Wow, thats a pretty sweet pre made solution, but I would bet it costs MUCH more than a strain gauge. 3 resistors, a diode, some wire and solder..

http://forums.pelicanparts.com/uploa...1110855946.jpg

Tech specs on DL-1 data logger.

Will it work?

Yup, any of the analog input ports will work. 12 bit resolution will be more than enough to give you all the accuracy you need. As long as you know how to get the data out and into a spreadsheet it will be a no brainer. With everything you got I would put sensors on all four corners to impress all your other racing buddies with data loggers. Show them who's the king of the data analysis mountain. ;)

Well....from the datasheet for the laser dodad, the Micro one needs 10-30V in and outputs an analog 0-5V signal....which looks to match up with one of the 0-5V analog inputs of the datalogger. But I'm no rocket scientist...

http://forums.pelicanparts.com/uploa...1110856525.jpg

You might have missed the post where Jack said he wants to do this for much less than $100. I bet that laser unit costs at least several hundred dollars.

I just stumbled on this thread. This was my original idea:
http://www.spaceagecontrol.com/ptmain.htm
this company makes very high resolution string potentiometers. Suspension travel is an application that they have been used for and I am sure they could provide you with a pot that has the right travel, frequency response, and resolution. I am also sure that it would a good deal more than $30.

Mr. 350hp has the right idea. Through the whole thread I kept thinking "strain guages are pretty cheap but how can he log the data for <$30?!?!?" I didn't know you already had something that would work. I found a site:

www.entran.com that sells strain guages for $15 ea if buying 1-9. You'd probably want to buy three since you destroy a few trying to glue them on. I assume you have coil springs. This wouldn't work very well with torsion bars since access to the bar would be a hassle. All told you might go over $30 but with this method you can get real results that can be used to compare ducks to big RS wings. You could also mount a strain guage to the support arm for your RS wing and use it to measure drag. Then you could compare drag and downforce for different angles on the wing!!

Down Force What Down Force
 

I'd use a Tinus Olsen loadcell and a lap top running labview 7.1 That way you could map out what is happening at dif speeds Its all a function of the PID, heck maby even write a program then it could be mounted on the trunk latch and measure the down force there as well

"Its all relatively easy" (!?) relative to what?

This is hard to watch this unfold.
I did expect to see the "wheatstone bridge" crossed a bit earlier. . . but now expect Poisson to jump out from behind the Mohr-circle. ooooh the suspense. :cool:

oh, but at least it will be cheap.

Theres an idea . .. WWII pilots used light triagulation to measure their height off the water, on dam-busting runs.

We have laser-pointers now. :cool:

A laser-pointer and a lipstick cam are all ya need.

With a laser-pointer mounted at an angle, pointed at the ground, any up/down motion would show an exagerated movement of the laser dot. (the steeper the angle, the more exagerated the movement of the dot)

has there been any progress in the measuring of the downforce in this project?

When the F1 cars come to Indianapolis in June get yourself down to one of the racing camps and find out what systems they use to retrieve their car's suspension telemetry essentially how the suspension weights and unweights. All that information is stored in an onboard computer and is transmitted to the paddock during the race and typically adjusted with the use of a laptop. As everyone knows without the proper downforce, these cars would be impossible to control, I would imagine driving behind in the vortex of one of these cars must be like flying a cessna through the jet wash of a commercial jetliner.

Down force should be the weight difference on the car as wind is blown over the vehicle in a controlled environment like a wind tunnel. All serious competition cars are tested in a wind tunnel.

Err, Harlan. Wasn't Jack looking for a $100 solution? I think $100 might get Jack to Indiana, maybe. Telemetry and on-board ECUs and sensor circuits are available, but you're looking at more than a few bucks aren't you?

BTW, I don't think active suspension (or at least telemetry-controlled ride height) is allowed in F1 as it once was.

I suspect his silence indicates he's either working on a solution or he's cruising around the Malibu mountains.

Sherwood

As far as F1 goes each team pretty much has a proprietary computer system, mclaren builds their own, ferrari has magnetti marelli and so on and so forth. I am pretty sure Penske racing sells suspension sensors, just need to look around, looks like a long hood shock with a wire on it. If you wanted to go that far im sure you could store the data on a pda or a laptop. Quite useless unless your running full car telemetry. As far as the F1 boys changing settings during the race, that was outlawed years ago along with active, turbos and ground affects.

I think a more cost effective way to measure airflow would be utilizong tufts of string and the lipstick camera that Jack already has. Just re mount it looking down from the roof or from inside the car. Anything else and your getting into big bucks and hitting the wall on the law of dimishing returns. If nothing else what do the track times tell you.

In a perfect world I could have a motec or mclaren ecu and datalogger with realtime wheel, suspension, tranny and engine sensors giving input. Then top it off with a yaw, pitch, roll and pitut tube and then youve got the means to implement an active suspension. Oh the lunacy...

Bill V. has tried pitot tubes w/o much success. They do work well on aircraft... Steve Vogel's book that I posted about some time ago should have info if anybody wants to pursue that further.

There is bound to be some sensor around somewhere that can give displacement data for cheap....

I just installed the data logger tonight, but I still haven't sourced a set of ride height sensors from a Range Rover. I have my local British repair shop keeping an eye out for me. The goal is to get some take-offs from a Range Rover that's given a simpler suspension, and then wire them into the DL1 and have it average out particular segments of a flat stretch of road so that I can compare.

Here's a question, though. Would it be sufficient to have two ride height sensors instead of four? I can't think of a testing situation (on a straight-line road) where downforce would vary from side to side in a significant way. Am I missing something?

Jack,
Four height sensors might indicate lift or downforce where you might least expect it. Better to get the broader picture if it doesn't necessitate needless complexity.

MHO,
Sherwood

Many GM autos use a ride height sensor. If you are trying to source some used units for cheap they might be a lot easier to find than range rover's.

yeh - unless the sensors are really spendy for each one. Easy to wire in 2 more, and allocate 2 more channels. You wiill not be worried about the cycle time of the logger to read the inputs for your application. Then you'll know if any side to side effects are being caused by any aero aids.

Be sure to test these puppies against each other at 2-3 positions....

The first rule of laboratory science is to not trust the over-priced "lab-grade" crap the vendor sells you...

Eliminate the sensors and other variables
 

Jack,

This is how I would tackle this issue if I did not have a wind tunnel. It is true that too many variables can really throw a monkey wrench in your tests. So your focus should be on eliminating the variables.


1. Place crosshairs at the dead center of your wheels and on your front and rear bumper.

2. Set up a trackside camera on a firmly mounted tripod. This way you will be measuring on the same segment of road and you will be eliminating the terrain variable.

3. To eliminate the acceleration variable you must pass the camera at a constant speed. So you are looking to shoot the car at a constant speed of 10mph, 20mph, 30mph etc. with each different tail.

4. Pick a still day. Wind usually calms at about 6:00 PM on a summers day.

When you have completed all the test photos, you can then analyze the crosshair position relative to each other. This should give you a clear picture of how down-force is being distributed across the entire car.

In the end this is really what you want to know, isn’t it? To find the actual downward force of the wing won't tell you how it affects the car as a whole.

A distant camera like that would be useless. The kind of data resolution jack needs for this project should be in the sub millimeter range.

Go add 20 lbs to either end of your car and see how much it deflects.