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We used XRP drills a number of years and in our experience they are pretty well bullet-proof. We bought brand new discontinued versions off EBay for $45 (then). We cut off the pinion gear that came with it and got an EDM shop to drill a hole in it for the correct size of the motor we planned to use. We mounted small fans close to the motor to help get the heat out of the brushes etc. The 3 speeds of the transmissions were great for prototyping. Design for the medium speed and if it turns out too slow or fast switch to the better speed. We mounted the dewalt via a standard muffler clamp around the handle mount.

We reused the drill speed controller for a variable speed reversible motor tester which is part of our test tool kit. We put an amp meter and a 40 amp circuit breaker in line with it and connected it to a standard battery connector.