Wednesday, June 18, 2008

Introduction to Data Acquisition

My new Traqmate GPS data acquisition system arrived the afternoon before I left for Miller. The system is pretty easy to install. I put the main unit on the transmission tunnel just behind the console. It’s mounted using some strong elastic shock cord and a quick-disconnect hook for easy removal. The Display Unit is mounted to a empty cassette tape shell. The tape fits in the OEM radio and makes a convenient location high in the center of the dash.

One nice feature I used on the drive out to Utah is the “Drive” function. It displays speed and time during road trips. It shows that with my miniature 215/45-17 tires the speedo is only 2 Mph off. I had expected 3-4.

The only problem is that in “Drive” mode it is recording way points. I didn’t realize this and was surprised to discover that on the second lap of the first session the memory filled up and it stopped recording laps. I cleaned it out and used it successfully in the second session.
From a driver development perspective here is what I learned.

The track mapping is really good. It clearly shows when the driver moves off-line to pass, or to avoid other cars. This accuracy allowed me to ID which corners are still troublesome because the lines through them are pretty thick (showing a bunch of different lines. In corners that I had nailed, the lines are thin and sharp. This served to confirm that a lot of corners still needed work, but I already know that.

My second focus is on small segments of the track – specifically segments that lead onto the longest straights. At Miller these corners are “Work Out”, “Precision”, “the Attitudes”, “Tooele Turn”, and “Release” with the last the single most important.

Focusing on segment times allows the driver to understand the relationship between entry speed and exit speed and how they impact segment times. At the same time I looked at 2D loads (Accel/Deccel and Left/Right). When combined, this data shows, how braking and turning impact segment times.

This analysis showed many things

1. I was braking too early for turn 1 (Sunset Bend). This was shown by the fact I was threshold braking then coasting for 10-15 feet before the turn in. Remember Sunset bend at the end of the front straight where top speed is 130+ slowing to 76 at turn in. There is significant trail braking as well as. After the analysis I started braking later and carried the braking much deeper into the corner (almost to the apex on the fastest laps).

2. The Black Rock Hairpin is a tricky corner. It’s a increasing radius deal with a little helpful camber around the outer edge. It can be done a number of ways (single-apex, double-apex, no-apex, etc.) Analysis showed that although the camper on the edge was helpful (+1 Mph), the longer distance negated the advantage so early single apex line was the fastest.

3. “Release”, the corner leading onto the longest straight is a 160 degree banked turn. The best line appears to be a late turn-in (using all the the pit-exit lane) and get on the power just after turn-in. The banking makes exit speed easy to find quickly. The trick to “release” is entry speed. On my fastest lap my segment entry speed was 67 Mph resulting in max speed of 131 on the straight. A segment entry speed just 2mph slower results in a max speed of 126 (a loss of 5 Mph). On my fastest laps I was just tickling the rev limiter at the brake zone.

4. Embarrassingly, my fastest time through turns 1,2,3 (a set of Right-Left-Right sweepers) came on a warm-up lap. I went into 1 a little slow and was flat out through 2 and almost flat through 3. This is much different that my original technique of a little right-foot braking for 2 and a little more left-footed for 3. Each time I over-slowed the car with the right foot in 2, which costs time all the way to 3.

GPS Data Acquisition is a really powerful tool and it will require significant work to use effectively. I really want to see throttle position, brake pressure, and RPMs. This additional data will provide more information about both vehicle and driver performance. I’d also like to log Oil Pressure just in case.

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