Push Rod Load Cells

[proutyc]

Little off topic so not sure where I should have posted this, but hoping for some guidance.

We race cars similiar to V de V or CSR (depending on which side of the ocean) but are lucky enough to have open aero rules (ground effect tunnels etc etc). Therefore I was wondering whether anyone thought that using load cells off a something like an indy car would be of value as a downforce tuning devise and also for helping with car balance?

Good idea?

Just to put these cars in context, they are similiar to Juno, Nemesis, Radical or as we do it homemade cars (chassis was done in CAD and very simple suspension analysis freeware) so we not talking big budgets here.

Secondly if yes is it a s simple as connecting to my datalogger and measuring 4 lots of 0-5 voltage and calibrate the result using my corner weight scales?

Thanks in advance

[Jersey Tom]

Getting corner loads is certainly a potentially valuable thing.

Could also get a rough idea of this using linear pots to measure suspension travel (though you'll be neglecting shock loads, which may or may not be a big deal). Up to you, and your budget.

[proutyc]

Thanks Tom.

Yeah we did something similiar to that with linear potentimeters on my sister car when testing my new rear wing on his car this year and was good to see the change in ride height based on DF and acceleration.

Part of my logic for the load cells was that it should help with the balance too. Its been a few years since I have jumped in a car so having the data help me understand understeer or oversteer or the mixture of the two may be helpful too.

[DaveW]

I agree with JT. It is worth remembering that PRL are not the same as CPL (contact patch loads). They are the wrong side of hub inertia forces &, more importantly perhaps, suspension linkages are not necessarily orthogonal. Hence some part of the vertical load may not be transmitted by the push rods, & some part of the lateral &/or longitudinal load may be reacted by the push rods.

Any "lost" vertical load component can be effectively eliminated by calibrating the load cells in situ, either by using corner weight scales & manually cross-weighting the vehicle, or by using a multi-post rig. The latter can also be used to help to understand & set up the suspension.

[747heavy]

Secondly if yes is it a s simple as connecting to my datalogger and measuring 4 lots of 0-5 voltage and calibrate the result using my corner weight scales?

maybe in addition to the allready good advice povided by JT & DaveW, I would like to point out some possible poblem areas to you.

General speaking, I think it´s a sensible approach to what you want to measure (downforce).
If you only want to know your downforce levels, some filtering of the data is needed, to take away the effects of track inputs and inertia effects (load transfere during braking, cornering and acceleration etc.).
But this is "doable", and you will get valuable informations out of these four sensors (not only for aero development/setup) IMHO.

One thing, I would like you to keep in mind, is that loadcells and even more so "strain gaged" pushrods (most teams apply strain gages to the pushrods or rodends of the pushrods themselve) have some challenges.

Apart from "creep over time", temperature drift can be a serious issue with strain gaged suspension components.

Therefore keep and eye on your readings and do some plausibility checks from time to time, e.g. keep an eye on your total "weight" when the car is in the pitlane (@ operation temperature).
If your car is xxkg heavier (with the same fuel load) at the end of the day sitting in pitlane, chances are that you see the effects of "drift&creep" in your loadcells/pushrod sensors.

I have seen more then ones, teams (even on pro-level) getting all excited over their latest aerodevelopments, just to find out later, that their "gains" where coming from measurement errors from within their data logging system.

some quick reading on the topic can be found here.
http://zone.ni.com/devzone/cda/tut/p/id/3432#toc0

it´s possible to compensate for it, just wanted to make you aware of the problematic to avoid some pitfalls.
If you use comercial loadcells for your measurements, chances are, that they allready compensate internally for the above mentioned effects.
But they come with a price tag as well , and are rather bulky sometimes.

Good luck

[marcush.]

I can only underwrite 747h views .Having done force measurements on small rods in the engine bay area near a turbocharger one of the challenges was to get a decent temperature compensation.
Usually you do that by having a copper wire installed with the Straingauge but this leads to its own problems when time effects overlap so in the end it was really a matter of measuring parts temperature near the straingauge and relate the straingauge output to the part temperature which brought some useful loadmeasurements.I´d guess a hub or pushrod application does not face enourmous heat changes but still the delta t between hot and cold will definitively have a big impact on straingauge output.

[proutyc]

Many thanks to the four of you. I was hoping one of you would chime in with insight but am very appreciative that you have all supplied valuable input. I value you guys as some of the most knowledgable people on here and the people I trust with data.

I'm thinking of using some used Indycar ones as they appear to have a built in amp and temp compensation.

I'm really trying to use these to help create an optimum ride height and rake levels to maximise my LD ratio's for different tracks. I hope I can help answer the following.

1. When should I use front fender extractor (gills)
2. Best front ride height maximise LD
3. Rake and with rake at what speed. What I mean here is do I run a softer rear 3rd spring so that it compresses and allow optimum rear aero for whatever that tracks fast corner allows.
4. My car run an Naca Eppler wing profile so it be great to maximise its efficencies
5. End plates for both front and rear again LD driven.
6. Maybe understeer and oversteer characteristics to can be defined

As you can see I'm keen to test a number of things and I think that using these cells would create more insight and better value for money than using some CFD programs

Keen to understand if there are some other metrics you believe I may find interesting using these

Thanks again.