Wheel Slip Indicator?

[bbarn]

For what it is worth...

Couple of things to consider (if you haven't already). If the tires are the same size/type (extremely) identical, it is very easy to build one of these devices. Consider that the two wheels you are measuring will change size throughout the run, if the tires are different materials, widths or thicknesses, they will grow at different rates.

In some examples on streamliners, you will have turned aluminum wheels on the front and "traditional" rubber wheels on the drives. The drive wheels will grow at a faster rate and more by percentage than the aluminum wheels will. The different rate and amount of growth will show as wheel slip.

At lower velocities, the rate of growth will be less of an issue than at higher velocities. When designing for the faster velocities, you may need a more sophisticated logic circuit with some tire growth data to be used for making adjustments.

In the extreme example, the 28.5" MT Bonneville tire will grow 15% over static height at 400 mph while an aluminum wheel will grow at a much lower rate. If you do not compensate for the growth rate of the two tires, the faster you go (even with zero slip), your indication will be that wheel slip is occurring.

Even with two traditional wheels, running a Goodyear on the front and a MT on the rear, they will more than likely grow at different rates. It will not be as extreme as the turned aluminum/MT combination, but it will be different. Since you want to keep wheel slip to a small percentage (3-5%), the minor differences in growth rate might wreak havoc on your indications without applying corrections.

[Peter Jack]

If the rear tires are growing more than the front and the car is a rear wheel drive car, the circumference of the rear tires will be larger and assuming no actual slippage, the tire slip will in fact show as a negative number because the rear tires will turn at a slower rate compared to the fronts. (I think my old teachers used to refer to that as a "run on sentence".)

Pete

[bbarn]

If the rear tires are growing more than the front and the car is a rear wheel drive car, the circumference of the rear tires will be larger and assuming no actual slippage, the tire slip will in fact show as a negative number because the rear tires will turn at a slower rate compared to the fronts.

Pete

You are very correct sir - negative slip would be indicated. Unless you know the rate of growth/difference at a given speed to compensate for it, your indicator will be useless.

[robfrey]

Front tires will also probably grow.

[blackslax]

I realize that tires grow and such. That is more of a symantic arguement. 

I was merely trying to say that for a couple hundred dollars, some good thought, and a clever nerd, it can be easily done.  as for the growth, a $100 plc could be used to control the whole thing and formula to correct growth; be it linear, logrythmic, boolean etc. coulde be programmed in. 

All that is needed is some mental and physical sweat equity, not a $5000 motec.

[donpearsall]

I have been working on a prototype since I started this thread and realized that there was nothing off the shelf and cheap. I should have something to show before Speedweek and if it is functional I will offer it for sale. I will keep you updated.
Don

[saltfever]

Don, I realize that as soon as you start something like this, the "add functionality list" grows almost exponentially. However, please consider a speedometer. Don't laugh. The resolution on a tach is terrible. One or two tick marks on the tach can be as much as 15mph. To be able to distinguish 50 or 100rpm at speed, is impossible. However, for licensing runs you want to be able to guesstimate a few mph. The tool you are designing will have far better resolution than a tach if it is to discriminate small differences between the front and back wheels. You are automatically building in precision that is needed. Why not take advantage and provide not only slip but speed?  The Apollo GPS I have used was not useful but maybe newer units are better.

[donpearsall]

That's a given! As a programmer, I am all too much aware of "feature creep". Here is the exterior design & LCD layout.
Don

[bbarn]

That's a given! As a programmer, I am all too much aware of "feature creep". Here is the exterior design & LCD layout.
Don

Wow, looks a lot like what I had designed! 

Guess I'll have to do the HUD display and integrate it with the other engine indicators just to be different!
http://www.microvision.com/vehicle_displays/head_up_displays.html

Watch out for the creep, it has cost me $100s of thousands in implementation fees over the years. Programming would be a lot more fun if it weren't for the end users wouldn't it?

[fredvance]

Will it store/log its data?

[donpearsall]

Fred, the first version won't, because it is just an indicator, but that is something that will be a feature.
Don

[saltfever]

The LED layout looks perfect for me. Will you have a prototype at SW?

[manta22]

Our new Buick LaCrosse has a heads-up display and I love it!

Regards, Neil