Speaking of roller-blade wheels (and otherwise very off-topic, sorry), I have a recollection of a design for Robotica (with a flame thrower, or net flinger, or something else impractical) which had the rear wheels driven forward/back with a differential, and a set of roller blade wheels studded onto a driven rotating cylinder (mounted longitudinally) as a steering mechanism - the wheels rolled forwards and back, but pushed sideways when the cylinder was rotated.

Interesting design, and not one Ive seen duplicated. It might be an option for anyone feeling challenged in the speed controlled department. :-) Other than wasting power on steering (in the same way that Firestorms driven differential does), it didnt seem like such a bad idea.

Just my tuppence of interjection.

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Fluppet