Example (a) Lightweight Runabout
Weight 250 Kg without batteries. Range required 50 miles at 30 mph. Assuming 2 Kw required at 30 mph, for 1 hour 40 mins total energy is 3.33 Kw hrs.
We know from experience that a good leadacid battery will give about 25 watt hrs per Kg* at the 1 hr rate, therefore 3.33 Kwhr will require 3333 divided by 25 = 133 Kg of battery. (* allowing 80% depth of discharge).
Suggested battery pack 4 off 12 V monoblocs weighing 3335 Kg Total Wt: vehicle 250 & batteries 133 + driver 75 Kg Total wt = say 460 Kg.
Assuming 20 inch dia wheels (0.51 M) speed at 30 mph is 506 rpm. If motor speed is 3400 rpm on 48 Volts, gear ratio (R) is 3400 divided by 506 = 6.7 Torque at wheels T = Mgsd/2. Assuming 16% slope T = 465 x 9.81 x 0.16 x 0.51/2 = 186 NM Torque at motor is 1/6.7 of this, i.e., 27.6 NM.
If a Lynch motor is used this torque is given at about 220 Amperes, which is just greater than the continuously rated current  permissible for moderate hill climbing & while accelerating.
Example (2) Electric Racing Car, 100 mph
Assuming vehicle weight of 400 Kg without batteries, and low drag coefficient such that 50 Kw are required at 100 mph (67 BHP), then about 21% of this should be required at 60 mph, i.e., 11 Kw. To run for one hour would require 440 Kg of battery @ 60 mph. Therefore total vehicle weight = 400 + 400 + 75 (with one occupant) i.e., 915 Kg.
Assuming 26" dia wheels (0.66 M) speed at 100 mph requires 1302 rpm. Motor speed at different voltages is as follows (assuming 4 motors fitted):
Volts 
48 
60 
66 
72 
RPM 
3400 
4250 
4675 
5100 
Power Kw/ motor contin 
8.64 
10.56 
11.48 
12.24 
Power BPH/motor contin 
11.6 
14.15 
15.4 
16.4 
Drive Ratio (100 mph...) 
2.6:1 
3.26:1 
3.58:1 
3.92:1 
Torque req at wheels 
492 
492 
492 
492 
Torque at motors 
189 
151 
137 
126 
Torque avail at motors (NM) 
260 max 
260 
260 
260 

100 cont 
100 
100 
100 
Acceleration of .166 g would give time of 060 mph in 16.7 secs. Full current on 60 V gives 0.33 g in 060 mph in 8.4 sec. Some overloading of the motors can be permitted in racing. Bigger safety margins should be allowed in normal running. Note that the high top speed gives a low drive ratio, and thus relatively poor acceleration and hill climbing. Greatly improved performance will be obtained by fitting a gearbox or CVT (Continuously Variable Transmission).
NOTES:
1 Continuous 200 A.
2 Calculated for 16% gradient = .16 g acceleration
3 4 motors  absolute max @ 475 A. 62 NM
4 Max current would reduce to 440 Amps.Lynch Motor Co. Ltd., PO Box 919,
To calculate Gear Ratio required by an Electric Vehicle:
Torque = Mgsd/2 (See formula 5)
Plot this out for different values of Slope from 1 in 4 to 1 in 10. Then calculate how fast the vehicle can run up each slope to keep within the power available on 60 v Lynch motor = 10.5KW
Assuming M = 1100 Kg
g = 9.81 M/sec/sec
d = 0.5 M (diameter of wheel)
Then Mg d/2 = 2698
ie Torque = 2698 x Slope (expressed as fraction ie. 25% = 0.25)
Table is then as follows:
Gradient 


Torque (NM) 
Overall Gear Ratio (1) 
Max speed on gradient M/sec 
MPH 
Double Motor Gear ratio 
MPH 
1:4 
25% 
0.25 
674 
27:1 
4 
9 
13.5:1 
18 
1:5 
20% 
0.2 
539 
21:1 
5 
11 
10.5:1 
22 
1.6 
16.7% 
0.167 
447 
18:1 
6 
13 
9:1 
26 
1.10 
10% 
0.1 
269 
11:1 
10 
22 
5.5:1 
44 

NOTES: (1) Ratio required to keep Torque at motor below 25NM (2) Speed below which power is less than 10.5 KW.
We have several Ford Fiestas running for 2 or 3 years with single motors. The motor can be run at higher currents for short periods  eg 2 x continuous torque for 5 secs, eg for climbing ramps and curves. This should not be relied on for continuous running. Nevertheless the double motor gives much more margin on hills and accelerating from rest.
Our doublemotor Fiesta, with gearbox, gives over 50 m range with leadacid batteries and over 40m driven hard in quite hilly country. We do not think the expense of NiCd is necessary. Our customer, John Pochin, of Barkby, Leicester, UK, has been running a Lynch electric Fiesta for three years and is pleased to share his experience. Phone: +44 (0)116 264 0863 or Fax: +44
(0)116 269 5646
NOTE: The double motor uses two Lynch armatures linked together mechanically. The armatures can be connected electrically in parallel or in series, allowing max applied EMF and current of 60 Volts 400 Amp, or 120 Volts 200 Amp respectively. Max. continuous power output in both cases is 21KW.