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EE4701 Preliminary Design Presentation. Ben Maderazo Justin Smith. Presentation Goals. Present our own requirements analysis and design decisions for critique Defend our decisions and explain why our design will perform better than others
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EE4701 Preliminary Design Presentation Ben Maderazo Justin Smith
Presentation Goals • Present our own requirements analysis and design decisions for critique • Defend our decisions and explain why our design will perform better than others • Prove that we are ready to begin assembling and testing our robot for competition
Team Goals • Apply KISS principle in hardware implementation to save time • Spend more time on algorithm development and application than hardware • Win competition
Competition Rules • Each robot must fit within a twelve inch cube • Each match will be the best of three rounds with each round lasting no longer than fifteen minutes • The ball may be captured, pushed, or kicked into the goal • Robot and ball position will be monitored by an overhead camera • To enter into the competition, each robot must pass preliminary qualification tests
Preliminary Qualifications • Robot must travel from one goal to other and back in less than two minutes • The robot must capture a ball and return it to the home goal in under five minutes • The robot must retrieve three balls, one at a time, and return them to its home goal in fifteen minutes while avoiding an immobile obstruction
Robot Subsystems • Information processing • Obstacle detection • Locomotion • RF reception • Ball capture • Power
Information Processing Subsystem • Must take data from other subsystems, process it, and issue commands.
Analysis • Speed • Must be done 10x per second • Mathematical Computation • Addition, subtraction, and absolute value • Arc tangent
Requirements • 3 input ports for switches • 2 A/D converter ports for IR sensors. • 2 PWM output ports for H-Bridge. • Ability to send and receive 4 serial transmissions. • Ability to compute basic math and binary operations. • Ability to compute the arc tan function. • Ability to use interrupts.
OOPIC • Advantages • Virtual Circuits • Interrupts • Object Oriented Programming • Predefined objects • Unlimited serial ports • Disadvantages • Slower than the PIC
Math Coprocessor • PAK-II • Features • Communicates Serially • 20Mhz • Performs sin, cos, tan, inverse functions, square roots, powers, and many other functions
Obstacle Detection Subsystem • The robot will need to detect objects in its path to pass the second round of qualifying. • It is not certain if this will be used during the contest.
Analysis • Distance Requirements • Robot travels at max 2 ft/s • Estimate .5s for robot to stop after detection • .5s x 2 ft/s = .5 ft
IR Detector • Advantages • Long Distance • ~4” to 3’ • Disadvantages • Higher power • Ability to test at set times to save power
RF Reception • RF Reception will be used to receive data and instructions from the Vision System. • The part will be supplied by Bryan Audiffred and there will be little room for design in this subsystem.
Ball Capture • The robot will be required to capture a ball, know if the capture was successful, and secure it.
Requirements • Can only control one ball at a time • Must be able to effectively capture and release balls • Must be able to provide feedback of success or failure
Hardware choice • Construct a housing on the robot chassis that will encase the ball • Use a generic servomotor to close a gate at the entrance of the housing • Interior is lined with material to reduce inertia of the tennis ball • IR emitter, receiver pair on sides of the housing to determine if ball captured
Locomotion Subsystem • Fetching a ball and returning that ball to a goal requires some type of locomotion. • Locomotion involves steering, a propagation system, equipment to drive the propagation, and control circuitry to operate the equipment.
Minimum Requirements • Speed of at least 0.14 feet per second. • Ability to alter the heading and direction of travel. • Ability to stop.
Locomotion: Introduction to Steering • To compete well in the 6’ x 8’ area, robots will need a tight turning radius. • The chassis configuration must also be taken into account when analyzing the problem of steering.
Locomotion: Steering Analysis • Robot must be able to rotate 360° without changing its position • Robot must be able to rotate a minimum of 3° at a time
Locomotion: Steering Hardware • Differential steering system • 2 Wheels driven by two separate motors and 2 casters for support • Use formula Vi / Rt = Vo / (Rt+D) and derivations to calculate velocities and turning radii
Steering Hardware Continued • Tires: ‘Lite Flite’ Foam tires have a 3” diameter and are made of a foam rubber compound
Locomotion: Introduction to Motor • Drives the propagation and steering systems • A good balance of power and precision is desired • Efficiency considerations must be taken into account
Locomotion: Motor Requirements • To be competitive with other robots, we want our robot to travel an average of 1 foot/second. • To achieve this speed with our 3” wheels, only around 100 rpms are needed. However, to account for friction, the motor can be geared down to increase the torque.
Locomotion: Motor Hardware • 2 Mabuchi FA-130RA-2270 motors with Tamiya 70097 Dual Motor Gear box • The gear box has ratios of 58:1 and 203:1 • The motor has an operating range of 1.5-3.0 volts • The stall current is 2 amps
Motor Hardware Continued • At max efficiency, the speed is 6990 rpms. Using the 58:1 gear setting and 3” wheels, the projected speed is 1.6 feet per second. Our goal of 1 foot per second is easily accomplished with this motor and gearbox combo.
Locomotion: Introduction to Motor Driver • External circuitry is needed to interface the motors with the mcu • This circuitry helps the motors run efficiently and safely • Allows motor to operate at various RPMs as well as forward and reverse
Locomotion: Motor Drive Requirements • Drive two motors simultaneously • Must be able to output from 1.5 to 3 volts • Must be able to output up to 2 amps per motor at stall torque
Locomotion: Motor Driver Hardware • Lynxmotion Dual H-bridge • All that is needed is to hook up mcu input lines, motor output lines, motor power supply, and 5V Vcc
Power: Introduction • Power efficiency much more crucial in battery powered devices • Batteries can add significant weight • Robot will need adequate voltage and amp output • Need batteries to power MCU and motor
Power: Requirements • H-bridge we chose requires 6 volts to drive the motor and max of 4 amps if both motors stall • MCU must have voltage regulated to 5 volts • Robot must compete in an undetermined number of matches so rechargeable or extra batteries may be needed
Power: Hardware • 2 prepackaged Rechargeable Nickel Metal Hydride battery packs • Smart charger • 9V battery with a voltage regulator for MCU
Power: Hardware continued • Maximum 30 amp discharge rate. • As high as 3000mah capacity nickel metal hydride.All cells are matched. No cell memory, you can recharge the pack without fully discharging • Voltage: 9.6 volts
Power: Hardware continued • 2000ma constant output current for any voltage battery pack • Charging current will reduce to trickle charging at 50mah when battery pack close to full, then green LED will be on • For 3000 mAh battery pack, charging time is about 90 minutes
