quote:

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i hate to say this but..

be VERY wary of those (seeming, from the photo) small rod ends in bending on the upright pickups

this is meant as constructive criticism

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Thanks for the comment (don't worry, this is our first car so we're not really in a position to take offense at any valid criticism)

Yeah, I guess those rod ends in bending are reprehensible, and the judges will have a field day with it (wait till they see the suspension pickups!), but they're 3/8" and will have a much shorter moment arm once the suspension is decently aligned- in theory they should hold up fine. We went with this setup because AFAIK it offers easier packaging and fabrication than sphericals, and that was a priority for us.

Marc
www.enaf1.com

high quality 3/8" RE's should last a while

just keep an eye on them hey, or you might lose a front corner

my reccomendation is to check they are not bent as much as possible, also pull em out and fluoro magnetic test 'em every 5 hrs of driving until you're confident.

regards

Frank

I have to go with Frank on this one. Make sure you did your maths correctly on this one fellas, rod ends in bending are not the best idea.
Originaly we thought they would last but then had 4 guys re-do the sums on such a topic to discover that they would go buy-buy in the first hard braking corner.

Good luck, the car looks good!

Dusko
Curtin Motorsport

Just wanted to add my $.02 regarding the rod ends in bending issue. We designed for 1/4" rod ends everywhere last year, and I managed to bend the outboard fronts after doing some braking tests. We replaced 'em and kept on testing until I broke a corner off the car. BAAAAAD. Anyway, we switched to heavy duty 5/16" shank ends on the outboards (which thankfully didn't require an upright redesign)and went back on our merry way. These held up, although the rears would bend after a lot of driving because they were (gasp inserted here) screwed out so far for static camber gain. Never broke anymore of 'em though, even after we lost a rear wheel and added massive crankcase ventilation to the F3 via a large hole in the oil pan. Moral of the story: 3/8" rod ends should live, but you will join me in suspension design Hell in the eyes of the judges!

Lacy Lodmell
Vandals Racing 2003
University of Idaho FSAE

quote:

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Originally posted by Lacy Lodmell:
Just wanted to add my $.02 regarding the rod ends in bending issue. We designed for 1/4" rod ends everywhere last year, and I managed to bend the outboard fronts after doing some braking tests. We replaced 'em and kept on testing until I broke a corner off the car. BAAAAAD. Anyway, we switched to heavy duty 5/16" shank ends on the outboards (which thankfully didn't require an upright redesign)and went back on our merry way. These held up, although the rears would bend after a lot of driving because they were (gasp inserted here) screwed out so far for static camber gain. Never broke anymore of 'em though, even after we lost a rear wheel and added massive crankcase ventilation to the F3 via a large hole in the oil pan. Moral of the story: 3/8" rod ends should live, but you will join me in suspension design Hell in the eyes of the judges!

Lacy Lodmell
Vandals Racing 2003
University of Idaho FSAE

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That's what we wanted to hear.. :P

Seriously, we know that it shouldn't be made this way, but at the time we built this, we were only 17 y-o, hence severely missing experience. Unfortunately, we don't expect to have time to change the tabs design, but if we do, be sure we'll do so.

Thanks for the comments guys!

Didier Beaudoin
Team Leader -
École Nationale d'Aérotechnique

We have run rod ends before, 3/8" on the top and 7/16" on the bottom of a pushrod suspension system. We have never seen one break or bend at all and have driven the car quite a bit. Personally I think that they do work, however you could make it lighter by using the spherical bearings. Again, I am fully aware of the problem with them, however if it truly was a safety issue I would think that the rules would be changed accordingly to ban their use.

Brent

www.ucalgary.ca/fsae

Looking at your pics and we noticed that the plumbing for you brake system looks a bit odd. First, the aluminum fittings typically are not used due to the fact they can burst(look into steel). The fittings may survive however you are asking more of them then they are designed for. Also, we were wondering if the hard line you are using is aluminum due to its high luster in the pics(this would also be a no, no).

Finally, the fact that you are using rubber flex line, may cause you to lose some pedal. Smaller diameter hard line (of the ferrous variety) would also decrease your loss of pedal.

Just trying to prevent an accident.

The 40oz Killer!

1/4" sphericals all round are perfectly adequate (rod ends are fine inboard). We have had no problems in three years.

You just have to design the load paths correctly. Are wishbones are 16mm od 0.9mm wall thickness mild steel BTW.

Ben

University of Birmingham
www.ubracing.co.uk

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Originally posted by Wizard:
Looking at your pics and we noticed that the plumbing for you brake system looks a bit odd. First, the aluminum fittings typically are not used due to the fact they can burst(look into steel). The fittings may survive however you are asking more of them then they are designed for. Also, we were wondering if the hard line you are using is aluminum due to its high luster in the pics(this would also be a no, no).

Finally, the fact that you are using rubber flex line, may cause you to lose some pedal. Smaller diameter hard line (of the ferrous variety) would also decrease your loss of pedal.

Just trying to prevent an accident.

The 40oz Killer!

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I beleive our aluminium tubing is sutable for this application. It is in fact aluminium lines taken directly from aeronautics. It is used on hydraulics systems on aircrafts and it can stand up to 1000 psi easily. The only trouble we have with them is packaging. Anyone using lines like ours?

As for the front lines, they aren't rubber; they're actually Aeroquip steel braided hoses that can resit to a 1500 psi pressure, so I'm not expecting them to break anytime..

Thanks for your concern.

Didier Beaudoin
Team Leader -
École Nationale d'Aérotechnique

Didier,
Our brake system pressures run about 1300psi under "normal operation", and all of our brake system components are rated for 3000 as far as I know.

Also, Carroll Smith advised against using the aluminum hard line. Apparently he'd seen it fatigue and fail at an inopportune time, and the weight savings aren't very much considering the added risk.

University of Washington Formula SAE ('98, '99, '03, '04)

quote:

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Originally posted by Denny Trimble:
Didier,
Our brake system pressures run about 1300psi under "normal operation", and all of our brake system components are rated for 3000 as far as I know.

Also, Carroll Smith advised against using the aluminum hard line. Apparently he'd seen it fatigue and fail at an inopportune time, and the weight savings aren't very much considering the added risk.

University of Washington Formula SAE ('98, '99, '03, '04)

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Hmm.. You got me concerned now... AFAIK, our break lines can be heat treated to stand up to 3000 psi, and the number I told about the flex hose was on the top of my head. I think it can support more than 1500 psi..

But if Caroll Smith told it wasn't recommended to use hard lines, we'd better get them off... I'll talk about it to my teammates.

Didier Beaudoin
Team Leader -
École Nationale d'Aérotechnique

Denny,

Our normal operating pressure is 750-800 psi, at least in theory (100-120 pound braking force on the pedal, which is about what Bob Woods recommended as a guideline on the old Escribe list, I believe). The aluminium lines we're using are rated up to around 1200-1500 psi in untreated form and like Didier says, heat treating might be a good idea- a panic stop would probably bring the pedal force up to 200 pounds or so and that's not a very good time to have your lines bust up.

I wouldn't be too concerned about the flex hose though, IIRC they will hold nearly 2000 psi, which is enough for a panic stop.

Thanks for the info guys-

Marc
ÉNA

I looked through the Smith books, and he actually does recommend aluminum or stainless hard lines in Nuts, Bolts, Fasteners, and Plumbing. "If it's good enough for the FAA, it's good enough for me", p.208.

I remember now what he remarked on our '99 car, that the brake light switch was heavy and only supported by the aluminum hard line, which could lead to vibration and fatigue. So that's an installation problem, not a general ruling out of aluminum hard lines.

Your system pressure will vary with tire size, rotor size, load transfer, piston sizes, etc, so those numbers look reasonable.

University of Washington Formula SAE ('98, '99, '03, '04)

Yep, we have largish front rotors and some serious overkill on the rear brakes, so we might not need that big of a hydraulic pressure.

Been a while since I've done the calcs but I believe that was corresponding to a 1.2G deceleration. Then again there's a massive amount of guesstimates involved, so I'm eager to see if the math holds up in real life (that won't be anytime soon though, considering the two feet of snow that just crapped down on the city)

While we're on the subject, has anyone come up with approximate μ data for common FSAE brake pads? We're using the Wilwood Polymatrix D compound and I wonder how it compares to the values mentioned in Tune to Win.

Marc