Types of Transmission

Gears & gearboxes

Make sure to check out power transfer first!

Gears are wheels with a bunch of little teeth that act as levers that push off of each other. See the videos below for a demonstration.

Gearboxes are an assembled set of gears that intend to get a large gear ratio in a small volume. See the videos below for a demonstration.

Just as review: The main purpose of gears is to transfer mechanical energy from one shaft to another. Gears can be used to interchange rotational speed and torque. Rotational speed is the speed at which the gear and its shaft are rotating, and torque is the rotational force the gear applies. By changing the gear ratio, you can change the rotational speed and torque of the shafts. On our robotics team, most motors rotate their shafts too fast and with not enough torque for our applications. We use gears, sprockets and chain, belts and pulleys, and gearboxes to exchange speed for more torque.

Gearboxes are useful because they hold all the gears in place into one compact box. There is a picture of a gearbox attached to a motor at the bottom of the page.

Gearing can also help adjust the placement of a motor with respect to the axle you wish to rotate using idler gears, belts, etc. You will see some examples throughout the lessons.

Gears cont.

There are numerous but gears are used up close to transfer power by the meshing of gear teeth
Gears are practically a wheel of small levers pushing each other
Two meshed gears spin in opposite directions
Medium backlash ('play' in between in the gears which results in the movement of one gear that does not result in the movement of the other)

Gear Definitions

Pitch - the set distance between two teeth

Pitch diameter/pitch circle diameter - it's the imaginary diameter of where the widths of the teeth and spaces in between the teeth are equal

These are the same for sprockets and pulleys

Spur Gears

- Used to transfer power between two parallel shafts

Bevel Gears

- Bevel gears are used to transfer power between two shafts at an angular difference (typically 90 degrees))

Worm Gear

- A worm gear and a spur gear can be used to transfer power between nonparallel shafts. Typically used to gain a large torque multiplier.

Gearboxes cont.

In FRC the team usually uses gearboxes with most of the parts provided by VEX, REV Robotics, or Andymark. Otherwise, a custom assembly of gearing is used (which is rare). Only VEX and REV will be mentioned here, see https://www.andymark.com/categories/gearboxes for more details on Andymark's options.

Vex Versaplanetary

This is a planetary gearbox designed for FRC motors. This has been the primary gearbox the team has used because it's easy to assemble, modify, and use. It's downsides is that it's not the strongest gearbox for high reductions and it takes up a very large profile when used with the primary motor we use, the NEO motor.

https://www.vexrobotics.com/versaplanetary.html

REV MAXPlanetary

This is a planetary gearbox designed for FRC motors. This is a new gearbox the team is interested in because it's easy to assemble, modify, use, and mount. It is strong, can handle large reductions, and is easily compatible with the NEO Motor. Its downside is that is expensive and any attachments and addons to the Versaplanetary are not compatible and would require buying all of the addons from REV.

https://www.revrobotics.com/rev-21-2100/

VEX clamping gearbox

This a gearbox that is easily compatible with NEO motors and the primary build system the team uses, Aluminum 2x1. It can provide a single reduction but it can't provide more than that on its own.

https://www.vexrobotics.com/217-4156.html

Two or more motor gearboxes

A gearbox that utilizes more than one motor effectively multiplies the amount of power by the number of motors, so two motor gear boxes would have double the power, three triple, etc. On most FRC gearboxes there wouldn't usually be more than three.

These gearboxes are usually for drivetrains and some have dog shifters or ball shifters in order to have more than one reduction.

Sprockets

Sprockets utilize teeth to drive a semi-flexible chain which drives another sprocket
Gear ratio equations are the same
Sprockets spin in the same direction
Typically pretty heavy (metal chain)
Large backlash
Example: Bicycles!

Pulleys

There are also varying types of pulleys
Timing pulleys utilize teeth to drive a flexible belt which drives another pulley
Other types of pulleys use a smooth belt to drive another pulley or they can use rope
Gear ratio equations the same
Low backlash in timing pulleys
Typically pretty light
Example: Drill Press Transmission

Tensioning and Position

The position of each shaft matters according to the pitch diameter of the power transfer methods
Gears need to have pitch circles that touch
Sprockets and timing pulleys need to have their chain or belt tight enough (not too tight though - tension - see graphic) around each in order to drive correctly
Tension can be achieved with either perfect center distances between sprockets or pulleys with a perfectly sized belt or chain
Tension can still be achieved through a tensioner that deflects the chain or belt
See below for a graphic on tensioning and graphics on center to center distance equations for sprockets and pulleys

What now? To check out more resources of course!

First

How do you align these in CAD?

Great you know how these power transfer and transmission systems work, now check out how to do it in Onshape!

Alignment in CAD

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