Types of Belts

Flat Belts

Simple rectangular cross-section
One or both sides can be specially coated to increase friction with pulleys
Pulley is slightly convex to keep the belt centered on the pulley and prevent it from falling off
~98% efficiency
High flexibility (can be used effectively with small pulleys)
High pretensioning forces/bearing load
Use outer diameter of the pulleys to calculate transmission ratio

V-Belts

Reduced bearing load
Wedge-shaped cross section
Higher friction than flat belts due to wedge shape
Higher torques can be transmitted with the same pretensioning force
Two+ belts can be placed parallel to each other to increase power transmission as well
Belt only contacts the pulley on the inclined flanks (does not touch the bottom of the groove)
Groove angle of 38° or 32° depending on pulley diameter
Each belt is specially designed for a certain range of pulley diameters
Different way of calculating transmission ratio (nominal width/neutral axis)

Type of V-Belt	Description
Classical	Height to width ratio of 1:1.6
Narrow	Height to width ratio of 1:1.2 Smaller width with the same power transmission Or higher power transmission with the same width Higher speeds (because of lower mass) Less flexible Can come in cogged form (notches, that kind of look like teeth, cut out of the bottom) to increase flexibility Higher efficiency than classical
Wide (a.k.a. variable speed)	Height-width ration of 1:2+ Good for heavy power transmission and when large speed changes occur Usually cogged
Double (a.k.a hex)	Two V-belts back to back, basically Can drive pulleys on either side
Kraftband	Multiple V-belts connected by a cover plate Helps ensure individual belts don't fall off the pulley

Coating Type	Description
Wrapped	Covered with a special rubber fabric Increases friction Protects belt form harmful environments
Raw	No rubber casing More flexible Higher power transmission and efficiency Can be ground to narrower tolerances

Timing/Synchronous Belts

Toothed to eliminate slippage
Used when precise positioning is required
Higher power density (can use smaller belts and pulleys for a bigger load)
More expensive
Require less tension (and cause less wear)

Round Belts

Round cross section
Used more for motion transmission than power transmission

Chains

Longer length
Better in high temperatures
Needs lubrication and more maintenance

Timing Belt Specifics

The list above is an introduction I guess, but really we want to be using timing belts. Any other type of belt doesn't have teeth and relies only on friction, causing it to slip occasionally, which is bad for our purposes.

Tooth Profiles

Note: Belts with the same type of tooth profile and pitch may not be interchangeable, due to differences in manufacturer's designs

Type	Description	Pros	Cons	Picture

Type	Description	Pros	Cons
Trapezoidal	Trapezoidal shaped teeth Most common	Can transport good amounts of force Low backlash	High wear rates (with high torque/speeds)
Curvilinear	Rounder teeth	Improved torque and speed capabilities Less belt ratcheting (jumping)	Higher backlash than trapezoidal
Modified Curvilinear	Slight improvements to the curvilinear design	Highest torque and force transmitting capabilities Least likely to ratchet	Higher backlash than trapezoidal

Pulley Mounting

Type	Details

Type	Details
Set screws	Low and medium loads Low cost Pulley location can't be adjusted easily if shaft is keyed
Split hub	Shaft collar with a clamping screw Low cost Medium loads Moren easily adjustable than set screw + keyed shaft
Quick disconnect bushing	Slide on and attach to face of pulley Tighten on the shaft as they are tightened High loads
Taper lock (a.k.a keyless bushing)	Similar mounting to QD bushing but inside the pulley(?) High loads Flexible for design Can only mount on one side

Belt Drives