suspension for spool

[Marvel]

Hello,
I am in the process of searching different suspension set ups for different differentials.
The cost being major constraint
I was wondering if it is possible to use a spool while going with the conventional double wishbones upfront.
What all major changes i may have to do if i go with this option.
Also, is it possible to go without a differential and have the chain/sprocket set up connected to the axle?

[Marvel]

Hello,
I am in the process of searching different suspension set ups for different differentials.
The cost being major constraint
I was wondering if it is possible to use a spool while going with the conventional double wishbones upfront.
What all major changes i may have to do if i go with this option.
Also, is it possible to go without a differential and have the chain/sprocket set up connected to the axle?

[mech5496]

I'm not quite sure if you mean running a spool or a solid axle. If you mean just using a spool, you can definitely go with double wishbones... What you practically do is removing the differential and replacing it with what essentially is a tube/shaft. You will again need CV Joints of some type. Then you bolt the sprocket directly to the spool. This setup allows you to run a single spool-mounted rear brake, reducing weight and unsprung mass.
If you mean using a solid axle, you need to re-design the whole rear suspension. There was a really interesting car in FSAE Michigan in 2010 running a solid axle setup, but I do not remember which university that was (an orange/blue car with CVT, any help here?!). You might want to take a look there. also note that the lack of a differential will induce massive understeer especially during turn-in, at least with "conventional" suspension set-ups.

[mech5496]

Actually if you are interested in running a solid axle setup, you might want to take a look here:

http://fsae.com/eve/forums/a/t...25607348/m/781103883 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/781103883)

http://fsae.com/eve/forums/a/t...20865051#94620865051 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/80120065051?r=94620865051#94620865051)

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Marvel:
Hello,
I am in the process of searching different suspension set ups for different differentials.
The cost being major constraint
I was wondering if it is possible to use a spool while going with the conventional double wishbones upfront... </div></BLOCKQUOTE>
Marvel,

Your suggestion seems very similar to Rob Woods' "Uni of Buffalo" (US) car from a few years back. Search for more information on that car (there are countless posts, links, etc.).

Also look for info on Oz-Olly's "Uni of NSW, ADFA" (Australian) car, currently running, which uses beam-axles front and rear (see Harry's link above).

Most teams that have gone this way have been small (few members) and have "cost being a major constraint". Nevertheless, they have usually performed above expectation.

This simple beam-axle/spool type car has, IMO, huge potential in FSAE. However, like everything else, it will only work well if done right.

A new team taking this different route does not have much to copy, so you have to figure a lot of it out for yourselves. But if you post your ideas here, preferably as draft concept sketches, I will be happy to comment on what I see as right or wrong, and suggest changes. I am sure that others here will also offer useful advice.

For a start, I suggest you consider a rear spool as on the Buffalo car, together with a front beam-axle similar to ADFA's car.

Z

[Adambomb]

IMO a spool and solid axle are quite complementary. A solid axle setup can easily make best use of a spool's behavior. Combine the two and you have a very low weight, low cost, easy to build, reliable solution. I think that if pulled off properly, it could be quite competitive.

[mech5496]

Found the picks of the car I was talking about!


http://img705.imageshack.us/img705/4931/dsci0052b.jpg
http://img684.imageshack.us/img684/2353/dsci0053e.jpg

Turns out to be Buffalo's 2010 car, and IMHO one of the most interesting cars on that competition (together with Maryland).

[Offtopic mode on] Z, keeping "simplify, then add lightness" in mind, i would really like to see a car like Buffalo's, with simple straightforward solutions, but with a Jawa 500cc E85 engine packed behind drivers back with rearward leaning cylinder and 2-gear transmission - it will make a hell of impression, plus if well executed it would be really low cost and could kick some serious ass on a comp..... /[offtopic mode off]

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by mech5496:
... keeping "simplify, then add lightness" in mind, i would really like to see a car like Buffalo's, with simple straightforward solutions, but with a Jawa 500cc E85 engine packed behind drivers back with rearward leaning cylinder and 2-gear transmission... </div></BLOCKQUOTE>
Harry,

That is pretty much the "brown go-kart" concept I have been pushing for some time.

A simple chassis with only enough tubes to satisfy the regs, all masses inside the wheelbase, minimum number of ball-joints, etc., etc. I would probably over-engineer it, with larger than normal, high-quality bolts, BJs, bearings, etc. But it would still be very light, because minimal part count, and compact.

One of the big advantages of the Buffalo spool, as Rob has pointed out, is that they are high quality 7075 items that can be bought off-the-shelf, together with associated hardware, at relatively low cost. A result of the large speedway aftermarket in US.

However, even a De-Dion style beam-axle with chassis mounted diff and half-shafts makes a simple suspension. The "stressed" chassis can end just past the seat-back/main-hoop, like on the Buffalo car. A "Model-T" style front-beam, like on the ADFA car, only needs 3 or 4 chassis hard-points, again simplifying things.

And another big advantage of front and rear beams is the ease of feeding aero loads direct to the wheels. The wings or undertray can be fixed to any convenient points on the beams - simpler than trying to feed loads to uprights that keep wobbling about! http://fsae.com/groupee_common/emoticons/icon_smile.gif

(Hint: One way to do it is turn each beam into a wing...)

Z

[mech5496]

"Floating" undertrays....Hmmmmm...http://fsae.com/groupee_common/emoticons/icon_biggrin.gif That's exactly what I had in mind! Beam axles maintaining the same wheel camber regardless the chassis roll, undertray mounted to them and fully exploiting ground effect, as it can be set to a minimum distance from the ground, lots of downforce without much drag. Add some beam-monted wings if you want more! Now polish that thing a little bit (in your third car, as first goes without aero, second with it) adding composite and aluminum parts and trying to lighten everything up, and boom! http://fsae.com/groupee_common/emoticons/icon_wink.gif Now I have to go and found a University, as I really want to go that way (but our faculty will probably kill me if I try that now...http://fsae.com/groupee_common/emoticons/icon_biggrin.gif)

[Z]

Harry,

Yes, that is a good three year plan for a team wanting maximum reward from minimum money.

A three part car:
1. Front beam/wing, with wheels as end-plates.
2. Rear beam/wing, ~"~.
3. Streamlined driver's seat/tub/fuselage tying parts 1 & 2 together. (Oh, and "necessary ballast" screwed to back of seat).

If any rainy days over Xmas I'll try and do some sketches.

Z

[rjwoods77]

Z,

If you are going to draw it up here is how it will work cheapest,strongest and stiffest while leaving the most possible room for aero. I thought about how to make a dual beam axle years ago after I made designed our car and thought it would be a neat idea.


For review:

http://www.eng.buffalo.edu/Stu...ewsletters/May08.pdf (http://www.eng.buffalo.edu/Students/Organizations/sae/formula_web/newsletters/May08.pdf)

Our wheelbase was 64 inch. The rear axle centerline from the main roll hoop plane which was vertical was 19 inches. That places the front axle centerline at 45 inches from mail roll hoop plane. The front roll hoop centerline which was vertical was 9 inches in front of the front axle centerline. This makes the main roll hoop centerline to front roll hoop centerline dimension of 54". Our car had a lot of leg room as well.

Dual beam axle layout:

Subtract 4 off the wheelbase to get to 60" minimum which you can do by moving the rear axle forward by 4 inches. So instead of 19" you are now at 15". Assuming a torsion tube size of 3" (ACPT corvette aftermarket carbon driveshaft) you would need to move the front axle centerline forward by 9" to get to front bulkhead centerline + .5" to be tangent to front bulkhead (1.00 inch tubing) + 1.5" for half diameter of carbon tube + 1 inch clearance to front bulkhead tangency for a grand total of 12". Subtract 12" front axle centerline forward shift from the 15" rear axle centerline which leaves you with 3" from main roll hoop centerline to rear axle centerline. Use the same 3" torsion tube (again ACPT corvette aftermarket carbon driveshaft)in the rear with the same 1" +.5" torsion tube clearance so that the 3" OD carbon tubes both have a 1 inch clearance to the tangency of the main roll hoop and the front bulkhead.

Dual beam axle construction:

On the rear you use a 1.75" OD 600cc splined 7075 sprint axle that is $250. The 3" carbon torsion tube is coaxial to the rear axle and attaches to two birdcage much like we did albeit with a steel torsion tube on the 2008 car. Instead of a satchell link you would use a pure longitudinal 4 link just like a 600cc sprint car but use a mumford link instead of a j-bar. The longitudinal links would connect at the front roll hoop and maybe even on sliders to be super adjustable. Lay the dampers transversely and use the mumford link rocker arms as the damper rocker arms.

One the front since you are forward of the front bulkhead there is no need to make a convuluted u shape beam axle. Just use the 3" OD carbon tube at wheel centerline height that has a birdcage on each end. Each birdcage then has a live spindle ala dirt track cars bolted to it. Again four pure longitudinal links that connect at the front roll hoop. Also by having the beam axle a wheel centerline height beam it makes it super convenient to bolt the steering rack to the beam axle ala 600cc sprint car which gets it completely out of the way of the pedals due to its height. Again use a mumford link for transverse control and lay the dampers transversely and use the mumford link rocker arms as the damper rocker arms.

This would tie all the longitudinal forces into the main rollhoop, the rear tranverse/damper forces into the main roll hoop and the front transverse/damper forces into the front bulkhead. The driver would practically sit on the rear axle.Engine packaging would be a laydown longitudinal single cylinder with 3 speed or a cvt to single chain final drive (sidewinder car?) University Illinois Urbana Chaplain (UIUC) did a rear setup like this with a forward side mounted 600cc 4 cylinder (i.e. a converted 600cc sprint car) in 1997? and finished 7th overall I believe.

[rjwoods77]

I noticed a couple errors. I meant to include that on the rear suspension mount the mumford link the back of the main roll hoop. The mumford link would sit below the axle. The entire mumford and dampers would sit in a transverse plane along the back of the main roll hoop. The same setup for the front suspension in the transverse plane along the front of the front bulkhead. In this configuration you would run the main roll hoop supports forward to the front roll hoop.

Also I meant to say kingpin setup instead of live axle for the front suspension.

Also meant to say panhard or jacobs ladder instead of J bar.

For those of you who don't know what a mumford link is:

http://www.not2fast.com/chassis/mumford.gif


How front beam and steering would work:

http://www.hyperracing.com/Ass.../images/01-001-2.jpg (http://www.hyperracing.com/Assets/Hyper_images/images/01-001-2.jpg)

How the rear beam works:

http://www.hyperracing.com/pag....aspx?product=05-000 (http://www.hyperracing.com/pages/home/products/online_store.aspx?product=05-000)

[swong46]

That rotor looks like it is mounted to the wheel center. Have teams in the past use that setup on independent suspensions?

[mech5496]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:

If any rainy days over Xmas I'll try and do some sketches.

Z </div></BLOCKQUOTE>

I would give it a go on CAD, but then I'm quite sure I will want to build it, so I better do nothing at all....

Nevertheless, I was thinking of it last night and what I have in mind definitely reminds me of the Lotus 88 "double chassis" concept. Plain beam suspension front and rear, maintaining constant wheel camber, then mounting an undertray and/or wings to them. What you have is essentially a "rolling aero"; a suspension with all the aero loads feed directly to wheels. Then just put a chassis on the top of it with a clearance of lets say 30mm, keeping in mind the minimum suspension travel rule. You can set front wing and undertray height to a minimum (accounting only for tire deflections), as their distance respectively to the wheel center is constant. Now i think about it again, I just might give it a shot in CAD... http://fsae.com/groupee_common/emoticons/icon_biggrin.gif
One thing that really puzzles me is how to transmit torque from the engine to the wheels. Rob, if I'm not mistaken, your 2010 car had a chain/sprocket final drive. How did you compensate for the sprocket mis-alingment due to chassis roll? How about excessive squat during acceleration? (I assume you can partially treat the second one with appropriate link geometry).

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by mech5496:
... How about excessive squat during acceleration? ... </div></BLOCKQUOTE>
Harry,

As you say, a chain driven spool's "anti-squat/lift" can be set by side-view geometry.

Here is a sketch I prepared earlier...

https://lh5.googleusercontent.com/-cTTmIQ9a27Q/TvHQ24CoryI/AAAAAAAAAH8/VJHR8n6dYvo/s800/MechAntiFg7.jpg

The n-line of 7d-top-left gives anti-squat, while 7d-bottom-right is pro-squat.

Note how small difference in drive sprocket position gives quite large difference in anti-squat.

Z

[rjwoods77]

Harry,

The angle of the axle in relation to the body roll was relatively small (no more than 3 degrees if I remember correctly) but I allowed for some compensation by making the primary sprocket slightly thinner to allow the chain some lateral tracking. We ran a 428 chain which requires .280" sprockets. The aluminum rear sprocket was that size but the primary was .250" There was no chain bind. There was roll understeer built into the rear suspension so the axle would become non-parallel with the chassis in both the top and rear views at times. The magnitude of the articulation of the axle skew was small but it moved around a bunch. This is a reason I would favor a 4 link with Mumford lateral control over what I did before and/or what UNSW did because you would be able to tune in some interesting things into you car to combat lack of a differential. Roll understeer and oversteer being a couple of those variables.