Intelligent Motion Systems MDriveAC - Manual (Page 59)

A-8 MDriveAC Plus Microstepping Hardware - Revision R121707
Relevant to Firmware Version 3.0.02
Nominal Output Torque
Calculate the nominal output torque using the torque values from the MDrive’s Speed/Torque Tables.
Nominal output torque (T
N
) is the actual torque generated at the Planetary Gearbox output shaft which
includes reduction ratio (i), gear efficiency (η) and the safety factor (s
f
) for the MDrive. Once the reduction
ratio (i) is determined, the nominal output torque (T
N
) can be calculated as follows:
T
N
= T
M
× i × η ÷ s
f
or:
Motor torque × reduction ratio × gear efficiency ÷ safety factor = nominal output torque.
For gear efficiency (η) refer to the Mechanical Specifications for the 7:1 Planetary Gearbox designed for
your MDrive.
For motor torque (T
M
) see the appropriate MDrive Speed/Torque Table. Dependent on which
MDrive you have, the torque range will vary. The torque will fall between the high voltage line and the low
voltage line at the indicated speed for the MDrive. (See the example Speed/Torque Table below.)
The Speed/Torque Table above is for an MDrive23 Double Length Motor. This MDrive will produce a
torque range of 51 to 95 oz-in in the full voltage range at the speed of 2000 Full Steps/Second (600 RPM).
Please note that this is not the usable torque range. The torque output to the Planetary Gearbox must
include a safety factor (s
f
) to allow for any voltage and current deviations supplied to the MDrive.
The motor torque must include a safety factor (s
f
) ranging from 0.5 to 0.7. This must be factored into the
nominal output torque calculation. A 0.5 safety factor is aggressive while a 0.7 safety factor is more conser-
vative.
Example:
The available motor torque (T
M
) is 51 to 95 oz-in.
NOTE: You may specify a torque less than but not greater than the motor torque range.
For this example the motor torque (T
M
) will be 35 oz-in.
A 6.75:1 reduction ratio (i) has been determined.
Gear efficiency (η) = 80% from the appropriate table for the Planetary Gearbox which is used
with an MDrive23.
Nominal output torque would be:
Motor torque (T
M
= 35) × reduction ratio (i = 6.75) × gear efficiency (η = 0.8) ÷ safety factor (s
f
= 0.5 or 0.7)
35 Ч 6.75 = 236.25 Ч 0.8 = 189 ч 0.5 = 378 oz-in nominal output torque (T
N
)
or
35 Ч 6.75 = 236.25 Ч 0.8 = 189 ч 0.7 = 270 oz-in nominal output torque (T
N
)
With the safety factor (s
f
) and gear efficiency (η) included in the calculation, the nominal output torque
(T
N
) may be greater than the user requirement.
140
120
100
80
60
40
20
0
99
85
71
56
42
28
14
0 1000 2000 3000 4000 5000 6000 7000
Speed in Full Steps per Second
Torque in Oz - In
Torque in N - cm
24 VDC
45 VDC
75 VDC
Figure B.1: MDrive23 Torque-Speed Curve