Loco Braking on descent??

[yachtjim]

I am relatively new to this whole train thing aside from what little experience I have as a kid. I am building my layout now, part of which requires a grade. Its about 3%. So far I have bought Bachmann DCC locos just to have something to run around as I figure things out. I have 2 GP40's and 2 GP38's. The 38's are way quieter. When going down the descent with some rolling stock the loco's will act as though they are slamming on the brakes, then release, then brake, etc. Its very annoying. What causes this and what is the workaround? I should note that I enjoy the trains running slowly, at full throttle they do not do this.

 

[fiend540]

What DCC system are you using?

 

[yachtjim]

Digitrax Empire Builder

 

[NYC_George]

I had a lot of problems with this in the past. The 30 and 40 car trains I run that descended my 3% helix grade were too much weight for the engines to hold back. The cars pushed the engines down the grade surging and stopping them repeatedly. I was in need of some back EMF decoders. I bought 3 Lenz silver decoders for my Atlas 420C’s and 3 Digitrax DH165A0 for the Atlas GP-40’s. Both brands have back EMF which sort of acts like a dynamic brake. They both work but the Lenz brand seems to do a better job at this and work right out of the box. The Digitrax brand asks you to set some EMF values before it is turned on. The Lenz is better bet for this problem but much harder to install in the Atlas GP-38 GP-40 etc. type models.

If you haven’t seen my helix video click on this link.

http://www.youtube.com/watch?v=uyzgL8tRKic

With the back EMF working notice how the loco’s negotiate the grade no matter how many cars are pushing.

NYC_George

 

[Selector]

The caterpillering effect you see is partly due to the mechanics of the locomotive's drive mechanism with some cogging, but most of it is due to resistances in the axles on the various items of rolling stock. Also, loose couplers and mismatched couplers can add to the mix.

Some cars roll more freely than others. Have you tuned all the sideframes with The Tool from Micro Mark? They get dog hairs, human hairs, house dust, insect bits, bits of plastic, or burrs left over from the molding process....any number of problems can affect a car that is otherwise properly weighted......OH....are your cars all properly weighted?

All this to say that there isn't just one thing at work here. Spend some time over the next week cleaning up your truck sideframes on your rolling stock, fix and coupler problems, and if you still see this going on, you can safely conclude that it is mostly due to your engine's drive mechanism.

-Crandell

 

[hamltnblue]

If your decoder has back emf (BEMF) try turning it off. That and what selector said

 

[Alcomotive]

I had a lot of problems with this in the past. The 30 and 40 car trains I run that descended my 3% helix grade were too much weight for the engines to hold back. The cars pushed the engines down the grade surging and stopping them repeatedly. I was in need of some back EMF decoders. I bought 3 Lenz silver decoders for my Atlas 420C’s and 3 Digitrax DH165A0 for the Atlas GP-40’s. Both brands have back EMF which sort of acts like a dynamic brake. They both work but the Lenz brand seems to do a better job at this and work right out of the box. The Digitrax brand asks you to set some EMF values before it is turned on. The Lenz is better bet for this problem but much harder to install in the Atlas GP-38 GP-40 etc. type models.

If you haven’t seen my helix video click on this link.

http://www.youtube.com/watch?v=uyzgL8tRKic

With the back EMF working notice how the loco’s negotiate the grade no matter how many cars are pushing.

NYC_George

George I really enjoyed all your videos of your layout on youtube they are fantastic!

 

[Cjcrescent]

The caterpillering effect you see is partly due to the mechanics of the locomotive's drive mechanism ...-Crandell

Crandell is right, this is almost all due to the gear slack in the engines mechanisms. The cure is simple, thrust washers placed on both ends of the worm at the top of the gear tower. The locos do need to be disassembled to insert these.

BEMF decoders will help some. But the problem still lies in the amount of slack on the worm.