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Energy Model and
Measurement for DC Motors
in PPRK
Yongguo Mei
Sep. 18, 2003
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Outline
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PPPK
Energy model
Experiment design
Future work
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PPRK
• Palm Pilot Robot Kit
• Cheap, easy to build, and
fun
• Created by two Carnegie
Mellon Robotics Institute
research groups
• Desktop Robotics, fully
autonomous robot
controlled by a Palm
handheld computer
• Open resource available
from their website
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PPPK (continued)
• Central control Unit: BrainStem, General
Purpose Module
• 3 MX-400 Servo Motors, driving three
wheels
• 3 GP2D12 infrared sensors
• Connect to PDA through RS-232
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Power source and consumers
• Source: Hobbico HydriMax 6.0V Battery,
or 4 regular AA alkaline batteries, precious
• Consumers: GP module, sensors, DC
motors
• Not consider PDA here
• Concentrated on the speed control of
motors to save energy
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DC Motor
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Circuit Model
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V = iR + Ldi/dt + Vemf
T = Kti
Vemf = Ktω
T– torque
ω– angular velocity
Kt – torque constant
P=V*i
Convenient, but
enough?
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Other factors
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Saturation caused by high current
Non-linear commutation effect
Eddy current losses
Frictions
No general accepted model
How do we handle all of these?
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From another direction
• Real measurement to get the energy
model for our Robot?
• Few people did this before
• Avoid the complicated theoretical analysis
• A viable way for our problem
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Possible format
• For specific Motors and working
environment, Power is a function of the
velocity and acceleration
• What are possible formats?
• Polynomials with highest exponent 2
• P(v,a) =
c(1)v*v+c(2)v*a+c(3)a*a+c(4)v+c(5)a+c(6)
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Possible format
• Second-degree polynomial is enough
• It can incorporate most of the factors
mentioned previously
• Compare this with other models
• Can this model be extended to other
Robots?
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Experiment design
• MX-400 Pro Servo motor
• Three lines: ground, power
and control
• Measure voltage and
current by Data Acquisition,
DAQ
• Program by Labview to
process the data
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Experiment Design
• Accerelation, constant
speed and Deceleration
• Rotation
• Speed control by c
program, hope not too
difficult!
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Future work
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Real measurement
Energy optimal control
Motion planning
Multimover problems
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