after a bit of a play on solidworks to analyse the brake pedal as detailed in the "book" i have come up with some interesting results



old profile results

this is the pedal assembly as detailed in the book, with 150 kg force applied to it
see this thread

The red area around the front face of the pedal (with the black arrow) is showing an area of concentrated stress

from what i can tell that "bend" is unnececary and weakens the pedal,

this is the results of the test if that "bend" is ommitted and a straight line is drawn between the pad of the pedal and the bump stop


results of new profile

this is the edited profile of the brake pedal (see the book for the original)


edited profile of brake pedal

can anyone see why such a modification couldnt be carried out? i cant imagine that they put that dip in for no reason, maybe for comfort? and ideas?

matt

There's no reason not to omit the bend.

It does give a little more room for the larger foot, but even the prototype has a constant curve from top to bottom.

It's interesting to see that analysis and compare it with the one I did which used a 300kg force as an ultimate test, which showed a buckling failure along the length of the pedal.

I once came upon a tractor round a country bend and stood on the middle pedal so hard that I banged my head on the roll bar, but it's still fine. I suppose it's all relative, and the good thing is that using FEA you can take parts to destruction and beyond without risk.

Now the serious bit.

You need a holiday, get out for a walk or go for a pint - Anyone who does stress analysis for "fun" has serious problems!

Cheers

Chris

" I banged my head on the roll bar, but it's still fine"

head or rollbar? how's the pedal

Caber

quote:

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Originally posted by chrisgI once came upon a tractor round a country bend and stood on the middle pedal so hard that I banged my head on the roll bar, but it's still fine.

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The pedals fine, the roll bar has dandruff on it and the head's never been much use anyway!

Cheers

Chris

Just put 10mm rad in the high stress point and all will be fine.

Regards

Jason

What's the factor-of-safety solidworks gives you for those designs? You need to determine your maximum design load (1500N would seem reasonable from the information posted in your other thread) and THEN add a generous factor of safety. This will be 5 or even 10x for such a critical component in the automotive industry. Remember your Solidworks model is an idealised result and doesn't model fatigue over many operations, nor take into account surface condition, corrosion etc etc. Also your restraints aren't totally realistic, nor is the perfect alignment of the load to the part (in reality you will have torsional load too).

Not trying to put down your efforts, but you need to be aware of all the factors that need to be taken into account. Fatigue life is a very important consideration for a component like a brake pedal and you need to apply a large safety factor unless you have total control over the material and all the factors mentioned above. You certainly dont want a single application of your design load to be ANYWHERE NEAR yielding the material at ANY point. As I said - 5 to 10x safety factor should be applied. Trimming weight off the brake pedal just isn't worth it unless you really know what you're doing with the design/FEA.

Liam

[Edited on 26/8/08 by Liam]

Liam, you comments are much appreciated,

I certainly realise that solidworks only gives a rough idea and any results should be taken with a pinch of salt

to be honest, if anything i am trying to add weight to the pedal, and hopefully make it a little easier to make

the restraints are admittedly, a little simplistic at best, i just used them to analyse just that small bit of the pedal with the bend in it.

Chris, in my defence cosmos is my new toy and i already had the brake pedal in solidworks and just wanted to have a play, not trying to pick faults, just as a matter of interest

and if anyone is interested, the second pedal design with a 150kg load has a factor of safety of 3 (minimum) with the simplistic restraints

thanks for your comments everyone

Matt

I wouldn't say take them with a pinch of salt - that package can be both useful and accurate - just be aware of it's limitations and that there is more to consider when designing a real-life component than response to a one-off ultimate load. Fatigue strength can be an equally, if not more, important consideration than ultimate strength.

You're not re-inventing the wheel designing a brake pedal - so check out existing ones on production cars. Those that are a simple sheet cut-out similar to the above will be a good 6mm or more thick and quite deep in profile too. There are plenty of more sophisticated but equally sturdy designs too - check out lotus elise pedals (mmm nice)



Have a look at what's out there and you'll get an idea of how strong a brake pedal is typically designed to be. I made mine kind of like an I-beam. Sheet cutout profile like the roadster above, but with front and rear strip faces for torsional rigidity. Certainly wont be worried about it buckling after a few panic brake efforts

Liam
Rescued attachment DSCF0018small.JPG

quote:

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Originally posted by LiamI made mine kind of like an I-beam. Sheet cutout profile like the roadster above, but with front and rear strip faces for torsional rigidity. Certainly wont be worried about it buckling after a few panic brake efforts

Liam

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Matt,
what effect does that stress have? Is it going to bend the entire pedal or is the pedal going to break or is it not going to do anything? It is interesting to see where the stress-points are, but I feel that this doesn't matter in this situation.
How is the stress with 2x3mm steel plate instead of 1x5mm?
cheers