DC Motor Control

mouse

EE 496

Advisor: Dr. Tep Dobry

Team Members

• Ikaika Ramos– Overall Project Manager– Chassis Fabricator– Hardware Specialist

• Aaron Tsutsumi– “Jack of All Trades”

– Algorithm Constructor– Software Innovator

Brief Overview

• Another Micromouse…Zzzzz

– Abide by all IEEE Regional 6 Micromouse Rules

– In response to last years Regional 6 Winner

• Propulsion Design Difference– DC Motors – Control Method

Block Diagram

Power Supply

• Chose to use lithium polymer batteries over nickel-metal hydride because of higher energy density– Higher energy density = Smaller

size, less weight• Using switching voltage

regulators because of high efficiency– Decided to use a self-contained

package to avoid having to calculate values for external components and to keep size small.

Sensor System

• Used same components as our previous mouse since we were familiar with it.– Sharp GP2D120 sensors and

Maxim MAX114 analog-digital converter.

• Decided to use a different sensor configuration.– Using four sensors instead

of three, two outer sensors on outside point straight forward to help align during a 45 degree run.

Motor Control

• PWM– We chose to use Pulse Width Modulation to control the

speed of the motors because it is simple to implement.

• H-Bridge– H-bridges will be used to control the direction of the

motors.

• Encoders– We chose to use optical encoders to help determine the

position of our mouse.

PWM

• A pulse-width modulated signal is a rectangular waveform with a varying duty cycle.

• A longer duty cycle means the voltage is on for longer and the average voltage applied to the motor is higher and vice versa.

• Will be implemented using the PWM generator on our microcontroller.

H-Bridge

• DC motors only have two leads. The direction it spins is determined by which terminal has power applied and which is connected to ground.

• An H-bridge consists of four switches (in our case BJTs) and depending on which two are closed, allow the motor to operate in either direction

• We chose to use an L298 chip from STMicroelectronics because it has two H-bridges in one package.

Encoders

• We decided to use optical encoders over accelerometers.– Accelerometers were harder

to implement, and may not have been accurate enough.

– If the mouse was not accelerating or decelerating, we would have had to assume and calculate our position

• The optical encoders give us a more definite position reading.

• We chose the HEDS-9100 encoders because of size limitations.

Microprocessor

• Rabbit 3100 Core Module– Uses a Rabbit 3000 microprocessor.

• Software P.I.D Controller– A software Proportional-Integral-Derivative

controller is a feedback system that will allow us to more accurately control our system.

Rabbit 3100

• We chose the Rabbit 3100 over other microprocessors.– Other models we researched

would have been harder to implement.

– Chose the Rabbit 3100 because we could reuse our programming cable and it had pulse-width modulation capability.

– Also found that it had quadrature decoders which help us to use the encoders.

Software P.I.D. Controller

• Motors are not a digital type of device. A sharp change in voltage level doesn’t instantly change the speed of the motor. We have to take this time constant into consideration.

• We will use a PID controller to fine-tune the operation of our motor.

• Takes readings and calculates an error value.• Tries to get the system to settle at the correct value as

quickly as possible.• A PID controller modifies the error signal in three ways to

determine the best correction.• Still needs to be implemented and fine-tuned…

Proportional – Integral – Derivative

• The proportional part of the modification is simply multiplying the error signal by a constant to adjust for the current error.

• The integral part of the modification is multiplying the error signal by the result of an integral to adjust for error in the past that hasn’t been corrected yet.

• The derivative part of the modification is multiplying the error signal by the result of a derivative to try and predict the future error correction required.

• The sum of these corrections (once the constants have been fine-tuned) should be a system that reaches an accurate steady state as soon as possible.

Tracking, Mapping, Solving

• Using old code, modified for this mouse.

• Plan on possibly implementing different solving methods.

• Plan to implement a few modified flood-fill (Bellman) algorithms

What remains to be done…

• Connect PCB board to external modules

• Programming the mouse

• Fine-tune PID controller

• Troubleshooting / Debugging

• Write up our 30 page paper

Gantt Chart21-May 10-Jun 30-Jun 20-Jul 9-Aug 29-Aug 18-Sep 8-Oct 28-Oct

Research Parts

Research Software Implementation

Get Samples of Parts we can Get Samples For

Order Parts not Being Sampled

Test Microprocessor/Microcontroller

Test Motors/PWM

Test Encoder

Test Batteries

Test H Bridge

Build Chassis

Design Circuit

Assemble Circuit

Implement Straight Movement

Implement Turns

Implement Alignment

Implement PID

Tune PID

Final Troubleshooting/Debugging

Paper Write-Up

“Because this is a design review, I will expect everyone to ask at least TWO questions sometime

during your session.”

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