[107] What size gear could I add to your #25 design to increase torque by around 3x?

Torque is measured from the center of the shaft to the pitch diameter divided by 2 of the sprocket in inches or feet and is able to move (rotate) with a force at this measurement tangential to the pitch diameter circle. The smaller this pitch diameter is, the less torque is required by the motor to turn the sprocket under load. If you are starting with a large sprocket, say with a pitch diameter of 5 inches (2.5 inches radius), it is easy to reduce the size of the drive sprocket to increase the mechanical advantage. All you need to do is take the 2.5 inches and divide that by 3 to find the new pitch radius.