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Choosing the Correct Motor

Choosing the Correct Motor. Michael Ciavaglia January 6, 2001. Choosing the Correct Motor. Agenda Michael Ciavaglia ... Who am I? Work Examples Power Examples Motor Curves Motor Power Effective Gear Ratio and Power Power Needed vs. Effective Power. Choosing the Correct Motor.

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Choosing the Correct Motor

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  1. Choosing the Correct Motor Michael Ciavaglia January 6, 2001

  2. Choosing the Correct Motor Agenda Michael Ciavaglia ... Who am I? Work Examples Power Examples Motor Curves Motor Power Effective Gear Ratio and Power Power Needed vs. Effective Power

  3. Choosing the Correct Motor Michael Ciavaglia B.S.Mechanical Engineering ‘93 University of Michigan M.S.Mechanical Engineering ‘99 Purdue University Advanced Development Group Electro-Mechanical Systems 5 Issued Patents (~ 5 more in process)

  4. Choosing the Correct Motor Work Work = Force * Distance Example 1: A box weighs 130 lbs and must be moved 10 ft. The coefficient of friction between the floor and the box is .5 . How much work must be done??

  5. Choosing the Correct Motor Work f = mu*N = .5*130 f = 65 lbs so… Work = f * dist Work = 65 * 10 = 650 ft lbs

  6. Choosing the Correct Motor Example 2: The arm weighs 10 lbs and moves 3 ft vertically. The mechanism that contains the balls weighs 5 lbs. The balls weigh 3 lbs. The mechanism and balls move 6 ft vert. Work = Force 1*Dist 1 + Force 2*Dist 2 = 10 lbs * 3 ft + 8 lbs * 6 ft = 30 + 48 = 78 ft lbs

  7. Choosing the Correct Motor Power Power = Work / Time = Force * Distance / Time Note: There is only a certain amount of power available.

  8. Choosing the Correct Motor Power Example 2A: Desire this motion to be completed in 10 seconds. Power = 78 ft lbs / 10 seconds * (60sec/1min) * .02259697 = 10.6 Watts

  9. Choosing the Correct Motor Power Example 2B: Desire this motion to be completed in 3 seconds. Power = 78 ft lbs / 3 seconds * (60sec/1min) * .02259697 = 35.3 Watts

  10. Choosing the Correct Motor Speed-Torque Curve

  11. Choosing the Correct Motor Current-Torque Curve

  12. Choosing the Correct Motor Power-Torque Curve

  13. Choosing the Correct Motor Combined Motor Curves

  14. Choosing the Correct Motor Motor Power Motor Power = Power Available = Free Speed / 2 * Stall Torq. / 2 * C.F. where: Free Speed is in rad / min Stall Torque is in ft lbs Conversion Factor = .02259697

  15. Choosing the Correct Motor Speed Free Speed (rev/min) * 2 Pi (rad/rev) Torque Stall Torq. (in oz)*(1 ft/12 in)*(1 lb/16 oz)

  16. Choosing the Correct Motor Drill Motor Free Speed = 20000(rev/min) *2PI(rad/rev) = 125664 rad/min Stall Torque = 650 (Nmm)*(1 lb/4.45 N)* (1 in/ 25.4mm)*(1 ft/12 in) = .48 ft lbs

  17. Choosing the Correct Motor Drill Motor Power = Free Speed / 2 * Stall Torque / 2 *Conv. Factor = 125664 / 2 * .48 / 2 *.02259697 = 340 W

  18. Choosing the Correct Motor Available Power from FIRST Motors Bosch Motor Only 340 W Bosch Motor w/ Gear box in HIGH 260 W Bosch Motor w/ Gear box in LOW 230 W Fisher Price Motor Only 140 W Fisher Price Motor w/Gearbox 91 W Delphi Sliding Door Motor (MFG: Taigene) 69 W Globe Motor Only 63 W Globe Motor w/ Gearbox 50 W Delphi Seat Motor (MFG: Keyang) 31 W Delphi Window Motor (MFG: Valeo) 22 W

  19. Choosing the Correct Motor Required Max Torque Torque = Force * Moment Arm = 10 lbs * 1.5 ft + 8 lbs *4.5 ft = 15 ft lbs + 36 ft lbs = 51 ft lbs

  20. Choosing the Correct Motor Pick Which Motor: Delphi Window Motor ?? Delphi Seat Motor?? Globe Motor?? Delphi Sliding Door Motor??

  21. Choosing the Correct Motor Try Globe Motor w/ Gearbox Working Torque = Stall Torque / 2 = (15 ft lbs @ 12 V) / 2 = 7.5 ft lbs

  22. Choosing the Correct Motor Determine Gear Ratio Gear Ratio = Torque Needed / Torque Avail = 51 ft lbs / 7.5 ft lbs = 6.8 :1 Use Spur Gears with 90% efficiency

  23. Choosing the Correct Motor Effective Gear Ratio Try: 6.8 = 2.5 * 2.7 Eff. Gear Ratio = Ratio*Eff.*Ratio*Eff. = 2.5 * .9 * 2.7 * .9 = 5.5

  24. Choosing the Correct Motor Effective Gear Ratio Try Two Stages of 3:1 Eff. Gear Ratio = Ratio*Eff.*Ratio*Eff. = 3 * .9 * 3 * .9 = 7.3

  25. Choosing the Correct Motor Effective Power With Two Stages of 3:1 @ .9 Efficiency & Globe Motor w/Gearbox Power @ 50 W Effective Power = 50 * .9 * .9 = 40.5 W

  26. Choosing the Correct Motor Power Needed vs. Effective Power Power Needed = 35.3 W (from Ex. 2B) Effective Power = 40.5 W Note: The effective power is true only if system is operating at or near Peak Power.

  27. Choosing the Correct Motor Q: Could you lift a 200 lb man through 90 degrees of rotation at with a one foot moment arm??

  28. Choosing the Correct Motor Q: (In your mind should be…) IN HOW MUCH TIME !!

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