PowerGrip® GT® Belt Drives

Useful Formulas and Calculations
Drive Design
Speed Ratio = rpm (faster) = PD = N
rpm (slower) pd n
Where: rpm = Revolutions per minute
PD = Larger pitch diameter
pd = Smaller pitch diameter
N = Larger sprocket grooves
n = Smaller sprocket grooves
Horsepower = (Q) (rpm)
63025
Where: Q = Torque, pound inches
rpm = Revolutions per minute
Be sure to use torque and rpm values at the same
shaft; do not mix torques and rpm’s of different
shafts.
Horsepower = (Te )(V)
33,000
Where: Te = Effective tension, pounds
V = Belt speed, feet per minute
Design Horsepower = hp x SF
Where: hp = Horsepower Load
SF = Service Factor
Torque (pound inches) =
63025 (hp)
rpm
Where: hp = Horsepower load
rpm = Revolutions per minute
Design Torque = Q x SF
Where: T = Torque load
SF = Service factor
Service Factor = Rated T a
(T e + T c )
Where: T a = Rated belt working tension, pounds
T e = Effective tension, pounds
T c = Centrifugal tension, pounds
Belt Speed (V) = (PD) (rpm)
3.82
Where: V = Belt speed, feet per minute
PD = Pitch diameter, inches
rpm = Revolutions per minute of same pulley
The exact belt pitch length, in inches, can be found
as follows:
Pitch = 2(CD)(Cos ) + π (PD + pd) + π (PD - pd)
Length 2 180
= Sin -1 ( PD – pd )
2CD
Where: CD = Drive center distance, inches
PD = Large pitch diameter, inches
pd = Small pitch diameter, inches
The approximate center distance in inches can be
found as follows:
Center Distance = K + K 2 - 32(PD - pd) 2
16
K = 4PL - 6.28 (PD + pd)
Where: PD = Large pitch diameter, inches
pd = Small pitch diameter, inches
PL = Belt pitch length, inches
The exact center distance can be calculated using
an iterative process between the center distance and
belt length equations above. The exact center
distance has been found when the two equations
converge.
Span Length =
CD 2 -
(PD - pd)2
4
Where:PD = Large pitch diameter, inches
pd = Small pitch diameter, inches
CD = Drive center distance, inches
The arc of contact on the smaller pulley in degrees
can be found as follows:
Arc of Contact = 180 - (
60 (PD - pd
)
CD
Where: PD = Large pitch diameter, inches
pd = Small pitch diameter, inches
CD = Drive center distance, inches
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