[PhantomPholly]

If voltage is the same but current draw is higher, you can overload your controller.

Once the smoke comes out, you can never put it back in...

 

[PhantomPholly]

Thank you very much for your reply. Nothing seems to be damaged as I turned it off straight away and all turned back in a few minutes later. Just to confirm, it’s nothing at all to do with the larger battery correct?
Is there anything around this problem or will I have to put the old motors back in?

I'm not one of the more knowledgeable experts here, but if they are DC motors then voltage is what determines their safe operation, while Amp Hours (the size of the pack) determines how long you can run the motor without recharging.

Any time you get smoke you are damaging something. It may not die right away, and it is even possible that if you turn it off quick enough it will still function for a normal lifetime - but that depends on how lucky you are.

Is there anything I can do to give it a little bit more torque?

Of course. Get a new controller matched to the bigger motor(s). Almost anything is possible given enough budget. Whether it is worth the money is a question you have to decide for yourself. That's why it's called "experimental."