Motor surges when started

[whart57]

I'm installing a Zen V12 decoder into a Colonel Stephens railbus (scratchbuilt). The motor is a small Chinese can type - 8mm diameter - and the chassis has run well on a DC test track. However running on DCC the chassis surges forward before settling back to speed step one. After that it accelerates and decelerates fine and steps ups smoothly through the speed steps.

 

What can I do about that surge though? I've tried changing the start voltage CV, giving it values of 4, 2 and 1, but that doesn't fix the issue. It's almost as if there is a setting to wallop full power to overcome "stiction" which I don't need.

 

Any ideas?

[RHF9019]

Try setting CV66 to 1.

[whart57]

Thanks, I will try that

[34theletterbetweenB&D]

Zen decoder manual might be useful.

https://www.dccconcepts.com/wp-content/uploads/2019/02/Zen-2019-Manual-DRAFT.pdf

[whart57]

Well changing the value of CV66 doesn't make the problem go away and turning BEMF off entirely - CV61=0 - removes all slow speed control, the railcar goes into bat out of hell mode.

 

More experimenting needed but at the moment the chassis is more sensitive to pick up issues than it ever was under DC. Probably needs a bit more weight.

[Nigelcliffe]

Suggested solutions: 

 

a)   A decoder much more capable of running small motors, fitted with a stay-alive.  I'd look at a Zimo MX615, and suitable stay-alive crammed into available space.  

 

b)   battery radio control.   This is what I did for a 4mm scale Wickham Trolley recently.  Battery under the curved roof, radio receiver under the floor along with motor, gearbox, etc..   Doesn't have any pickups to worry about...

 

 

 

- Nigel

[whart57]

OK, a goodly load of lead shot onto the floors of the railcars and slow running is much improved. The chassis are compensated but as the power is picked up via uninsulated wheels on one side of each vehicle, I suspect it may need to run for a bit to polish where the axles pass through the bearings. I also upped CV2 (start voltage) to 2 and changed CV3 to 8 to increase the acceleration. It now behaves as if the driver has heavy feet. I can live with that for now.

Edited September 18, 2023 by whart57

[Carnforth]

Any reason why you cannot add wire pick-ups from the live side wheels soldered direct to the frames? Relying on bearings to flow current is fine once running but I wouldn't rely on that alone. HTH

 

Edited September 19, 2023 by Carnforth

[whart57]

Scraper pick-ups on small non-driven wheels? I'd rather not. To tell the truth I try to avoid wire pick-ups, they are like running with the brakes applied. Drivers and coupled wheels get enough push from the motor to overcome the friction but carrying wheels need such a light spring that they don't make a good connection anyway. The exception is if the wire presses on the axle, in which case it's more or less like the bearing anyway.

[Nigelcliffe]

52 minutes ago, whart57 said:

...... The exception is if the wire presses on the axle, in which case it's more or less like the bearing anyway.

 

There is a difference between pickup in the bearing and a thin bit of springy wire on the axle (typically phos-bronze wire).  And the bit of wire does a much better job.    The 2mm scratchbuilders have been using a bit of springy wire resting on the axle to aid pickup from split frame chassis for decades.  Known in 2mm circles as "Simpson springs", they are not really springs, but a pickup.    

As you're building something small and light, adopting well tested methods from the 2mm world might be worthwhile.  

[whart57]

My scratchbuilding experience is in 3mm scale so I did bring some of that up into my 4mm scale light railway modeliing. I like the idea of these Simpson springs though, once the exhibition is out of the way I'll try that. Shame Eileens is no more though, getting hold of enough phospor bronze wire might be tricky.

[Nigelcliffe]

41 minutes ago, whart57 said:

My scratchbuilding experience is in 3mm scale so I did bring some of that up into my 4mm scale light railway modeliing. I like the idea of these Simpson springs though, once the exhibition is out of the way I'll try that. Shame Eileens is no more though, getting hold of enough phospor bronze wire might be tricky.

 

N gauge rolling stock coupling springs.   Straighten it out, does the job.