well if theres a problem with the bec on your computer just get a UBEC and use that instead should be ok on 12 cells then.

TBH the mgm controllers are not the best example of where sensorless technology is nowadays with the braking problems etc but those problems are probably fixed now in the latest software.

The grasshoppper is a very simple car and originally came with a 380 size motor i suspect that one of the purple can feigoa motors would fite nicely if you get low enough kv you could use a mamba 1/18th controller if you use a higher voltrage with low kv motor you could use cells smaller than subc for this or possibly lipo.