Download Brushless Motors

Brushless Motors
Spring 2007
1. Introduction
2. Brushless DC Motor Characteristics
3. Experimental Procedures
4. Report
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3. Experimental Part
a) Connect the driver circuit to the motor as shown in the diagram
below.
P2-4
Power Gnd
P1-10 +VHall
P1-1 Gnd
P1-13 Hall2
P1-14 Hall3
P2-5
High Voltage
Advanced Motion Controls
Brushless PWM Servo Amp
B15A8
See Appendix A for
schematic.
P1-12 Hall1
P2-3 P2-1 P2-2
Mtr C
A
B
Be very careful that the sensor leads and the motor leads are
correctly connected. You must have your connections checked
by the instructor before proceeding. The 50-Ω rheostat, R1,
must initially be set to maximum resistance. R2 should remain at
50 Ω throughout the experiments. ∂
______________________________________________
∂ The
“A” student will have noted the absence of an Equipment List. By
now you should be able to collect a reasonable set of experimental tools
with but minimal coaching.
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b) We will first view the waveforms of the voltages that are applied
to the motor power leads. With the DC wall voltage at 40 VDC
as measured by VM1, apply power to the circuit. Adjust R1 to
obtain a steady speed of 3000 rpm. Obtain printouts of the
voltages between points A, B, C, and chassis ground; also obtain
printouts of the A-to-B and A-to-C line-to-line voltages. In both
cases, note the relative time displacements and magnitudes of the
waveforms.
c) Next we will verify that the no-load motor speed is proportional
to applied voltage. Vary the voltage to the motor in 5 volt
steps from 0 to 30 volts by using several settings of R1.
Record the motor speeds and the VM2 voltages.
d) Finally, we will measure the motor’s speed-torque
characteristic. With R1 initially set at 50 Ω, adjust R1 to keep
VM2 = 15 VDC as you load the motor with the dynamometer.
Record motor speed, torque, VM1, VM2, armature current I,
and power for armature currents from minimum to 5 Amps.
Do not exceed 5 A. Repeat for VM2 = 30 VDC.
e) With all power connections removed, measure all 3 DC lineto-line motor resistances.
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4. Report
a) Present graphs of the waveforms that you observed in part
3b. Explicitly indicate the relative time displacement and
voltage magnitude at each point on the waveform where it
makes a significant change. Comment cogently.
b) Present in tabular form the data from part 3c with no-load
speed in rpm. Using the data in this table, plot no-load speed
(rpm) versus applied voltage. From this plot/data deduce, an
approximate functional interrelationship between no-load
speed and applied voltage.
c) From the data taken for part 3d, plot the torque (ft-lb) vs. speed
(rpm) for the motor with 15 VDC applied. On the same axes, plot
also the data for 30 VDC applied. Infer the stall torque of the
motor and the no-load speed at both voltages. Comment on their
characteristics. Do the graphs match theoretical expectations? A
simple “yes” or “no” answer here does not suffice.
d) How would you reverse the direction of rotation of this motor?
e) Calculate the number of magnetic poles that this motor has.
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Appendix A
Notes:
1. Set S4:S1 to [On On OFF On] to put it in Open Loop, 120 degree phase
on sensors and Test Mode.
2. Turn Pot4 all the way counter clockwise. This sets the duty cycle to the
maximum.
3. Short P1-4 to P1-5 and P1-6 to P1-7 to zero out the other inputs to the
summing amp.
4. Run the motor up to 6.2 A and tweak the current limit to reduce the
current to 6A. See Datasheet for B15A8 Brushless Servo Amplifier from
Advanced Motion Controls for more information.
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