Servo - September 2011

• Gear Type: Use a rack and pinion gear to change circular motion to linear motion. Use a bevel gear to change the direction of rotation. For a large reduction in RPM, use a worm gear. For everything else, use a spur or a helical gear.

• Gear Ratio: The relationship between the number of teeth on two gears. Changing the gear ratio will influence the amount of torque or speed a gear has. To increase torque, a smaller gear should be mounted on the motor and a larger one on the wheel. To increase speed, do the opposite.

• Hubs: The protruding part of the gear that contains a bore for mounting gears. Using a gear with a hub is generally recommended because if you use a hubless gear, you will need to bond the gear to the shaft by using glue, epoxy, or solder. This also makes replacing the gear much more difficult, so if you do use a hubless gear, use a more durable metal one in lieu of plastic.

Hub Diameter: • Diametral Pitch: The number of teeth in an inch of the pitch diameter. The diametral pitch of two corresponding gears determines if the gears will mesh together properly. The ratio of the number of teeth between two gears must be the same as the ratio between the two gears’ diametral pitch.

• Bore Size: The diameter of the bore (hole used for mounting gears). It is obviously important to choose a bore size that will allow you to mount the gear properly. The bore size should be slightly bigger than the motor shaft on which you are mounting it and should fit snuggly. If you find yourself unsure about which size to choose, it is better to choose a slightly smaller size which can then be reamed out with a drill to the size you desire.

with a larger face width because the increased surface area will distribute the force over a larger area.

Susie selects the highest face width that will fit inside her Ant-weight shell. For the material, Susie chooses plastic because it is less expensive and weighs less than other materials. If Susie was building a bigger bot, she might want to consider a metal gear that could better withstand the force of an impact with another heavy bot.