Thank you all for your positive comments / feedback.
You are right Giles about the Faller references. We got quite a few at the show. plus a lot of people who assumed that it was Faller, , , until I did a 3 point turn. at which point you get the raised eyebrows and the puzzled look. And then the questions.
To explain the workings I shall have to break it into installments.
I'll start with the Scarab, as thats where it all began. Operating Upper Benllech at the Croydon MRS exhibition in 2012 we discussed how the big yard and long road down the back was a fantastic opportunity to run road vehicles, but Faller wouldn't do the job, even if we could slow them down, the manouvers needed for the yard required better control than a buried wire would offer.
Scammell Scarab.
As mentioned previously, the scarab started life as the Merit kit. It uses the tractor chassis, seriously hacked about to clear the gubbins, plus structure to support the steering and stiffen things up. The front steering yoke is cut from brass box section, and uses a romford crank pin for the vertical axis.
The actuation uses a proportional actuator from indoor micro aircraft. I found Micron Radio Control particularly useful.
The actuators are used to operate the rudders on aircraft (they do OO scale radio controlled airplanes!) and use a pair of magnets pivoting inside an electromagnetic coil. It doesn't have a lot of power, and I ended up adding some extrs soft iron to centre the steering as even the lightest spring was too much.
The actuator drives the steering via a link arm from brass wire (thats about 1mm dia for scale reference).
I can't remember why I mounted the coil on the vertical axis, I had a good reason that had something to do with space, it does mean the connections have to cope with both axis of movement, so they use a simple ball and cup made by filing a collar on the link to match a countersink. A minature eclip holds it together.
The yellow circle above the front wheel is the surface mount LED, it lines up with a short length of fibre optic in the nose to create the lens.
The PCB on the far side is a RX43d-v5 from the deltang range. It is a little large and I originally used the Rx45-v5 but had a slight polarity incident with the trailer connection and it went phut. I had the Rx43 ready for the next project so in it went. One day I might correct it, but the wires are glued into their routing so it will need some impetus for me to change things. The strange black blob is the head and shoulders of the driver. there was so little of him left, that I decided to stick with a sillouette in the window rather than attract attention by giving him colour.
The motor gearbox is mounted between the frames, its has an epicyclic gearbox in the black section. it came from Precision Microdrives who do a wonderful range, they look very similar to those on the mikromodellbau etc websites, I dont know whether one gets from the other or they have a common source. But Precision Microdrives also provide a full data sheet as they are really targeted at commercial clients. I have also bought gearmotors from Gizmozone who also provided the bevel gears (and the previously mentioned eclip). The rear axle runs in metal bearings inserted into the mouldings to reduce friction and hopefully, wear.
You can see the extra space infront of the motor, where there used to be a lower ratio gearmotor. It felt painfully slow when I first built it. However, after the Chapel show, I will be changing back. Incidently, this is the third motor. Number 2 was so fast I could race my son's RC integra down the hall, until straight line stability got the better of me!
The result is a very small model.
With the entire drive train, steering and control fitted into the tractor. Which leaves only the battery to fit on the trailer.
That does present its own challenges. I'll cover the 5th wheel coupling in a day or two if your interested.
Hope that all makes sense, but please ask if you have questions.