Space Frame Chassis Torsional Stiffness

[Duncan Manning]

I am writing to you from Cardiff University, UK. I am currently involved in the design and testing of a tubular space-frame chasis for our entry into the 2004 SAE Formula Student race series. One of my tasks is to design and build a torsional test rig which will allow us to measure a practical stiffness value for the chassis. After much searching I am struggling to find any information on similar projects which have been carried out in the past. If anyone has any information about such test rigs (which I am sure must exist!) then I would be very greatful in receiving it! Thankyou, Duncan.

Duncan Manning

[Duncan Manning]

I am writing to you from Cardiff University, UK. I am currently involved in the design and testing of a tubular space-frame chasis for our entry into the 2004 SAE Formula Student race series. One of my tasks is to design and build a torsional test rig which will allow us to measure a practical stiffness value for the chassis. After much searching I am struggling to find any information on similar projects which have been carried out in the past. If anyone has any information about such test rigs (which I am sure must exist!) then I would be very greatful in receiving it! Thankyou, Duncan.

Duncan Manning

[Angry Joe]

This is how we did it, and I think it is the best way.

Fully assemble the suspension of the car to the uprights, but either replace the shocks with solid links or find a way to lock them in place. Clamp three of the suspension corners on solid surfaces at the uprights, hang a load off the fourth, and there you have it! Measure deflection with a dial indicator or something.

Make sure your engine and any other structural parts are in the chassis.



Lehigh Formula SAE Alumni
Team Captain 2002-2003

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[awhittle]

But Joe, how do you know when you have the correct answer?

Remember to have one corner (say the right front) on a sliding support so that you allow that corner to move laterial and longitunial as you measure vertical deflection on the left front. Preload the left front with some load to take up the slop, and then add more weight and measure again. 1500 ft-lbs/degree would be about right with a loaded car weight of about 700 lbs. 2000 woiuld be better.

Hope this helps

AW

[Angry Joe]

We did eliminate preload by lightly loading the constrained suspension. All three other points were clamped. Did this affect results? Probably, but I think we got pretty close, and that's as much as you can ask for without spending ridiculous amounts of time.

We got 1700 ft-lbs per degree. Respectable, and in no way inflated (I'm not knocking anybody, but I have heard some very questionable methods for testing this)



Lehigh Formula SAE Alumni
Team Captain 2002-2003

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[dancin stu]

I designed and fabricated a rig last year while on my placment, used for testing road cars. if you want any details i can give you some off the board.

[Duncan Manning]

Stu - That would be superb!!! Do you have any picture of the rig that I could look at?

Duncan Manning

[dancin stu]

Yeah, can sort something out, email me on stuartchamberlin@yahoo.co.uk and i'll discuss it some more