# Performance calculator

From: Barnett Williams
Date: Sat, 11 Mar 2000

I have made an Excel spread sheet which calculates the energy used by a vehicle while traveling through city traffic. In it I can add or remove stop signs and rolling hills. The vehicle weight, rolling resistance and CdA are all adjustable. It is useful for figuring out the impact of changing certain parameters like aerodynamics, rolling resistance, weight, and regenerative braking. When I insert parameters for a fully faired, electric trike (CdA=.6 sq. ft, Crr=0.05, mass =86 lbs, rider mass = 210 lbs, motor efficiency = .8, gearing efficiency =.9 and a charging efficiency =.95) and use 2 stops per kilometer, flat land, I get a 45 % increase in range when I use regen braking. The top speed was limited to 50 kph and a 750 watt motor was used with a 100 watt*hour battery pack. The range with the regen was 11.36 kms and without it the range was 7.82 kms. This seems like a pretty useful feature to have. I used a smaller battery back than one might want, just to limit the amount of calculations necessary. The 86 lb vehicle would likely have a 500 watt*hour pack. I doubt that full 45% increase could be realized under similar real life condidtions, but it gives an indication of the upper limit.

The trike is of course a very high performance imaginary vehicle. It is possible to build such a vehicle with conventional materials and design constraints. Many racing desgins could be modifed to satisfy the cirteria given above. The poorer the performance of the vehicle, the less advantage one will get from a regen system.

Using 76 lb bare trike with a CdA of 3 sq. ft and Crr of 0.01, the range without regen is 4.95 km and with it the range is 6.055 km. Here the increase in range is only 22% and the range itself is almost cut in half.

You can find the calculator at
http://www.eng.uwaterloo.ca/student/bkwillia/index.html
Drag as many lines down as you require.

Barnett Williams

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Thursday, 29 January 2009