From the current rule set

2.2.
Legged Robots [Walkers] can weigh up to twice the specified weight in all classes. A
walker must employ moveable legs to support its weight. Robots with rolling or sliding
mechanisms will not be classified as walkers.

Believe me, if I could have built a shuffler that weighed 60lb in the featherweights with a 30lb disc, I would have done already