september 15, 2007 d.giandomenico pwm motor control with ifi robotics victor884 electronic speed...
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![Page 1: September 15, 2007 D.Giandomenico PWM Motor Control with IFI Robotics Victor884 Electronic Speed Controller David Giandomenico Lynbrook High School Robotics](https://reader038.vdocuments.site/reader038/viewer/2022103022/56649d8b5503460f94a715cc/html5/thumbnails/1.jpg)
September 15, 2007 D.Giandomenico
PWM Motor Control with IFI Robotics Victor884Electronic Speed Controller
David GiandomenicoLynbrook High School Robotics
FIRST Team #[email protected]
(408)343-1183
![Page 2: September 15, 2007 D.Giandomenico PWM Motor Control with IFI Robotics Victor884 Electronic Speed Controller David Giandomenico Lynbrook High School Robotics](https://reader038.vdocuments.site/reader038/viewer/2022103022/56649d8b5503460f94a715cc/html5/thumbnails/2.jpg)
September 15, 2007 D.Giandomenico
Linear Speed Control
• Simple Linear Speed Control uses a fixed voltage source and variable resistance† in series with the motor to control the applied voltage
• Voltage not delivered to the motor is dropped across the variable resistance.
• Inefficient whenever <100% voltage is applied
† The series pass element, here described as a “variable resistance,” would commonly be a power transistor controlled with a regulator circuit.
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September 15, 2007 D.Giandomenico
Switching Speed Control
• Control power to the motor by rapidly opening and closing a switch connected to a fixed voltage source.
• Ideal switch doesn’t dissipate power – Power in an ideal switch is zero, since either the
current through the switch is zero, or the voltage across the switch is zero .
![Page 4: September 15, 2007 D.Giandomenico PWM Motor Control with IFI Robotics Victor884 Electronic Speed Controller David Giandomenico Lynbrook High School Robotics](https://reader038.vdocuments.site/reader038/viewer/2022103022/56649d8b5503460f94a715cc/html5/thumbnails/4.jpg)
September 15, 2007 D.Giandomenico
Basic H-Bridge
www.mcmanis.com/.../images/basic-bridge.gif
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September 15, 2007 D.Giandomenico
Basic MOSFET H-Bridge
roko.ca/articles/hbridge/bridge1.gif
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September 15, 2007 D.Giandomenico
IFI-Robotics Victor 884Electronic Speed Controller (ESC)
www.ifirobotics.com/.../victor-884-250-a.gif
Full H-Bridge, composed of 4 groups of 3 IRL3103 MOSFETs, each rated at 45A continuous at T=100C
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September 15, 2007 D.Giandomenico
Pulse Width Modulation• PWM – A general method of conveying
power or data by varying the duty cycle† of a square wave to convey either power or data.– †Duty cycle is the percentage of time the square wave is ‘high’.
• FIRST Robotics uses the PWM method to two ways:– Send control data to IFI Robotics Victor88x Series
Electronics Speed Controllers (ESC’s), common hobby servos, etc.
– Deliver switched power from Victor Series ESC’s to motors.
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September 15, 2007 D.Giandomenico
PWM Method of Data Transfer to Servos and Victor ESCs
2.0 ms
1.5 ms
1.0 ms pwm = 0d
pwm=127d
pwm=254d
14.0 ms~20ms-40ms
Typical r/c pwm signals. Values are not verified - example only.
25X/sec to 50X/sec
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September 15, 2007 D.Giandomenico
PWM Method of Power Delivery used byIFIRobotics Victor884 ESCs
• PWM technique varies the duty cycle of a square wave signal.www.societyofrobots.com/images
Duty Cycle
~20%
~60%
~90%
f = 120Hz, T=1/f =8.3msfor Victor884 ESC only
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September 15, 2007 D.Giandomenico
Linear vs. PWM/Switched Motor Control
Simple Linear PWM/SwitchedControl Method:
Vary Applied VoltageControl Method:Vary Duty Cycle
Inefficient Efficient
Motor Speed is proportional to applied voltage
Motor speed is not linearly proportional to duty-cycle
Current draw is continuousHigh peak currents at low duty
cycle; Not continuous.
Good speed regulation Poor speed regulation
Efficiency is the reason we use switched power controls.
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September 15, 2007 D.Giandomenico
How does switched/PWM power control adversely affect your robot?
Robot drive system is not linearly proportional to driver’s input at the joystick.
Poor motor speed regulation when load changes when using a switched ESC (e.g. Victor884) to set a constant speed on a system such as a ball conveyor, or robotic arm.
Closed loop systems (controlled motor speed systems with feedback) will either not be stable at low speeds, or sluggish at high speeds.
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September 15, 2007 D.Giandomenico
3.1 ms
8.3 ms
0A
5A
10A
f = 1/8.3ms = 120Hz
Duty Cycle =3.1/8.3 = 37%
Motor Current using anIFI Robotics Victor884 ESC
2006 Fisher Price Motor
commutator noise
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September 15, 2007 D.Giandomenico
Motor Current vs. Pulse Width
4.7 A
10.0 A
19.0 A
4.7 A
10.0 A
19.0 A
3.4 ms
1.7 ms
1.1 ms
2ms/div
As duty cycle decreases,motor slows, causing the motor’s EMF to drop, andthe peak current to rise.
2006 Fisher Price motor turning “ball launcher” wheels.
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September 15, 2007 D.Giandomenico
2
4
6
8
10
12
0
100%
75%
50%
25%
0%
%Is
Vo
lts
T =1/f
EMF(Speed)
Motor EMF (Speed) vs. Duty Cycle
2
4
6
8
10
12
0
100%
75%
50%
25%
0%
%Is
Vo
lts
T =1/f
EMF(Speed)
2
4
6
8
10
12
0
100%
75%
50%
25%
0%
%Is
Vo
lts
T =1/f
EMF(Speed)
2
4
6
8
10
12
0
100%
75%
50%
25%
0%
%Is
Vo
lts
T =1/f
EMF(Speed)
2
4
6
8
10
12
0
100%
75%
50%
25%
0%
%Is
Vo
lts
T =1/f
EMF(Speed)
2
4
6
8
10
12
0
100%
75%
50%
25%
0%
%Is
Vo
lts
T =1/f
EMF(Speed)
With a constant load, the average torque over period T is constant.
Torque = Ki I, average I is also constant.
Iavg=DC x (12V – EMF)/R
with DC tp/T
So, for a constant load, the green area must be constant.
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September 15, 2007 D.Giandomenico
The Math
DCV
RIVEMF
battery
avgbattery 1
vNLbattery KV VKEMF and
R
–EMFVDCI battery
avg
)(
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September 15, 2007 D.Giandomenico
The Math (continued)
DCV
RIVEMF
battery
avgbattery 1
DCI
I
s
avg
NL
1
DCT
T
N
N
s
avg
NL
1
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September 15, 2007 D.Giandomenico
Steady State Speed as a Function of Duty Cycle
DCT
T
N
N
s
avg
NL
1
%25%15/ savg TT
For a typical system designed for good operating efficiency,
1/ DCTT savg
savg TTDC /0 0
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September 15, 2007 D.Giandomenico
Steady State Motor Speed for Linear and Switched/PWM Power
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0% 20% 40% 60% 80% 100%
% Duty Cycle
% N
o L
oad
Sp
eed
10% Load - Linear
10% Load - PWM
20% Load - Linear
20% Load - PWM
DCT
T
N
N
s
avg
NL
1
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September 15, 2007 D.Giandomenico
Duty Cycle vs. Steady State Speed
s
avg
NL T
T
N
N 10
1
1
ss
avg
N
N
T
TDC
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September 15, 2007 D.Giandomenico
Duty Cycle vs. Speed
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
100.0%
0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0%
% No Load Speed
Du
ty C
yc
le
Load=30%
Load=20%
1
1
ss
avg
N
N
T
TDC
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September 15, 2007 D.Giandomenico
Excess Available Torque for Linear and PWM-Switched Speed Control
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
100.0%
0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0%
% No Load Speed
Exc
ess
Ava
ilab
le T
orq
ue
(%T
s)
Linear
PWM Switched
Load=20%Ts
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September 15, 2007 D.Giandomenico
Solutions for adverse affects of switched/PWM power
Robot drive system is not linearly proportional to driver’s input at the joystick.
Solution: 1) Driver compensates.
or 2) Use closed-loop control.
Poor motor speed regulation when load changes when using a switched ESC (e.g. Victor884) to set a constant speed on a system such as a ball conveyor, or robotic arm.
Solution: 1) Use gears or other speed reducer to pick speed. or 2) Use closed-loop control.
Closed loop systems (controlled motor speed systems with feedback) will either not be stable at low speeds, or sluggish at high speeds.
Solution: Reduce proportional gain when speed is low.
![Page 23: September 15, 2007 D.Giandomenico PWM Motor Control with IFI Robotics Victor884 Electronic Speed Controller David Giandomenico Lynbrook High School Robotics](https://reader038.vdocuments.site/reader038/viewer/2022103022/56649d8b5503460f94a715cc/html5/thumbnails/23.jpg)
September 15, 2007 D.Giandomenico
PWM Motor Control with IFI Robotics Victor884Electronic Speed Controller
David GiandomenicoLynbrook High School Robotics
FIRST Team #[email protected]
(408)343-1183