Best decoder for a coreless motor

[Ighten]

 

I have been slowly changing everything over to DCC on the layout and anything with a 3 or 5 pole motors is working like a dream.. Even Ring fields I converted myself are running perfectly at all crawling speeds.. This DJ models BR41xx though is an entirely different story..

 

I have finally got into it and cleaned it out and checked space for adding stay Alives but the big issue is it won't even run properly on a straight bit of clean track.. it's just start stop start randomly as it attempts to get from A,B.

 

The current decoder is a Bachmann 6 pin 36- 568A which is a zimo chip.. now I have already changed CV 56 to 155 as Zimo suggest for coreless and that made little difference.. pushing it to 255 seems to have improved it slightly it now only stops every 1 foot and starts again instead of every 3 inches. Is this chip just no use on a coreless motor (which seems pathetically small). Other things I have tried are checking it still runs fine on DC, it does. .. pushed CV 2 to 44 just to give it some oomph... Turned DC off.. 

 

I couldn't find any capacitors anywhere to cut off on this motor,  they are either hidden inside the motor or it never had them (do coreless not need them).

 

Anyone recommend a 6 pin DCC that loves coreless or am I missing something obvious.

[Izzy]

The basic Zimo cv settings for coreless are cv9 - 51 & cv56 to 133 rather than 155. Not sure if the latter will make much difference though. I totally agree with your comment of pathetically small re the motors size. I use this size of coreless motor in 2mm 2FS (7x16) but it’s just plain silly IMHO to expect them to be able to cope with a 4mm one. Wickham trolley perhaps but not anything else. 

 

Given the use of a Zimo with its superior motor control - you won’t find anything better - I’d suggest adding stay-alive will be the answer. Any capacitors may be on the pcb so unless you ditch it and hardwire in a decoder you’re stuck with them. Doing this would probably give the room to install a decoder plus small stay-alive pack in the space in the smokebox though. Nip & tuck but doable.

 

Bob

[34theletterbetweenB&D]

The 'something obvious' that springs to mind is defective track power supply to the decoder; pick ups not maintaining reliable contact, momentary short or a poor wiring connection. The smaller the decoder the more sensitive to this defect. It can be masked by a 'stay alive' but my preference is always to fix the root cause.

 

Quick test, with the model on the bench apply DCC track power to the decoder: if the mechanism then runs reliably the problem is between rails and decoder, nothing to do with the motor.

[whart57]

It should be remembered that after a momentary break in power on DC the volts come through as before. Inertia will help the motor through this particularly if a flywheel is fitted. On DCC though, a return after the break means the chip has to reboot and then wait for the next data packet, all of which may take a fraction of a second but is still noticeable. If acceleration/deceleration is programmed then it will be even more noticeable The "does it work on DC" test is an exclusive one - if a loco is a poor performer on DC then it isn't going to get better with DCC, not if it works on DC it will work with DCC.

 

Temporarily wiring a light in to the chip might be a useful diagnostic. If the light is not lit steadily when turned on then it is a power supply issue.

[whart57]

1 hour ago, Izzy said:

The basic Zimo cv settings for coreless are cv9 - 51 & cv56 to 133 rather than 155. Not sure if the latter will make much difference though. I totally agree with your comment of pathetically small re the motors size. I use this size of coreless motor in 2mm 2FS (7x16) but it’s just plain silly IMHO to expect them to be able to cope with a 4mm one. Wickham trolley perhaps but not anything else.

 

Or a Colonel Stephens railbus set

 

As a more general point it would help if people just put a descriptor in for what CVs are, particularly the higher numbered vendor-specific ones. We should know what most of the lower-numbered NMRA standard ones are but the vendors doing their own thing is another matter.

[Nigelcliffe]

My limited experience of DJM items in 4mm scale has been "new chassis , the DJM one is a disaster".   

 

If the Zimo can't be made to run the motor, then start looking at the mechanism.   As suggested above, supplying DCC directly to the chip (skipping all the pickups) would rule those out.    It also takes out the need for any stay-alive devices at this stage of investigating.   

Are there any other components on the DJM PCB ?   They may be making things worse.  

 

Could try turning down the BEMF influence in the decoder CV's, that may help, but at the risk of reduced quality of control.  One might find a sweet spot.   (if the DJM chassis is like the J94 design, it induces variable BEMF from the motor due to the way the gearing and rods in the chassis can "fight" each other). 

 

I suspect it will be as Izzy suggests.   There's nothing to be done with such a pathetic little motor.   

 

 

( I have used a smaller motor on a 4mm scale Wickham trolley, but that's a 4volt radio-control solution to making a small model ).  

 

[Ighten]

Thanks... Those settings do seem to show some improvement especially turning acceleration and deceleration off weirdly.

 

It does now constantly stutter for a second on point frogs (which are all live ) so it must be as one wheel actually straddles  the gap ; which makes me think the others need an axle brush soak to try to clean inside the split chassis. I have already cleaned an excess of brown grease out of the gears.

 

 

[Izzy]

It was because of the split axle current collection that I suggested stay-alive as the best long term solution. Been there, had the problems irrespective of motor size or decoder make……

 

Bob

[Nigelcliffe]

I've not got any measurements, but looking at the photos, I'd think the newer Zimo "Stacco" stay-alive circuit with two small super-caps might fit.  Probably need to throw out the 6-pin socket to create the space, and then wire direct to decoder.    That should give more than enough run-on time to overcome any momentary drops in pickup.  

 

- Nigel

[Ighten]

Is that like this one... Anyone have a good link how it all fits together. Only stay Alives I'm used to are hm7000 😂 lol

https://www.digitrains.co.uk/zimo-high-power-stay-alive.html

[whart57]

I find a test track like this to be a useful thing to have:

 

 

The length of powered rail is not critical but it should be shorter than any total wheelbase of a six wheeled loco or motor bogie. The idea is that a loco has to run smoothly through even though pick up on one side is only through one wheel. It really highlights pick-up issues. It should go without saying that you test a locomotive both ways ........

[Nigelcliffe]

3 hours ago, Ighten said:

Is that like this one... Anyone have a good link how it all fits together. Only stay Alives I'm used to are hm7000 😂 lol

https://www.digitrains.co.uk/zimo-high-power-stay-alive.html

 

Yes, that's one.    Some other Zimo retailers are significantly cheaper.

 

How to fit it together - read the instructions 😀  

You need both the Staco-3 instructions (come with it or Zimo website) and the decoder instructions (Zimo website). 
You'll need to attach two wires from Staco to the "positive" ("Pluspol" on some diagrams) and "ground" ("mass" on some diagrams) of the decoder. 

On a six-pin decoder, both of those are solder pads on the decoder.   

And then join the two capacitors in series with each other, and attach the pair of capacitors to the other two wires from the Staco.   

 

There's a certain amount of:  if you can't follow the manufacturer's instructions then don't go blowing up electronics parts.  

 

I did say that I didn't know if it would fit, just that from a photo I thought it might fit.  

 

 

- Nigel

Edited December 28, 2023 by Nigelcliffe

[WIMorrison]

Sven van der Hart has some very useful coreless motor settings on his website. I know that they work as I have re-motored several locos using his motors and I only use Zimo decoders and his comprehensive set of CV.

 

Digital (tramfabriek.co.uk)

 

I would recommend that you start with these settings and perhaps modify for your specific loco.