Best way of meassuring downforce at race car

[Uwe]

Do you know where I can buy and what is best load cell to meassure downforce on race car?
Load cell can be install insted spring top hat or maybe at conection between car base and shock absorber..

Does something like this exist?

(I am not interested in CFD,I need real life values plus I dont know work with CFD,and I will first must make drawing of my car in CAD,which is impossible to do it 100% correct,so this option is too complicated and potentaily very inaccurate)

[Billzilla]

Try Aliexpress.

[Greg Locock]

Load cells like that do exist https://au.omega.com/subsection/low-pro ... cells.html .

The way we'd do it is to strain gage the suspension arms in their loaded directions, calibrate them in the lab by applying a load to the contact patch in 3 axes, and develop a matrix so we can sort out how much of the signal is due to each direction. This isn't perfect, but if we compare it with wheel force transducers we get sufficiently good results, and can then use normal wheels, and put the car through potholes and kerbstrike without risking the expensive and fragile WFTs.

[Uwe]

Load cells like that do exist https://au.omega.com/subsection/low-pro ... cells.html .

The way we'd do it is to strain gage the suspension arms in their loaded directions, calibrate them in the lab by applying a load to the contact patch in 3 axes, and develop a matrix so we can sort out how much of the signal is due to each direction. This isn't perfect, but if we compare it with wheel force transducers we get sufficiently good results, and can then use normal wheels, and put the car through potholes and kerbstrike without risking the expensive and fragile WFTs.

That will only work if shock absorber is at angle with suspensions arms,so when downforce increase, arms are in tension and stretch.
But if schok absorber is prependicular to arms(like road car often has at front suspensions), then for small arms angles almost nothing happend(very little compression or tension at arms) during vertical load caused by downforce

[NathanE]

Would it be simpler (from a measurement not calculation perspective) to measure suspension deflection and use that, combined with knowledge of spring rates, to calculate load?

[Uwe]

Would it be simpler (from a measurement not calculation perspective) to measure suspension deflection and use that, combined with knowledge of spring rates, to calculate load?

Problem is how messure small downforce values,if every wheel has only 5kg of downforce,imagine how small spring compression will be,how small is that angle at suspension arms..plus every bumps,braeking,acceleration,curve will cause suspension,spring to move..so I will need some software to averaged data

[Greg Locock]

That will only work if shock absorber is at angle with suspensions arms,so when downforce increase, arms are in tension and stretch.
But if schok absorber is prependicular to arms(like road car often has at front suspensions), then for small arms angles almost nothing happend(very little compression or tension at arms) during vertical load caused by downforce

Bending?

[Uwe]

That will only work if shock absorber is at angle with suspensions arms,so when downforce increase, arms are in tension and stretch.
But if schok absorber is prependicular to arms(like road car often has at front suspensions), then for small arms angles almost nothing happend(very little compression or tension at arms) during vertical load caused by downforce

Bending?

If put strain guage directy at shock absorber body(6cm diameter) ,will he notice deformation or it is too stiff?
Did you try it?

[Greg Locock]

no, bending of the arm under the clevis of the shock absorber. it's basically a scatter gun technique, stick lost of strain gages on, then define a correlation matrix to known inputs.

[Big Tea]

Would laser or radar to the surface not work? A reflection of a laser at an angle is multiplied at the receiver by the deflection angle ?

[Vyssion]

jjn9128 and I have actually written a tech article for the site already which talks about this.

https://www.f1technical.net/features/21963

[Tommy Cookers]

search Automotive section Engineering Projects on topic list page 9
for 2014 post originated by user name Belatti - titled 'Brake Pressure Sensor based LOAD CELL'

iirc he found this to be the answer - and did the same job as you for $50 or something
(Argentina being economically difficult)

[Uwe]

jjn9128 and I have actually written a tech article for the site already which talks about this.

https://www.f1technical.net/features/21963

You think laser will be more accurate option than strain guage or load cell?

If road has even small bump of 2mm, laser will think downforce is increased,isnt laser good option only for very flat road like race track is?

[godlameroso]

jjn9128 and I have actually written a tech article for the site already which talks about this.

https://www.f1technical.net/features/21963

You think laser will be more accurate option than strain guage or load cell?

If road has even small bump of 2mm, laser will think downforce is increased,isnt laser good option only for very flat road like race track is?

So you take time average. You do a lap, and plot average ride height, make aero adjustment, plot average ride height. If average ride height decreases over a lap, you can be confident you increased downforce.

[Uwe]

jjn9128 and I have actually written a tech article for the site already which talks about this.

https://www.f1technical.net/features/21963

You think laser will be more accurate option than strain guage or load cell?

If road has even small bump of 2mm, laser will think downforce is increased,isnt laser good option only for very flat road like race track is?

So you take time average. You do a lap, and plot average ride height, make aero adjustment, plot average ride height. If average ride height decreases over a lap, you can be confident you increased downforce.

Yes but track time is very expensive,so I must test aerodynamic modifaction at road first.
If road is not 100% flat or it has small stones on it ,laser will read wrong values..
Isnt it?