Perhaps it’s in the rulebook and I’ve simply managed to not find it, but we currently plan on climbing by extending a set of pistons below us to reach Hab Level 3 height. While I’m fairly confident this is legal in the last thirty seconds (though if I’m wrong, that would be good to know), would it technically be legal to extend below us at other times/in other parts of the field (disregarding that this could be potentially disastrous)?
The relevant rules here are R25 and G23.
On most of the field your bumpers need to stay below an imaginary plane 7.5" off the ground. Extending legs under the robot would raise the bumpers up, out of the bumper zone. G23 provides an exception for the rule, allowing you to use your legs if the robot is “completely in its HAB zone”. This exception is not time-limited, so you can use your legs any time as long as you’re in the HAB zone.