27 replies to this topic

[cedarsf1]

Can you guys give me a recommendation on a portable data logger, one I can take use between cars? I have an app on my iphone, but I question how accurate it really is.

It would be great if there was an portable datalogger that accurate, and it would be even better if it could also synche with a GoPro camera.

All I need is vehicle speed, lap times, and segment times.

Thanks!

[NotAPineapple]

Can you guys give me a recommendation on a portable data logger, one I can take use between cars? I have an app on my iphone, but I question how accurate it really is.

It would be great if there was an portable datalogger that accurate, and it would be even better if it could also synche with a GoPro camera.

All I need is vehicle speed, lap times, and segment times.

Thanks!

I think phone based aquisition systems are a waste of time. The GPS is useless for anything other than a very very rough sketch of the track (so forget trusing the sector times) and the accelerometers typically update too slow.

I'd recommend the DL1 from www.racetechnology.com. We used it at uni and since then its had a number of improvements. I don't know how it handles video though. Depending on how much you want to spend of course there are full data+video packages available from racetechnology, AIM, Stack and Cosworth (formerly PI) that I can think of off the top of my head.

For the DL1 you just need to rigidly mount it somewhere in the car (like I assume you did with your phone) and put the GPS antenna on the roof (its magnetic so needs no other attachment). Then you log GPS position, speed, lat/long acceleration and yawrate without anyother connection to the car.

[John Brundage]

Traqmate works with or without a camera and does well.

[cedarsf1]

If you buy an external GPS receiver (one that plugs into the phone), shouldn't you then be able to get accurate lap and segment times, as well as speed? The Bad Elf GPS receiver is advertised as having a 2.5 meter accuracy.

[examateur racer]

Cedar, have a look at the Racelogic VBOX site. website

There is a VBOX Sport that costs about £250 and bluetooths to your iphone also uses a free bit of software called Circuit Tools that you can map and look at parameters.

I myself have used PI both dash2 and clubman, also Racetechnology and although each one has features the racelogic products just works out of the box.

I bought a VBOX Lite with an OLED option, wired it into 12V mounted 2 cameras and put the GPS aerial on the roll over bar and went out to practice, immediate results, box logs automatically and the software is easy to use. You can mount it anyway up, whilst when I used Racetechnology logger you had to mount it a specific way and tell the software.

So my advice:-

Just position and speed mapping use a VBOX Sport

Want cameras then use a VBOX Lite

Good Luck!

PS Pineapple Racelogic use 20Hz GPS engines so they are accurate enough for amateurs

Edited by examateur racer, 14 August 2013 - 11:30.

[cedarsf1]

The only problem is that the Racelogic VBox lite is $1600.

Shouldn't an iphone app connected to an external GPS be totally accurate?

[cedarsf1]

What do you guys think of this:

 

http://stoppani.net/products.html

 

Wouldn't the high-resolution GPS module that they sell provide accurate data?

[Canuck]

For the $150 it would take to try it out, try it out (assuming you have an iphone / ipod.  Spend more than that on a bad meal and a movie with the family.

[cedarsf1]

Never mind the family and the bad meal--a $150 is what my local track charges for a track day, so I don't want to blow it on something that may or may not work. Really, the worst thing is having any kind of tool that you can't trust. 

 

I'm wondering if anyone knows how accurate the external GPS module would be with an iphone 5. I'm quite surprised that there has been so little response to this post. If you guys are into technical stuff, how can you not be interested in data loggers? I mean, how do you know if anything you do to try to make a car quicker really works without having some truly objective data to show you?

 

So, my question is, why would such a set up not be as accurate as a full Traqmate or other such system. I have a Traqmate and it's great, but I don't always drive just one car, so having a portable set up would be an ideal solution for at least giving me a baseline to measure lap times, segment times, and vehicle speed. Thanks!

[murpia]

If you guys are into technical stuff, how can you not be interested in data loggers? I mean, how do you know if anything you do to try to make a car quicker really works without having some truly objective data to show you?

'Us guys into technical stuff' are most definitely interested in data loggers.

 

But usually we're not interested in explaining why a $150 consumer-grade GPS iPhone add-on isn't going to be much use for real engineering work.

 

Regards, Ian

[desmo]

When I noticed GPS first used as a telemetry channel, it was using DGPS with little transmitters on the side of the track.  Maybe if you had a crack for the military dither!

 

How good are the cheap little accelerometers in phones now?  Getting as good as pros used 20-30 years ago perhaps? Maybe not. 

[cedarsf1]

The accelerometer isn't very important for me because I'm only interested in track time/segment time, and in vehicle speed, all of which requires totally accurate GPS. If it's off by 1/10th of a second, then that can really take you down the wrong road in trying to figure out how to improve your segment times.

[Canuck]

Heh. I like your assumption that nobody is interested in loggers. I use a Garmin gps unit on my bicycle daily and have ridden certain sections more than 400 times one way (and 400 the other way). The distance it records is nowhere near close enough to gauge a 1/10th second variance. Hell, the thing rarely (never once yet) records the same distance out and back within 25 meters.

I don't think the smartphone platform is the issue, it's the bargain gps receiver that goes with it. As for the accelerometers - the units I work with daily cost, at production volumes, more than some proper logging systems and even they aren't accurate enough on their own to do what we do.

I think you'll find that the lack of interest isn't the concept (logging), rather the specific logger (a high-school boy's toy).

[Canuck]

Actually, if your velocity through a given section gives you a distance per tenth of a second that is significantly greater than the total accuracy (5m if it's +\- 2.5) spread then it's probably worth the $150.

[NotAPineapple]

The eternal problem with GPS is that its noisy and easily disturbed by buildings, bridges, pit buildings etc. In other words, even an expensive GPS is going to give a sht signal.

 

At work we use a 70k€ inertial + GPS system that can give a couple of meters accuracy in position if the conditions are perfect clear sky, no buildings, no bridges and after a 15 minute dynamic warm up excersise. This level of accuracy is ok but still not that great if you want to use it to chop the track up into reliable sectors to pick fractions of a second. A lot of the cost in these industrial inertial platforms are in the algorithms which use the accelerometers, gyros and base stations to correct the GPS signal which in practice is usually quite an unreliable signal.

 

So you can be sure that your $100 special simply isn't going to give you the repeatability and noise rejection required for anything other than making a pretty track map. It needs accelerometers and gyros to work with it to correct the crap coming from the GPS. If you really want to reject the random noise, you need a static base station as well. I'm positive that there aren't any decent algorithms in an iPhone app that will reliably stich together GPS and inertial sensor data to give you a decent trajectoy accuracy.

 

Still, the best way I have seen to split up tracks is to use a lap beacon at the start line and cut the sectors using a distance calculated from the wheelspeeds.

[kikiturbo2]

The only problem is that the Racelogic VBox lite is $1600.

Shouldn't an iphone app connected to an external GPS be totally accurate?

 Performance box costs 600 bucks and will do everything you want..

[cedarsf1]

Thanks for all your replies. I never realized that GPS-based systems can be so unrealiable.

 

NotAPinapple wrote: "till, the best way I have seen to split up tracks is to use a lap beacon at the start line and cut the sectors using a distance calculated from the wheelspeeds."

 

How would you calculate the distance from wheel speeds? Are there lap timers using computers to calculate this?

[RDV]

How would you calculate the distance from wheel speeds? Are there lap timers using computers to calculate this?

 

PI, Motec and Marelli do it this way, speed is actually derived from wheel RPM over time, what is logged is distance. That said it varies lap by lap depending on wheel slip, which in turn depends on lockups, etc, they usually average lap by lap to give compare. It's accurate enough for most work, are you looking for 1/1000?

And yes, either a master beacon from track, or your own dedicated one, usually at start-finish line so times match official timing.

[Canuck]

Throwing this off the top of my head - if you were to count rotations, say by piggy-backing another sensor on the ABS ring, it's a pretty straight-forward calculation to determine distance travelled as long as the wheel isn't spinning (choose a front wheel). A reasonable extension of that might measure rotation of all 4 wheels to determine (or measure) rear wheel slip, a pair of inexpensive 2-axis accelerometers could be used to further validate the data (ie all 4 wheels locked but car still travelling). Add "segment" buttons that the driver can use to slice up the track and you've got a nifty little logger. This presumes you (or your friends) can design and build hardware and write firmware I suppose.

I have a little Dataq general purpose data logger I picked up a few years ago to help me troubleshoot an intermittent problem in a pre-OBD car. Cheap - $50 or so. I suppose you could use something like that as the interface between a laptop and whatever sensor network you put together and turn it into useful data in Excel or or some other data-processing package.

[Canuck]

RDV snuck that in there while I wasn't looking. What he said.

[Greg Locock]

One refinement used in road cars - when accelerating use the non driven wheel pair, when braking use the rears.

[murpia]

One refinement used in road cars - when accelerating use the non driven wheel pair, when braking use the rears.

Here's how mid-00's F1 did it:

 

No brake pressure, take average front.

Brake pressure, take fastest front or rear.

Unless, Kalman-filtered processing of longitudinal G suggests all 4 wheels locking or under-rotating, in which case use observer speed.

 

Regards, Ian

[Canuck]

What's observer speed?

[murpia]

What's observer speed?

The speed output of the Kalman filter was called 'observer speed', although a quick Google suggests that wasn't strictly correct terminology.

 

http://en.wikipedia....i/Kalman_filter

http://en.wikipedia..../State_observer

 

GPS receivers also have Kalman filters in them to estimate the true speed & position of the receiver in the presence of noisy readings. It's one of the (many) reasons why consumer GPS's aren't that accurate, as the filter is generic rather than tuned to the dynamics of a specific vehicle. You would expect a hiking GPS, a bicycle GPS, a road car GPS, a boat GPS, an aircraft GPS and an aircraft GPS all to use different filter tunes, but typically they don't (especially the cheaper ones).

 

Probably RaceLogic VBoxes, Race Technology DL1's and possibly the MoTec GPS modules have filters tuned for race cars.

 

Regards, Ian

[CSquared]

I have a Traqmate and it's great, but I don't always drive just one car, so having a portable set up would be an ideal solution for at least giving me a baseline to measure lap times, segment times, and vehicle speed. Thanks!

 

Why can't you move the Traqmate between cars? Isn't that the cheapest answer and also gives you a more accurate comparison of the cars?

[gary76]

I have been using a 'DigiDash' ( www.etbinstruments.com) for a few years. I was completly 'green' to data logging but after awhile I soon got the hang of it. It has its limitations but it is not expensive and certainly easy to use. The one I use does not have GPS but uses the track beacon.

Wheel speeds and distance traveled is a bit of a problem if you are looking at brake lock-ups and differential work since the std system has one sensor and only two trigger magnets. I learnt a lot from it and it did help the driver!

Gary

[indigoid]

(yes, old thread)

 

So I have been working on my own motorcycle-mounted datalogger for a while as a personal project, and out of frustration with the OEM tripmeters I decided to implement my own - one that isn't limited to a mere 999km. I am using Haversine to calculate the distance between lat/long datapoints, which looks prone to error from altitude differences. But along the way I found that I was getting a lot of apparent error in the GPS data which I believe is caused by two things

 

- GPS "teleporting" where the receiver decides to alter the subset of satellites it is deriving its position etc data from (hence the GPS "noise" when the sensor is stationary)

 

- Insufficient significant digits in the floating point math implementation in the microcontroller - this can be addressed by moving to a different MCU platform, which I am presently investigating

 

The internet seems to think that combining inertial/satellite data can help. I found these:

 

http://www.sbg-syste...nertial-systems

 

I am going to have to brush up on my math, regardless, to make any sense of Kalman.

 

edit: of course, a much more expedient route may be to tap the ABS wheel speed sensor line on the bike (or sniff the data from CAN) and use that instead. Also works in tunnels.

Edited by indigoid, 23 December 2013 - 12:12.

[NotAPineapple]

Like I said, the GPS signal is a noisy terrible signal. With a lot of work with accurate inertial sensors you can correct it.

 

You wil get much better accuracy with a wheel speed sensor, plus like you say it will work in tunnels.

 

This page shows you basically why GPS itself is a useless signal:

http://www.oxts.com/...eed-comparison/

 

If you use this to measure displacement, you will be measuring a lot of noise so you distance will be higher than reality.