Well, I have Rover, which weighs a little over 4.5kgs, so it should be able to beat Carcinus at least

If you like you can have a go Jamie . Over the past few days I have taken all of the wiring out and resoldered them to every connector and motor tab there is and despite the simpler system it still doesn't work half as well as when we were using 2 different makes of controller. To be honest, the bits you did work as well as when you did them, its my dodgey electrics that have ruined it, maybe it just doesn't like me