I think most 540 size motors will run on 3s. They're not going to last very long but they'll run. You'll probably need access to a com lathe and brush supply. I run brushed motors on 2s all the time without any problems but 3s will be hard on the brushes and comm. I've ran them on 8 cell nicad batteries with no problems other than accelerated brush and comm wear. lipo can put out amps faster than nicad, though so you'll want to watch the heat pretty close. I'd put a brushless motor in there if it was me.