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

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

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

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

8. Same power!

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

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

12. Cam As a Transmission FOLLOWER CAM moparmusclemagazine.com

15. Da Vinci Cams

16. 16 US 6468286

17. 17

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

19. What is a bearing? A BEARING REDUCES DEGREES-OF-FREEDOM

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

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

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

23. Rulon bearings

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

25. More sliding joints BINDNO BIND

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

27. Shaft

28. SUPPORTING SHAFTS YES! NO!

29. Bearing misalignment OFFSET ANGULAR

30. Bearing load radial thrust

31. JOINING SHAFTS ? Offset misalignment Angular misalignment

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

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

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