The shaft is turned and has a 4mm square milled on the end, directly next to the motor on the shaft a pulley slides over and is held in place with a grubscrew (there's a flat milled onto the shaft for this, the pulley powers my front wheels) then it passes through the armor and sits in a bearing. The wheel then slides over the end of the shaft and is held in place with a keyway.

I'd strongly suggest putting a bearing as close to the motor as possible and on the other end of the loading point (in this case a wheel)

It's shown quite well here;
http://www.teamstorm.com/feathers/forcex.htm
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