1. Drive Module Design Which Allows Wheel Flexibility Tom Ore FRC 525

2. A Random Thought… After we got back from Champs I started thinking about various discussions around wheel configurations In general, the process is you make your best guess about how the game will play and then select your wheels The rest of the robot is designed around the wheels (okay, that may be overstating it a bit)

3. A Random Thought… Sometimes the game doesn’t play out as expected and your wheel choice may not be the best one It’s often difficult to do anything about it because the robot is designed around the wheels I wondered what the drive base would look like if you designed it for maximum wheel flexibility

4. A Random Thought… So here is my thought: – Design a drive base for maximum wheel flexibility – Wait until deep in the build season before deciding which type of wheel to use – As competition weeks go by, it may be handy to change your wheel choice

5. A Random Thought… What if the wheel configuration could be changed in a few minutes? – You could even change wheel configurations before each match This assumes driver training and software issues could be handled

6. How to do it… With our suitcase bot, we could use either mecanum wheels or traction wheels – It was just a 4 wheel setup and the traction wheels were not geared/chained together What I wanted for this exercise was an 8 wheel drive setup which could use traction wheels, mecanum wheels, or omni wheels

7. What Options to Include I decided to stay with a single speed gearbox I thought about two speed, but it didn’t fit nicely into what I wanted to do – maybe this is an exercise for another time Many teams use combination mecanum/traction or omni/traction and I wanted these to be possible

8. What Speeds? We used a 12T / 60T single reduction with 4 inch wheels in 2014 and were pretty happy with the speed I can see going a bit faster or slower VexPro makes 4 CIM gears: 11T, 12T, 13T and 14T The 11T and 12T work on the same center distance as do the 13T and 14T

9. What Speeds? GearingCIMMini CIM 11T / 60T13.8 ft/sec16.1 ft/sec 12T / 60T15.0 ft/sec17.5 ft/sec 13T / 60T16.3 ft/sec19.0 ft/sec 14T / 60T17.5 ft/sec20.5 ft/sec

10. The gears in a module… The two outer gears are the 60T output gears The center gear is a 60T idler on a dead shaft The CIM gear on the left can be either an 11T or 12T The CIM gear on the right can be either a 13T or 14T Therefore, you can change speed by swapping CIM gears and/or the position of the CIM

11. A section through the middle of the shafts

12. A section through CIM / output shaft

13. A section through the idler shaft and pivot

14. All three wheels side-by-side (All VexPro wheels)

15. Assembly Sequence The following slides show the assembly sequence of the module

16. Press bearings into outer plate

17. Press bearings into inner plate

18. Press bearings into center gear

19. Press bushings into pivot

20. Slide gear and washers into pivot

21. Slide shaft through and put this assembly aside

22. Add piston pin and spacers to outer plate and hand tighten screws (with threadlocker)

23. Slide shafts through bearings

24. Add washers to the shafts

25. Slide gears onto shafts

26. Add washers

27. Put pivot assembly into place

28. Put inner plate into place

29. Add screws (with threadlocker) and torque screws on both sides

30. Add washers and screws to center pivot shaft (with threadlocker), torque

31. Install retaining rings

32. Put CIM washers on inner plate

33. Put CIM into place

34. Install CIM screws and torque

35. Add washers, CIM gear, and retainer clip

36. Repeat sequence to build two right hand and two left hand assemblies

37. The module is attached to the frame rail with ¼” button head screws

38. A complete side to the drive base I’ve ignore bumper brackets and how this rail would attach to the rest of the frame I haven’t done any structural analysis

39. Fixed Modules For the following configurations, the modules are attached directly to the frame with the desired amount of drop in the center wheels

40. 1) 8 Traction wheels, the 2 center wheels dropped (center wheels chained together)

41. 2) 4 traction / 4 omni, 2 center wheels dropped (2 center wheels chained together)

42. 3) 4 mecanum wheels

43. 4) 4 omni wheels

44. 5) 8 omni wheels

45. Floating Modules For the following configurations, the modules are allowed to float. Maybe use when the floor is uneven.

46. 6) 4 traction, 4 omni (probably shouldn’t use chain with floating modules)

47. 7) 8 omni wheels

48. 8) 8 mecanum wheels (this would look cool at least)

49. Powered Modules The following configurations would use a pneumatic cylinder to force the wheels up or down

50. 9) 4 traction / 4 mecanum

51. 10) 4 traction / 4 omni

52. 11) 8 traction (maybe use when you don’t want to be turned easily)

53. 12) 4 omni / 4 mecanum (can’t be pinned by side force, can still strafe)

54. 13) Mecanum / traction switched on one side (maybe if CG isn’t near center of robot)

55. 14) Omni / mecanum switched on one side