Aluminium rail pick-up

[Martin Wynne]

@James Walters

Hi James,

I have just been watching your latest Bexhill West video about your cassette system:

That's very ingenious! But there is one thing worrying me.

Using aluminium alloy as running rails is a bad idea, especially for P4.

Aluminium has a very thin but hard oxide layer on the surface which is a poor electrical conductor. If you clean or cut into it, the oxide surface reappears within a fraction of a second in air.

This means that electrical pickup from a rolling contact on aluminium alloy causes significant sparking. Which creates a build-up of burnt crud on the wheels, which makes the problem progressively worse. You will be in for a lot of frequent wheel cleaning.

In P4 it is even worse, because P4 wheels have such shallow flanges that any significant build-up of dirt on the wheels can reduce the effective flange depth to such an extent that you start getting derailments. This is the well-known "Sunday afternoon derailments" effect on large P4 layouts at exhibitions (although there aren't very many large intensively-run P4 layouts around). Nowadays a lot of exhibition halls are air-conditioned, which has much reduced this problem from general atmospheric dust and dirt on model railways.

I suggest running ordinary nickel-silver rail along the cassettes instead of relying on the the alloy angle for electrical pickup. That might mean that the the angle doesn't need to be metallic and you can use something laser-cut instead.

If it was anything else sliding along aluminium alloy you could arrange some sort of sliding contact or pick-up plunger which would work much better than a rolling wheel contact. Unfortunately that's not going to look too good on a finescale P4 locomotive.

I just know that several folks will now say that they have been using aluminium-angle cassettes for years without any problems. But I remember hours spent cleaning wheels at club exhibitions, and the difficult-to-remove black line which appears along the angle after a long operating session.

There was a similar problem with the old H&M solenoid point motors when they changed from using brass contact rivets to aluminium rivets in the integral polarity changeover switch. I remember drilling out the burnt aluminium rivets and replacing them with roundhead brass screws and nuts.

I hope you don't mind my posting this publicly. I'm not keen on writing emails and private messages when I know the information will be of interest to many others.

cheers,

Martin.

 

[James Walters]

Thank you Martin for taking the time to express your thoughts, and no, I don't mind you posting this publicly. Far from it. I'll be the first to acknowledge I'm feeling my way through this with little to no experience. I've only progressed as far as I have thanks to the generosity of those who have shared their experiences with me and I can't think of anyone better placed to give advice on trackwork than you.

Now, one of the advantages to aluminium angle as I saw it was that the angle would effectively do two jobs, provide the running rails and also add stiffness to the cassettes. I believe Colin Chapman used to have a similar philosophy when engineering his Lotus cars. He liked components to be dual function as it reduced weight and improved the simplicity.
But in this case, design efficiency will be counter-productive if it will reduce operational effectiveness, so I shall put my thinking cap back on and consider how to replace the stiffness in a neat and tidy manner.
One benefit which has already come to mind is that I could produce some PCB sleepers which would interface with the electrical connectors I am proposing to use more simply, so already there is a small win.
As mentioned in the video this is all currently an experiment, I'll enjoy considering all improvements.

Thanks again,

James

 

[AndyB]

Yes, the reason aluminium does not corrode is because it is highly reactive, which sounds like a contradiction. The rapid oxidation at the exposed surface seals and protects the metal from further corrosion.

About fifty years ago a lot of houses in the US were built with aluminium rather than copper wiring. It caused a lot of problems at the terminations and housing went back to copper. Aluminium is still used for transmission but it requires special termination methods.