Tamiya Twin Motor Gearbox Modification

Tamiya manufacture a number of gearbox kits for models, this application sheet looks at their Twin Motor Kit (70097). The kit uses an FA-130 motor that operates on 1.5 - 3v, with a current draw of 0.66 - 1A up to 2.2A when stalled. This gearbox can be configured for two different ratios:-

Standard Ratio (Pictured)
58:1 gives 269 g.cm torque at 230 RPM at 3v

Low Ratio
203:1 gives 941 g.cm torque at 65 RPM at 3v

When considering the standard ratio configuration the torque is low for minisumo. The size presents some problems when using the Sports Tyre Kit (70111) as it's width cannot brought within the minisumo limits without removing the mounting lugs.

In low ratio configuration we get a much better torque and the mounting lugs are positioned within the wheel rim. As pictured above we can clearly see the axle's and hub's protrusion that are to be modified.

To reduce the over all width we have cut the 50mm axle down to 36.5mm and cut the hub down from 21mm to 16mm. This allows the wheels to be fitted much closer to the gearbox body as pictured. Taking the usual care for hand tools, these modifications can be made with a small hacksaw with rough edges cleaned with a files. All other assembly is completed in line with Tamiya's instructions.

The Tamiya 70097 gearbox sells in the UK around £10-15, with the 70111 tyres around £5-8. (2006)

Comments and discussion on this application are welcome, there is a Topic set up on the MiniSumo Forum.

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