Stronach-Dutton Road-rail tractor

[Jeff Schumaker]

Is Foul Ol' Ron driving?

Jeff S.

[Hugh Norwood]

The new motor and gearbox are from Rod Allcock; he very kindly let me have it to try out. It has a 12V Mashima motor with a reduction just over 50:1. I think the Tomytec chassis was about 13:1, so it's much better, but still not enough for what you might call controlled motion. I would guess that increasing the reduction ratio further would also increase the torque? It is a bit touchy about starting off.

[Graeme Dunbar]

It looks very good in the video, but I see your point - the benefit of all the gearing is being undone by the big driving wheels. It's almost as if you need something like the belt drive  as used on Mamod traction engines, or friction wheel rim drive as used in some Nigel Lawton drives.

Radio control servos have significant gear reduction, but I'm not sure any are small enough to fit. On second thoughts (after a quick check), possibly small enough with the case and electronics stripped out, but arranging the drive to the wheels would be a real challenge:
http://www.hobbyking.co.uk/hobbyking/store/__95774__HobbyKing_8482_HK_5320S_Ultra_Micro_Digital_Servo_0_075kg_0_05sec_1_7g.html

[rod335]

A rather evil thought occurred to me. Why not just replace the front bogie with a Portram chassis? (Runs for cover.)

[Graeme Dunbar]

That's a good point.

I almost got there. It crossed my mind that if it was a steamroller a small pair of driven railway wheels could be hidden between the large solid (free-wheeling) rear wheels, but why anyone would want a road-rail steam roller I don't know. Perhaps it is something B.S Johnson would come up with?

As always, Angst Lesspork continues to fascinate!

[danny]

You could always drive the rail wheels as well so that it would be more controllable, but without losing the benefit of the road drive on gradients. It depends whether you are going to model the steep gradients of the prototype system.

[Hugh Norwood]

You could always drive the rail wheels as well so that it would be more controllable, but without losing the benefit of the road drive on gradients. It depends whether you are going to model the steep gradients of the prototype system.

The problem with that would be getting the two to go at the same speed!

[Hugh Norwood]

I have got a motor/gearbox from a Polish firm, that has a 324:1 reduction. The trouble is the final gear on the axle is only a few millimetres in diameter, and I'm worried that the gear will just come unstuck, or shred itself....

It was only ever an exercise in proving a point (which it has done), but I'd like to get something that works a bit better...

[danny]

You could always drive the rail wheels as well so that it would be more controllable, but without losing the benefit of the road drive on gradients. It depends whether you are going to model the steep gradients of the prototype system.

The problem with that would be getting the two to go at the same speed!

A bit like locos with separate motor bogies or double heading.

[Hugh Norwood]

Some news in the offing.....

[Jeff Schumaker]

Nice work, Hugh.

Jeff S.

[Hugh Norwood]

Here we are: the Mk2 Roadrail tractor. This is powered by a Portram bogie under the front wheels (and like the real thing, it can be demounted - I have a modified showman's that can be hitched on as well...)

https://youtu.be/IxoLdKmvtTY

[Hugh Norwood]

This was remarkably easy to do. Firstly I had to source a Kato Portram tram, then take it to pieces (quite a miracle of tiny engineering). This left me with two motorised chassis.



As you can see from the photo, I modified one by sticking on a pivot and support made from styrene strip. The motor leads also hav eto be soldered to the pickups.

Converting the road tractor was simply done by drilling a hole up into the front wheels support, then sticking in a short length of stiff wire. I added a short piece of styrene to bear onto the bogie.



And here it is in the test track. I have added some sideframes to hide the wheels. The bogie just needs a coat of matt black now.

[Jeff Schumaker]

A very simple conversion. Well done.

Jeff S.

[rod335]

Really does need a 150 ohm (or bigger) dropper resistor if you haven't already fitted one.