I started a post about this problem on the main board because I thought the jumping was caused by lash in the drive train. It is not.
Engine is a HO Athearn Blue Box F7b. I am running a DH 123 and DCC system is a SEB with DT 400. Every time I start the engine, it jumps a half inch stops. After it stops as I increase the throttle it starts moving like it should.
I started with CV 2 at 8 and now have it at 20. After it jumps with the CV at 20 it moves at 1% power. (DT 400 shows a power range from 0 to 99)
Any ideas?
Cuda Ken
I hate Rust
I experienced something similar with my Digitrax system and a DT400 with respect to an Atlas Trainsmaster w/QSI sound.
Would stop, then start again but only move very slowly until I clicked the throttle up or down at which point it would resume speed.
Was operating it on right throttle. The left throttle was set to 2 or 3. When it stopped and then started again, it was switching to the left throttle setting. In this case, the DT400's left throttle is default for DC equipped locos.
I went in and set DC compatability mode to OFF in the Atlas engine. No problem since.
Increasing CV2 is only going to make the jump worse. A BEMF or at least a decoder with better torque compensation would smooth it out. The motor just needs to big a kick ot get moving, and with only bumping CV2 higher and higher it just makes a bigger jolt at speed step 1, but once moving it doesn;t need that much voltage to move.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Randy, I thought you did not want to run BMF when using it in a consist, that is why I am using a DH123. Am I wrong?
DC is still mode has not been turned off.
Ken
Ken.
The TCS decoders have a setting for CV10 to turn off BEMF at a preset speed step. On most of mine I have them switch off BEMF at speed step 10. This allows great slow speed and starting and no jerking and wheel spinning on the main line.
As for the slack action in the drive train. The BB Athearns are famous for too much fore and aft movement of the worms in the truck towers. Some KD washers between the worm and bearing will help immensely in smoothing out the start up. When the worm turns and slams against the bronze bearing it stalls the motor momentarily until the decoder compensates for the stall. Adding some shims will keep the worm in one spot and transfer the torque to just turning. If there is too much fore and aft movement there is a tendency to jam up the universals also.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
Turn off DC mode. Problem solved.
cudaken Randy, I thought you did not want to run BMF when using it in a consist, that is why I am using a DH123. Am I wrong? DC is still mode has not been turned off. Ken
You typically don't want to run BEMF with a consist but if you have issues like this you might have to. Try running it with just the loco that jumps and leave it off on the other one. DC mode usually causes runaway trains and not jumping. It should be turned off either way if you don't use DC.
Springfield PA
It's possible for there to be a problem, but it depends on the decoder. I have a Stewart/Bowser FT AB set, the A unit has a TCS T-1, one of the newer ones with BEMF, and the B has a Tsunami, which also has BEMF. They don't fight each other.
The Digitrax decoders with BEMF come defaul set to have no BEMF in consist, but only advanced consist - using CV19. Default consisting with a Digitrax system uses command station assisted consisting so the individual decoders do not 'know' they are in consist and the BEMF stays active. My old P2K Geeps with DH163L0 did buck each other a bit when consisted. I think it comes down to how well the BEMF works, the TCS BEMF is self-adjusting and I've seen it with every install - when I first run a newly installed decoder the loco runs a bit rough at first, then it seems to settle down, and stays that way from then on. Not sure if it really is storing anything in the decoder's memory but it sure acts like it.
cudaken ... Every time I start the engine, it jumps a half inch stops. After it stops as I increase the throttle it starts moving like it should...
...
Every time I start the engine, it jumps a half inch stops. After it stops as I increase the throttle it starts moving like it should...
Make sure CV65("kick start") is programmed to 0 and see if that helps.