Gearboxes

From Combat Robot

Gearboxes are some of the most useful devices in combat robots, used to effectively turn motor power into a usable form for driving wheels, appendages, and weapons.

Theory and considerations

An electric motor will usually turn at a high speed with little torque. Although directly coupling wheels and weapons to motors has been done, the feasibility of this design decreases rapidly with increasing robot weight. Thus the usefulness of a gearbox and its gearing comes from principles of lever mechanics, and is used to convert this high speed, low torque power into a lower speed, high torque output. Note that this does not mean the power is increased - only its characteristics are changed.

An additional, often overlooked benefit of gearboxes is having all the axles and bearings for gears isolated from the rest of a chassis, as one independent unit. Not only does this mean that if the gearbox is damaged, it can all be replaced quickly, but the modular, self-contained gearbox is isolated from the misaligning effect damaged frames would have on built-in gearboxes.

For more information on gears themselves, see Gears.

For tips on calculating the proper gear ratio for your robot, see Optimum gearing.

Common gearbox types

• Spur gearboxes use spur gears and are the most common gear reduction type. These gears can only transmit power radially. Thus, spur gearboxes will have in-line shafts which can either be concentric with the motor or offset, the advantage of which is the ability to mount smaller wheels and conserve space. At high speeds, straight spur gears can be noisy due to teeth impacting while meshing. Most popular gearmotors for "sublight" bots use spur gears for low cost at some reduced strength.

• Helical gearboxes overcome the strength limitations that spur gears suffer due to low (two) tooth contact area between adjacent gears. Helical gears have slanted teeth that enable more tooth contact area, enabling a smaller gear to transmit more power and to do so more quietly. Helical gearboxes are more expensive than a comparable spur gearbox as a result of more complex manufacturing. They are found in heavier motors (such as NPC wheelchair motors) for Heavyweights and Superheavyweights.

• Planetary gearboxes have concentric in-line shafts and multiple teeth in contact at any one time, resulting in a strength increase over other designs and featuring high space efficiency. These can be found with both spur and helical gears. The most common example of planetary gearing in combat robotics is the cordless electric drill gearbox, which offers a compact drive solution to lighter weight combat robots. Planetary gearboxes are more typically more expensive than comparable spur gearboxes due to complex manufacturing processes.

• Bevel gearboxes use angled gears to change the angular (usually 90 degrees) to the axis of rotation. The gears may have a straight or helical toothform. Bevel gearboxes with a 1:1 ratio are called miter gearboxes.

Component links

A comprehensive list of vendors can be found on the parts page.