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Design

Mechanical

The steel chassis base served as a housing for the microprocessor and wiring harness. The box-like design had a hinged lid that provided easy access to the electronics system inside.

The robot arm was driven by a motor at the center of two large gears, which drove two smaller gears using a timing belt system.

The drive train featured a two-wheel drive and front sled. The rear wheels were driven independently by separate motors, and turning was achieved by driving one motor at a higher speed than the other.

The robot "hand" was a simple steel sheet metal U-bracket which would lower onto the pet's magnetic head. The base of the arm was mounted on a Lazy Susan bearing and powered by a servo, allowing it to rotate about the z-axis

Electrical/ Software

Early on, it was decided that the electrical system would be built in a modular style in order to conserve space as well as make troubleshooting and repairs as simple as possible. The system was composed of the following main components:

  • The TINAH Board (in-house designed and built microcontroller board)

    • All inputs and outputs are received and sent by the TINAH board. The TINAH reads both analog and digital signals, and was standard issue to all teams. The TINAH had the following inputs and outputs:

      • 3 DC motor inputs (2 for driving the robot, 1 for the arm)

      • 1 servo output (1 for the lazy susan)

      • 3 analog inputs (3 for IR reflective sensors (QRDs) for tape following and animal tape detection)

      • 5 digital inputs (2 for rotary encoders for the wheels, 1 for rotary encoder for the rainbow gear, and 2 for end switches for the rainbow gear)

      • The programming language of the TINAH board is C++, allowing for modularized programming for versatility, simplicity and ease of use.

         

        In order to navigate the course by tape following, a PID control system was implemented from readings of the QRDs.  Other portions of the code included methods/functions that updated readings and counts from the rotary encoders to determine how many revolutions the gears had rotated.  As well, each arm movement was a separate function that utilized motor stop and starts commands, servo angle outputs values, and digital reads from end switches on the rainbow gear and from the encoder method described above. 

  • The Motor Power Board

    • The high powered motors used by Betsie demanded a higher current draw than the TINAH could deliver, and so this board was powered at 15V nominal directly from the battery. The TINAH’s PWM outputs were used as inputs to H-Bridge cards slotted into the power board in parallel and the H-Bridge cards delivered high current output to the motors

  • H-Bridge Cards

    • Mosfet based cards for driving PWM controlled high current motors

  • The IR Power Board and IR Circuits

    • Power board and auxiliary connectors provided +/- 9V and ground rails to the IR circuits.  The circuits themselves consisted of an amplifier, band pass filter and peak detection system, and transformed a 10kHz sine wave IR signal to an analog voltage proportional to the intensity of the signal.

  • Satellite Boards

    • These boards provided input to the TINAH from specific small sensors, such as the wheel encoding circuitry and the reflectance sensors

 

All components were connected using a header pin based interface with modular cables.  Replacement parts were made so they could simply be swapped in if any issues occurred.  The system performed well during the building and testing phases, and was scalable so any additional inputs were very easy to accommodate. 

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