I was building my MARS river and have recently finished it. When I coded the Micro Bit and powered it on. Only one side of wheels on on the rover actually worked. I did some troubleshooting of my own and discovered that only some certain outlets actually worked while others didn’t. The Rover works on batteries and each battery works. Therefore something must be wrong with the motors.
Sorry to hear you were having problems with the MARS Rover kit.
Can you please confirm what batteries you are using to power the kit? The Rover draws a fair bit of power so you’ll want a good set of NiMH AA batteries. Alkaline batteries don’t have enough current so often only sometimes work or won’t work properly.
As part of your troubleshooting did you swap the motors from the working side to the non-working side to see if the fault followed the motor?
Are you able to post some photos of your Rover kit, sometimes a second set of eyes will make all the difference when troubleshooting.