gear ratio

To optimize your robot's performance, you should select a planetary gearbox rather than a spur gearbox to achieve your desired gear ratio on high-load mechanisms like drivetrains and arms. According to Game Manual 0, a gear ratio (or gear reduction) defines the relationship between the input and output rotations of a system, where speed and torque are inversely proportional. Gearing down increases torque at the expense of speed, while gearing up increases speed at the expense of torque .

Game Manual 0 strongly advises against using spur gearboxes for high-load applications because they stack gears on a single plane where only a few teeth carry the entire load, making them highly vulnerable to stripping under shock loads. In contrast, planetary gearboxes utilize a sun gear and multiple planet gears to distribute the load across more meshing teeth, offering superior durability and shock resistance .

If you need to adjust your system's speed and torque without swapping the motor's gearbox, Game Manual 0 suggests you can change the spool size on a linear slide system to achieve a similar effect. Alternatively, you can build external reductions using gears, belts, or chains, which are perfectly acceptable to run in a spur configuration even though built-in spur gearboxes are discouraged .

For adjusting external ratios, Game Manual 0 notes that using extrusion systems makes it easy to slide gears into mesh at various distances. This allows you to easily customize your external gear ratios compared to using pre-spaced channel holes .

Was this right?

Sources16

Gearbox Internals

Game Manual 0·CC BY-NC 4.0

Fundamentally, a gearbox is just a collection of gears and an enclosure that connects them. Gearboxes have an output ratio, the final Gear Reduction between the motor input and the final output shaft.

Term: Gear Reduction — Also known as a gear ratio. In any rotational power transmission system (typically involving motors and servos in FTC®), a gear ratio defines both the number of rotations of the system's input and the number of rotations of the output.

For instance, a NeveRest 20 gearmotor consists of an unmodified NeveRest Motor and a planetary gearbox that has a gear ratio of 20:1 (or, when spoken, "20 to 1"). This means that in order for the output shaft of the gearbox to rotate 1 time, the input shaft of the motor must rotate 20 times. Gear ratios are one of the most important design considerations about a power transmission component.

Any motor or servo has two properties: speed and torque (or rotational force). These two properties are inversely proportional, meaning that increasing speed decreases torque, and vice versa. For instance, if one wishes to make a mechanism faster at the expense of torque by doubling the speed of that 20:1 gearbox, they would decrease the gear ratio by a factor of 2. Since 20 divided by 2 is 10, the new desired ratio would be 10:1 (this is referred to as gearing up). However, if one wishes to double torque instead, making the system more powerful and robust at the expense of speed, they would increase the gear ratio by a factor of 2, leaving them with a 40:1 ratio (this is referred to as gearing down).

The most common ways of gearing up or down are using gearboxes, gears, sprockets and belt-driven pulleys, all of which exist in various sizes.

In FTC, gearboxes may be more common than you think. Nearly every motor and servo has a gearbox attached or built-in to it. These gearboxes are either spur or planetary.