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Belts & Pulleys

Belts and Pulleys Basics

Common Terms

Pitch Diameter
Outside Diameter
Pitch Length
Number of Teeth
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
The Outside Diameter also known as OD refers to the outside diameter of the pulley.
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
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. 1.
    Belt pitch to be used
    1. 1.
      3mm for GT2/GT3 belts
    2. 2.
      5mm for HTD Belts
  2. 2.
    Number of teeth for both pulleys
  3. 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=ToothCount1+ToothCount22πxPitchCC=\frac{Tooth Count_{1} +Tooth Count_{2}}{2π}{x Pitch}
The equation below shows the center distance for equally sized pulleys.
CC=BeltToothCountPulleyToothCount2CC=\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"

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

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, 45, 50, 53, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 104, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 160, 170, 180, 190, 200, 225, 250
15mm
30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 104, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 160, 170, 180, 190, 200, 225, 250
18mm
25ft