Current status: STOLEN! If you have seen this car, email me!
The above vehicle is a Tamiya Mini. That's right, just about the smallest and weediest raceable car you can get has been bought by Dan, Lover Of Huge Tractor Tread Tyres and Multi-Horsepower Drive Systems. The Mini's a front wheel drive, all-plastic cheapie that, in stock form, handles atrociously, thanks to being based on Tamiya's "M-Chassis"
The M-Chassis is actually pretty fun to tinker with. Like many Tamiya designs it's quite modular, and can be built as front or rear wheel drive, front or rear wheel steer (rear wheel steer is one for the nuts), or, if you're a true adventurer, twin motor four wheel drive with or without four wheel steer. Tamiya sell it only in the sane front-steer, front or rear wheel drive variants. You can get quite a lot of bodies for this short-wheelbase chassis, from caricatured Japanese cartoon-cars to Volkswagen Kombi vans, complete with surfboard on top.
The standard M-chassis has a suspension design only a beancounter could love. A single coil-over friction damper (not an oil filled shock) joins the left and right A-arms at each end, with a bit more bounce provided by little springs that push against the centre chassis and the A-arms. This design means that when, say, the right side suspension is compressed, the dampers push the left side suspension down, encouraging body roll - which, for less savvy readers, is A Bad Thing. Apparently you can get semi-tolerable performance out of a stock Mini by careful damper and spring tuning.
Bugger that.
If you want to race your Mini in the stock class, you have to live with the standard Sway-O-Matic suspension. Since the stock mini class is, so far as I can see, mainly about remembering to slow down a bit for the corners and avoiding the inexpertly piloted newbie cars, this is not really such a big deal.
If you want to race in the Super Cooper class though, all you need to have is the same wheelbase and track, and a stock (27 turn single wind) motor. Good stock motors look like, and cost only slightly less than, modified motors. They're good for about 110 watts from a 7.2 volt pack, or about a seventh of The Mammoth's power, depending on load - the harder you load an electric motor, the more power you get out of it. The standard sealed-can Mabuchi 540-type motors, such as come with the Mini kit and also feature in zillions of cordless tools and similar applications, are considerably less powerful.
There's also the Super Duper Cooper class, which allows modified motors; personally, I'm in favour of a new class requiring completely stock cars but motors of 12 turns or fewer (300 watts plus...), which we could call Super Duper Pooper Scooper.
But I digress.
I set out to turn my Mini into a proper independent suspension design. There are a number of hop-up kits available to do this, but that ain't no fun. So I bought me some little dampers, and some carbon fibre tube, and set to work. Here's the result.
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| The pink springy things are the laydown shocks for the front suspension, driven through bellcranks by pushrods that come up from the front hub carrier hinge pins. I had to do a bit of shaving to get clearance for the right pushrod over the gear housing - the left one's easy. | The angled-out shocks are a somewhat sub-optimal design, but the fatness of the shock bodies made them foul the main left and right ladder rods if they were mounted any further out. Clevises on the ends of the carbon shock extension rods keep the thrust pretty much on-axis. |
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| Each bellcrank is made from two plastic servo discs, cut down to a 90 degree arc for the outer, clevis-connecting part and less for the other side. The pushrods have ball joints at each end. Observe see-through nylon bolt joining two sides of bellcrank; it saves a few grams of weight but mainly just looks cool. | The rear suspension is less exciting than the front. The drilled right angle plastic that bears the ball mounts for the top of the shocks is fixed to the superfluous rear steering mount knobs - the M-Chassis front and rear share a lot of parts, resulting in unused extras like this just asking to be employed for means other than that intended. The bottoms of the shocks are ball-jointed to the outer hinge pins, again; I just bought up a few longer Tamiya hinge pins and used the protruding length. |
Copyright © Daniel Rutter 1998. Last modified 13-Nov-2007.
