NiMH cells should be discharged to .9v per cell (not 0) and charged at 1-1.5c immediately prior to using. It is usually best to store them at about 60% capacity.
If they've been laying around a long time I find it helps to charge them at a really low rate, like 2 amps the first time to help get them back to full capacity.

If your speed control has lipo cutoff you'll need to disable it before running NiMH's or it'll frequently cut out as the total voltage is lower than Lipo packs.