Transcript ENG H193 - Drive Train Calculations

Engineering H193 - Team Project
Drive Train Calculations
Week 3 Day 1
Spring Quarter
Gateway Engineering Education Coalition
P. 1
Engineering H193 - Team Project
Drive Train Calculations
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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
Gateway Engineering Education Coalition
P. 2
Engineering H193 - Team Project
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
Gateway Engineering Education Coalition
P. 3
Engineering H193 - Team Project
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
Gateway Engineering Education Coalition
P. 4
Engineering H193 - Team Project
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
Gateway Engineering Education Coalition
P. 5
Engineering H193 - Team Project
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
Gateway Engineering Education Coalition
P. 6
Engineering H193 - Team Project
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
Gateway Engineering Education Coalition
P. 7
Engineering H193 - Team Project
Motor Performance Curves
Different Power Settings
Stall
Usable performance
Torque
No Load Speed
Speed
Spring Quarter
Gateway Engineering Education Coalition
P. 8
Engineering H193 - Team Project
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
Gateway Engineering Education Coalition
P. 9
Engineering H193 - Team Project
Grading for Power Train Calculations
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
Spring Quarter
Gateway Engineering Education Coalition
30
P. 10