1. Gears, Pulleys, Sprockets, and Bearings Information about power transmission and uses for each type. Robotics 101

2. Why do we need Gears and Pulleys? Why do we have gears? Why do we have pulleys? Geek Easy Work Can Tow or Push Heavy Objects! Easy Work Can Lift Heavy Objects! Nothing To It! Geek Wow, How Easy…Keep On Moving Titanic! Muscles on a Geek? Come On!

3. Torque, moment, or moment of force, is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist to an object. Mathematically, torque is defined as the cross product of the lever-arm distance and force, which tends to produce rotation. Torque = Radius X Force Or Force = Torque / Radius What is Torque?

4. Gears Spur Gears 1:1 Direction -X=Y (Opposite) X Gear Y Gear X Teeth=30 Y Teeth=30 Speed- X=Y Speed Ratio- X Pitch Diameter/Y Pitch Diameter= 1 X Teeth/Y Teeth= 1 Teeth X Gear X Pitch Diameter Y Gear Y Pitch Diameter

5. Gears Speed Ratio- Compare either ratio of # of teeth or diameters as both have same proportion: # of teeth/min = (X teeth * RPMx) = (Y teeth * RPMy) = X teeth = RPMy = 30 =1.875 Y teeth RPMx 16 Or RPMx/RPMy = 1/1.875 =.533 = 16/30 X PitchDiameter = 1.875 * Y PitchDiameter X Teeth/Y Teeth= 30/16- Y=1.875X Speed- RPMy=(1.875)RPMx or RPMx=(.533)RPMy Torque Ratio- Ty/Tx=.533 (Note: It is the inverse of the speed ratio) Ty= Tx/1.875 = Tx(.533) Efficiency of Spur Gears: Approximately 95% X Gear X Pitch Diameter X Teeth=30 Y Teeth=16 Y Pitch Diameter ΤxΤx ΤyΤy

6. Multiple Stage Gearing Top View d=x d=3x Ratio Gear #1- 3:1 Ratio Gear #2- 3:1 Motor d=x Out In

7. Test Direction- In direction = Out direction Speed- Output = Input/(3*3) = Input/9 Speed Ratio- 9:1 Torque Ratio- 1:9 Output Torque= Input Torque X 9 If the motor input RPM (revolutions per minute) is 5400 and input torque is 2 ft.*lbs. 1) What is the output speed in revolutions per second (60 seconds in 1 minute)? 2) What is the output torque in Newton*meters if 1 N-m=0.71ft-lbs.?

8. Answers Answer #1: 5400/9= 600RPM/60= 10 revs per second Answer #2: 2ft-lbs*9= 18 ft.-lbs.* 0.71= 12.78 N-m

9. Gear Types Bevel (90° Angle) Internal (Planetary) Rack and Pinion (Linear Motion) Spur (Normal) For all Gears: Higher Pitch= More Teeth Larger Face Width= More Force Must Match Pressure Angle

10. Gear Rules and Types FIRST Rules: −Any gear −Any type −Any manufacturer Plastic (Lighter, Smaller Load) Brass (A Little Lighter (mainly due to small width), Good Load) Steel (Heavy, Excellent Load, will need to trim down gear on lathe for weight)

11. Pulleys The only difference is the belt connection method 12’’ 3’’ Speed- Y= 4X Speed Ratio- XDiameter = 12 = 4:1 YDiameter 3 Torque Ratio- Y= X/4 Efficiency of Pulleys: Approximately 90% X Pulley Y Pulley

12. Pulley Belts & Uses Pulley Belts V-Belt Timing Belt Uses: -Ball Chute (2012) -Drivetrain (2014, 2015) -Climbing Obstacles Problems: -Slipping -Belts coming off pulleys (No Sideways Torque)

13. Chain and Sprockets −The only difference is the connection method −Instead of Belts (Pulley) −Instead of Teeth (Gears) Types of Chain −Plastic Light loads, breaks easily −Steel Heavy loads (drivetrain) Types of Sprockets −Nylon Light loads −Aluminum Heavy loads (drivetrain) Plastic Chain Stretches- Steel is the way to GO! Nylon Sprockets Crack- Aluminum is the way to GO!

14. Chain and Sprockets Bicycle Chain

15. Bearings Bearings- What Are They? Problem!

16. Bearing Types Type 1: Softer Material like Bronze or Aluminum Type 2: Ball Bearing Type 3: Roller Bearing Shaft

17. Bearing Types Sintered Bronze Bearing with optional oil impregnation Ball Bearings Needle Roller Bearings Clutch One Direction Also Available Steel Balls Steel Cylindrical Rollers Can be sealed or unsealed

18. Bearing Types Pillow Block Bearings −Self Aligning −Used when you need some compliance in alignment.

19. Issues to be aware of with bearings Misalignment of bearing systems can over-restrict them, causing higher friction and unnecessary force on systems. Be careful of over-restricting things that want to be able to move. Dirt, debris, and chips can get into bearings, especially open bearings: it increases friction and resistance. (Therefore protect bearing services when machining on or near the robot) Exceeding the recommended load for a bearing can shorten or even end its life and lead to need for replacement- or may add friction to the system causing overload on motors causing them to fail. Motors have internal bearings you don’t see, so avoid excessive loads on shafts- beware of pounding on motor shaft ends (installing or removing items on motor shafts). Use proper techniques to avoid damaging internal shaft supports in the motor, by not applying excessive loads. Don’t stand or lean on the robot! No matter how sturdy it “seems”- we have had bent wheel shafts, and gotten frames out of square. In trying to make weight we lighten up areas where possible, but the robot may be less robust.