Motor Performance Beach Cities Robotics – Team 294 Andrew Keisic November 2009

Topics System Requirements Key Motor Characteristics Governing Equations System Efficiency Supermotors Gear Ratios

System Requirements After performing top level systems engineering analysis and creating whole robot concepts, it’s time to flow down requirements… What do you need to move? – Torque How quickly do you need to move it? – Speed How much margin do you want? – Factor of Safety

System Requirements Designing is all about tradeoffs Speed vs torque Low CG vs reaching high Weight vs features Control vs power

System Requirements Requirements Before designing a robot, we must know what it needs to do The design requirements usually stem from the game Strategy plays a big part in the requirements Decide the requirements as a team

Key Characteristics Cycling Analogy… If you were cycling what do you think would be the key measures of your performance?

Key Characteristics 5 values determine the performance of a motor Motor Description Spec Voltage (V) Free Speed (RPM) Stall Torque (N*m) Stall Current (Amp) Free Current (Amp) Bosch Drill 2003 (No Gearbox) Bosch Drill 2003 (High Gear) Bosch Drill 2003 (Low Gear) Bosch Drill 2002 (No Gearbox) Bosch Drill 2002 (High Gear)

Governing Equations Speed and operating Voltage

Governing Equations Stall torque and operating voltage

Governing Equations Free speed current and operating voltage

Governing Equations Speed and Torque

Governing Equations Current and Torque

Governing Equations Who does more work? Doing 1, 10ft trip carrying 10lbs Doing 10, 10ft trips carrying 1 lbs Work Work = Force * Distance

Governing Equations Mechanical Power Power is the key! The rate of work a motor can output! Power = Force * Distance / Time Note: w is in RPM

Governing Equations Maximum Mechanical Power

Governing Equations Electrical Power

Governing Equations Motor Efficiency

Normalized Performance Graph Note: Torque on x-axis

Motor Performance: Quick Reference

System Efficiency Where do you lose power?

System Efficiency Where do you lose power? Gear interfaces Spur gears ~95% Chain sprockets ~95% Worm gears ~70% Electrical wiring

Super-motors! How do you effectively combine different motors? What gear ratio do you use between them?

Super-motors!

How do you effectively combine different motors? Infinite choices, but 3 key ones Match free speed velocity Match maximum power Match maximum efficiency