Traqmate vs iPhone 3G (G-Tac Pro)

Traqmate vs iPhone 3G (G-Tac Pro) - accelerometer only

This is all based a single track session with the G-Tac Pro app, so it is by no means complete, but here's what I've observed...

G-Tac Pro only logged one GPS sample and then apparently couldn't get any more, so this comparison is limited to accelerometer data only, which theoretically applies to the original iPhone as well.

Setup

Car: 1983 Porsche 944, built to NASA 944-Spec rules
Weight: 2600-2650 lbs with driver and fuel
Tires: Toyo R888 225/50-15
Location: High Plains Raceway - Byers, Colorado - 5000 foot elevation
Date: April 19, 2009 8:20 am
Air Temperature: 35-40 F
Track Conditions: Damp with some water remaining from a recent blizzard and rain
Session Format: Race group practice, conservative driving

Traqmate Complete version 2.10
- Sensor unit mounted flat on top of center tunnel between front and rear seat area
- Recording at 40Hz

-vs-

G-Tac Pro version 2.0.1 running on an iPhone 3G (iPhone OS 2.2.1)
- Mounted flat on top of center tunnel, in front of Traqmate, with the top of the iPhone pointed towards the front of the car
- Recording at 30Hz (no other option)

Summary Comparison

	Traqmate	G-Tac Pro	Difference
Top Speed	100.10 MPH	98 MPH ^*	2 MPH (2%)
Max Accel	0.48 G	0.49 G	0.01 G (2.1%)
Max Brake	0.91 G	0.85 G	0.06 G (6.6%)
Max Left	1.15 G	1.04 G	0.11 G (9.6%)
Max Right	1.01 G	0.95 G	0.06 G (5.9%)

^* G-Tac indicates that Top Speed is based on GPS data, but it didn't seem to get any GPS information for this session, so maybe the accuracy would be improved if it did?

Side-by-Side Comparison with Video

The video camera was aimed too high and was a little out of focus, but you can still see what's going on in the downhill segments. The speed and track map are based on Traqmate data.

WMV file download (right-click, Save As...)

This video was made with RaceRender 0.95, using G-Tac Pro raw accelerometer data saved into a .CSV file, and two instances of the Traqmate data (one set to show G-forces only, the other showing speed and track position).

Conclusions, Speculation, and Ramblings

I don't think anyone expected the iPhone 3G to compete on the level of Traqmate and others, but if you already have the phone, it's hard to resist the relatively low cost of datalogger apps like G-Tac Pro. Although this app samples accelerometer data at 30Hz, the data seems a little too smooth at times, so I suspect that the iPhone hardware is a bit slower to react. Either way, it can still be useful for things like video overlays and your own benchmarks. Getting a good GPS signal is a problem with the iPhone 3G in a vehicle... I saw the same problems with the LogBox app, so it's definitely the hardware. The Traqmate has a GPS antenna that magnetically mounts to your roof, but obviously it would be a bad idea to put your iPhone on the top of your vehicle. I've had better GPS results with it velcroed on the top of the dashboard in a Chevy Blazer... The best I saw was two GPS samples per second and 9 meter accuracy, which isn't bad, but most of the data was closer to only one sample every few seconds and 17 meter accuracy, and there were some significant gaps. It's going to take some testing to find the best mounting location in your particular vehicle. If you could get the iPhone to reliably receive a good GPS signal, I think these iPhone apps would have decent potential for track use... They would just need some desktop software that would interpolate the GPS readings based on accelerometer data, and then do some analysis.