Driving the Car - With one gear and heaps of torque (300Nm from the twin motors) Driving is simple and effortless and the car rapidly gains speed and without a body the sensation of speed is greatly exaggerated.
The experience of driving and fine tuning a light weight EV designed around a central battery box has been a lot simpler than a petrol powered car. Basically it was plug everything in and check that the motors are running in the right direction, fine tune the two throttle pots, tighten the drive belts and very little else to do.
The concept of twin motors independently driving the two rear wheels has worked perfectly and the motor torque and speed characteristics automatically distributes power to the two rear wheels without the need for an "electronic differential". There has been some drifting in the adjustment of two separate throttle pots that send signals to their respective motor controller. This doesn't cause problems in normal driving and in the future will be addressed by going back to one throttle pot with an electronic splitter.
The EV is being used around a farm with a small tray and is proving convenient, smooth and quiet and with the short range trips typical around the farm, the battery pack does not get discharged below about 85%.
The large section size of the chassis box provides excellent stiffness and there is no discernible scuttle shake and the design will continue to be tested over rough farm roads to prove the strength and reliability of the concept and to expose any weaknesses.
The level of performance of the motors far exceeds that which can be explored on gravel farm roads and some track time will need to be booked in the future for further performance testing. The gravel farm tracks do provide an excellent testing ground for testing torque vectoring systems to get the best performance on slippery gravel roads and a future project to develop an Arduino based torque control system is planned, although not in time for the current Arduino challenge.
Range, Speed and Recharge Time
Update May 2014 typical energy consumption 0.74Ah/km (106wH/km), normal driving, gravel roads.
It uses around 1% of the battery's charge per kilometre on unsealed farm roads and off road, so that equates to 100 km or 60 miles per charge.
For my application and testing, the range is a lot more than required around the farm and the pack was sized more to ensure safe peak current draw than range. The advantage is the extra pack capacity gives a mobile power source around the farm.
Speed is excessive for farm tracks and haven't explored the upper end of the speed range, this will have to wait for track time. On the tree lined farm tracks I wouldn't go more than 100km/h or 60mph. Estimated top speed is around 160km/h or 100mph but dependent on the aerodynamics of the body as the car good low end torque geared for a top speed of 200km/h (1:3 motor to drive ratio, 6000 rpm motor speed) although it will not be able to reach speeds this high without a low drag, streamlined body. A lower gear ratio is planned and will increase acceleration to 100km/h which is faster than needed.
The recharge time is about 5 minutes per 1% of charge or 8 hours for recharge from fully discharged using a 10amp 240 volt single phase battery charger. The charge rate is not linear and as the battery approaches fully charged, the charge rate drops off.