the method I have uses 1 motor for forwards and backwards and 1 for turning. I think we have to remember what the disadvantage of a walker over a wheel is. Its nothing to do with motors or complex movements, yes a wheel is simpler but the main advantage is the smooth continuos movement. So as long as the leg doesnt give you a smooth continuos movement its ok. This means shufflers dont get the weight advantage because they are a hybrid of a leg form but provide the advantages that wheels give - The smooth continuos movement.