Belt Transmission for Tamiya M-Chassis Cars
There’s no shortage of interesting hop-ups for Tamiya’s popular lineup of M-chassis mini cars, but some upgrades are less about performance than they are about flashy looks (nothing wrong with that, by the way). But if you crave killer looks and hot performance, then Tech Racing* has just the hop-up for your M-car: a trick beltdrive conversion that matches go-fast looks with realworld performance.
The belt conversion is pure simplicity; a pair of blueanodized aluminum side plates sandwich a ball differential and a pulley-equipped layshaft. The spur gear is attached to the layshaft and is driven directly by the motor pinion. Any “standard” spur gear can be used, and Tech includes a 102-tooth, 64-pitch spur. The completed tranny is a direct replacement for the original Tamiya tranny.
There are three primary advantages to the Tech beltdrive transmission. The biggest advantage is increased efficiency over the stock gearbox-efficiency that will give your M-chassis better acceleration, higher top speed and longer run time. The belt tranny simply has fewer intermeshing parts, and the use of 64-pitch gears further increases the smoothness of the drive train.
The second major advantage is the included ball diff; unlike the stock Tamiya gear diff, which does not allow any slip, the Tech ball diff can be adjusted to help soften the power delivery and thereby avoid wheel hop or wheelspin. The ball diff accepts the original dogbones and is quite smooth.
Finally, the Tech belt conversion allows much greater flexibility in the gearing department; whereas the original car offered only three pinion choices, the conversion tranny allows a much greater range of pinions and spurs in 48- and 64-pitch flavors.
On the negative side, I was a little disappointed to find there is no provision for mounting the kit steering assembly on the Tech unit; it’s for a rear-drive chassis only. But unlike the stock transmission of rear-drive Mcars, Tech’s belt tranny does not require a reverse-rotation motor; any off-the-shelf stocker or modified motor will drop right in. At first, the rear-only design didn’t make sense, but when I considered that the Mini Cooper and the MX Lowdown are the only front-drive M-chassis Tamiya has produced, the rear-drive configuration seems appropriate. Less appropriate are the included bushings, which are out of place on such a trick piece of hardware. I replaced the 10x15mm bronze bushings that support the ball diff with a pair of bearings from DuraTrax. I also replaced the two bushings on the layshaft with 5x8mm bearings.
I found the Tech belt conversion much quieter than the stock gearbox, and run time increased dramatically when it was geared similarly to the kit’s stock setup. However, the greater efficiency of the belt system allows higher gear ratios to be used effectively, and that’s when things get interesting. Geared up, the Tech belt transmission can propel an M-car to speeds well beyond the handling capabilities of the narrow, shortwheelbase chassis. It’s fun in a straight line, but watch those turns! In sum, the Tech Racing belt-drive conversion is a well-engineered hop-up that can dramatically increase the performance (and appearance) of rear-drive Tamiya M-chassis cars. -Louie Patterelli
Copyright Air Age Publishing Jun 1998
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