GPS as lap timer

[MWP]

4m you are talking about hand held correct?
Cos when using gps to get co-ordinates for constrained centres (PSM's and OIP's etc) they have an accuracy better than +/-10mm
Also you only really get positional lag when in an urban canyon( reflection and distortion of the signal) or with thick cloud as the cloud attenuates the signal.

Okie dokie, ill take your word for it then

[RE99IE]

I'm a bit of a skeptic of GPS technology as a lap timer. I've played with a lot of GPS at work and they are not that accurate half the time in the sub meter reading. The only way to get high accuracy out of them if you use Differential GPS and they cost a lot. We use DGPS receiver that are accurate up to 1.2 meters.

To get the most out of any new technology lap timers, they need to be at least in the ~.01 seconds accuracy.

[SRacin]

To be honest. Im not sold on GPS either as a lap timer. However someone from the local trck swears by his GPS setup, and it does look pretty trick. He uses a msd G2X.

http://www.msdignition.com/g2x/?utm_...m_campaign=G2x

i thinks its around 1k USD. Which is not bad considering its logging capabilities. I looked at the mychron lite TG which is a good IR system which can be had off ebay new for around 250 USD with all the tx and rx kit, but in order to be able to add the logging capability you need to get the TG log which takes the price upto around 1k anyway.

Currently im using an old palm IIIc PDA running my own lap timing software (inspired by PocketC Lap Timer), with a remote button I hit as pas start/finish. This is pretty good considering no capital expenditure (alothough a fair few hours of programing). And can also log times to a text file. There is also an expansion box (which the name escapes me at the moment) but you can also get this thing which allows logging of all sorts of signals (thoughts are TPS, Brake position, rpm etc) to a pda text file. My next little project is to build/buy an IR reciever as plently of people use AIM/Mychron's locally so if i can get an IR trigger working can use someone elses TX.

Cheers
Logan

[takai]

After testing mine out, its within 0.05s of Natsoft. So im not so worried about it, after all its a tuning thing, rather than reality.

The biggest boon for me is to be logging everything off the ECU, and also the G-forces from the Wiimote.
Plus once you interpolate the G-sensor with the GPS location you get a pretty good map of where you differ each lap.

and then when your computer crashes you lose all your logs for a while...

[DX20VT]

I've used a driftbox for abit.
They do fairly good job.
Found it has issues with continuous chained tight radius corners.
Otherwise its a nice bit of kit.
Software that comes with it also isnt too bad.
Costs about $300-$400 i think.

Just depends where you want to spend your money

I use the circuit version, Performance box,

and it it as accurate as the transponder timing system available such as the AMB systems that most circuits here use, accurate to within about .05 sec, and about as accurate as the beam type timing syatems like motec and AIM.

Plus you get all the other rhings such as track mapping corner speeds and overlaying laps etc etc.

But from memory they are worth way more than the $300.

[skiddz]

if you guys really want to, *if* you could track down a decent aerial photo of suitable clarity and resolution you could digitise it using MapInfo and then enter your gps/ lap data and then lay that over the map to show the different lines you take, on different laps (if thats an issue) and then! if you felt like analyising it further take the ecu logged data and geocode it in such a way so you can see where on each line you accelerated changed gears etc. its all possible but it depends on the quality of data you are using ie. accuracy of the aerial photo and the appropriate co-ordinates to digitise it.

just a thought

[takai]

skiddz: already done. Simply bought the photo of Mallala from Mapquest and went for gold.

[skiddz]

well there ya go!

out of interest what program did you use to register the image and over lay the data?

[takai]

Some commercial stuff at work. Overlaying is done in photoshop. No automated way to do it atm. Plus i lost it all when my HDD died

Still have the original map at work though, so i can start again when i get back around to it.

[skiddz]

id call that an inaccurate way of doing it.... photoshop is by no means an accurate program makes pretty pics but thats it. if you can get your mits on MapInfo 9.0, register the image with it then enter your ecu data and gps data in the tables geocode the data with regards to time (you will have to have a separate table for each lap and set of ecu data) then overlay it, however you will need the MGA coordinates of 4 points of the photo to register it in Map Info

[takai]

Photoshop with a GPS input is actually pretty damn accurate, well with regard to creating diagrams.

One of the mapping guys at work (its all he does 8hrs a day) uses this plugin, and then creates excellent quality maps (and he has to, they are used for critical surveying etc). I just gave him the data, and he plotted it in. Just needed to know the GPS coordinates for the S/F line.

[DX20VT]

Just out of interest, here is what I think you are talking about from my GPS laptimer.

Took about 2 minutes to create this with the software and google earth,

[ed]

takai - i downloaded the chronogps and got it running on my PDA (with inbuilt GPS) but it seems to log everything backwards (as in counter rotation) i assume this is a southern hemisphere bug?

how did you overcome it?

also, i cant seem to save the file as anything. albiet im just learning with this software, but i want to take th log files off my PDA and put it on the computer. what are the files called, and what can i do with them once on my PC?

[ed]

found this:
http://www.gonmad.co.uk/nmea.php

meanwhile, cant find anything on southern hemisphere upsidedown-ness

[takai]

Interesting, im not getting any southern hemisphere upside downness...