Recently I was building a prototype for a LEGO tank chassis and I tested it, but my finger got caught between the gears, resulting in my finger getting cut. Are there any ways to prevent that from happening?

  • 2
    You're a trooper, being able to work through the pain so you could type in this question with your mangled fingers ;)
    – JohnnyB
    Commented Aug 12, 2019 at 17:22
  • You could use a/some clutch gear/s while prototyping, if you get stuck the mechanism will stop. Or some sort of push button attached to the battery box that you have to keep pressed. If you let go, the motor will stop at once.
    – Uli
    Commented Aug 12, 2019 at 19:27
  • @Uli Unfortunately I have no clutch gears, and I don't really want to have a non-toggle type switch on the battery box. Commented Aug 12, 2019 at 21:52
  • @technicguy1 Okay, I see. Anyway, can you add an image of your prototype?
    – Uli
    Commented Aug 12, 2019 at 22:37
  • Do you need to put your fingers near it while the system is running?
    – Craig
    Commented Aug 13, 2019 at 22:27

2 Answers 2


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Here's an idea for a stop switch using a remote control and one's wrist.

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Place your wrist on the switch to start the motor. With your hands free you're still able to carefully adjust your running gears. But what if something (or someone...) gets stuck?

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Just lift your wrist and the motor will stop immediately. No need to quickly flick that switch on the battery box anymore.


If your geartrain contains z24 gear you can substitute it with z24 clutch gear. It has built-in safety mechanism - it would slip under certain toque and as result of this it will stop transfering motion if gears placed after it would stop or get blocked.

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