Q-Drive Installation Manual
Issue 1.5
Page 30
Copyright © 1996 Quin Systems Ltd.
6.1
Choosing a motor
The choice of motor for a particular application depends on several factors. Some of
these are given below.
•
Maximum torque required.
•
Continuous torque required (r.m.s.).
•
Maximum motor shaft speed.
•
Maximum acceleration rate.
The torque is the turning effort required from the motor in order to accelerate the
mechanical load or system at the desired rate. It is usually measured in Newton metres
(Nm), gram centimetres (gcm), pound feet (lb. ft) or ounce inches (oz. in). In order to
calculate the torque required from the motor, it is necessary to find out the following
information about the mechanical system.
•
The reflected total inertia of the system or load, at the motor shaft.
•
The reflected total friction of the load.
•
The internal motor inertia and friction.
•
The maximum acceleration rate of the motor.
•
Any gear or pulley ratios in the mechanical system.
For example, consider a motor driving a load via a belt and pulleys. The total torque
required from the motor is given by:
where T
= total motor torque required
D
1
= diameter of motor pulley
D
2
= diameter of load pulley
I
L
= inertia of load
I
M
= inertia of motor
= acceleration at motor shaft
F
L
= friction torque of load
F
M
= friction of motor.
T
D
1
D
2
------
2
I
L
I
M
+
t
2
2
d
d
θ
D
1
D
2
------
F
L
F
M
+
+
=
t
2
2
d
d
θ
