A couple of months ago, I bought a couple of 18v drills and tried to extract the motors from em. The first one went fine, but with the second one, the screw to remove the chuck was too worn for a screwdriver to work on it- I then decided (wrongly I now realise) to saw off the chuck, but in doing so, I sawed off the gearbox output shaft as well. Recently, I came into possession of a couple more 18v drills for free, but they're different brands to the motor and gearbox that I do have- the one I orginally extracted is Nielsen, whereas these ones are different (one is Makita and the other one is Milwaukee. My question is, would I be able to use one of these motors and gearboxes, for drve in a robot, alongside the motor and gearbox that I already have, or would they not work together? Another thing is that whilst the original drill had onyl forward and reverse, these two have adjusatble speed settings- don't know if that affected gearbox design in such a way that it would make them incompatible.

Thanks.