Saturday, July 6, 2013

A Battery Compartment Cover For A Lego R/C Dune Buggy

Pictured below is a garage sale find.

My son picked it up for very little. It's in fine condition and complete, except that it's missing its battery compartment cover underneath. Here's a view of that.

This may be a bit challenging; we'll see how it goes.

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I have some 0.024" thick aluminum that will serve for a cover. The most intricate part of this will be the cover's rear edge, so I'll start with that. Once I have that so it fits, I'll cut a rectangle the correct width from the oversize piece of aluminum stock, and the remainder of the work ought to be fairly straightforward.

Here's a view of the rear edge's layout done on masking tape.

I can cut most of that with a nibbler, then file to the layout lines.

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So Far, So Good

The rear edge fits perfectly.

I'll finish this tomorrow. The union here doesn't like me to work overtime.

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Front And Rear Edges Both Fitted -- SUNDAY, JULY 7, 2013

The front edge turned out to be a bit of an ordeal; it needed two shallow notches to accommodate the two latches. That took a fair amount of trial-and-error filing to get it right. Anyway, it's done now.

The remaining edges are simply a flush fit to the perimeter of the battery compartment, so I just have to trace the outline from above, and cut it with snips.

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All Cut To Shape

It's nearing completion.

I tried it out with the battery inside, and that 0.024" thick aluminum appears to be quite adequate for the job.

I'll laminate fish paper[1] to the cover's upper (inner) surface with double-sided tape, both for the sake of electrical insulation (not that it's really needed), and to lend the cover a little extra strength. The good effect that lamination has on the strength of thin materials is remarkable.

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Fish Paper Lamination Done And Painted -- MONDAY, JULY 8, 2013

I hadn't meant to paint the fish paper side, but my ancient roll of fish paper was badly discoloured, and looked awful, so I painted it 'camouflage khaki'. Here's a view of that.

[It says 'camouflage khaki' on the spray-paint can. It looks like a pretty good facsimile of 'light/medium grey' to me. Whatever.]

I'll let that paint harden for a day or two or three, then I'll do the flat black painting of the underside, and this thing will be well and truly done.

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Fully Painted, But With A Revision -- SATURDAY, JULY 13, 2013

The light colour on the upper surface turned out to have been a mistake -- it showed a little at the sides and didn't look right. So, I made the cover flat black all over, and added an 'UP' label to the insulated side, like so.

And that's as done as it's going to get. Here's a view of the car with the cover in place.

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Another Revision -- TUESDAY, JULY 16, 2013

My son pointed out a potentially misleading characteristic of the 'UP' label I added to the insulated side of the cover. Consider --

To access the battery, one turns the car upside down. It would not be wildly illogical, then, to replace the cover with the word 'UP' facing 'up' -- i.e. ultimately upside down.

I guess the simplest fix for that would be to replace 'UP' with 'IN', like so.

There; that should take care of that.

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[1] Fish paper is a tough, thin (0.010") elecrical insulating material. I tend to think of it as belonging to the days of vacuum tube electronics, but it's still used and is still available. Why it's called 'fish paper' is a mystery  to me; it neither looks like nor smells like fish. Were I to go fishing, it wouldn't occur to me to take any fish paper with me. Were I the proprietor of a 'fish & chips' establishment, I wouldn't serve fish & chips wrapped in fish paper -- that's what newspapers are for, like so.

If anyone knows why 'fish paper' is called 'fish paper', I wish they'd explain it to me.

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