Whenever you drive/walk in soft terrain, the wheel/leg is constantly climbing the ramp created by it sinking into the terrain. In a perfect system, this determines how much power you need to move. This is why trains are so efficient. A hard wheel on a hard rail has very little deflection -- so excellent efficiency.
Wheels have to climb that ramp for every inch of travel. Legs get to step forward and only take that penalty for each step. If everything else is the same, the legs win on soft terrain.
But everything else is never the same :-). The early legged vehicles used linear motions, which means you have these very long sliding surfaces. This is heavy and the drive system efficiency dominates over the terrain interaction efficiency. Add in the fact that you have multiple axis to drive and the weight and drive losses really add up.
Modern dog and human style walking robots are MUCH better on efficiency than those early designs. However, they require enough sensing and compute to dynamically balance. Legs can do things that wheels can't, but you have to have smart enough software to take advantage of that. The compute available for a high radiation environment is a fraction of what is in your smartwatch. Wheels are still winning on energy efficiency, but at least it's getting closer.
I worked on Dante at CMU and Marsokhod at NASA Ames; and was in the same group that developed Ambler.
Whenever you drive/walk in soft terrain, the wheel/leg is constantly climbing the ramp created by it sinking into the terrain. In a perfect system, this determines how much power you need to move. This is why trains are so efficient. A hard wheel on a hard rail has very little deflection -- so excellent efficiency.
Wheels have to climb that ramp for every inch of travel. Legs get to step forward and only take that penalty for each step. If everything else is the same, the legs win on soft terrain.
But everything else is never the same :-). The early legged vehicles used linear motions, which means you have these very long sliding surfaces. This is heavy and the drive system efficiency dominates over the terrain interaction efficiency. Add in the fact that you have multiple axis to drive and the weight and drive losses really add up.
Modern dog and human style walking robots are MUCH better on efficiency than those early designs. However, they require enough sensing and compute to dynamically balance. Legs can do things that wheels can't, but you have to have smart enough software to take advantage of that. The compute available for a high radiation environment is a fraction of what is in your smartwatch. Wheels are still winning on energy efficiency, but at least it's getting closer.
I worked on Dante at CMU and Marsokhod at NASA Ames; and was in the same group that developed Ambler.