Formula SAE pics

[FG!!]

2k frames per second, right? That price sounds high. Let me know if you want a reccomendation for an alternative source.

Our school went with Motec with the data logger. I'm pretty sure they're still using it five years later, so it's a good investment and the digital readout is professional looking. That was before the tec3 came out, though. It seems like a pretty good system for a fair ammount less.

[LaureltheQueen]

Laurel, I really like that idea of putting on Auto-x's to make money. Now I just need to find enough tarmack.

How about the school parking lot on sundays? Sunday is the only day that autocrosses are held around here!

[93forestpearl]

We have a bunch of small lots, but I think the one in front of Darand might do the trick. I'm gonna look into it.

FG!!- this camera does 200K frames per second. two hundred thousand. At an amazing resolution. Each frame can be a whole megabyte. It stores the video on the machine untill you send it to a computer after you are done recording. IT was pretty amazing. But it doesn't take much to make a gigabyte video file.


As of now we are just gonna go with the Power Commander be cause we don't much funds to work with (zero as of right now). If I can get AMSOIL to come through, since they are based in Superior, WI, we would have a decent chunk of change to work with. We are lacking a lot of stuff that other schools have. We don't even have a pipe bender.

I haven't looked at the Megasquirt yet, I'll have to check it out.

[BAC5.2]

most bike frames using air shocks have what, a ~2.5:1 leverage ratio? not sure what leverage ratio you will be going fo rwith cantilever suspension but I'd assume its close.
Offroad terrain produces more hard hits to bottom the suspension, and generally a lot more harsh shock movement than a FSAE car will see on nice smooth tarmac. seems to me that the main suspension movement will be a lot less harsh of hits than a mtb will see, and mainly from braking and cornering forces.
the car will weigh ~500lbs/4=125 pounds per corner. so the air shock will be running at a lot less than maximum psi, and under less harsh conditions than normal, so durability is *probably* not going to be an issue.
so I disagree that the vehicle will be putting a higher load on the shock than the typical mountain bike. the coil vs air battle more seems to be an issue of weight, tunability, and cyclic load affecting spring rate as you mentioned. but for an autocross of like 30 seconds, I would doubt that excessive heat is going to come into play. now for something like the baja cars, coil suspension is going to be far superior.
93forestpearl, what are the autocross times, and what is your opinion of the suspension hits the car will take? what is the weight bias of the car?
BAC5.2, what kind of weight savings could actually be seen by using air shocks over coils? I dont really keep track of the weight of air shocks. both my bikes have progressive 5th elements, hell Im not even sure what they weigh.

Yea, the car only puts 125lbs on each corner, but what about weight shift and transfer? What happens to that 125lbs when you get full on the brakes, trying to haul a 500lb car to a stop?

A coilover will be a better option, and well worth the weight penalty, IMO.

My downhill bike had a leverage ratio of about 2.75:1.

The swinger will give you great flexability. You can tune for almost any circumstance, and instead of having a linear spring rate, you can have a progressive rate.

Why is that good? Lower static spring rates (lower rating on the coil). Why is THAT good? GREAT bump sensitivity. What does THAT mean when the going gets smooth? INCREDIBLE body control.

Picture this. You set everything up based on the curb weight of the vehicle. Hop into the car, and adjust preload (sag). At this point, you can push down on the car, and it becomes more difficult to compress the suspension, the further down you push. Linear spring rate. You'll hit the bumpstops eventually.

That's fine, and you can increase spring rate to stiffen up the ride and keep the car off the bumpstops.

But you increase the spring rate, and you lose sag. Losing sag is not a good thing. Why? If you are riding at full extension of the shocks, and you nail the gas, what is the front end going to do? No compliance, means the front end is going to want to lift. Sag gives you the buffer to control the lift of the front end (by using rebound control).

So fix it? Well, you could add more suspension travel, and let a softer spring deal with progression.

But why would you do that? This just expands the range to cover the problems you are experiencing. You just now have to move a further distance to get things to happen.

OR, you could have a helper. Keep your spring rate low, but utilize the volume adjustment feature of the Swinger.

Add some volume to the chamber, and your well on your way.

Now, you compress the assembly, and it becomes exponentially more difficult to compress. Helping prevent bottoming out. So now, you can keep your spring rate low, and have an exponentially stiffening shock, that still allows you to sag a proper amount, retaining the buffer to control lift and extension during cornering (helping prevent the "peeing on the apex" syndrome common among cars).

So you have that motion taken care of.

That covers preload, rebound, and volume adjustments of the swinger. You've got 3 adjustments left.

You have the pedaling threshold adjustment. That is, you can adjust initial load required to begin compressing the shock. Kind of neat, you could tune lots of little things with this, but it's likely that you'd want to leave this chamber empty and not use this function. It wouldn't really help anything, with the loads your experiencing anyways.

You have the most important adjustments next.

High and low speed compression.

NOW, you can tune for low-frequency movement (accelerating and braking forces would constitute low-speed movement), and high-frequency motion (bumps in the road, and such).

Kinda neat!

The Swinger Air only has 4 adjustments, none of which are compression related. Fox makes air shocks that have compression adjustments, but Fox rear shocks tend to be less reliable. Like I said, I've serviced a TON of FLOAT rear shocks.

There's a TON of possibility for tuning with the coilover shock, and you don't really need to worry about cyclic heat loading, like you would with an air shock.

As for Megasquirt, you could probably build the unit for around $200 or $300 or so.

And why is your motor going to taper off at 10k+? Gixxers don't make peak power until well above that.

Oh, and yes, motorcycle transmissions ARE dogboxes. No synchros, just clunk it into gear, and your good to go. Downshifting, a clutch should be used, but for upshifting just lift throttle and bang it into gear. It should be durable enough for a few races if you really beat on it. You might want to consider stock piling a few Gixxer trannies if you can. They can usually be found for cheap in the spring and summer. That's when people wreck most often.

[93forestpearl]

With the restrictor, most teams have reported that they just cannot pull enough air through that 20mm hole for the motor to be effective after 10k. That is why we're working on a tuned-port intake to maximize our usable powerband. Same goes with the 4-2-1 header.

I think I might add a little anti-squat to the rear suspension, but I'm not gonna put any anti-dive in the front. With only two inches of travel, its not that critical. With our weight biased slightly to the rear, transfer to the front won't be huge like a front engined production car. Ever wonder why Porche's have such good stopping distances?

I still need to decide on a pitch center for the car. I need to keep it at the CG or higher or the pitch moment will be huge, which is bad.

So yea. With the inboard setup that has the pushrod and a rocker, I can have 2" of wheel travel, but use the shock's full travel. There will be a leverage ratio, of which I haven't decided on yet. Like I said before, I'm mainly working on the geometry untill I find some loot, although I'm pretty much where I want to be in the front. The software does help figure all of that out, but trying to learn what people take ten years to learn in just a couple months is pretty daunting. Especially with 13 engineering credits, a job, and other shit to design for this car. Thank god I don't have a girlfriend.

I'm still trying to get ahold of the FSAE tire guy at goodyear. I've got some negative camber under bump, roll, and steer, but I need to know how much is best. I'll be able to adjust the static camber with everything built, but that will compromise other things like my kingpin inclination, scrub, and so on down the line. Suspension is always a huge compromise in every direction. Its amazing how an 88MB program can cost $1800, although we didn't pay that for. If you are a shop trying to set up a cars suspension, it would be invaluable. Next summer I'm gonna fix the geometry on my buddies GSR, so it is proper with the car lowered.

Gotta go help put in the new clutch in the motor.

[BAC5.2]

Why only 2" of travel? You don't think that will limit your tunability? You would have almost zero effective sag. Is that what FSAE cars usually have? Aren't you worried about bouncing the bumpstops?

Even MotoGP Motorcycles have more travel than that, and MotoGP courses are smoother than a babys ass.

[93forestpearl]

Teams have pushed 1.8g in these things. They are very stiff. 1" bump and 1" droop. Our wheelbase is only 70 inches, but the track width will be 60". There is a fair amount of points in the tilt-table. But anyways, we want to keep roll to a minimum. As in less that one degree or there abouts. Therefore we can't have alot of travel at the wheels. We wouldn't be able the be that low to the ground either. The nose can stick up to 18" past the front of the tire.

The suspension on F1 cars only moves when they hit those curb things (whatever).

Check out this video (23MB) These guys have a nice car.

http://dilbert.cen.uiuc.edu/soc/sae/for ... promo2.mov

[93forestpearl]

We set the engine in there, at about where it needed to be, and noticed the second to last member on the top rear of the frame needes to come out since its in the chain's way. Also, the design of the rear portion is inherently weak because there is no triangulation back there, just a box. So we need to redesign a lot of the backend, and we are going to make the motor a stressed member of the frame. I just wish we were'nt using mild steel, this thing is really gonna be a pig.

Some dipshit took off the throttle bodies and smashed one of the clips for the injectors. That put me in a bad mood for a while.

In my arena, I was revising some drawings for the a-arm ends. We are gonna get going on some carbon tubes. They are gonna be pressure molded inside either pvc or copper pipe. We coat the pipe in some thin wax so it doesn't stick, lay the carbon up inside, run a surgical tube through it, and dial up some air pressure. We need one layer with the weave at 90/0 degrees to the axis and two more at 45/45. We have a pretty good sized roll of carbon in the material science lab so we don't need to buy any, which is nice.

I'm curious as to what the assembled arms will weigh. I'm trying to make the ends as small as possible. At 1.5g, there would be roughly 750 lbs of force between the two. But at 4g from a decent impact, that would be 2000lb. I saw a news special one time where this guy had a g-meter on the suspension of an exploder. When it hit a pothole about 6in deep it recorded 7g. I'm thinking we won't come anywhere near that. Espcially with so little unsprung weight. I'd like to find the young's modulus for carbon, but I can see it being a pain in the ass. thank goodness for Catia.

[skid542]

I pressume you have checked www.matweb.com for young's modulus of the carbon?

[FG!!]

yeah, that frame could use some improvement. your belt line is way way low. i would check your torsional stiffness. they always like to hear about that in the design review anyway.

[93forestpearl]

I ordered an Advanced CAD/CAM book for Catia the other day. When I get that, I should be able to figure out how to do some FEA on the frame and all the other parts I'm designing. My buddy found a copy of Catia, but so far cannot find a crack.

[FG!!]

Alot of grad students require FEA for their work, maybe check with your department's administration to see if you guys have any seats. I heard Catia wasn't very user friendly, but i've never tried it. I learned fea on ANSYS, which was hell. I've since tried the solidworks and unigraphics fea plugins and they are extremely intuitive, no training required (besides learning about convergence and a few other basics.)

[93forestpearl]

Solidworks is made by Dasault (sp) systems, as is Catia. Catia was really intuitive as well, I feel. Definately much easier than Mechanical Desktop. Catia makes it really easy to go back to drawing of any plane to alter or add to it. I guess that is what I appreciate about that particular program. I just need to figure out some FEA.