I had an old fashioned Hot Lap timer in my car this past weekend and had problems with it. Actually other people had the same inconsistencies. I was looking at a Droid App by Trackmaster. Does video and lap times, speed.

Harry's lap timer just recently became available for android. The I phone crowd likes it. I haven't used it yet but have downloaded it. The suped up version is in the works.

Thanks Woody Ill check it out!

http://aimsports.com/
I have this setup on my kart and its great..

I have Trackmaster on my phone and it's well worth the five bucks or whatever it was. Works very well and is pretty intuitive. The coolest part is that you can send your laptimes to Twitter or Facebook!

how are these things getting a signal from a base station?

They must pick up a signal when passing some sort or marker, right?

I think they use GPS. The Trackmaster is cheap and they say you can use for autocross too. I think I going to get it.

Yeah, a GPS point that the user can define. You can do it on the phone, or on a computer and send it to the phone. Basically all you need is one GPS point (the starting line), or you can put in multiple points for sector/split times. The GPS on the phone knows when it passes that point, and records that information in the form of laptimes/split times.

Trackmaster does all sorts of other stuff. You can do a "LiveView" which lets you track the car on the course via a laptop or second phone. It also measures top speed, G-forces (roughly) and several other parameters within the phone's capabilities. The phone will actually call out split times and lap times if you select that option too.

I'm going karting this weekend for my bachelor party - I'll try to post my datalog on here so you can check it out.

An external Bluetooth GPS reciever is recommend for all the phone based setups.

Yup, that too. Helps increase the resolution of the information being sent between the phone and sat. But I've run without it and no problems.

Start and stop at our autox is in different places.

You can set that up when you do your course walk.

The problem with GPS is that at it's best it has about 1m (3 feet) spread. At it's worst, it can be 50 or more meters (well over a 100 feet).

So, the weaker your signals are at the track, the less accurate a GPS based system will be.

I recall that the 3 foot accuracy was just recently opened up for public use, but I don't believe older units take advantage of that.

They end up very accurate. For instance, an AiM Solo is usually within .001 of the official AMB loop. I'm not sure about other systems, but AiM also tells you how many satellites the system has locked onto and what the accuracy is.

I used to make the same argument and once I started using a GPS based system, I found out how good they really are.

It's largely an accuracy versus precision argument. The FCC and military still has ultimate say-so on the precision available to the private sector for any hand-held devices, and all upper-end GPS units have a different set of rules. In layman's terms, they finally figured out that hand-held GPS units aren't precise enough or applicable to be used as homing devices. But they are accurate. As in, the exact location of your point at start/finish may not be exactly where the GPS says it is, but the GPS can repeatedly pickup that point to a degree which is sufficient to satisfy the demands of what we're talking about here. Most modern smartphones have a refresh rate that means they're sampling enough every second that your GPS-recorded time versus the actual time is only an error of less than about .01% (total guess). Of course that depends on antecedent conditions (cloud cover, solar flares, tsumamis, etc) At least that's how I understand it all.

I actually work with this stuff on a daily basis (worldwide GPS based fleet tracking) and there is no way that i would replace the race track transponder with a GPS unit if i was at all concerned about accuracy.

Sorry Andy, I must admit I'm pretty new to the geospatial field and I just work with a bunch of satellite guys. Of course I defer to your expertise

I wasn't suggesting moving from a track transponder/timing gate if someone already had that setup. But for those looking for a simple track day or autocross solution, I think GPS is a good cheap alternative.

When I ran the Chumpcar race at Sebring last year we had a transponder on the car, but I also had my first-gen smartphone in the car with Trackmaster logging laps. I never did run any margin of error, but as I remember, what I was seeing on the Trackmaster log was within 1/10 second of the transponder laptimes.

See if this works for you guys, but this is what a session looks like. I wasn't driving this one, so don't be too hard on me

http://www.mytrackmaster.com/#SessionPlace...ZXNzaW9uGOfaAQw

I'm not a GPS expect, but have 1,000s of laps that match the AMB timing loop. I also have talked to lots of the data companies and they have similar information on the accuracy of the GPS units. Pro teams find it be accurate that most have abandoned beacons.

The GPS units also add things like sector times, corner speeds, and predictive lapping, all while you are still on your lap. No comparison to a beacon.