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Wraptor™ User Manual
1.4.2 Conversion ratios
Joint rotation is measured in encoder counts at the motor shaft. To convert between the motor angle and the joint angle, use
the following table:
Example Calculation- Determine the GCL encoder count value needed to move an inner link by 90º:
1
link
90
º
360
1.4.3 Brushless Motors
The Wraptor™ utilizes advanced DC brushless servo motors. Because the motors have no brushes, and thus less inherent
friction, they achieve a better torque/mass ratio than typical brushed servos. There is also no need to replace worn brushes
after the motors have been in service over a period of time. The following table shows Wraptor™ motor properties.
Parameter
Number of Phases
Number of Magnetic Poles
Rotor Magnet Material
Commutation
Peak Torque
Steady State Torque
Torque Constant
Motor Constant
Position Feedback for Spread motor
Position Feedback for inner and outer link motors
© 2007 Barrett Technology®, Inc.
service@barrett.com
Table 2 – Conversion Ratios
Ratio
GCL Encoder Count : Motor Revolution
Motor Revolution : Inner Link Revolution
Motor Revolution : Outer Link Revolution
Motor Revolution : Spread Revolution
Re
49
Re
v
motor
v
º
1
Re
link
v
Table 3 - Wraptor™ Motor Properties
Document: D2000, Version: AB.00
4096
EncoderCou
nts
1
Re
motor
v
Value
3
6
Highest-Grade Neodymium Rare-Earth
Sinusoidal Space-Vector Brushless PWM
0.65 N-m
0.10 N-m
0.065 N-m/amp
1/2
0.042 N-m-W
3 Digital Hall Sensors X 6 Motor Magnet Poles:
18 states per motor revolution that are interpolated
into 4,096 positions/motor rev. so true spread joint
resolution = 360/(18*18.28) = 1.1 degrees.
Absolute Magnetic Encoder Sensor on Motor Shaft:
Absolute 4,096 positions/motor rev. via magnetic
encoder, so inner and outer link resolutions are
0.0018 & 0.0023 degrees respectively.
Value
4096:1
49:1
39:1
18.28:1
50176
GCL
Counts
=
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