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Here a video testing power and Wireless Remote Receiver control
https://www.youtube.com/watch?v=mVBGGn8pqfk

Not always. If you have gears or any type of metal with hard sharp edges, you create a stress riser. Sanding down or softening edges can make parts stronger . In this case, the gears might be engaging poorly due to tooth shape. softening the edge might make a better engagement. That's just my guess...