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Machine Elements

Machine Elements. Transmissions, Bearings, Shafts. TRANSMISSIONS. Matching the torque and speed of the motor to the torque and speed of the task. Torque (oz-in). Operating point. Load torque. Speed (rpm). Motor torque-speed curve. Stall. No-load. Load torque. Changes with motor V.

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Machine Elements

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  1. Machine Elements Transmissions, Bearings, Shafts

  2. TRANSMISSIONS Matching the torque and speed of the motor to the torque and speed of the task

  3. Torque (oz-in) Operating point Load torque Speed (rpm) Motor torque-speed curve Stall No-load

  4. Load torque Changes with motor V Increasing V Torque (oz-in) Speed (rpm)

  5. Small DC Motors • Plain motors: spin fast, low torque • Gear motors: spin slow, high torque • More voltage = more speed and more torque • Less voltage = slows down, but torque down • If spin too fast, bearings fail • If too much current, coil heats up and melts

  6. Stall too wimpy! Torque (oz-in) No-load spins too fast! Speed (rpm) Motor complaints Solution: A transmission  gets you on a new T-S curve

  7. After: high torque at low speed Before: low torque, high speed T2 = n*T1 v2 = (1/n)*v1 5:1 Transmission 25 Torque (oz-in) 5 Speed (rpm) 10 2

  8. Same power!

  9. Belt Drive Slow, strong turntable Fast, weak motor

  10. Rim Drive Slow, strong turntable Fast, weak motor

  11. FOLLOWER CAM Cam As a Transmission moparmusclemagazine.com

  12. Da Vinci Cams

  13. US 6468286

  14. BEARINGS and SHAFTS Getting things to spin by transmitting rotary power

  15. BEARINGS A BEARING REDUCES DEGREES-OF-FREEDOM

  16. SPECIFICATIONS • Ability to constrain motion • Friction • Load • Lifetime • Fabrication/Mounting • Cost

  17. TO SLIDE OR TO ROLL? Rolling elements: Low friction, complex, expensive Sliding elements: Simple, high friction

  18. Tapered Roller Bearing Angular contact roller bearing timken.com

  19. Rulon bearings

  20. Sliding bearings (prismatic joints) D L/D = 6 to 10 L NO BIND BIND

  21. More sliding joints BIND NO BIND

  22. KH Linear bushing Danahermotion.com alibaba.com linear bearings

  23. Shaft

  24. SUPPORTING SHAFTS NO! YES! NO!

  25. Bearing misalignment OFFSET ANGULAR

  26. Bearing load radial thrust

  27. JOINING SHAFTS ? Offset misalignment Angular misalignment

  28. A classic binding problem ? one shaft, 4 supports= binding!

  29. Coupling methods rigid coupler, press-fit or glue or set-screws flexible coupler

  30. Or, just tape ‘em together electrical tape or fiber reinforced tape

  31. Machine Elements Transmissions, Bearings, Shafts

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