Pickups on an 0-4-2T - how?

[Ruston]

Evening all,

 

I have recently built a scratchbuilt 0-4-2 chassis for an old Hornby/Triang Nellie ( https://www.rmweb.co.uk/community/index.php?/topic/120431-show-us-your-pugbashes-nellieboshes-desmondifications-jintysteins/&do=findComment&comment=3549346 ) . The project is finished now and although the chassis works fine as a mechanism it only has pickups on the driven axles, which does cause problems on a few places on my layout. These same places don't cause 0-4-0 tank engines, with even shorter wheelbases, any problems.

 

Initially I did fit some thin nickel silver wire that pressed down on the treads of the carrying axle that were also supposed to work as springs (the axle was retained in horn guides and bore no weight except for the spring force) but they didn't work well as pickups and all they did was to prevent the axle from turning and take weight from the driven axles, which resulted in slipping at changes of gradient, so I'm after some advice on fitting pickups to the non-driven axle and weight distribution on 0-4-2 models in general.

 

I'm also working on a Mk.2 version of the chassis, which should alleviate the problems of loss of adhesion at changes of gradient by taking the weight on the drivers and putting it evenly between the leading and centre axles by use of beams. The carrying axle is free to rock on an adjustable screw pivot.

Ignore the all metal wheels as these are only for setting up purposes.

 

Edited May 11, 2019 by Ruston

[Guest WM183]

I would think due to split chassis design that adding wipers of thin nickel silver wire to the rear of the trailing wheels would be pretty straightforward? Also, you'll likely want the weight quite far forward, even over the front axle; tension on the rear will tend to lift the leading axle.

[Brassey]

I treat my 0-4-2's as 0-6-0's and have the trailing axle load bearing with beams throughout.  Standard n/s wiper pickups on all wheels work for me:

 

[Miss Prism]

31 minutes ago, Ruston said:

(the axle was retained in horn guides and bore no weight except for the spring force)

 

I find it difficult to believe the trailing axle bore no weight, but if that was so, it is inevitable the axle would be unable to turn if any form of pickup was used on the axle.

 

Where is your CofG?

 

[Ruston]

25 minutes ago, WM183 said:

I would think due to split chassis design that adding wipers of thin nickel silver wire to the rear of the trailing wheels would be pretty straightforward? Also, you'll likely want the weight quite far forward, even over the front axle; tension on the rear will tend to lift the leading axle.

It's not a split chassis. The all metal wheels are just what I have to stand it on for now. It will have plastic wheel centres and so will need pickups.

[Guest WM183]

Oh! I didn't look quite close enough. Regardless, some pickups for the trailing axle from thin NS wire should be quite easy to do. 

[Ruston]

1 minute ago, Miss Prism said:

 

I find it difficult to believe the trailing axle bore no weight, but if that was so, it is inevitable the axle would be unable to turn if any form of pickup was used on the axle.

 

Where is your CofG?

 

I don't know exactly where but somewhere forward of the centre axle as the loco as it is runs quite happily on 4 driving wheels with the rear axle removed. This is with the bunker full of lead too!

[Captain Kernow]

Dave,

 

On my replacement chassis for the Hattons/DJM 14XX, I used wiper pick ups on the backs of the four driving wheels, plus additional pick ups on the tops of the flanges of the rear drivers, plus a similar arrangement on the top of the trailing wheels. I've used thin (and flexible) P/B strip from Eileens for this purpose.

 

 

Edited May 11, 2019 by Captain Kernow
Typo

[Ruston]

Thanks, Cap'n. Does the rear axle take any weight on it?

[Ruston]

I have put the proper wheels in the new frames and have pushed them with a locomotive through the tightly curved point that was the site of most of the trouble and found that with the carrying wheels going first into the facing point they were being forced to one side and were binding against the spacers between wheels and frame. I'll either have to rebuild the frames with narrower stretchers or mount the carrying axle on a pony truck. I'll probably bodge it by filing the frames thinner behind the carrying wheels in order to allow more side play.

[Captain Kernow]

On 11/05/2019 at 21:29, Ruston said:

Thanks, Cap'n. Does the rear axle take any weight on it?

Hi Dave,

 

Not much weight on the rear pony wheels. I've balanced the chassis and body so that the majority of weight is on the two driving axles. The rear axle is very slightly sprung.

 

If I was doing another one (which is still possible), I would build the chassis with twin-beam compensation, using a High Level SlimLiner gearbox (originally designed for 3mm scale).

 

[DCB]

I think a bit of lateral thinking is required.  The trailing axle needs to have as little friction as possible, and that means split axle pick up.  That doesn't mean the loco has to be split chassis only the trailing axle. I wonder if plastic axleboxes with brass bushes wired to the motor etc would do the trick?  Split axles themselves are do able for carrying wheels simply by sawing he axle in half and rejoining with an insulated sleeve. As Bacjhmann found out it doesn't really work for driving wheels.

I think lack of weight not lack of pickups could be the reason for the OPs pick up issues.

[Ruston]

That sounds like a cunning plan. The horn guides are made to take an 1/8th axle but the wheels I will be using come with a 2mm axle, so it should be easy enough to cut the steel axle and sleeve it with plastic tube, with a plastic rod to insulate the two halves and the 2mm steel axle sticking out at each end.

 

I eased the back-to-back measurement on the trailing axle, and milled about .5mm from each of the frame plates around the carrying wheels and it now pushes through the problem curve with no problem and with the carrying wheels revolving. I'll be buying the proper wheels and a gearbox for it this weekend, so by this time next week it may be up and running again.

[Ruston]

I have it working again but it has gone from one set of problems to another. It now has all-wheel pickup and will go around the problem curve and points but now it doesn't always stay on the track when running through trailing points on the curved part. It's fine running in forward gear through them but in reverse it appears that the weight is transferred to the smokebox end and so the unpowered rocking axle doesn't have enough weight over it to stay on the rails. The whole loco now rocks back and forth on the pivot beam.

 

All fixed and working well now.

Edited May 29, 2019 by Ruston