Suspension kinematics...

[Jersey Tom]

This is an engineering degree program, and Matlab is more or less just used as a calculator?

In any event, doesn't need to be Matlab. There must be some commonly used programming language in the department. Could do it in any variety of languages. I suppose you could even do it in Excel.

[LFR1Legend]

yeah we are taught the basic MATLAB data interp (Newton-Raphson, spline, ect ect) but when it actually comes down the application part there is not much help. It's a pain! So I'm trying to find ebooks and all to teach myself. I thought about actually taking the Excel/VBA route but thats going to be a lot for me to do and still design and build this car. Not enough hours in the day!!

[Jersey Tom]

Well.. no matter how you do it.. it's pretty simple.

Write some equations out..

Sum of forces (SAE y-axis) = blah + blah + blah ...
Sum of moments (SAE z-axis) = blah + blah + blah ...

For which, given a set cornering condition, your only real independent parameters are steering angle and sideslip angle.

For that given cornering condition you know sum of forces = (whatever) and sum of moments = 0 [steady state].

Two equations, two unknowns.. solve it up. Can do it in Matlab, in Excel as a goalseek, or in whatever.

[LFR1Legend]

Thanks for the help JerseyTom, I think I've got it figured out....now to make some sort of GUI and make it monkey-proof for the team in the future (I'm thinking just use MATLAB's GUIDE product--probably a lot more code and junk involved with it but shouldn't require a lot of time). Thanks again though!!

[The_Man]

Thanks for the help JerseyTom, I think I've got it figured out....now to make some sort of GUI and make it monkey-proof for the team in the future (I'm thinking just use MATLAB's GUIDE product--probably a lot more code and junk involved with it but shouldn't require a lot of time). Thanks again though!!

I think Matlab is way simpler than that.

[scarbs]

From my discussions with Technical directors any analysis of front suspension is all but pointless. The cars have such a surfeit of front end grip, they can afford to throw away the book on kinematics in favour of wind tunnel results. The front suspension movement is minimal the compliance of the front tyres counts for more than geometry of RC\IC positions and camber change curve. They will point to the rear suspension as a better insight into how to control a tyre, but even then the diffusers demands to place wishbones in a cascade behind the diffuser means that even then the set up is compromised. Equally there’s a lot of other kinematics going on, with KPI, pushrods mounting on the uprights, antidive\squat and ackerman.

From what I’ve been told on flexures is their pivot is effectively taken as the centre of the flexure

I’ve not got set up sheets to confirm, but I believe I’d 2-degrees of static camber is more likely

[The_Man]

First we threw away the Roll centre concept saying that it is a bunch of imaginary lines that we throw in the air and has a diminishing significance anyway due to the super stiff race cars. Now its disappointing throwing away the kinematics book, feels like so much has gone to waste.

So what is really done the wishbones are basically placed where the direct air flow the best? This probably does explain the huge variation in the location of roll centres in Formula One cars.

Aside: Can anyone please point me towards some good reading regarding flexure joints might be useful for an other unrelated project I am working on. I goggled but always ended up with stuff about orthopaedic flexure joints.

[mep]

I have searched now for some time to find some proper photos of older F1 cars and found those.



For me the McLaren MP 4-4 shows a close to ideal IC position on the opposite site of the car with low suspension pick up points on the chassis.
The Ferrari is more a compromise for good aero with a high nose and proper kinematics with a single keel suspension layout and parallel wishbones.
The modern no keel layout seems to have just aero advantages with a high nose and clean surface under the nose with the downside of a low RC and positive chamber gain under roll and bump.
It is what scarbs also says, suspension design driven by aero design these days.

From my discussions with Technical directors any analysis of front suspension is all but pointless. The cars have such a surfeit of front end grip, they can afford to throw away the book on kinematics in favour of wind tunnel results. The front suspension movement is minimal the compliance of the front tyres counts for more than geometry of RC\IC positions and camber change curve. They will point to the rear suspension as a better insight into how to control a tyre, but even then the diffusers demands to place wishbones in a cascade behind the diffuser means that even then the set up is compromised. Equally there’s a lot of other kinematics going on, with KPI, pushrods mounting on the uprights, antidive\squat and ackerman.
From what I’ve been told on flexures is their pivot is effectively taken as the centre of the flexure

I’ve not got set up sheets to confirm, but I believe I’d 2-degrees of static camber is more likely

Have you asked that just recently or some time before?
It would be interesting how much the suspension moves vertically and how much tha chassis rolls at the front and at the rear, especially at the rear, because you can see the movement in onboard views.
KPI, antidive/squat, ackerman is hard to analyze just with some pictures.

[Jersey Tom]

Aside: Can anyone please point me towards some good reading regarding flexure joints might be useful for an other unrelated project I am working on. I goggled but always ended up with stuff about orthopaedic flexure joints.

There's nothin to read, man. It's a beam that bends. Simple concept. I have a flexure A-arm off a Lola champ car.. the flexures add surprisingly little to the wheel rate.

Manage the buckling in compression, and the fatigue in bending.. and you're set.

Easy.

[Conceptual]

mep,

F1 composite A-arms are attached without pivot joints (they use "flexures"), and thus are designed to be flexible suspension elements. They are not like conventional steel tube A-arms with spherical joints at the inboard/outboard attach points, and thus would not be subject to the same kinematic motions under bump and droop.

Other comments:

- 5 degrees of negative camber is normally a lot of camber. But based on the wear patterns those front tire treads show, it doesn't appear to be a problem.

- the parallel geometry of those upper and lower front A-arms would result in very little camber gain under bump, which would normally affect braking stability. But with 5 degrees (or whatever?) of static camber, maybe it's not an issue.

- It's my understanding that most suspension travel on an F1 chassis is due to the tire sidewall flexing. Care to try working out the relative chassis motions due to this tire sidewall flexing?

Regards,
Terry

One has to wonder if the 5 degrees of camber might be done purposefully to reduce the effective width of the front tyre. With all of the complaints about them being too wide, perhaps the teams have compensated by running ALOT of camber?

Thoughts?

[Jersey Tom]

mep,

F1 composite A-arms are attached without pivot joints (they use "flexures"), and thus are designed to be flexible suspension elements. They are not like conventional steel tube A-arms with spherical joints at the inboard/outboard attach points, and thus would not be subject to the same kinematic motions under bump and droop.

Other comments:

- 5 degrees of negative camber is normally a lot of camber. But based on the wear patterns those front tire treads show, it doesn't appear to be a problem.

- the parallel geometry of those upper and lower front A-arms would result in very little camber gain under bump, which would normally affect braking stability. But with 5 degrees (or whatever?) of static camber, maybe it's not an issue.

- It's my understanding that most suspension travel on an F1 chassis is due to the tire sidewall flexing. Care to try working out the relative chassis motions due to this tire sidewall flexing?

Regards,
Terry

One has to wonder if the 5 degrees of camber might be done purposefully to reduce the effective width of the front tyre. With all of the complaints about them being too wide, perhaps the teams have compensated by running ALOT of camber?

Thoughts?

...doubt it.

Honestly don't even know what you mean by "effective width."

[The_Man]

There's nothin to read, man. It's a beam that bends. Simple concept. I have a flexure A-arm off a Lola champ car.. the flexures add surprisingly little to the wheel rate.

Manage the buckling in compression, and the fatigue in bending.. and you're set.

Easy.

What material are these then usually? Aluminium/CF/Titanium?
Approximately how much freedom do these allow(like the angle through which it can flex)?

[riff_raff]

The Man,

If you're bonding to carbon composite, the metal of choice (due to galvanic compatibility) is normally titanium. Plus, titanium alloy has properties that make it an excellent choice for the bending stress/fatigue loading conditions that an A-arm flexure requires.

The reason flexures are preferred for A-arm attachments, is that they eliminate the varying joint friction that spherical bearings inherently have. This makes achieving a consistent suspension set-up easier, since the friction and dampening effects of the spherical joints is eliminated.

Regards,
Terry

[PlatinumZealot]

One has to wonder if the 5 degrees of camber might be done purposefully to reduce the effective width of the front tyre. With all of the complaints about them being too wide, perhaps the teams have compensated by running ALOT of camber?

Thoughts?

THAT IS EXACTLY WHAT I WAS THINKING!!!

[PlatinumZealot]

I am making an Excel file that tracks suspension movement..The movements are plotted in an excel graph. Sort of rudimentary at the moment, it will improve when I understand vectors better. I actually would be using MATLAB if I had went to classes when i was in school..

I have a question, When a camber is changed on a wheel, is there a way to find how much the tyre is compressed.. that is, the new contact patch location and the new lower ball joint height?

Looking on those F1 tyres.. makes me wonder if the cars are raised when you increase the camber or if it stays the same height due to the tyre compressing.