Erratic slow speed with Hornby Schools R2181

[Seacommander]

I am steadily working through my collection of locos converting them from Zero 1 to DCC. I have an Elite controller. All has gone well so far with all locos to date running smoothly, however, but my Schools (R2181) has very erratic slow running. Because of limitations of space in the tender drive (3 pole Ringfield) I have fitted a small LAIS860012 decoder. At the very low speed end of the range the loco performs erratically. As I slowly advance the speed control the loco accelerates then suddenly slows down and regains speed with further advancing of the speed control. It does this about 2 times before it gathers speed more consistently. I have tried various settings of CVs 2, 5 & 6 but to no avail. Recommendations elsewhere suggest switching off BEMF and/or changing the speed step that BEMF switches off - all to no avail.

Again because of limitations of space I have fitted the same model of LAIS decoder into my Bachmann N Class and Nelson and performance has been good - although with perhaps more refined motors.

I have fitted R8249 decoders to my other two 3 pole Ringfield tender drive locos and they respond well. 

Any ideas or recommendations of a solution would be welcome. If all else fails I will perhaps have to try 'shoehorning' an R8249 into the tender after a bit of surgery.

[jane1707819582]

yes the space is limited in the schools ,i fitted the 8249 at the very rear of the tender with the wires trimmed 

you could try the x 9659 there are fewer wires on this decoder and will wrap around the rear of the tender more easier 

[2e0dtoeric]

It might seem a silly question, but did it run smoothly at slow speeds BEFORE you converted it?

If it didn't, you are fighting a losing battle.

If it did, try replacing the brushes, and giving the mechanisms a good clean and lube.

[Seacommander]

Thanks for the replies. I thought about locating an 8249 at the rear of the tender but was a bit concerned about the proximity of the two phosphor bronze strips (extensions to the tender pick ups I think) that run upwards. Will have another look.

The loco worked well on Zero 1 but will wire it up for a test on DC. Brushes should be OK because the loco has probably only ever had about 2 hours running. I did clean the commutator thinking that it may have been dirty but this did not improve performance.

[Seacommander]

I have now checked running using my pulsed DC controller and motor response is smooth and progressive - for a 3 pole Ringfield. The erratic running I refer too is consistent ie the acceleration and points where speed slows down followed by acceleration again always occur at the same stage in progressively increasing the speed control knob. Reading about similar responses on other forums strongly points to a conflict of some sort in the CV settings concerned with speed and acceleration but the solutions offered have not fully cured the problem with my Schools.

[Fishmanoz]

Are such problems reported on other forums for the 8249 or some other decoder?  There is very little on the 8249 you can adjust beyond Accel, Decel, and BEMF. 

[Seacommander]

For LAIS decoders and possibly TCS - both of which I understand share very similar technology and firmware.. Yes, I know the 8249 has very little scope for tuning response.

[Fishmanoz]

Oops, sorry, forgot you said at the top it has LAIS fitted, was thinking you already had the 8249. Form what you’ve said, I’m assuming default settings don’t work (or reset by writing 8 to CV8 to check) and 3-point speed curves don’t work either. Have you tried the more complex loadable speed curves?  I found info on these by downloading the LAIS manual. 

[ColinB]

I am thinking of converting my old Hornby Stowe to DCC. It is the ringfield motor version, with the motor in the tender. Having looked at the space in the tender, did you consider putting the DCC chip in the loco, it looks as if there is enough room to even put a socket in. I will need to put a transistor circuit in to buffer the smoke units electrics. So a LAIS decoder is OK for Ringfield motors?

[Seacommander]

Hello ColinB. I wanted to avoid putting the decoder in the loco so as not to have a plug and socket to connect to the tender. There is indeed loads of room in the loco if you want to locate the decoder there. I have managed to fit a Lais 860012 decoder in the tender but am now using a Hornby R8249 - thinking it may have improved the erratic running - without success. I have finally come to the conclusion that there is a problem with the motor since the tender drives for my 9F and Britannia both work well with the Schools loco and the Schools tender drive is still 'iffy' with the 9F and Britannia locos. Apart from the Schools my remaining 13 locos run well on a mixture of R8249 and Lais decoders. The 9F and Britannia both have 3 pole ringfields and the R8249 decoders work really well with them and I have a couple of Lima ringfields that work equally well with Lais decoders.

[Fishmanoz]

Colin, just because you have a tender drive Ringfield doesn’t mean yours is the same as the Schools and your question would be much better asked in a separate thread with an appropriate title like “Converting a Tender Drive Stowe to DCC”.  The thing is, there are 3 and more types of Ringfiled motor installations with different conversion requirements. Do a forum search on Ringfield and you will find many previous threads, one quite recent, with relevant info.