JackOlsen

Since I can't afford a wind tunnel, and I've been restlessly building aero pieces for my 911 (front and side skirts, diffuser, underbody panels, wings), I'm looking for a way to determine the change in downforce with different pieces, wing-angle changes, etc.

I have a DL1 data logger on the way, which can average and interperet data. But I'm looking for a way to measure relative changes in ride height, presumably over a long, controlled flat straight section of road. (It would be nice if they worked on the track, too, but it would be a good start to have them work on a straight roadway.)

I've had some good suggestions -- a bicycle wheel on a mount on either end of the car, with the angle changing as the car rises/falls, and a potentiometer of some sort generting a voltage variation that can then be measured and processed. Someone else suggested strain gauges on each of my four coil springs, although my initial look at the technical requirements for this seem daunting, in spite of the low price of the strain gauges.

There are laser measuring devices that Nascar teams use. They cost $5000 each for the good ones and $1000 each for the cheapo ones.

I'm looking to spend practically nothing. And that's why I'm going out with this to all of you -- guys who are smarter than me.

Any ideas?

Mark Hald

Something like THIS might be at the core of what you want to do, Jack.

Unfortunately, it can't be cheap. Places that don't list their prices never are...

HarryD

Jack,

How much is too much? In industry, there are Ultrasonic level sensors that use 24 VDC and genernate a 4-20 ma signal that is proportional to height. cost of the transmitter is $4-700. You can see some of them here: http://www.omega.com/toc_asp/subsect...K03&book=Green. There may be less expensive ones as well but I will let you do the search.

They also have displacement gauges here: http://www.omega.com/toc_asp/subsect...&book=Pressure

Poke around the Web Site a bit and you may find something that will measure what you need at a cost you like.

Dan Cobb

Jack,
Consider a any of the following options:
1- Ultra low-cost 'bubba-tech' method:
Rig a bracket on your moving suspension parts that will firmly hold a sharpie marker against a reference point on a non-moving portion of the inner fender. Mark a horizontal line while the car is at rest to be the zero point. As the suspension compresses, the marker will make a vertical line.
Simply measure the line after the trial to determine the amount of compression/downforce generated.
2- A few bucks more "not-so-bubba-tech":
This method will require a bit of knowledge about your car. Make a setup for each corner that is as follows: Picture a drinking straw with a pencil inside it. Place an O-ring (from your local hardware store) around the pencil and nopw push it up into the straw. The O-ring will move along the pencil and indicate the distanc eth pencil was moved.
3- Better yet:
Mount a dial indicator on the non-moving portion of the suspension and set it to measure vertical suspension deflection. It will retain the largest deflection value obtained.
4-Attach a piece of measured styrofoam to the underside of the fender above the tires with duct tape. The tire will easily 'burn away' the foam that is in the way at the highest compression point. Then compare the before and after thicknesses. (I like this one the best)

These were just a few ideas off the top of my head.
I hope my approach to 'practical engineering' leads you in the right direction.
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HarryD

Jack,

Another alternative is to use a microswitch mounted at a fixed location and then have an arm on the moving part of the suspension trip it as it passes. It will not give you a continuous level reading but you will be able to tell when you get a certain amount of displacement. If you want to get fancy, put a few in a row to get a few data points.

What does your data logger read? Digial inputs (on/off) or a changing voltage or current?

911pcars

As mentioned in a previous reply on PParts (it must not have been clear), go to Pik-a-Parts graveyard for cars (or equivalent) and cannibolize some ride height sensors from one of several vehicles that offered them as factory equipment. They are linear or rotary potentiometer-types, but with the linkage already configured to measure a 5 volt reference source into an ECU.

I know many late model Mitsubishi Diamantes had them (not real popular) as well as many SUVs and other luxo cars. Others can perhaps contribute what they know.

The stick and reference pointer method works too. Maybe you could rig up a geometrically positioned arm to exaggerate suspension compression; have it pointed at some graduated marks; recorded by a remote video camera; somehow record relationship with vehicle speed (audio or visual).

Glad to see your test project is moving along.

Hope this helps,
Sherwood

Dan Cobb

Best one yet Jack:
Buy 4 replacement antennae shafts or extending pointers like used for a presentation.
Mount them directly above any moving part of your suspension and extend them until they touch.
Measure their length before & after your test run and you will have a manual set of ride height sensors.
I'm going on the theory here that you wanted to basically spend nothing, that eliminates any electrical means of monitoring or calculating, but it still leaves us a ton of ways to get the data.
+++

TAREK

Here you go

http://www.advantagemotorsports.com/Sensors.htm

Scroll down to see the suspension travel sensor, for approx $250, depending on travel range. Can't beat the $250, given aggravation and time and cost of small parts from radio schack or hobby store, with questionable results. Just my 2 cents.

Let us know what you decide on using

Tarek

two914s

I have owned many Porsche's recently and also own a 1997 Land Rover Range Rover. Every Range Rover has poteniometers that measure the height of each corner so that the air suspension can level the car. Unfortuately, after 100K miles, these air systems develop cronic AIR LEAKS and must be constantly returned to a dealer to reset the computer. I have just been through a year of this struggle but finally replaced the entire air suspension system with a coil spring replacement kit.

As a part of this conversion, I removed all the ride height sensors. They are sitting on my work bench.

If you go to ANY independent Land Rover repair shop they will show you a PILE of discarded air suspensions components where they have converted the customer's car to coil springs. Not all mechanics remove the ride height sensors, but they do absolutely nothing if you remove the air suspension.

So, get a 6 pack of room temperature ale, head down to your independent British repair mechanic, and explain what you want to do. I would think they would be very happy to see these parts not going to the land fill. Jaguars also have smilar sensors, so maybe they would be of a better shape.

I would try to get about 8 of the sensors so you can play with them and just in case one or two isnt working perfectly. Sometimes they get water in them if the particular Range Rover has been used for serious off-roading.

If your 6 pack of ale doesnt result in the desired sensors, just let me know and I will send you mine.

They should be relatively easy to adapt to the 911 suspension.... at least as easy as anything else.

Feel free to call me at 404-323-0173 --Sterling Skinner, a rambl'n wreck from Georgia Tech and a Hell of an engineer!

JackOlsen

Thanks, guys. My DL-1 will read variable voltage, and then do the sampling and averaging to make the measurements more meaningful. The Range Rover (or other) ride height sensors sound like a good idea. I'll go talk to the shop that works on my Jaguar and see if they've got any lying around.

I'm out of the country for the next two weeks, but I'll update you all then.

In the meantime, any more ideas are appreciated.