Belts & Pulleys

Belts and Pulleys Basics

Common Terms

Pitch Diameter

Pitch Diameter also known as PD is the circle that is formed while the belt and pulley are meshed together and which the belt rotates around. If you wish to find the PD, reference the formula below.

(Pitch x Number of T) ÷ π

Outside Diameter

The Outside Diameter also known as OD refers to the outside diameter of the pulley.

Pitch Length

Pitch Length also known as PL is the length or circumference of a belt. If you wish to find the PL, reference the formula below.

T x Pitch

Number of Teeth

The Number of Teeth, T, is simply the amount of peaks that are around the pulley. If you wish to find T, reference the formula below.

PL ÷ Pitch

Calculating Center to Center

How to Use WCP 's Belt Distance Calculator

WCP now offers a built-in calculator to provide all our customers with piece of mind when designing with belts and pulleys. If you are interested in viewing our calculator or knowing how to use it, see below for more information.

Use this calculator to find the correct center to center distance for belts (WCP Belt Calculator)

You will need a few pieces of information when using the WCP Belt Calculator:

1. Belt pitch to be used

   1. 3mm for GT2/GT3 belts

   2. 5mm for HTD Belts

2. Number of teeth for both pulleys

3. Approximate distance between centers of the two pulleys

The Output from the calculator will give you the belt center to center as well as the tooth count for the closet belt to the values entered. It will also give you the information for one belt size higher and lower.

Center to Center Equations

The equation below shows the minimum center distance that should be used.

$$CC=\frac{Tooth Count_{1} +Tooth Count_{2}}{2π}{x Pitch}$$

The equation below shows the center distance for equally sized pulleys.

$$CC=\frac{ Belt Tooth Count -Pulley Tooth Count_{}}{2}$$

The examples below are places where a looser belt may be beneficial. Subtracting center distance can help reduce the overall load of the system which in turn reduces motor load and power consumption.

• First Stage Reduction: -0.000 to -0.003

• Intake Rollers: -0.015 to -0.020

• Conveyor System: -0.015" to -0.020"

Recommended Applications

GT2 Belts

• First stage reductions

• Motor to flywheel

• Low load

HTD Belts:

• Intake or conveyor systems

• Drivetrains

• Medium load

GT2 Belts and Pulleys (Product Page)

GT2 timing belts are intended for lower load applications such as the first reduction in a gearbox, or motor to flywheel. GT2 belts use a smaller pitch than HTD belts, which means you can use larger reductions in those tight fit areas of your robot.

All GT2 Pulleys will now be clocked and engraved. An alignment notch has also been added to help with clocking multiple items together during assembly.

GT2 Pulleys

Bore	Width	# of Teeth
8mm SplineXS	9mm/15mm	16
Falcon Spline	9mm/15mm	16
RS550 Motor/RS775 Motor/BAG Motor	9mm	12
1/2" Hex	9mm	24, 36, 48, 60

These pulleys are compatible with GT2 and GT3 belts.

GT2 Belts

Width	# of Teeth
9mm	45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 140, 150, 160, 170, 180, 190, 200

HTD Belts and Pulleys

Synchronous timing belts are lighter and more efficient than chain. Once set up, they require no tensioning or adjustment. The HTD profile is ideal for FIRST ® Robotics Competition applications - its deep tooth profile allows it to better handle high reversing loads, such as those found in an FIRST ® Robotics Competition drivetrain.

All HTD Pulleys will now be clocked and engraved. An alignment notch has also been added to help with clocking multiple items together during assembly.

HTD Pulleys (Product Page)

Width	Bore	# of Teeth
9mm/15mm	8mm SplineXS	12
9mm/15mm	8mm Key, Falcon	12
9mm	1/2" Hex	15, 18, 24, 30, 36
15mm	1/2" Hex	15, 18, 24, 30, 36

HTD Belts (Product Page)

Width	# of Teeth
9mm	30, 35, 40, 43, 45, 50, 53, 55, 60, 64, 65, 70, 75, 80, 85, 90, 95, 100, 104, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 210, 220, 225, 230, 240, 250, 260, 270, 280, 290, 300
9mm Double Sided	100, 125, 150, 175, 200, 250, 300
15mm	30, 35, 40, 45, 50, 55, 60, 64, 65, 70, 75, 80, 85, 90, 95, 100, 104, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 210, 220, 225, 230, 240, 250, 260, 270, 280, 290, 300
15mm Double Sided	100, 125, 150, 175, 200, 250, 300
18mm	25ft