Making a steam reverser work?

Discussion in 'Workbenches, including workshop techniques.' started by SECR25, 2 December 2018.

  1. SECR25

    SECR25 Member

    Hello All,

    I am after some help with an idea I have had for a very long time.
    Basically I would like to make a Steam Reverser work on a 4mm SR Q class?

    Ideally it would work with changing the directional button on a controller, changing the polarity. I found this online after a heck of alot of searching-

    Roger Amos - model railways: modelling ideas

    But I have no idea how to make the solenoid assembly or where to start??

    Any help would be very much appreciated.


    Chris White
  2. Neil

    Neil Western Thunderer

    In the past I made solenoids as a part of my apprenticeship, it was the nineteen seventies so memory is a little hazy. You'll need an insulated former (plastic tube and end end pieces) and some enamelled copper wire. Wind the wire round the former in the manner of cotton on a bobbin, tape it down leaving the ends sticking out, scrape off the insulating enamelling on the ends of the copper wire and connect to supply. There are a number of youtube videos on making basic solenoids.

    For the application suggested in your link it's all going to be a bit experimental (wire thickness, number of turns, size of former) but perhaps the biggest difficulty will be sourcing a suitable magnet. Do please share how you get on.
  3. Scale7JB

    Scale7JB Western Thunderer

    Not so tricky in 7mm, but in 4mm I take my hat off to you..!

  4. michl080

    michl080 Western Thunderer

  5. SECR25

    SECR25 Member

    Thank you for your replys chaps!

    Looks like it will all be abit of trial and error but I will document my findings on this forum when I hopefully get round to constructing the locomotive next year at some point.

    JB, if it works, I do plan to do it on my own 7mm builds too but they are nearer the bottom of the queue, on my build list.

    Kind Regards

    Chris White
  6. Scale7JB

    Scale7JB Western Thunderer

    If you're doing it in 7mm, i'd use a different method with servo's personally. But it would be interesting to see how the solenoids work.

    Giles likes this.
  7. Giles

    Giles Western Thunderer

    +1 for servos. you can get very small linear servos which could be used as is, or re-purposed (they are 3.7v) to dirve through a link or v small bowden cable.
  8. Scale7JB

    Scale7JB Western Thunderer

    Apologies for the video quality, this is nearly 10 years old!

    Wagonman, SECR25 and Len Cattley like this.
  9. Nigel Cliffe

    Nigel Cliffe Western Thunderer

    If you wander over to RMWeb and the 2mm section, you'll find Nick Mitchell's 9F. That has the reverser operating the valve gear using a small motor with a high ratio gear head fitted to it, and an eccentric crank.

    Should be a doddle to make that fit in 4mm scale where there's much more space :)

    Whats on your 2mm Work bench - Page 79 - 2mm Finescale

    If going down the servo route, and using DCC control, then Zimo decoders have the ability to control a servo on a modified special function output. It needs a couple of small electronic components added (transistor, resistor, etc.). Can set various positions in CV settings. I have used it in the past.

    - Nigel
  10. SECR25

    SECR25 Member

    I had originally thought of using servo's and bought a small micro servo to do the job. Linear would be much better, do you have any recommendations?
    Is it possible to operate it nonDCC, with the polarity change of the motor?

    That K2 is amazing, a true piece of craftsmanship!
    The 9f video I've already seen and was blown away by it, especially as it's 2mm..

    Kind Regards

    Chris White
  11. michl080

    michl080 Western Thunderer


    you may want to check these

    linear micro servo | eBay

    I have ordered one and it looks and works nicely. Just trying to figure out where to use it :)

    SECR25 likes this.
  12. Susie

    Susie Western Thunderer

    Hi Chris,

    If you want to control it non-DCC then I can suggest using the same or similar method that John Noble used for his S scale Ivatt 2-6-2T locomotive. This used a separate motor to drive the weighshaft. When reversing direction, by using diodes and wiper contacts, the power was fed to the reversing motor first, power not being transfered to the main motor until the reversing motor had done its job. These days using servos it should be easier to fit in. The write-up was originally published in the S Scale Gazette, but was reproduced in full in the MRN for July 1964, pages 409 and 410.

    The SSMRS archives are available, to members only, on our website, but I can send you a copy of the relevant volume if you like.

    Last edited: 2 December 2018
  13. Nigel Cliffe

    Nigel Cliffe Western Thunderer

    For a non-DCC solution, my first approach would be to look at battery radio control for the reverser device. Then its independent of the track, and can be set as required to any advance/retard of the valve gear - thus put it in full forwards for accelerating a train, but notch back towards mid-position for coasting and decelerating. The Deltang radio receivers will do the job nicely, and have a reasonable following in model railway circles. One needs to fit the smallest battery, and a method to connect the battery for charging. There ought to be space for those. Micron radio control is one retailer for Deltang receivers and small Lipo batteries. Choose a radio transmitter which allows the servo angle to stay fixed (ie. not the type where the control stick automatically comes back to centre).
    If the setup is arranged so mid-gear is the default rest position, then if the radio or battery fail, the loco keeps running on DC in mid-gear as if it was a fixed valve gear loco.

    It would be possible to tie things to the DC motor, but I think its going to be complicated and, ultimately, unsatisfactory. A real loco doesn't run in full forwards all the time, so need a method to change the valve setting whilst its moving.

    - Nigel
  14. SECR25

    SECR25 Member

    Hello Susie,

    I would very much like to see the John Noble article and work out if DCC is going to be easier in the long run. I've a few DCC sound fitted locomotives but most of my stock is analogue still.

    All the advice has given me alot of food for thought, I've even found these on an auction website-

    10pcs Micro Screw Stepper Motors Miniature 2-phase 4-wire stepping motor driver | eBay

    Not sure if they would be up to the job? Thoughts very much appreciated .

    Kind Regards

    Chris White
  15. Steph Dale

    Steph Dale Western Thunderer

  16. Nigel Cliffe

    Nigel Cliffe Western Thunderer

    stepper motors are not servo motors. They may look superficially similar on the outside, but control is different.

    Servo - three wires: 0v, 5v and a signal wire. The signal comes from a control board which generates servo pulses.

    Stepper - four wires. They are controlled by connecting combinations of wires, in turn, to a power source. Each connection causes the motor to move, and to make it rotate smoothly, a sequence of connection combinations has to be made (typically several hundred combinations are sent). A small controller board is usually used to create those combinations.

    DCC and servo is fairly simple, but needs a DCC decoder with the ability to drive a servo motor (Zimo, some ESU, possibly others). But may have limited options in how many positions the drive gear can adopt - it may be only two or three positions are possible.
    DCC with a gear-head motor is simple (Nick Mitchell's example).

    - Nigel
  17. SECR25

    SECR25 Member

    Hello Steph and Nigel,

    Thank you for stopping me from making a silly mistake!
    I'll find a linear servo and DCC if this is going to be simpler.

    The one thing that I'm not great on is electrics, most other things I can do.. 20171226_102524.jpg

    Kind Regards

    Chris White
  18. Steph Dale

    Steph Dale Western Thunderer

    Aah, my personal favourite. If that's built from the DJH kit you've done well!

  19. SECR25

    SECR25 Member

    Hello Steph,

    Well the running plate, boiler and dome are DJH! Rest of the kit is a no go.
    Chassis scratchbuilt in Nickel silver and a modified sefinecast tender with lots of added detailing.

    The U1 class was worse, 3 different kits and scratchbuilding to get it right.

    Btw did you finish your exSECR Continental?

    Kind Regards

    Chris White
    AJC likes this.