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.
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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!
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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.
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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)
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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.
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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
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Sum up
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A
win is always a good thing.
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Two
victories in two autocross events.
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The Electric Imp leads the D Modified Autocross championship.
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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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