Friday, July 13, 2018

Short Circuit

Short Circuit was a great 1980s film that I quite enjoyed as a kid (not my favourite 1980s film but not bad all the same), but when it comes to railway modelling the last thing you want is a short circuit; it's more likely to end in tears and you pulling your hair out rather than laughing hilariously. Now imagine my surprise that I've had to solve a short circuit issue on Canopus.

In fairness I think this issue is down to the original wheels the kit was designed for not being available when I bought mine and so a different set were provided. Originally both wheels were isolated from the axle. This means that you had to fit pickups to the wheels on both sides of the model, but that the model itself was insulated from the track. The replacement axles have only one wheel isolated and the other is live to the axle. This means that I only have to fit pickups to the isolated wheels as I can just connect the motor direct to the chassis as the power will flow from the wheels to the axle, through the bearings and into the chassis. So far so good; I hate fixing and adjusting pickups so I'm more than happy to halve the work involved.

The problem though is the trailing wheel. If you remember from a couple of posts back the wheel is mounted on a metal truck that pivots from the chassis. Now while both wheels are isolated from the axle, there is enough movement to allow the wheels to both touch the chassis and for the back of each wheel to touch the pony truck. If this were to happen to the wheel on the same side as the insulated driving wheels we'd have a short as both rails would now be connected to the chassis.

My solution to this involves two modifications. The easiest bit was to ensure that the wheel couldn't short against the chassis frames. I've fixed this by putting a piece of masking tape on the inside of the frame. To try and make sure it doesn't come off I've run a small bead of superglue around the edges and then painted it black to hide it against the frame (it's unpainted in the photo). Making sure the wheel can't short against the pony truck was harder. I went through a number of ideas for this but in the end I thinned the truck slightly and then glued a thin piece of plastic to the side (so that with the plastic the truck is still the right width).

As far as I can tell these two modifications should ensure that the wheel now can't cause a short circuit, but the real test will of course come when I finally wire up the pickups and test the loco on the track. Fingers crossed.....


  1. Another film that I've never seen.
    I did wonder if you were going to get a short through the pony truck. A thin smear of epoxy is a good insulator as well.
    I hate wiring up pick-ups as well, a job that I shall be doing myself very shortly. In fact I'm not keen on any wiring job. But unless I start building push along trains (tempting, I'd save money on motors and gears) or go clockwork its something that I have to put up with. I do prefer the one side live approach though. Half the pick-ups is half the hassle.

    1. Yes, fitting pickups is definitely my least favourite step of a build, so only having to do half is fine with me. Fortunately I spotted the problem before I went any further so it was easy to modify -- I did only glue the pony truck stretcher in place rather than soldering it as I wondered if I'd need to modify it further.

  2. Is it possible to use plastic wheels?

    1. The thought had crossed my mind, but I didn't have any to hand and I didn't want to wait for some to be delivered before I could do any more to the kit.