7 3/8 x 9 1/4 T echnical / Build Your Own Electric Vehicle / Leitman / 373-2 / Chapter 5
Chapter 5: Chassis and Design Degree of incline 1% 2% 3% 4% 5% 6% 8% 10% 15% 20% 25% 30% 35% 40% 45%
Incline angle O 0° 34' 1° 9' 1° 43' 2° 17' 2° 52' 3° 26' 4° 34' 5° 43' 8° 32' 11° 19' 14° 2' 16° 42' 19° 17' 21° 48' 24° 14'
sin O 0.00989 0.02007 0.02996 0.04013 0.05001 0.05989 0.07062 0.09961 0.14838 0.19623 0.24249 0.28736 0.33024 0.37137 0.41045
Fh (in pounds) 9.9 20.1 29.6 40.1 50.0 59.9 79.6 99.6 148.4 196.2 242.5 287.4 330.2 371.4 410.5
a (in mph/sec)
1
2 3 4 5 6
Table 5-2 Hill-Climbing F orce F h for 15 Different V alues of Incline
Table 5-2 shows the hill-climbing force Fh, for 15 different incline values for a vehicle weight of 1,000 lbs. Notice that the tractive force required for acceleration of 1 mph/sec equals that required for hill-climbing of a 5 percent incline, 2 mph/sec for 10 percent incline, etc., on up through a 30 percent incline. This handy relationship will be used later in the design section. To use Table 5-2 with your EV, multiply by the ratio of your vehicle weight. For example, the 3,800-lb. Ford Ranger pickup truck of Chapter 10 going up a 10 percent incline would require 3.8 3 99.6 5 378.5 lbs.
Weight Affects Speed Although speed also involves other factors, it’s definitely related to weight. Horsepower and torque are related to speed per equation 3: hp 5 FV/550 where hp is motor horsepower, F is force in pounds, and V is speed in ft/sec. Armed with this information, Newton’s Second Law equation can be rearranged as a 5 (1/M) × F and because M 5 W/g (10) and F 5 (550 3 hp)/V, they can be substituted to yield a 5 550(g/V)(hp/W) Finally, a and V can be interchanged to give V 5 550(g/a)(hp/W) where V is the vehicle speed in ft/sec, W is the vehicle weight in pounds, g is the gravitational constant 32.2 ft/sec2, and the other factors you’ve already met. For any
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