Design of lightweight robots for over-snow mobility

Snowfields are challenging terrain for lightweight (<50 kg) ground robots. Deep sinkage, high snow-compaction resistance, traction loss while turning and ingestion of snow into the drive train can cause immobility within a few meters of travel. However, for suitably designed vehicles, deep snow offers a smooth, uniform terrain that can obliterate obstacles. Key requirements for good over-snow mobility are low ground pressure, large clearance relative to vehicle size and a drive system that tolerates moist, compactable snow.A small robot will invariably encounter deep snow relative to its ground clearance and thus must travel over the snow rather than gain support from the underlying surface. This can be accomplished using low-pressure tracks (<1.5 kPa). Even still, snow-compaction resistance can exceed 20% of vehicle weight. Also, despite relatively high traction coefficients for low track pressures, differential or skid steering is difficult because the outboard track can easily break traction as the vehicle attempts to turn against the snow. Short track lengths (relative to track separation) or coupled articulated robots offer steering solutions for deep snow.This paper presents guidance to design lightweight robots for good mobility over snow based on tests of two custom-designed over-snow robots, SnoBot and SnoBot-2, and driving experience with two commercially available robots, PackBot and Talon. Moreover, we used the present guidance to design SnoBot-2, and it displays excellent over-snow mobility. Because many other considerations constrain robot designs, this guidance can also help with development of winterization kits to improve the over-snow performance of existing robots.