought.

From an electrical viewpoint, there are several failure modes in DC motor drive circuits which can cause abrupt motor stoppage when power is removed.  The general principle is when power is removed, the circuit should electrically isolate the motor windings from the drive circuitry.  Otherwise if you load the motor, you get regenerative braking.  If you short the windings you get abrupt stoppage.  So if there is a problem in the isolation mechanism, then you could exhibit your symptoms.  I realize this may not help you at all since there's no end-user troubleshooting guide that I'm aware of for this part of the circuit.  However, one thing you can try if you are up to it is to remove any other loads from the board and confirm you still have the violent stoppage.  There is a 12-pin connector that goes to the lights and speaker, and a 4-pin connector to the smoke unit (if you have smoke).  These two wire harnesses pull straight out.  Leave just the 5-pin connector to the motors and the 7-pin power connector.  You won't have lights or sound but the engine should operate forward, back, change speed, etc.  If the abrupt stopping goes away, then you definitely have an electrical problem.

Good suggestions, Stan

 Barry,  I have had 3 or 4 PS2 engines, and they all coasted a bit.   That's what surprised me about this one.

Stan,  Thanks for the excellent suggestions.   I will give it a go and report back.

I had the engine up on test rollers with the shell off.    There does not appear to be anything binding the motors.    And the problem affects both motors simultaneously.  

I sent a message to the vendor about it.    He suggested I find someone with DCS and have them do a "factory reset".    I did so.   But the factory reset made no noticeable difference.   I am waiting to hear what the vendor has to say about that.

Seems like an electrical issue since with it up on rollers a flywheel of just about any size would be enough to effect a gradual spin-down on power loss.

Did you confirm it abruptly stops in both fwd and rev the same way?

Is/was it practical to remove the smoke and light/speaker harnesses to see if they had any effect?

Is the battery connected/charged?  Does the engine exhibit shutdown sounds if you remove transformer power?

I know you say there is no binding, but is there friction when turning motor flywheel by hand?  Maybe a bent axle, wheels pressed to close to truck frame, gears tight?  G

Stan,   Yes, it does the abrupt stop the same way in both directions.    At this point, I didn't want to remove anything.

GGG,    The battery is connected and charged.    It gives the correct shutdown sounds.     Each flywheel turns smooth and easy by hand.  

I've been offered a couple of options by the vendor:   Return for full refund, return for repair, or keep with partial refund (waiting to hear exact amount of partial).

Guys,   I haven't heard back from the vendor yet.    I suspect the partial refund would be somewhere close to 50%, based on his earlier comments.    But I'd like to know what you all think of (1) Return with full refund <vs.> (2) Keep with approx 50% partial reimbursement. 

Thanks.

I don't know why I thinking this... but suspect a faulty engine  MUX board . Doesn't  a blue wire from the mux board  go to the tack reader, If it's disconnected the engine will still run but very erratic.

GGG  might know.

JoeMack, what is the model number of this loco and what year was it built?  How many turns of the flywheel does it take, for one complete revolution of the driving wheel?  Most MTH diesels have a gear ratio of 10.5:1.  Is it possible that this one has a different, tighter gear ratio than your other Proto-2 diesels?

I've noticed that the flywheels in some of these locos are pretty small.  I've tried cementing brass washers onto the tops of the flywheels in an FT diesel to increase mass for running in conventional mode.  It's difficult to balance them correctly.  And over time the cement loosened and the washer went flying off.  Not a good solution IMO.

Personally I would remove each of the motors from their power trucks and inspect the worm gears for burrs.  Also look at the spur gears on side of the truck block.  Make sure there are no broken teeth (it happens!), and nothing caught in the gears.  Then apply fresh grease to the worm gears and reassemble, turning the flywheel slowly by hand as you tighten the motor mounting screw, to ensure a correct mesh.

In command-mode operation the PS2 electronics supplement the mechanical energy stored by the flywheels.  I strongly recommend that you test the locomotive on a nearby DCS layout, and also set the deceleration momentum to "1" or "2" for more gradual stops.

Good luck and please post your findings here!

If you still have the engine up on blocks or whatever, here's a simple experiment.  Get the motors running at some nominal speed. Then pull the 5-pin harness that drives the 2 motors (the one with the yellow and white wires).  If the motors abruptly stop as you've been seeing, then it's a mechanical problem in the motor, gears, whatever.  But if the motors gradually spin down, then it's an electrical problem; in other words something in the motor drive circuit is electrically loading down the motors.  I understand that you don't want to take anything apart but I think this would instantly diagnose whether it's mechanical or electrical.  If you think you might be willing to give it a shot, I will make a short video demonstrating what to do.

Ted,

The model number is 30-20010, built in 2011.

The gear ratio LOOKS like 11:1, but it must be the 10.5:1 you're talking about.

I don't want to remove the motors before I'm certain I'm keeping it.   But I will do this later if I wind up keeping it.

I had a guy do a "factory reset" on this engine, but it did not help.    Would a factory reset give you a "1" or "2" deceleration?

Thanks

Stan,

I'll hold off unplugging the harness for now.   But that's a good test.   I'll try it later if I keep this engine.   I can at least say for now that the flywheels both turn very smooth and easy by hand.   Thanks.