Sunday, Dec 30, 2007


03:15 PM


It takes an hour and a half to put back the 8.223 kWhrs we used in qualifying. With the help of our big fan, the batteries have cooled to the 30 degree (Celsius) ambient temperature.


We decide on the conservative race strategy of running only as fast as we need to win.
We have finished a 30 + mile (13 laps) race here turning 1:52s at 300 amps.
This race is scheduled for 15 laps; but at 1:52's, we will be lapped once and will only need to do 14 laps.
14 laps X 2.25 miles X 0.877 per mile = 27.626 kWhrs.


The other SPU turned a fastest lap of 1:53.369 in Saturday's race, so if we maintain the 1:52s we should be able to stay ahead.


Our other concern is that the motors overheated after about 6 laps at 400 amps. What will they do at 300 amps?


Since we expect to finish the race with some extra battery capacity left, we decide to lower the regenerative braking level from 300 amps to 200 amps. Giving up our extra capacity to allow the motors to work a little less hard.


The battery voltage is 387V. This works out to 4.07 volts per cell.


We are gridded 5th overall with only 4 Spec Racers turning faster laps. The other SPU starts in 15th place.

the grid-5th overall

The start is hard. With current limited to 1/2 power (300 amps), the Spec Racers have a real power advantage. The Spec Racer beside me beats me to the corner.

The start
The start
The start
The start
The start
The start

These Spec Racer's qualified around 8 seconds per lap faster than I am able to run now. They will get by.

My job is to get the cleanest fastest laps I can while they work past.
They are not important.
It is how close the other SPU car is getting that matters.

At the end of the first lap, I have a 12 second lead over the other SPU. I also have two more Spec Racers drafting past. The last one misjudges his braking and slides wide. I stick my nose in but he keeps the position.


I soon have a clear track and no one to play with.
I have 100 less ft-lbs of torque and 50 less horsepower than I had in qualifying (240 vs. 340 ft-lbs of torque and 150 vs. 200 horsepower) so I concentrate on carrying the speed into each corner.

I am increasing my lead by 4 seconds a lap.

out of Turn 9

Lap 6, my race engineer comes on the radio. "Your lead is over 30 seconds. Start saving the car."

We had planned how to do this. The motor is most inefficient at the full throttle, low RPM points. In other words, when I bang on the throttle coming out of the corner especially the slowest corners; the chicane and turn 9.


I try easing on the throttle as I exit the chicane. The car seems to sit there, so I slam on the throttle.

I try again at turn 9. I on the throttle. It doesn't feel right but I do it.

Each corner I carry the speed in. I ease on the throttle out. My times drop only 0.3 of a second per lap. KWhrs used per mile drops too. From around 1.04 to 1.00 kWhrs per mile (gross used) which means I am saving a mere 40 Watts every mile!


My gap continues to build at 4 seconds a lap.

"Are you going easy on the car yet?", James asks.


I am under the impression that over heating the motors is our biggest concern.
Lap 9, I begin to do more braking with the friction brakes and less with the regenerative brakes. Our 18% range boost has already been dropped to 12% by our decision to run the 200 amp regenerative current rather than our standard 300 amp limit. Now we are recapturing closer to 8%. Life is easy on the motors and the lap times stay the same.


Lap 11, we have a 52 second lead and I am lapping slower traffic.

lapping slower traffic

James again tells me to slow down and save the car.
To finish first, you must first finish.

It is agony.
I am gentle and slow on the throttle.
I am half way down the straight before I reach full throttle.
It feels incredibly slow.

My lap times drop to 1:55's. Three seconds slower.

The lead pack of Spec Racer pass me. This puts me a lap down on them and means my race will be one lap shorter.

a Spec Racer setting up the pass

Though I have no way of knowing, the Electric Imp's motors are doing great - steady at 150 Celsius, and well below their 175 degree limit.
However, I do need to worry about how much power we have used. All that skimping on regen has gotten us in trouble.


Turn 2. We have taken 28.640 kWhrs from the pack. As I roll on the throttle, pack voltage drops to 280. The inverters whisper electronic warnings and take steps. They limit current out to keep the voltage above 280.

I am so focused on maintaining my slow rhythm that it takes me a while to notice. "Is it me or is the car going slower?" I know which when I try full throttle out of the chicane.

The motors give me 45 horsepower.
I feel like I am parked.
I hardly need to slow the car for T9.

"What lap am I on?"
"Will I finish this lap?"

Through T10. I see the flag stand.
The checkered is waving.
A car streaks by me but it is only a backmarker taking a lap back.
I cross the finish line.
We have won!
View full video of race (206 MB - .wmv file)


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