Precision Robotics

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Precision Robotics

• R. M. Satterthwaite
• R. Shockency

Advised By Dr. B. D. Huggins Mr. C. Mattus
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Introduction

• Our objective is to create a low cost robotic
  platform capable of precise movements related to
  user inputs.
• Provide a basic platform for future projects to
  start from.

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Outline

• The Complete System
• Another fabulous drawing by Rob. Paint Rules!!
• Microprocessor
• The heart and soul
• Power Electronics
• H Bridges, the devil incarnate
• CPLD
• The motor reader
• Platform
• Bringing it all together into one cute package

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System
Note Paint is the best Graphics program on The
market.
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Microcontroller

• Data Processing
• CPLD interface to reduce work load
• Performs real time speed, distance, and turning
  calculations
• Acts as a memory device
• Crude Closed Loop Controller
• Speed control for 2 motors
• Distance control for 2 motors
• Turning control for 1 vehicle
• 500 Hz, 1791 Step Variable PWM

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User Interface

• Keypad Entry
• 2 Forward
• 8 Backward
• 4 Left
• 6 Right
• E Enter
• F Clear
• LCD Menu System
• Handles Single Commands

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User Interface
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8 Bit Representation of Motor Speed Used as a
Control Variable
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Closed Loop Control
5 Volts
0 Volts
0
1791
FFFF HEX
F900 HEX
Complement Point
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The PWM Signal

• 500 Hz
• 1791 divisions
• .0558 increments of the duty cycle
• CRCH, CRCL
• Sets the PWM Period
• FFFF-F900 6FF (Produces 2 ms interrupt)
• CCH1, CCL1
• Controls the Complement Point of the PWM
• The process is backwards because the hardware
  uses a count overflow to signify the end of the
  process.
• FFFF overflow point
• FFFF 0 Duty Cycle
• F900 100 Duty Cycle

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H-Bridges

• What are they?
• Power Transistor array with logic for direction
  control and breaking.
• Logic ports not very robust
• Destructive Noise
• Power and grounding
• Noise from motors
• Noise to encoder wheels

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The H-Bridge
Yes, electrons are blue.
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Intermission
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CPLD

• Why CPLD?
• Speed
• Non-volatile memory
• Easy diagnostics and testing
• Mass Production
• Two CPLDs Needed
• CPLD 1 Freq Counter/Angle (75 Utilized)
• CPLD 2 Distance (65 Utilized)

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CPLD - Counter

• Frequency counter for motors 1 and 2
• Real time calculations of speed for both motors
• Refresh rate of 10 Hz
• Cascaded counters (8-bit and 4-bit)
• First count 0 to 15
• 42,000Hz / 256 160, 160 / 10Hz 16
• Two counts, First count and Sum count
• Check and Sent

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CPLD Distance

• Distance calculation code
• Allows distance count in CM and M
• Max of 256 Meters
• Increments register for microprocessor
• 663 counts per CM
• 500 65.5 / 49.4 662.995 or 0.007 error
• 0.67CM error per 100Meters
• On CPLD 2, 4 registers, 2 Per Motor

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CPLD - Angle

• Angle calculation code
• Allows angle calculation to 1º
• 2 Registers, 1 0º - 179º, 1 180º increments
• Increments register for microprocessor
• At 38.88CM width, 225 counts per degree
• (38.88 p 662.995) / 360 224.935 or 0.03
  Error
• 0.1º error per 360º
• On CPLD 1, 2 Registers, 1 Motor

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CPLD - Addressing

• Interface to the microprocessor code
• 8 registers addressed on 2 CPLDs
• Enable and 4 registers each using 3 address lines
• Tri state buffer on EMAC bus lines
• Problems
• Cant tri state parallel port pins or
  microprocessor port pins
• Frequency input can not be same pin as clock

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Platform

• Cut and milled, then folded and bolted
• Symmetrical for turning
• Wheels encased for less stress on the motor
  shafts
• Casters allow for pivot turning
• Bearings Nylon for casters and drive wheels

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Platform

• Power switch and charging switch in one!
• Batteries and motors on bottom plate
• All electronics on top two tiers
• Hardboard for future changes is controlling
  hardware
• Central Disconnects

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Platform
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Electronics
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Complete System
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Its ALIVE!!
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Questions