Difference between revisions of "Self-Guided RC Car 3"

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(Motor Drivers)
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=== Motor Drivers ===
 
=== Motor Drivers ===
  
H-Bridge ICs
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To drive the rear and steering motors, I am using two (2)  [http://www.st.com/stonline/products/literature/ds/1373/l6202.pdf L6202 DMOS Full Bridge Drivers].
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The feature that attracted me to these drivers in particular was their SENSE outputs.  This pin outputs an analog voltage that corresponds to the amount of current being drawn by the motors.  It was my understanding that this voltage would spike to full scale when a motor stalls (powered but for whatever reason can't turn), but initial tests show a change between 0.02 V when turning and only about 0.10 V when stalled.  I expect that the analog capture of the controller will be able to distinguish between the two levels.  The voltage is dependent on the resistance between the SENSE pin and ground, but a resistor here also acts as a current limitor for the bridge.  Until I can get my hands on the recommended 0.15 ohm (!) resistor I'm just using a regular wire, which of course accounts for the extremely low SENSE outputs.
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The drivers can handle up to 1 amp of continuous current and up to 5 amps of current when pulsed.  Each driver requires three (3) inputs, one for each direction and an enable.  The enable is intended for pulse control, and I may end up sharing a common pulse between the two drivers, but I still have to see how the SENSE output acts when the motor is pulsed.  This may require a small capacitor to smooth out the SENSE voltage reading.
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Below is a picture comparing the footprints of the new IC bridges with the discrete component bridges from [[Self-Guided RC Car AI|SGRC2]].  The board with the new bridges also has a 5V power regulator setup to power the controller - this regulator is not involved directly in bridge operation.  As you can see, there is still plenty of room left on the breadboard for the 14-pin controller IC.  I am also leaving room for the accelerometer in case I decide to re-include it at some point in the future.  The compactness of the L6202's make up for the fact that they cost me about $5 a piece (plus S&H, of course).  I will most likely use the SMD version for the final soldered circuit.
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[[File:SGRC3 Bridges.jpg|300px|center]]
  
 
=== Infrared Sensor ===
 
=== Infrared Sensor ===

Revision as of 03:38, 21 November 2009

This is the wiki page for the Self-Guided RC car that TP is working on.

Overview

Background

This project is a continuation of my Self-Guided RC Car and Self-Guided RC Car AI projects, but enough [has changed / is changing] that I felt it deserved a new page.

The idea is to:

  • Build a RC car that controls itself, and
  • Have that RC car figure out HOW to control itself on its own, using some sort of adaptive learning routine.

The car's intristic goal will be to always be rolling.

Vehicle

"Standard issue cheap piece of junk from Radio Shack."

The car has two simple brushed DC motors. Rear drive motor has High/Low gear box with manual selector; steering assembly is spring-loaded to return to center when steering motor is not powered. Chassis came with a rechargable 9.6 battery and an on/off switch. I added the oversized terminal strip.

SGRC3 Chassis.jpg
Wire Purpose
Red Positive Lead from Battery
Black Ground from Battery to On/Off switch
Grey (thick) Ground from On/Off switch
Yellow Rear Motor Lead A
Green Rear Motor Lead B
Brown Steering Motor Lead A
Grey (thin) Steering Motor Lead B


Control

The following will be fleshed out later.

Controller

PIC

Motor Drivers

To drive the rear and steering motors, I am using two (2) L6202 DMOS Full Bridge Drivers.

The feature that attracted me to these drivers in particular was their SENSE outputs. This pin outputs an analog voltage that corresponds to the amount of current being drawn by the motors. It was my understanding that this voltage would spike to full scale when a motor stalls (powered but for whatever reason can't turn), but initial tests show a change between 0.02 V when turning and only about 0.10 V when stalled. I expect that the analog capture of the controller will be able to distinguish between the two levels. The voltage is dependent on the resistance between the SENSE pin and ground, but a resistor here also acts as a current limitor for the bridge. Until I can get my hands on the recommended 0.15 ohm (!) resistor I'm just using a regular wire, which of course accounts for the extremely low SENSE outputs.

The drivers can handle up to 1 amp of continuous current and up to 5 amps of current when pulsed. Each driver requires three (3) inputs, one for each direction and an enable. The enable is intended for pulse control, and I may end up sharing a common pulse between the two drivers, but I still have to see how the SENSE output acts when the motor is pulsed. This may require a small capacitor to smooth out the SENSE voltage reading.

Below is a picture comparing the footprints of the new IC bridges with the discrete component bridges from SGRC2. The board with the new bridges also has a 5V power regulator setup to power the controller - this regulator is not involved directly in bridge operation. As you can see, there is still plenty of room left on the breadboard for the 14-pin controller IC. I am also leaving room for the accelerometer in case I decide to re-include it at some point in the future. The compactness of the L6202's make up for the fact that they cost me about $5 a piece (plus S&H, of course). I will most likely use the SMD version for the final soldered circuit.

SGRC3 Bridges.jpg

Infrared Sensor

Sharp range finder mounted on a servo

Adaptive Learning

Simplied neural network routine

Current Status - Late Planning

All forseeably needed parts are on hand.

Work Log

No actual, ahem, "work", has been done yet, but a lot of contemplation has certainly been going on.

Current Issues

  • No actual work has been done yet.

Next Steps

  • Get to work