Weight Affects Speed

Degree of incline 1% 2% 3% 4% 5% 6% 8% 10% 15% 20% 25% 30% 35% 40% 45% Incline angle O sin O Fh (in pounds) a (in mph/sec) 0° 34' 0.00989 9.9

1° 9'

0.02007 1° 43' 0.02996 2° 17' 0.04013 2° 52' 0.05001 3° 26' 0.05989 4° 34' 0.07062 5° 43' 0.09961 8° 32' 0.14838 11° 19' 0.19623 14° 2' 0.24249 16° 42' 0.28736 19° 17' 0.33024 21° 48' 0.37137 24° 14' 0.41045 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 1

2 3 4 5 6

Table 5-2 Hill-Climbing Force F h for 15 Different Values 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