Sponsor/Customer: Dr. Ferat Sahin Multi Agent Bio-Robotics Lab Faculty Guide: Prof. George Slack Team Members: Matthew LeStrange – Electrical Engineering Vu Nguyen – Electrical Engineering Brandon Baker – Mechanical Engineering PJ Haasenritter – Computer Engineering

Problem: Several Senior Design groups have worked on building a “Tigerbot”, a 2-3 ft. tall walking Humanoid Robot. A continuing problem with off-the-shelf servo motors within their budget could not provide the necessary torque for the loads on the hip joints. The goal of this project is to create a low-cost servo that provides the necessary torque and speed for a walking robot. Additional goals are to have modular design a smart digital interface to communicate with the robot 2

High Level Customer Needs Design a high torque/high speed servo motor suitable for a walking robot Make the enclosure design modular to allow servo to be used in different robotic joints Modular gear box design for variable speed vs. torque, optional dual output shaft Design a communication interface to between servo motor and the robot controller send feedback and receive commands 3

High Level Specification Mechanical Provide sufficient torque for the hip joint (approx ~700 oz-in) Torque specs based on size/weight of the servo – ( oz-in/in^3 and oz-in/oz) 3 Gear Ratio Configurations Electrical/Computer Control Position using PWM or CAN bus interface Provide Feedback for position, current and Read control loop variables via CAN bus Operate on a 6-8V range Control Motor (CW, CCW, active brake and coast modes) 4

Concept Selection Summary Mechanical Enclosure, Aluminum vs. Plastic – Aluminum is easier to machine for producing a prototype – Good for Thermal Dissipation – Low Cost Encoder Selection (Potentiometer, Optical, Magnetic) – Most servos use potentiometer – Simple analog interface to microcontroller – Relatively easy to create dual output shaft H-Bridge Selection – Use discrete IC, smaller space, easy to implement all functions (CW,CCW, Brake, Coast) – Built in current sensing, short circuit and over temperature protection 5

System Architecture 6

Design Highlights (Mechanical) Aluminum enclosure – Multiple mounting options – Heat dissipation – Easily change between ratios with no changes to the enclosure Modular gearboxes – 3 Gear Ratios for variable torque output 211:1, 264:1, 330:1 Optional Dual Sided Output Shaft 7 CAD Model Cutaway View Mounting Holes CAD Model

Design Highlights (Electrical/Computer) 4.5V to 9V Battery Supply (Motor Limiting Factor) Small PCB Design (1.61 in 2 ) Robust H-Bridge – Automatic Temperature and Short Circuit shutoff – Current Monitoring – Active Braking 8 1.4” 1.15” PCB Top View PCB Bottom View Finished PCB

Design Highlights (Electrical/Computer) Multiple Servo Position control interfaces – PWM – Standard Servo Interface – CAN – Smart Interface 12-bit position and current measurement feedback system Robust, fault tolerant control system PID Control System – Field programmable PID Gains values CAN Bus Interface – Current, position, and status feedback – Control up to 31 servos on a single 2- wire bus – Servo configuration read/write: PID gains, maximum power, address, servo mode 9

Final System Results Operates from 4.5 to 9V PWM or CAN position control Working CAN feedback/communication system Initial Testing: 596 oz-in stall Torque Gears for different gear ratios (211:1, 264:1, 330:1) 10

Project Budget 11 Initial Budget $750 Electronics ( IC and other components, Development tools, motors, PCBs) $ Mechanical ( aluminum for enclosure, gears, steel rod for shaft, fasteners) $ Total Spent $ Note: Does not include Tax/Shipping charges for most orders

System Cost Current Design Material Cost 12 Cost per Servo (qty 1) Cost per Servo (qty 100) Cost per Servo (qty 1000) Electronics/Motor Mechanical Gears Grand Total Current Labor Hours PCB assembly: 1-2 hrs Gears/Shaft: 3-5 hrs Enclosure: hrs Assemble Servo: 1 hr Program/Tune/Test Servo: 1 hr Total: 16 to 23 hours

Future Improvements Increase motor size/torque output for 5 ft. tall robot – Minimal changes to electronics needed to use 12V supply Continuous 360ᵒ rotation, use 2 nd output from Potentiometer Additional Feedback (torque, velocity, temperature, stall warning) Add attachments to attach to standard servo horns 13

Design For Manufacture Improvements Simplify Enclosure Design – Injection Molded Plastic – Extruded Aluminum ($4-15/each) Cut all gears from stock – $7-16/gear vs. $ /gear & increased machine time – Buy compound gears 14 Potential Future Cost after Redesign Cost per Servo (qty 1) Cost per Servo (qty 100) Cost per Servo (qty 1000) Electronics/Motor Mechanical Gears Grand Total