Snowfields are challenging terrain for lightweight (<50 kg) unmanned ground vehicles. Deep sinkage, high snowcompaction
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 surface 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 cohesive snow.
A small robot will invariably encounter deep snow relative to its ground clearance. Because a single snowstorm can
easily deposit 30 cm of fresh snow, robots with ground clearance less than about 10 cm must travel over the snow rather
than gain support from the underlying ground. 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 preliminary guidance to design lightweight robots for good mobility over snow based on mobility
theory and tests of PackBot, Talon and SnoBot, a custom-designed research robot. Because many other considerations
constrain robot designs, this guidance can help with development of winterization kits to improve the over-snow
performance of existing robots.