A much simpler design than version one, you can't make them smaller than this.
Note that the red pin in reality would be black or grey, I just used red to
make a clearer picture.
The 4L axel can be switched to a longer axel if wanted, and it doesn't have to
be a stop axel.
The clutch gear would normally not be placed here, it's just to warn you that you
must use a clutch gear somewhere between the motor and the switch.