Engineering H193 - Team Project

Spring Quarter Gateway Engineering Education CoalitionP. 1

Drive Train Calculations

Week 3 Day 1

Engineering H193 - Team Project

Spring Quarter Gateway Engineering Education CoalitionP. 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

Engineering H193 - Team Project

Spring Quarter Gateway Engineering Education CoalitionP. 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

Engineering H193 - Team Project

Spring Quarter Gateway Engineering Education CoalitionP. 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

Engineering H193 - Team Project

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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

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WWN

WII

P

FI

Sum of Forces parallel to plane = 0 P - WII - FI = 0

7

3

Check the length and height of the ramp

Static (Const. Velocity) Analysis

Engineering H193 - Team Project

Spring Quarter Gateway Engineering Education CoalitionP. 7

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

Torque

Speed

Stall

No Load Speed

Usable performance

Static (Const. Velocity) Analysis

Engineering H193 - Team Project

Spring Quarter Gateway Engineering Education CoalitionP. 8

Torque

Speed

Stall

No Load Speed

Usable performance

Different Power Settings

Motor Performance Curves

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Spring Quarter Gateway Engineering Education CoalitionP. 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

P. 10

Engineering H193 - Team Project

Spring Quarter Gateway Engineering Education Coalition

Item Points

Cover Page 2

Sketch – Paths on Course 6

Average Speed Calculation 6

Sketch – Free Body Diagram 6

Show Computation for Weight

Calculation of Torque Required 6

On level and on ramp

Plot Required Torque and Speed 4

On Your Motor Curve

TOTAL 30

Grading for Power Train Calculations