consider if a simple data acquisition hardware was available for cheap, what would you do with it? what would you measure, and how could you really effectively use that data? for those of you have actually bought high end equipment, what have you found most effective in its use? and what was worthless?

many of us already video tape our races/sessions. when i was first starting out, i went home and looked back and recorded the entry RPM speed at each turn, every lap, so that i could gain confidence how fast i could and "have" gone into a turn, instead of second guessing myself everytime (i have a bad memory). what else do you guys use your recorded sessions for other than showing friends and posting on the internet for gits and shiggles...

so if you had available to record analog inputs like sensor voltages, or even linear motions through reading a potentiometer, what would you like to record? lets say you had limit of 4. i'd look at the driver's inputs and chassis output:

1: Throttle
2: Brake
3: Steering
4: acceleration (G's)

going thru past threads (see i actually use search...) some have mentioned looking at each wheel's motion, up and down. what do you think this can be used to determine?

what about engine outputs? rpms, air temps, oil temps? what good could this be other than possibly telling you what happened seconds before your engine blew...

im just looking for ideas on how to utilize this piece of hardware i have.

 

I think I'd start by using it to essentially instrument the driver - by measuring inputs of throttle (%), brake (on/off), and steering input. I'm speaking of myself but the car is way faster than I am so I figure I'll get the biggest net improvement by working on the weak link...

I wouldn't worry about what the car is doing (acclerations) until I knew that I was on the gas completely and early, wasn't sawing at the wheel, etc...

K

 

the wheels motion, or more importantly, the shock absorbers motion, will give you the shock speed if you take a time derivative. Looking at a histogram of the shock speed will then tell you how to tune your shock absorbers. The shape of the curve basically tells you how much time the shock is spending at any certain speed. ideally, the shock should be in bump for the same amount of time as it is in rebound. So, the histogram should be pretty much symetric about the y-axis if the y-axis is speed, negative x is bump, and positive x is rebound.
If you look at these histograms, you will also notice that your shocks spend much more time at low speed than at high speed, somewhat negating the usefulness of high speed adjustability.

so, the importance of wheel position is that you can get the shock speed, which aids in tuning of them.

my 4 choices would be:
front accelerometer for lateral Gs
rear accelerometer for longitudinal Gs
steering angle
linear pot on a shock, and move it around the car to tune each one.

What Daq system do you have?

 

It would also be very useful if your data acquisition system made it easy to correlate all these inputs that people are listing to exactly where you are on the track at a given instant. From a driving point of view, I don’t see how useful it could be to know that at time x the car was at 100% throttle if you don't know exactly where time x represents on the track. However, I would imagine if you were looking for just a telemetry system to monitor how your engine is running for example, then your instantaneous position on the track may not be so important.

 

For driver analysis, you'll want RPM, an accelerometer (Lat/Lon G's), steering angle and throttle position. With these four channels you can learn volumes about your driving if you have the right software. You'll also need a lap beacon to show the start of each lap.

The software is the key though... you need something that will calculate a track map, overlay laps, etc. Assuming you have that, you can compare laps to see exactly why one lap is a tenth faster than another, etc.

 

In terms of driver analysis, the TP, brake position, steering angle, and accel (lat/lon) are the most important 4 channels, in my opinion. You know when the driver is telling the car to do something and how the car reacts. Unfortunately, 4 channels isn't a whole lot (I realize that cost is an issue). Since I only have experience in a Formula Car setting, I'll start with that.

I don't particularly feel that RPM is as important to driver analysis, especially with a "clutchless" transmission. For engine performace, it is obviously hugely important to see how your cooling, fuel press., oil press., etc. are doing at various engine loads.

Wheel speeds are very important, especially if you can get sensors on all 4 wheels. When all 4 tires are planted on the road (ie not spinning or locked up), the wheel speeds are the same. Looking at the differences in wheel speeds can point out various "issues" the car is experiencing: lots of wheelspin, locked up wheels, limited droop travel causing inside rear to lift. This is nice especially for people who don't have a huge crew watching the car all over the track.

Shock Potentiometers: like said before, the pots display shock displacement or velocity (the analysis program will provide various "user-defined" functions). The shock displacement is handy for determining the maximum compression the suspension sees, as well as its steady state behavior. Look at the front damper displacements with lateral and longitudinal accel to determine optimal ride height. The shock velocity should be symmetric about 0 in/sec if things are working properly, but you'll also want to eliminate the really high shock velocitites both in bump and in rebound; look at the histogram and adjust your bump/rebound settings accordingly.

If you have enough channels/money I would also consider independent front and rear lat and lon accelerometers. Seeing the behavior of both ends of the car as it responds to the driver inputs is pretty damn cool. I'm looking into this for the FSAE car next year. Engine outputs are only important if you have a stand-alone system capable of on site ECU changes. However, seeing stuff like low oil pressure during high g-loads can point out a problem that could never be seen without a DA system.

This is an interesting topic...moreso since I'm the 2004 DA group leader for Michigan.

 

You want six things to start:

1. Lateral g's
2. Longitudinal g's (this gives you brake as well)
3. Throttle position
4. Steering position
5. Engine RPM (this will also show you shift points)
6. Vehicle speed via wheel speed (or GPS)

then you want a copy of Buddy Fey's book (out of print) or Simon McBeath's book (not as good by a long shot). Get a GPS based system and you don't need a lap beacon, plus you get sector times at any point of your choosing since GPS plots position vs time (track map) and gives velocity. Buy a Race Technology DL-1 ($900 est) http://www.race-technology.com....html and a good laptop if you don't have much money. otherwise Pi or Motec (software is much better) or anything in between. Damper position is expensive due to cost of pots ($250-$350 each), but you can do two at a time on a budget. Start with the six above first. So much data you won't know what to do with it at first. (the price of pots will kill you!)

 

Another book to check out is "Data Power".

If you are on a budget then "telemetry" is out of the question. Plus you need someone to be looking at the data while you run (otherwise what's the point). So unless you have a crew (or kr3w) then I would stick with the regular downloadable format. I believe that at least one of the Motecs has 1/2 recording along with telemetry, but it's damn expensive.

I would also be wary about getting all your brake information strictly from your longitudinal accel channel. Unless you stomp on the pedal and then jump off everytime you apply them, you will be missing some valuable data. If you only have 4 channels then take the 2 accels, though.

 

so, what exactly do you DO with ALL this information? that would determine what would be worth recording.

yeah, im not considering high end components like linear transducers, GPS and whatnot. but if you have used them, or have read HOW to use them, id be interested, otherwise, the simple tools available to me are basically analog voltage measurements, which you can use for thermocouples and resistance (cheap pots) and such. the one digital channel i have available is too slow to accurately measure RPMS unfortunately. i think that would best be utilized as a lap/segment divider quite frankly because i cant think of another digital input that would be slow enough to be measured.

as far as software is concerned, consider nothing other than numerical outputs. the dataq i have is generic, but is open software so you can develop your own software, but i dont know how to program (yet?). but crunching numbers in a spreadsheet is pretty much all i think i need at this point. instant graphical interface probably isnt necesssary as this would not be an in-car driver aid, just datalogging.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by descartesfool &raquo;</TD></TR><TR><TD CLASS="quote">Buy a Race Technology DL-1 ($900 est) http://www.race-technology.com....html </TD></TR></TABLE>

I just got one of those and used it for the first time this past weekend (Waterford Hills and Grattan). So far overall I really like it. I really do like the fact I can compare distance traveled, speed, times etc at any point on the track where I want. I was going to write a full report later on when I had some time.

Currently right now I am just running the data logger as is. In future I would like to add RPM, wheel speeds, throttle position, Steering position, and some others. However at this point in time, I really just need to learn how to read the data I have. So far, I think its a very usefull tool and I am very glad I got it.

 

btw, the hardware i have is well less than $100, not including the old Palm it uses to store the data. thats why im motivated to make this thing work as effectively as i can before i even consider spending $1000+ on anything else.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tyson &raquo;</TD></TR><TR><TD CLASS="quote">so, what exactly do you DO with ALL this information? that would determine what would be worth recording.</TD></TR></TABLE>

You plot certain channels together with respect to time or distance. For instance, look at TP, steering, and lat accel to see if you're getting on the throttle early enough; you can look at graphs of your lateral accel on one axis with long accel on the other and there's your effective traction circle.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">yeah, im not considering high end components like linear transducers, GPS and whatnot. but if you have used them, or have read HOW to use them, id be interested, otherwise, the simple tools available to me are basically analog voltage measurements, which you can use for thermocouples and resistance (cheap pots) and such. the one digital channel i have available is too slow to accurately measure RPMS unfortunately. i think that would best be utilized as a lap/segment divider quite frankly because i cant think of another digital input that would be slow enough to be measured.</TD></TR></TABLE>

So no pots, then. Things like steering will be a biatch without a linear pot or an angle sensor, and unfortunately I don't have the first clue how to make one like you're trying to do.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">as far as software is concerned, consider nothing other than numerical outputs. the dataq i have is generic, but is open software so you can develop your own software, but i dont know how to program (yet?). but crunching numbers in a spreadsheet is pretty much all i think i need at this point. instant graphical interface probably isnt necesssary as this would not be an in-car driver aid, just datalogging.</TD></TR></TABLE>

If you are using a program such as MatLab or even Excel you can plot the indexed data; the super cool programs that analyze the data don't do anything these programs can't do (the track map is a mystery to me though). It will have to be indexed with time (forget about distance), figure out what channels you want to compare (reading the books will help you answer that), and make some graphs. You can create new columns and perform math functions on them to get stuff like velocity, average speed, etc.

 

no, i DO mean to use potentiometers, just not EXPENSIVE pots. the linear transducers that most high end dataq systems use are really expensive, and really accurate. but im thinking of using &lt;$5 rotary or linear pots out of a digikey catalog.

yeah, everything is time indexed.

i am gonna try to see if the VSS is slow enough to measure speed accurately tho. maybe that will be something i can make my digital input useful for.

 

Gotcha...then as long as the digikey pots have a high enough frequency to be useful (our shock pots run at ~ 20kHz, but the steering doesn't need to be that high) that should be fine.

What system are you using?

 

looking at the accelerometer and wheel speed data and using integrations and kinematics, one should be able to get the approximate radii and straight lengths. that can give a close approximation of the path the driver took

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hondan00b &raquo;</TD></TR><TR><TD CLASS="quote">looking at the accelerometer and wheel speed data and using integrations and kinematics, one should be able to get the approximate radii and straight lengths. that can give a close approximation of the path the driver took</TD></TR></TABLE>

That's fine, but plotting it using Excel is where my knowledge is nonexistent.