new to data logging!
Discussion
hi all ive just bought myself a cheap data logger and display as i wanted something cheap but which i could monitor myself and link to my gopro.
i cant afford the really top quality kit so i got a race technology DL1 and dash 3 display. does anyone have any info on how i install this kit and what parameters i would benefit from? does the speed on the dash 3 get its reading from the DL1 via gps or do i need a wheelspeed sensor? cheers
i cant afford the really top quality kit so i got a race technology DL1 and dash 3 display. does anyone have any info on how i install this kit and what parameters i would benefit from? does the speed on the dash 3 get its reading from the DL1 via gps or do i need a wheelspeed sensor? cheers
BioBa said:
Speed is determined via the DL1 GPS which is more accurate than a wheel speed sensor.
Really?IIRC civilian GPS resolution is limited to around 3m (10 ft in American) by US Government (more accurate systems are classified as munitions). Assuming that you're using what are quite large front tyres for 13" fronts (195/530 R13) and only one magnet on the hub (AIM will handle 4 triggers thus quadrupling accuracy) then the wheel speed resultion is 1.665 metres.
GPS is only accurate to a few metres, but the drift from one reading to the next less than a second later is not that large. You might find that the lines you take in the morning session don't overlay onto the lines in the afternoon, but you will find that by aligning the start lines that the do match up. On the subject of what to log, I'd go for the following (mostly in order):
GPS/accelerometer
RPM --- at this point, you can learn a lot
Steering angle --- you can now deduce understeer/oversteer in a maths channel and blame car/driver
Throttle position --- How heavy is your foot?
Brake pedal pressure --- How's your braking technique? You now know exactly what's caused by the driver.
Wheel speed(s) --- Wheelspin and locked wheels for confirming suspicions.
Yaw --- Direct measurement of turning to confirm understeer/oversteer
Suspension travel --- Aero work...
GPS/accelerometer
RPM --- at this point, you can learn a lot
Steering angle --- you can now deduce understeer/oversteer in a maths channel and blame car/driver
Throttle position --- How heavy is your foot?
Brake pedal pressure --- How's your braking technique? You now know exactly what's caused by the driver.
Wheel speed(s) --- Wheelspin and locked wheels for confirming suspicions.
Yaw --- Direct measurement of turning to confirm understeer/oversteer
Suspension travel --- Aero work...
LCM said:
Really?
IIRC civilian GPS resolution is limited to around 3m (10 ft in American) by US Government (more accurate systems are classified as munitions). Assuming that you're using what are quite large front tyres for 13" fronts (195/530 R13) and only one magnet on the hub (AIM will handle 4 triggers thus quadrupling accuracy) then the wheel speed resultion is 1.665 metres.
Here is the info from the Racetechnology website which makes perfect sense to me:IIRC civilian GPS resolution is limited to around 3m (10 ft in American) by US Government (more accurate systems are classified as munitions). Assuming that you're using what are quite large front tyres for 13" fronts (195/530 R13) and only one magnet on the hub (AIM will handle 4 triggers thus quadrupling accuracy) then the wheel speed resultion is 1.665 metres.
" While speed is probably the most important parameter that anyone wants to measure using the data logging system, it is also the most inaccurate in a "conventional" system. The normal way to measure speed is to simply attach a pickup to a wheel to detect how fast it is rotating - but the rolling circumference of a tyre changes by 4% just with wear and temperature. Even worse, the error increases significantly under race conditions where the tyre is under load - typically the tyre slips by upto 20% under hard braking going into a corner. Measuring speed using GPS is now common practice in high-end systems - under typical conditions speed error is well under 1%!"
BioBa said:
Here is the info from the Racetechnology website which makes perfect sense to me:
" While speed is probably the most important parameter that anyone wants to measure using the data logging system, it is also the most inaccurate in a "conventional" system. The normal way to measure speed is to simply attach a pickup to a wheel to detect how fast it is rotating - but the rolling circumference of a tyre changes by 4% just with wear and temperature. Even worse, the error increases significantly under race conditions where the tyre is under load - typically the tyre slips by upto 20% under hard braking going into a corner. Measuring speed using GPS is now common practice in high-end systems - under typical conditions speed error is well under 1%!"
To quote Mandy Rice-Davis "He would, wouldn't he?"." While speed is probably the most important parameter that anyone wants to measure using the data logging system, it is also the most inaccurate in a "conventional" system. The normal way to measure speed is to simply attach a pickup to a wheel to detect how fast it is rotating - but the rolling circumference of a tyre changes by 4% just with wear and temperature. Even worse, the error increases significantly under race conditions where the tyre is under load - typically the tyre slips by upto 20% under hard braking going into a corner. Measuring speed using GPS is now common practice in high-end systems - under typical conditions speed error is well under 1%!"
But that's apples and pears - a 4% variability in source signal accuracy is not the same as a 50% difference in granularity.
thanks simon. the more info the better for me as im only just starting out in single seaters.and slicks etc!
did a track day which i felt went really well. only got overtaken once all day and that was in the morning session on a circuiy id never driven. but i did feel the car had a lot more to give,and that i was the limiting factor in not going much much faster!
thanks for the help!
did a track day which i felt went really well. only got overtaken once all day and that was in the morning session on a circuiy id never driven. but i did feel the car had a lot more to give,and that i was the limiting factor in not going much much faster!
thanks for the help!
LCM said:
To quote Mandy Rice-Davis "He would, wouldn't he?".
But that's apples and pears - a 4% variability in source signal accuracy is not the same as a 50% difference in granularity.
How come you ignored tyre slip error?But that's apples and pears - a 4% variability in source signal accuracy is not the same as a 50% difference in granularity.
I agree with you that with a wheel speed sensor I get more data points but in particular in corners and in breaking zones (the areas all racers are mostly interested) the wheel speed data contain errors which are far more significant than any inaccuracies of the gps data.
On the straigts the wheel speed sensor might be more accurate but the difference would be very very small.
Anyway I had to look up Mandy Rice-Davis. Unfortunately I did not remember my UK current affairs when I was 2 years old.
I certainly understand why PM Harold got week in the knees when Mandy came for a visit!
I used the same set up for a couple of years...its really very good...Display a little small but usable... analysis software is really excellent.
Essential Parameters
Speed. (dont want to enter the debate - either will do)
RPM
Long G - the trace tells you all you need to know about how you brake.
Lat G -
Oil T -
Oil P -
Water T
and Buy a video camera. they tell you why you were slower/faster in a section. THIs is a good cheap set up. you can get a license to merge data and video, but its time consuming and largely academic.
You can also configure the Dash to display a predicted lap time which is EXCELLENT..highly recommended.
Beyond that I would not venture...you can go mad with pots on steering, and dampers, and brake pressure and throttle....but the basic set up is good enough.
Good luck.
Essential Parameters
Speed. (dont want to enter the debate - either will do)
RPM
Long G - the trace tells you all you need to know about how you brake.
Lat G -
Oil T -
Oil P -
Water T
and Buy a video camera. they tell you why you were slower/faster in a section. THIs is a good cheap set up. you can get a license to merge data and video, but its time consuming and largely academic.
You can also configure the Dash to display a predicted lap time which is EXCELLENT..highly recommended.
Beyond that I would not venture...you can go mad with pots on steering, and dampers, and brake pressure and throttle....but the basic set up is good enough.
Good luck.
BioBa said:
How come you ignored tyre slip error?
I agree with you that with a wheel speed sensor I get more data points but in particular in corners and in breaking zones (the areas all racers are mostly interested) the wheel speed data contain errors which are far more significant than any inaccuracies of the gps data.
On the straigts the wheel speed sensor might be more accurate but the difference would be very very small.
Anyway I had to look up Mandy Rice-Davis. Unfortunately I did not remember my UK current affairs when I was 2 years old.
I certainly understand why PM Harold got week in the knees when Mandy came for a visit!
Because we're talking apples and pears.I agree with you that with a wheel speed sensor I get more data points but in particular in corners and in breaking zones (the areas all racers are mostly interested) the wheel speed data contain errors which are far more significant than any inaccuracies of the gps data.
On the straigts the wheel speed sensor might be more accurate but the difference would be very very small.
Anyway I had to look up Mandy Rice-Davis. Unfortunately I did not remember my UK current affairs when I was 2 years old.
I certainly understand why PM Harold got week in the knees when Mandy came for a visit!
I was questioning the original statement about GPS being more accurate. Because of the large cell size (3m x 3m or 10ft x 10 ft) and the fact that one doesn't don't know where in a 100sq ft cell the datum point is it is inherently a method of low precision. Whereas a wheel speed sensor is a method of high precision (with 4 magnets the signal interval is 400mm of circumferential travel). And they tell you different things!
We have to think about why one might want to measure and record velocity.
In my experience there are 3 significant reasons:
- to have something to put into the "my dick is bigger than your dick" discussions in the paddock
- to develop chassis dynamics
- to develop aerodynamics
- lie
- take any source signal you like and write a little maths channel where V = v*2 or any other constant that takes your fancy
If the third then road speed is irrelevant as calculations and comparisons need to be based on fluid velocity (airspeed).
As for Mandy Rice Davies, she appeared in the Daily Express (not a paper I would normally read outside BMTR's waiting area) today looking in pretty good nick for a lady in her late '60s which is more that can be said for her erstwhile companion Christine Keeler who looked worse than my mother did when she died at 93!
my main reason for this is to improve as a driver,and get the best from my car on a budget.i find it difficult on track to judge how fast im entering corners/braking zones on different laps with no speedometer so i dont know if im going faster or slower than previous laps.and im usually alone and therefore have nobody to time my laps for me, and timing is not generally allowed on trackdays
eg if i know the car will comfortably take the corner at 80mph, will it take it at 85,90,95?
thanks for the info to those who have tried to help!
eg if i know the car will comfortably take the corner at 80mph, will it take it at 85,90,95?
thanks for the info to those who have tried to help!
Interesting stuff. My $0.02.
Like 'andylaurence' I log all kindsa crap - but hardly ever use it - so would recommend 'mb26's suggestions although I'd add:
Throttle Position (so you can see how quickly and steeply your getting back into the throttle (and is easily done if your ECU is using throttle position)); and
Brakes On/Off (so you can compare braking points, and is easily done from the brake light switch (if you have one)).
With regard to your desire to log lap times at trackdays, a GPS system will 'silently' do this for you, whereas a wheel speed sensor will not, so the GPS system is fine for you.
With regard to the comparative accuracies of the two systems, I have to say that when comparing speeds indicated by my on-board, two magnets on the diff, wheel speed, system with the speeds indicated by the GPS based, Video V-Box, data (that we get when Nigel Greensall straps his kit to my car) I can't see a whole heap of difference.
This said, what I do notice with all of the GPS based stuff is that there seems to be a little lag and/or faffing about in low speed tight corners (say Druids) where the systems seem to be struggling to make up their minds.
This, based on very little (and being a bear of very little brain, I'm inviting anyone to correct me if I'm wrong) makes me wonder whether GPS systems increase in accuracy at higher speeds and in corners that are actually going somewhere. In other words, depending upon how many 3m2 boxes you've passed through in a given (very small) period of time.
Any thoughts LCM? Anyone?
Like 'andylaurence' I log all kindsa crap - but hardly ever use it - so would recommend 'mb26's suggestions although I'd add:
Throttle Position (so you can see how quickly and steeply your getting back into the throttle (and is easily done if your ECU is using throttle position)); and
Brakes On/Off (so you can compare braking points, and is easily done from the brake light switch (if you have one)).
With regard to your desire to log lap times at trackdays, a GPS system will 'silently' do this for you, whereas a wheel speed sensor will not, so the GPS system is fine for you.
With regard to the comparative accuracies of the two systems, I have to say that when comparing speeds indicated by my on-board, two magnets on the diff, wheel speed, system with the speeds indicated by the GPS based, Video V-Box, data (that we get when Nigel Greensall straps his kit to my car) I can't see a whole heap of difference.
This said, what I do notice with all of the GPS based stuff is that there seems to be a little lag and/or faffing about in low speed tight corners (say Druids) where the systems seem to be struggling to make up their minds.
This, based on very little (and being a bear of very little brain, I'm inviting anyone to correct me if I'm wrong) makes me wonder whether GPS systems increase in accuracy at higher speeds and in corners that are actually going somewhere. In other words, depending upon how many 3m2 boxes you've passed through in a given (very small) period of time.
Any thoughts LCM? Anyone?
Edited by Count Johnny on Thursday 3rd October 06:48
Count Johnny said:
This said, what I do notice with all of the GPS based stuff is that there seems to be a little lag and/or faffing about in low speed tight corners (say Druids) where the systems seem to be struggling to make up their minds.
This, based on very little (and being a bear of very little brain, I'm inviting anyone to correct me if I'm wrong) makes me wonder whether GPS systems increase in accuracy at higher speeds and in corners that are actually going somewhere. In other words, depending upon how many 3m2 boxes you've passed through in a given (very small) period of time.
Any thoughts LCM? Anyone?
Correct! This, based on very little (and being a bear of very little brain, I'm inviting anyone to correct me if I'm wrong) makes me wonder whether GPS systems increase in accuracy at higher speeds and in corners that are actually going somewhere. In other words, depending upon how many 3m2 boxes you've passed through in a given (very small) period of time.
Any thoughts LCM? Anyone?
Edited by Count Johnny on Thursday 3rd October 06:48
Particularly if one uses Time rather than Distance as the base/independent variable/x axis. You just can't get away from its inherent coarse granularity.
I've got everything logged on the SR8 but use little of it unless working on an issue (surprisingly to me BIG R don't seem big on accelerometers but use GPS for car dynamics - speaks volumes).
On the Force (a specialist tool if ever there was - with an AIM Evo 4 based system) the logging is broken into 2 components:
- detailed engine data is on the Life (much at 100 Hz) and "first look" engine data (revs, TPS, temps, EPDs and pressures) is summarised at 10 Hz on the AIM
- vehicle dynamics data (aero and chassis) is stored on the AIM (Lat, Long and Vert Acc, wheel speeds, suspension displacement (by corner), ASI and the GPS stuff), timing is based on the trackside beacon when testing (timekeepers when racing). IF I could get military grade GPS then this could provide a very good datum for wheel speed monitoring, but I can't so it doesn't.
A bientot mes braves.
The non-Radical car I have been racing has a PI research data logger on it and while it has been interesting to see the data, I still get more benefit from on board video, lap times and understanding what I feel through the car during a race.
I don't run a data logger on my Radical, just use onboard camera and remember what the car was doing, they are only twenty minute races after all!
I don't run a data logger on my Radical, just use onboard camera and remember what the car was doing, they are only twenty minute races after all!
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