Reversing valvegear?

alcazar

alcazar

Guest
Years ago, in MRJ, I saw an article on the building of a 7mm scale Finney A4. One of the things it had was working valvegear.

I'd like to incorporate something similar in my 7mm steam locos.

I have an idea how to move the valvegear, and have already sourced a tiny 12V motor with integral gearbox and an output of only 148 rpm, with which do do trials.

What I'm in need of is a wiring diagram showing how to do it on DCC...ideally so that the valvegear is selected by the choice of loco direction, and the loco doesn't move until the valvegear has set properly.

Sadly, the MRJ article had the all-important wiring diagram missing.

Can anyone help, please?
 
Osgood

Osgood

Western Thunderer
I haven't a clue as yet when it comes to DCC.

However - in a world bereft of ecectronic gizmos it should be possible to route the power command signal first to the valve gear motor, which would then position the valve gear such that either forward or reverse relays energised the drive motor in the desired direction.

A variable resistance linked to valve gear cut-off position could even regulate the power available to the drive motor so that effectively the valve gear acted as direction and regulator. So in full forward gear you had maximum current - reducing the cut-off would proportionally reduce the current and mid position would be regulator closed.

OK not prototypically spot on, but nevertheless reasonably close to real life control. (it effectively simiulates driving a locomotive on the reversing lever only - as if it had a stuck or leaking regulator valve).

There must be a really neat way of doing that electronically?

I'm very interested in the interface between human and machine, and have had the odd play with DCC - it certainly gives a better 'feel' for the real thing than a simple rheostat, but I've not yet found one which gives an outstanding representation of being in the driver's seat.

And not that I've tried it, but I find the whole concept of 'driving' a locomotive using function buttons on one's mobile phone decidedly odd - better for me a few hefty iron levers :thumbs: :D
 
Mike Sheardown

Mike Sheardown

Western Thunderer
Why not simply use a function button, then you could operate your reversing gear manually - just make sure that your 'small' motor, doesn't demand more current than the decoder will supply.

I guess you are thinking of doing this on a loco with a screw reverser rather than the pole type? Are you planning on using some kind of worm and gear drive?


Good luck with it

Mike
 
Len Cattley

Len Cattley

Western Thunderer
alcazar said:
Years ago, in MRJ, I saw an article on the building of a 7mm scale Finney A4. One of the things it had was working valvegear.

I'd like to incorporate something similar in my 7mm steam locos.

I have an idea how to move the valvegear, and have already sourced a tiny 12V motor with integral gearbox and an output of only 148 rpm, with which do do trials.

What I'm in need of is a wiring diagram showing how to do it on DCC...ideally so that the valvegear is selected by the choice of loco direction, and the loco doesn't move until the valvegear has set properly.

Sadly, the MRJ article had the all-important wiring diagram missing.

Can anyone help, please?
Click to expand...

Wouldn't MERG be able to help you on that?

Len
Wouldn't
 
alcazar

alcazar

Guest
Mike Sheardown said:
Why not simply use a function button, then you could operate your reversing gear manually - just make sure that your 'small' motor, doesn't demand more current than the decoder will supply.

I guess you are thinking of doing this on a loco with a screw reverser rather than the pole type? Are you planning on using some kind of worm and gear drive?


Good luck with it

Mike
Click to expand...


Yes, a home made worm and gear, probably a bored out 6BA or 4BA brass bolt and the nut running up and down it on a track, or sorts, with a linkage fastened to the nut and a pair of levers to move the reversing gear.

That, I can cope with, but I have no knowledge of DCC for the wiring.
 
JimG

JimG

Western Thunderer
I'll see if I can find the late John Noble's article in the MRN in the 1960s where he fitted operating reversing gear to an S scale LMS 2-6-2T. No DCC in those days, but his methods might give some ideas for a modern implementation. BTW, the locomotive is still alive and well and was seen at the recent S scale Autumn meeting.

Jim.
 
alcazar

alcazar

Guest
LOL, clever devil!

OK, now tell me, or show me how the reversing gear works? How was it done, please?

Jim: thanks for that, I'm reading and re-reading that article to see how I can make use of it.
it's a very similar idea to mine as to actually moving the gear, the electronics looks fairly simple too. Thanks.
 
ZiderHead

ZiderHead

Western Thunderer
I would have thought a micro servo would be a better option than a motor and worm for this. Do you want it to move proportional to the speed as well as doing the reversing?
 
ZiderHead

ZiderHead

Western Thunderer
Well my (very limited) understanding of driving steam locos is that the reverser acts as a continuously variable gearbox, so it not only switches direction but adjusts the valve gear to allow higher speeds or greater torque.

Just had a flick through the Zimo manual and those clever german chaps have done all the hard work for you - CV 185 is for live steam servo control and could be used to control your valve gear :)

CV #185 Special assignment for live steam engines

= 1: Steam engine operated with single servo; speed and direction controlled with speed regulator, stop is in center position.
= 2: Servo 1 proportional, on speed regulator, Servo 2 for direction.
= 3: as in 2, but: direction-servo is automatically in “neutral” if speed is 0 and F1 = ON; If speed
step > 0: direction-servo is engaged.

NOTE to CV #185 = 2 or 3: Servo 1 is adjustable with CV #162, #163 (end stops); with appropriate values the direction can be reversed as well. Servo 2 is adjustable with CV #166, #167.
Click to expand...
 
Osgood

Osgood

Western Thunderer
Although that would give proportionally greater valve gear movement as speed increased - we need full movement of valve gear to start, gradually reducing the position towards centre (neutral / off) as speed increases (i.e. notching back, less steam used).
 
alcazar

alcazar

Guest
Too complicated for me, and my locos will spend most of their time trundling round a shed, so a simple forward/reverse would do.
What sort of servo would I be looking for?
 
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