Homestead March 13, 2005

On track at "March Madness" autocross.

March Madness Autocross

Today's autocross is going to be run in a parking lot at Homestead /Miami Speedway. This is 15 miles from the race shop. We decide to try and drive to the site, make our runs and drive home without charging. This will require a strong, balanced battery pack.

The hardware and software of our battery management system is evolving. Now, at the end of a normal charge, we can individually boost the lowest cells to try and bring all batteries to the same state of charge. The limitations are we can only trickle charge at an amp or two and we need to specify manually which battery to charge. Because of these limitations, we do not have the cells as closely balanced as we would like.

There is .33 volts between the highest cell (#9) and the lowest cell (#39). We estimate that this is the difference of 30% in their state of charge.

The trip to the track is mainly 45 MPH back roads. We use 226 watt-hrs per mile. In theory, our pack contains 22.7 Kw-hrs. At this rate our range is 100 miles. But not today!

At the track, we adjust the spring seats to lower the car and bolt on the race wheels. The car is inspected and we are cleared to race.

Today's course does not include a single slalom. There are a lot of challenging turns with one or two chicanes. The toughest point looks like the entrance to the longest straight. I will need to get that right for a good time.

Run 1 and 2

Our race group is called and we line up. I drive the track in my head and prepare to drive it for real. There are two cars ahead of me.

Now, one.

Now I am up. ...The starter says "Go".

I give full throttle and the car leaps forward. Then slows. Then leaps forward. Then slows. I turn right, off the track and limp back to our tent. Oh, the joys of developing a new race car!

Splicing the throttle lead

The crew works fast but can not solve the problem in time for us to make our first runs. There is a half broken wire between the throttle pot and one of the inverters. The acceleration with both inverters pulls on the wire and opens the gap. This causes one inverter to shut down and the loss of acceleration rocks the car forward, reconnecting the wire. Once found, a cut and splice solves the problem.

Run 3

This run needs to be clean. I need to get a good time but not take chances. The fastest car in my class has all ready turned a 58.843.
I play it safe. A small lift in the first chicane. Not needed. Brake too early everywhere. The biggest time loss is in the left turn for the run back to the finish. I brake where I could keep the accelerator planted.
Still, the 57.451 puts me in the lead.

View Run #3 Video (9.56 MB)

Run 4

The crew collects data while I review the video of the run. I spot a number of places I can pick up more time.

This time I do not lift through the first chicane. My speed is 64.5 MPH vs. last run's 60.4 MPH before I brake for the hairpin.

Run #4 at March Madness autocross

The tires are warmer but squeal more as I work them harder. I lift, rather than braking in the final turn and carry more speed through the last gate.
I am going 5.7 mph faster at the line.

The competition beat my old time with a 57.353 but my new time, 54.865 is almost two and half seconds faster.

We have won!

View Run #4 Video (13.7 MB

Sum up

autocross 1st place trophies

A win is always a good thing.

Two victories in two autocross events.

The Electric Imp leads the D Modified Autocross championship.

Possible improvements:

Victory is great but a faster run was possible. Making four reliable runs is key to getting the best time.

Our new procedure of stopping between runs to review the data and video seems to gain us more than what we might gain by trying for another immediate run to take advantages of the heat in the tires and brakes.

Proper autocross tires would make warm tires even less important.

We average better efficiency on the way home, 209 watt-hrs per mile. Our total power usage for the day is 9.147 Kw-hrs.

With two victories in two autocrosses, we are now the point leader for the D Mod championship



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February 27, 2005
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