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Drive Train Calculations

Drive Train Calculations. Week 3 Day 1. P. 1. Drive Train Calculations. Draw pictures Make estimates Draw force diagrams Do calculations in terms of algebraic symbols - include ‘safety’ factors Substitute numbers Refine calculations as robot takes shape. P. 2.

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Drive Train Calculations

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  1. Drive Train Calculations Week 3 Day 1 Spring Quarter P. 1

  2. Drive Train Calculations • Draw pictures • Make estimates • Draw force diagrams • Do calculations in terms of algebraic symbols - include ‘safety’ factors • Substitute numbers • Refine calculations as robot takes shape Spring Quarter P. 2

  3. Drive Train Calculations • Speed Required - Example • Distance to be traveled - 20 feet • Time allotted – 1.5 minutes / 90 sec • Torque Required • Static analysis of robot on ramp • Constant velocity on ramp allows static analysis Spring Quarter P. 3

  4. Calculating the Velocity Required • Distance to be traveled - measure your path on the course - example 20 feet • Time allotted – 1.5 minutes - use 90 sec • V = Distance / time = 20 feet / 90 sec = 0.22 ft/sec • Assume the robot must go faster, example 0.25 fps or 3 inches / sec (allow for pick and deposit time) • Robot wheel is 1.75 in diameter, radius is 0.875 in • Motor speed required = velocity / (2*Pi*r) which is 0.546 rev/sec or 32.7 rpm Spring Quarter P. 4

  5. Calculating the Torque Required • Estimate weight of Robot - ~ 5 lb (use scale to weigh parts) • Handy Board and Motors • Drive Train - gears / axles / wheels / shaft encoders • Chassis - includes hot glue • Sensors - micro switches, CdS cell • Estimate internal Friction - FI ~ 0.5 lb. Try pulling or pushing robot on level ground using the spring scale. • Estimates of velocity and weight include some ‘safety’ factors Spring Quarter P. 5

  6. Static (Const. Velocity) Analysis Sum of Forces parallel to plane = 0 P - WII - FI = 0 P 3 WII 7 FI WN W Check the length and height of the ramp Spring Quarter P. 6

  7. Static (Const. Velocity) Analysis P - WII - FI = 0 WII = W sin (slope angle) slope angle = atan(3/7) = ~23 degrees WII = 5 lbs (sin(23)) = 1.97 lb P = 1.97 lb + 0.5 lb = 2.47 lb Torque = P x Radius of Wheel = 2.47 x 0.875 = 2.16 lb-in = 34.6 oz - in Stall Usable performance Torque No Load Speed Speed Spring Quarter P. 7

  8. Motor Performance Curves Different Power Settings Stall Usable performance Torque No Load Speed Speed Spring Quarter P. 8

  9. Drive Train Calculations • Is the required Torque divided between two motors? • If Torque and speed required don’t match characteristics, then gearing or motor change is required • What are critical factors? • Weight • Internal Friction • Time • Slope of ramp Spring Quarter P. 9

  10. Grading for Power Train Calculations Spring Quarter

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