Roebling Road Raceway 4/28/07

Session 2 - SARCC Race 2:24 PM

The tow truck brings us back to the pits. We pull the driver's seat and the cover over the controllers. As we start to trace the wiring, the cause of the problem becomes evident. The main connector to one of the controllers is wet.
 
Our 'slight' coolant leak must have gotten worse over test day. We refilled the radiator last night and enough coolant must have leaked out to form a small puddle. When I accelerated onto the track, the puddle rolled back into the connector. This shorted the throttle signal. The Siemens controller recognized that the voltage reading was above the value set as full on (3.8 volts) and shut down the system.
 
We seal the small leak and disassemble and dry the connector.
The computer reports all system 'Go'.
 
Battery voltage is 389. Battery temperature is 24.2 Celsius.
 
The race is 34.34 miles plus 4.04 miles of pace lap and cool down.
 
We set the current limit to 400 amps. Count 505 watts for the pace lap and 824 per mile, we should use 28.801 kw. We decide to bump the regenerative braking current from 200 amps to 300 amps to try and give us a cushion.
 

We line up in the 40th grid position.

Kokam on the grid
 
I am conservative into the first turn. There are a lot of cars crowding through one corner. I cut through traffic and pass 7 cars in the first lap. By lap 5, I am 4th in class - 23rd overall.
 
working traffic video (~1.34MB .wmv file)
 
Lap 6, I turn my fastest lap, a 1:26.719.
Lap 9, I am lapped by the leaders.
Lap 14, I turn a 1:26.756. 0.043 slower than my fastest lap, despite having 10 less horsepower.
 
fast lap video (~31.56MB .wmv file)
 
Going through the last corner, I feel a drop in power.
The voltage has sagged to 270 under load and the inverters are limiting the current to protect the batteries. The current goes down to below 200 amps but I am still at over 90 Mph (5303 rpm) when I cross the finish line. I have finished 4th in class and 15th over all. Not a bad result starting from the back of the pack.
 
the finish
 

End voltage is 313 volts. Highest battery temperature is 56 degree Celsius. The pack has delivered 31.595 kW-hrs from a pack rated for 35.150 kW-hrs at a .5C discharge rate. So under race conditions with maxim discharge set to 400 amps and maximum regenerative braking currents set to 300 amps, we are able to utilize 89.9% of the rated capacity. This is very impressive.

It is great to finish another 30 + mile race. The car ran hard and we continue to learn more about racing an electric car.

 
tire rub
 
We jack up the car and start prepping for tomorrow. Late in the race, I noticed the car rolling more and actually sitting on the right rear bump stop coming out of turn 5. The body roll was extreme enough to cause some more minor rubbing. We inspect the tires.
 
tire rubbing on the suspension
 

We can cure this by adding a small wheel spacer.

Even more serious are blisters on the rear tires.

 
blisters on the tires
 

Roebling Road is hard on tires and the Electric Imp is heavier than optimum for this compound. These blisters are caused by the tires overheating and rubber seperating from the belts.

This is odd. The car was still not turning in well and understeering mid-phase and on exit. Yet, despite the understeer, it is the rear tires that are blistering.

It is possible that I am hurting the rear tires breaking them free under braking to pivot the car. We must get rid of the understeer. We decide to try full stiff on the rear anti-roll bar and we raise the gas pressure on the rear shocks.

We mount new tires for qualifing. And up the amps to 500.

After about 1.5 hours battery temperatures have dropped below 45 degrees (C). Four hours later, the pack is fully charged. 392.4 volts at 38.7 degrees.

 


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Dec 31, 2006 Race 2 Moroso
Battery Beach, Jan 2007

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