Transfering Torque with LEGO Axles

Walkers with multiple pairs of legs spaced out from the frame subject axles to more stress than what they are typically designed to handle.   Furthermore, LEGO's plastic axles twist easily under torque, which can be especially problematic for walkers since such twisting can disrupt a walker's gait by delaying the leg's movement.  

How much do LEGO axles twist?

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The above experiment was run with LEGO's M-motor 8883, geared down in a 5:1 ratio - the same set up I used for TrotBot.

Plastic LEGO axle permanently twisted by a LEGO XL motor geared down by a 5:1 ratio

With some walkers the gait is smooth enough and the weight low enough that axle twisting doesn't harm the gait much.  However, with heavy and wide walkers, like the Mindstorms TrotBot I just finished, axle twisting can be a problem.   Fortunately, Brick Machine Shop makes stainless steel axles for LEGO:

These steel axles resist twisting and help to keep leg movement closer to the mechanism's designed movement.  They also fit more tightly, so cranks won't come off axles while operating your walker - but this also means it can be difficult to insert these axles into parts.  I usually use something like a flat piece of wood (Kapla block) to help press parts onto them, and needle nose pliers to take parts off.