Engineering H193 - Team Project Gateway Engineering Education Coalition Spring Quarter 2005 P. 1 Drive Train Calculations Week 3 Day 1

Engineering H193 - Team Project Gateway Engineering Education Coalition Spring Quarter 2005 P. 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 Gateway Engineering Education Coalition Spring Quarter 2005 P. 3 Drive Train Calculations Speed Required - Example only –Distance to be traveled - 20 feet –Time allotted – 2 minutes (120 seconds) but consider using something less like 90 or 100 seconds to be somewhat conservative Torque Required –Static analysis of robot on ramp –Constant velocity on ramp allows static analysis

Engineering H193 - Team Project Gateway Engineering Education Coalition Spring Quarter 2005 P. 4 Calculating the Velocity Required Distance to be traveled - measure your own robot's path on the course - example: 20 feet Time allotted – 2.0 minutes - example: use 90 sec V = Distance / time = 20 feet / 90 sec = 0.22 ft/sec Assume the robot must go faster, for example, 0.25 ft/sec or 3 inches / sec (allow for pick and deposit time, turning, obstacle avoidance) Robot wheel is 1.75 in diameter, radius is in Drive shaft speed required = velocity / (2*pi*r) which is rev/sec or 32.7 rpm

Engineering H193 - Team Project Gateway Engineering Education Coalition Spring Quarter 2005 P. 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

Engineering H193 - Team Project Gateway Engineering Education Coalition Spring Quarter 2005 P. 6 W WNWN W II P FIFI Sum of Forces parallel to plane = 0 P - W II - F I = Check the length and height of the ramp Static (Const. Velocity) Analysis

Engineering H193 - Team Project Gateway Engineering Education Coalition Spring Quarter 2005 P. 7 P - W II - F I = 0 W II = W sin (slope angle) slope angle = atan(3/7) = ~23 degrees W II = 5 lbs (sin(23)) = 1.97 lb P = 1.97 lb lb = 2.47 lb Torque = P x Radius of Wheel = 2.47 x = 2.16 lb-in = 34.6 oz - in Torque Speed Stall No Load Speed Usable performance Static (Const. Velocity) Analysis

Engineering H193 - Team Project Gateway Engineering Education Coalition Spring Quarter 2005 P. 8 Torque Speed Stall No Load Speed Usable performance Different Power Settings Motor Performance Curves

Engineering H193 - Team Project Gateway Engineering Education Coalition Spring Quarter 2005 P. 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

Engineering H193 - Team Project Gateway Engineering Education Coalition Spring Quarter 2005 ItemPoints COVER PAGE2 SKETCH - PATH ON COURSE4 AVERAGE SPEED CALCULATION4 SKETCH - FREE BODY DIAGRAM (Show calculation of robot weight) 4 CALCULATION OF TORQUE REQUIRED (On level surface & up ramp) 4 PLOT OF REQUIRED TORQUE & SPEED (On motor curve for your motor) 4 DECISIONS/CONCLUSIONS4 FORMAT/CLARITY/NEATNESS4 TOTAL30 Grading for Power Train Calculations

Engineering H193 - Team Project Gateway Engineering Education Coalition Spring Quarter 2005 Shop Availability and Shop Safety For this week the shop will be in Rm 208 Hitchcock on MWF from 8 am to 5:30 pm and on TR from 10:30 am to 5:30 pm Eventually we plan on using the EE wood shop in Caldwell. You will receive notice when the shop moves. The FEH staff members are responsible for the shop and we will follow all safety rules in the shop ! Remember your safety glasses. No open-toe shoes in shop or lab Must have a TA “buddy” with you in the shop Only two people per team in the shop at a time