Motor Performance Beach Cities Robotics Team 294 Andrew
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 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 Free Torque Current (N*m) (Amp) Bosch Drill 2003 (No Gearbox) 12. 0 19670 0. 87 127. 00 2. 50 Bosch Drill 2003 (High Gear) 12. 0 1550 11. 04 127. 00 2. 50 Bosch Drill 2003 (Low Gear) 12. 0 450 38. 03 127. 00 2. 50 Bosch Drill 2002 (No Gearbox) 12. 0 20000 0. 65 114. 00 2. 50 Bosch Drill 2002 (High Gear) 12. 0 1000 10. 00 114. 00 2. 50
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, 10 ft trip carrying 10 lbs Doing 10, 10 ft trips carrying 1 lbs Work = Force * Distance
Governing Equations Mechanical 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!
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
- Slides: 24