Had this little idea a few days back.
Replaceable Weapon Pulley Mockup.jpg
This would be a custom pulley attached to the weapon shaft (The hole is square for a reason)
If I wanted to change the ratio I could slide the pulley off the motor shaft, undo the 2 bolts holding this on, swap it for another then slide the other pulley back onto the motor shaft with the belt over it. Saves me totally dismantling the robot.
I don't think I will use it but its a interesting idea.