Can I do autox level timing using a phone?

At Mid Atlantic Car Fest this year, we are running the Dominon Oval.  The plan is timing two flying laps.  The first plan was just to use stop watch timing by hand.  We don't necessarily want to lug our autox level equipment all the way for that.  But I was wondering, if anything existed that I could use and maybe an app on my phone?  But my idea is like I place a sensor at the start line, and using an app start the clock and the car goes through, starts timing, then second time around clock stops.  Does that make sense? Does this exist?

There are lots of GPS timing apps for smart phones

Not very accurately, or at least reliably, unless you add an external GPS receiver. Almost all phones have very low-end GPS receivers that are barely good enough for turn-by-turn directions and if you try to use this for timing on track, the results are generally pretty inaccurate. If you do get an external 10Hz+ GPS receiver though, you can get pretty good timing info with a datalogging app like TrackAddict.

Are you trying to time your car, or are you running an event where you want to time 50 cars?

In reply to GameboyRMH :

Yeah but when one alternative being considered is a manual stopwatch, I'd wager the phone is more repeatable even with the base sensor. I know AIM interpolates their GPS data across the start/finish line, and I imagine the other timers do as well, so you don't need 10Hz data to get 0.1s timing. Precision and accuracy are different though. 

Have you called the local autox clubs to see if you can borrow their timing equipment?

In reply to cyow5 :

I've tried it it's sometimes surprisingly accurate, but at other times, probably when the satellite connection count drops, it can easily be off by over a full second. I'd definitely trust a manual stopwatch over a phone's internal GPS.

GameboyRMH said:

In reply to cyow5 :

I've tried it it's sometimes surprisingly accurate, but at other times, probably when the satellite connection count drops, it can easily be off by over a full second. I'd definitely trust a manual stopwatch over a phone's internal GPS.

And to be fair, I have not. I was about to recently and then a hurricance changed the plans. 

This doesn't address accuracy vs. precision. It might be off by 1s, but is it always off by 1s [for the same event where weather and satellites aren't changing much]? Not really a rhetorical question since I am going to admit to guessing here. If so, then it would be very useful for determining a fair winner. The stopwatch is subject to human error (and, at the very least, accusations of bias). The size or sound of the car could influence whether the operator is anticipating the finish line too much or not enough. As long as the error from the third-party is consistent, it could be more useful in this case than something that is inconsistent but averages the correct time. 

In reply to cyow5 :

No, not always off by 1S, in my experience you can get errors ranging anywhere up to about 1 second on the time you passed the start/finish line on a small track, which on 2 consecutive passes could throw your lap time off by 2+ seconds (a real example from some of my first tests with internal GPS). When it's working well it can get within a hundredth of an optical timing system, but that's maybe three quarters of the time in my experience.

theruleslawyer said:

Have you called the local autox clubs to see if you can borrow their timing equipment?

Most AX timing equipment is going to have trouble with multiple laps, I think.

With the Farmtek timer, for instance, your timing desk would have to turn the eyes off after launch and then back on again before the end of the second lap.  Easily doable, but not doing it will screw up lap times.

This sounds like something a raspberry pie and a laptop should be able to do with a simple light/lazer sensor and and a bright light or lazer on the other side of the track. 

In reply to dean1484 :

Garage door sensors would probably work. I could probably make a working system on arduino in under a day. You'd just need make system ignore triggers for a few seconds after the first so. Quick clock and bam. timer.

In reply to codrus (Forum Supporter) :

The latter