An M.G. Locost Build
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November 8, 2016
Still Welding

Update on our spare tire mount. We managed to get the new channel bolted in and the fuel tank installed without too much damage, and we're back on the road now with the spare tire firmly affixed. The best part of this repair may be that with only minor bodywork we were able to lower the spare tire another half an inch, which may not seem like a big deal but it keeps the spare from dominating the view out of the rear-view mirror, and also allows the spare to sit in the steel cradle that we built for it, instead of on the pile of rubber padding we had to stack on top of the steel cradle to make it fit.

  Installing new channel with paint almost dry
click to enlarge

As predicted, the new spare tire mount is way stronger than the old one. This became apparent as soon as we bolted on the long threaded rods that protrude from the back of the car. Three years ago when we first bolted those rods to our poorly-engineered flat mounting strap, we could wiggle them fairly easily, probably half an inch at the ends. We didn't think anything about it at the time, and assumed that bolting on the spare tire would fix it. Which it did, and so in our estimation we didn't need to worry about the spare tire anymore.

What we failed to realize was that even with the spare tire bolted on, the rods were still free to wiggle. And with the help of the heavy spare tire, they did, at pretty much every bump in the road. The flat mounting strap was just too flexible. This time when we bolted the threaded rods to our new channel mount, we couldn't wiggle them at all. Not even a little. I think we could've put a jack under the rods and lifted the back end of the car. So it seems once again we don't need to worry about the spare tire anymore, and this time I think we mean it.

Steel frame 3" longer than wooden prototype  
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Meanwhile this week we finished the frame for our junior-scale Locost. Not "finished" finished, of course, but the basic structure is done. We had no trouble fitting any of the tiny tubes, or bending the 3/8" round tubes in back, and we left plenty of room for whatever transaxle we end up installing, based on our extensive and proven experience in estimating component clearances. We didn't attach any brackets other than the seat belt mounts, and while at some point we'll have to attach a wiring harness, we don't know what it'll look like yet, so we're in the clear there.

With the frame done there's little left to get the car ready for the Maker Faire. Or maybe there is, we're not sure. We might weld up the suspension A-arms and trailing links, although we could always use the wooden parts from last year, although they might not hold up if someone tried to sit in the car. We're also thinking about making an 8" replica of our wood-rim Moto-Lita steering wheel, which wouldn't be hard so long as no one expects too much. The other pieces we need, like shocks, hubs, wheels, and tires, will be more problematic, since they have to be bought rather than made.

  Wheelbarrow wheels with tiny built-in bearings
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We expect that most of the drivetrain will use go-kart components, including the wheels, hubs, and a solid rear axle with a single disc brake. Right now we're having a little trouble sourcing wheels and tires. We want to use tires with a 14" diameter and a 3" width, a common size for wheelbarrows, but we're having no luck finding bolt-on wheels thin enough for wheelbarrow tires. Google 6" bolt-on wheels and you'll get mostly full-size car wheels in a 6" width. The few 6" go-kart wheels you find will also be 6" wide, or maybe wider. Go-kart guys like their wide wheels and tires.

We want bolt-on wheels no more than 4" wide, preferably narrower, and if anyone has them they're not making them easy to find. You might think, since we're using wheelbarrow tires, that we could just use wheelbarrow wheels. And so did we, but unfortunately there's no such thing as a bolt-on wheelbarrow wheel. They all have built-in bearings that slide onto the axle, which wouldn't be the end of the world except the bearings aren't really made for speeds much above a walk, and in any case we can't use them in back because the rear wheels have to be driven by the axle.

Starting point for the rear axle housing  
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So we gave up on that and started working on the rear axle design, or at least thinking about working on it. Last year our rear axle consisted of a wooden dowel with wheels bolted on the ends. That won't get it done this year because for one thing the wheels have to turn. What we've come up with so far is an axle housing based on a 32" keyed shaft with threaded ends, like the one we purchased recently from our local karting supply shop. We have yet to incorporate a motor, gears, or other items that might propel the car in a forward direction. Or any direction. But first things first.

The main thing the rear axle housing has to do is support the rear axle, preferably in a way that allows the axle to rotate, which usually means bearings, ball or roller, and something to mount them on. The next thing the axle housing has to do is hold up the back of the car, which probably means springs and shocks and the traditional Locost trailing link brackets. So we need brackets, and bearings, and a place to mount the bearings, and for some reason while we were thinking about all of this an odd thought occurred to us. What if we mounted the bearings right on the trailing link brackets?

  First axle housing parts in place
click to enlarge

So we made up a pair of trailing link brackets out of 1/8" wall, 1-1/2" square tubing, and then bought a couple of axle bearings, and darned if the bearings didn't fit perfectly in the brackets. Amazing. Like they were made for each other. We still have to figure out a way to connect the brackets together so the axle doesn't get all bent out of shape and bound up in the bearings, and also a way to mount the aforementioned motor, gears, and brakes. We can think of several ways to do either, not so much a way to do both at the same time. So we have a few details to work out.

In any case this is looking better than our original idea, which was to use a transaxle from a mobility scooter. That would've eliminated a lot of work, but three things: 1) Mobility scooters are narrow, and the axle would have to be seriously modified to widen it, 2) Mobility scooters have electric brakes instead of real brakes, and 3) Mobility scooters are not fast. They have a top speed of maybe eight mph, at best. Most of them top out at four mph. That's simply not fast enough. The giant cupcakes that roam the Maker Faire each year are way faster, and we will not be beaten by a cupcake.


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posted November 14, 2016 at 13:16:20  
You may want to check out Dennis Thomas's cyclekarts on youtube for some ideas.  
posted November 24, 2016 at 01:52:22  
great meeting you today Nick, I really appreciate that you took the time to come out of your way to show me your car. Enjoy the Jaffas. John Lee -New Zeland