You don't have drive motors on your robot? If you use the Maxi-style circut breaker for the 40A breakers, there is no other place to legally attach the ground wires to.
<R50> The 12V battery, the main 120-amp circuit breaker, the power distribution block, and circuit breaker distribution panels shall be connected as shown in the 2008 Power Distribution Diagram.
Take a look at the power distribution diagram distributed with the
rule book:
http://www.usfirst.org/uploadedFiles...on_Diagram.pdf
If in doubt, the FIRST Q&A is the ONLY authoritative place for answers.