Algodoo

Relatively simple mechanism normally used in a pulley system to control the amount of torque output by a hand crank. If this were used in any practical application, it would more than likely have a ratchet gear to prevent the system from turning backwards if you stop cranking.

Toggle "1" for 1:1 ratio
Toggle "2" for 3:1 ratio
Toggle all off for idle mode

Interesting feature to point out is that if both ratios are toggled "on" accidentally, the gearbox defaults to 1:1.

I'd also like to note that I'm using an axle to simulate a load because it won't engage in 3:1 if it isn't under load. Hit "Return" to toggle this on or off if you please.

Once again credit goes to s_noonan for the gear generator.
Spur Gear Generator II