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Thread: Beam Axles - Front, Rear or both.

  1. #231
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    Quote Originally Posted by Z View Post
    Jay,

    "[In FSAE] To get the 40/60 distribution I imagine you would have to run some very short linkages, or else run them alongside and underneath the driver..."

    All of these recent Beam-Axle drawings are meant to be quite general, and apply to a whole range of cars, not just FSAE.

    For example, along with Ralph's examples from a few pages back (ie. racing on very rough tracks!), I have also got PM's from Baja students, and other more general enquiries. So, I drew the B-A(2) and B-A(3) sketches with quite long links so that they would suit long travel suspensions, much longer than is needed in FSAE.

    In short, all the sketches would work fine in FSAE even if the physical links were MUCH shorter than sketched. Even with, say, 10" (250 mm) long links, the full bump or droop travel of 1" (25 mm) only changes the slope of the links by 1:10 (at most!), so much shorter links are NO PROBLEM.

    And the Cylindroid itself is a "virtual" thing, so it can be placed anywhere, even off at "infinity".
    ~~~o0o~~~

    "What are your thoughts on mounting the engine on the rear axle/arm with regard to driver controls? I imagine an engine moving about would have negative effects on throttle/clutch/gear control. Also there's the rule (assuming it's still a rule) that the intake must be hard mounted to the chassis. I guess one could argue that the suspension is part of the chassis but I could see it being an issue."

    Yes ... the main problem is the Rules...

    Again, considering the smoothness of FSAE tracks, I see NO PROBLEM with having an engine rigidily mounted to one of the "triangular" Axles, either the "Twin Beam-Wing" sketch, or B-A(2) or (3). With the engine mounted at the front of the triangle, nearer to the Body, it moves much less than the wheels when they go over bumps. And since no bumps in FSAE... (Or, looking at it the other way, many cars have won FSAE with effectively NO suspension at all...) And given that throttle/clutch/gear control can all be done via cables (and often are), I see no problems there either.

    In fact, I reckon the ideal candidate for such Beam-Axle-mounted-drive would be the electric cars! Mount the heavy but compact motor(s) near the front of the Axle "triangle", just under the driver's back (ie. where the gearbox is in TBW sketch), and then take a chain or toothed-belt reduction back to the no-CV-driveshafts.

    Importantly, the above amounts to "Outboard-Drive", so longitudinal n-lines have to be appropriately chosen. These are shown in B-A(1) as n2, but for good "antis-" they should have a LOWER slope, closer to that of n1. So either use a linkage similar to the TBW sketch, or if using linkages B-A(2), (3), or (4), then P should be lower, about the same level as R.
    ~~~o0o~~~

    "I don't think the front beam plus flat floor underneath would be allowed/safe. I'd imagine you'd have to have another floor over the top of the beam. Was this your intention?"

    Yes. The bottom-floor would be part of the aero-undertray. Any "cockpit-floor" above the Beam would be for the Rules.

    "If so I envisage a humongous front end..."

    Well, NO DIFFERENT to most Double-Wishbone FSAE cars.

    Most every FSAE DW car out there today has a "stepped floor". This rises up roughly 100 mm from the seat-base to the footbox, just to provide suitable attachment "nodes" for the lower wishbones. Then there is a R&P that necessarily sits above this floor so that the tie-rods can get out to appropriate pick-ups on the upright, and keep away from the wheel-rim. And then another "cockpit-floor" above the R&P, to comply with Rules.

    I figure many DW cars have this cockpit-floor at about 150 mm above ground (ie. at R&P location). Anyone care to share their numbers?

    Anyway, a B-A(5) type Beam-Axle, albeit bent into a very wide "V" for FSAE, should be able to fit under a similar height cockpit-floor. Note the Pitman-Arm and tie-rods can be in front of, or behind, the beam, and the beam cross-section can be a widish, lowish, RHS, as sketched. Add the 350 mm high foot-box template, and the underside of the steering-shaft and Bevel-Gear-Box can be less than 500 mm above ground (the template has big semi-circular cut-outs at top and bottom for the steering).

    It all looks very similar to most DW cars I have seen. From a quick check of photos, these have the top of their FRH at 600-700 mm above ground. Certainly, the tops of most noses at the front-axle-line are well above the tops of 13" front wheels (= 500+ mm diameter).

    Z
    Z,

    The Cincinnati 2013 car had the nose around 150mm off the ground. A few weeks ago, myself and a fellow UC alumni put together some rough conceptual drawings for a frame that had the top tubes maybe 20mm above the OE of a 10" FSAE tire, that would package direct acting dampers at both ends of the car, use pitman arm steering and a whole host of other fun things. It's possible, but people have to think outside the box of what is common. We were using SLA front and rear suspension as well, so there is plenty of weight to be saved with a rear beam as well. I personally like the way SLA packages with the new bullhead support rules.

    -Matt
    Matt Davis
    University of Cincinnati
    Bearcat Motorsports: 2012-2013: Suspension guy

    Bilstein: 2013 - ??: Product Engineer

    This post is a collection of my own thoughts and opinions, and in no way, shape or form reflects the thoughts/opinions of my company, my university or anyone else but myself.

  2. #232
    Matt would you mind sharing some of these drawings here? To be honest, a lot of things package well if you design with them in mind in the first place, even the much-hated longitudinal Z-bars. The thing is that most FS team members start thinking out of the box shortly after they have left the team...the old "marrying your favourite design" thing...

  3. #233
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    Quote Originally Posted by mdavis View Post
    A few weeks ago, myself and a fellow UC alumni put together some rough conceptual drawings for a frame that had the top tubes maybe 20mm above the OE of a 10" FSAE tire, that would package direct acting dampers at both ends of the car, use pitman arm steering and a whole host of other fun things.
    Matt,

    Yes, I would like to see those sketches too. Or similar from other ex-FSAEers. (Apparently that sort of thing is acceptable on this Forum. I've been getting away with it for years!)

    As Harry noted, the average student's time in FSAE is barely enough to understand "The Standard Car", let alone really push the envelope on an unusual design. And words do not convey the gist of these ideas nearly as well as sketches.

    So, with the goal of advancing the state of the art ...

    ... more radical "out-of-the-envelope" car sketches, please, from everyone!

    Z
    Last edited by Z; 12-03-2014 at 06:26 PM.

  4. #234
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    I don't think the cad work was ever completed, so it'll have to be hand sketches. I'm not nearly as good at drawing as Z, but I'll give it a whirl this weekend.

    -Matt
    Matt Davis
    University of Cincinnati
    Bearcat Motorsports: 2012-2013: Suspension guy

    Bilstein: 2013 - ??: Product Engineer

    This post is a collection of my own thoughts and opinions, and in no way, shape or form reflects the thoughts/opinions of my company, my university or anyone else but myself.

  5. #235
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    Alright, hopefully these images work reasonably well.

    Basically, the front takes a bit of inspiration from the BCMS 2011 car, where the lower inboard points are very near the centerline of the car. With a real and pinion, this makes for a very small rack. Or, kart steering could be used. That's the way I would do it here. The front lower points are shown with the 2 dots above the front lower frame rails. The front upper point is attached to the front node. The rear upper point is loaded into the front roll hoop. The other node is for a direct acting damper. I'm not 100% sure exactly where that node should be in 3d space, but that point should be close. Detail stuff to be sorted out later.

    Rear end would be a bulkhead, with all rear suspension points and the damper attaching to it. Beyond that, this frame should be more than stiff enough for whatever suspension stiffness is desired, even with sprung mounted aero and the increased spring rates that would come along with it.

    This frame was simply reusing a lot of our geometry from 2013, so there is certainly room for some improvement there. I think the ideal way to do it would be a swing axle in the rear, as that would allow moving the dampers further forward on the trailing link. The way the rules are written, the has to be a lot of structure right behind the roll hoop, so you may as well use it for more than just checking the rules box.

    I should also note that the engine model is not 100% accurate, it's of the older yfz450 engine rather than the newer 450r that we ran in 2013.

    Thoughts/feedback/discussion welcome.

    -Matt
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    Matt Davis
    University of Cincinnati
    Bearcat Motorsports: 2012-2013: Suspension guy

    Bilstein: 2013 - ??: Product Engineer

    This post is a collection of my own thoughts and opinions, and in no way, shape or form reflects the thoughts/opinions of my company, my university or anyone else but myself.

  6. #236
    Cool, thanks for sharing Matt! I believe there is a tad too much triangulation but other than that I like it and I agree on all your points. I am also searching my conversations with Rob Woods for a draft CAD I did for a twin beam interconnected e-car back in 2012 to share.

  7. #237
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    Quote Originally Posted by mech5496 View Post
    ...I believe there is a tad too much triangulation...
    What are you talking about??


  8. #238
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    If it works for the wall of death then it should work for FSAE...

    http://fb-troublemakers.com/wp-conte...69610362_n.jpg

  9. #239
    OK, so here is a draft design of mine dating almost 2 years back. Chassis is a dead simple monocoque (flat panels for ease of manufacture of the mold). Beams are at an initial stage, albeit in the fourth picture (the one with wheels) they are a bit more detailed, manufactured by an oval filament winded CF tube and bonded, sheetmetal inserts. It was done mainly as a packaging exercise on how to package a twin beam and how simpler teh subframe would be. Longitudinal Z-bars were running the length of the car, with splined ends to accommodate rockers. No DASD because pullrods were needed to package the twin Z-bars. Motor is our electric YASA 750, diff would mount inside the hole as it is now, no gearbox. Batteries are on both sides of the cockpit for low MoI and rearwards mass distribution.

    Comments are kindly welcome!

    5.jpg 6.jpg 8.jpg 1981_10200805592284782_226875813_n.jpg
    Last edited by mech5496; 12-10-2014 at 09:33 AM. Reason: Spellcheck

  10. #240
    Question for those who have used the late Bill Mitchell's WinGeo kinematics software, what solid axle suspension layouts are supported? I have only briefly played around with an older demo version of this software which as I recall only had templates for a three link and a NASCAR truck arm style layout.

    Thanks,

    Ralph

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