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The ADFA car had a full weight audit of the car and all components. I cant remember the figures exactly but the front unsprung was approximately 29kg and the rear 28kg. In comparison to previous ADFA cars with A-arms front and rear, this was only marginally heavier. And in comparison to sprung vs unsprung ratios, it was comparable with many other well performing cars running independent systems.
Z,
You are crazy. I like you
Z,
Thank you for the response. I am going to go ahead and model up my ideas with some decent detail. I am going to start referring to the Z-bar mumford link as the "Zumford Link". As for a rough idea of what that will be I am looking at modeling non parallel torsion bars (ala packard suspension)where the bars are closer together in the front and fan out toward the back. The mumford rockers will be of normal layout which means the are elevated a little bit above the lowest crossmember of the main roll hoop and bulkhead. The opposed lever arms will then sit directly under the rockers and connect into the point where the pullrods (i.e lateral force members) of the axle attach to those rockers. So the front lever arms pivot on the torsion bars inside of where the two pullrods attach to the rockers whereas in the rear they are on the outside of the pullrod attacheents.
Rob,
Re: Z-Bar/Mumford Links
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Oops, I didn't think my above answer through properly (under Suspension Linkages). http://fsae.com/groupee_common/emoticons/icon_frown.gif It won't work as stated!
In fact, the Z-bars will only provide anti-heave springing, and only one bar is needed, though two will double the stiffness.
The problem is that the Mumford outer diagonal links only provide "lateral" control of the beam (wrt the virtual RC), and they don't allow individual "vertical" control of each side of the beam.
However, you can still use two longitudinal Z-bars as you explained (closer together at the front than rear) and just connect them to the beams with short links. (Edit: These links must be more vertical than the Mumford diagonal links!) These two Z-bars will control body heave and roll motions.
Furthemore, you can fit a spring between one Mumford rocker and the chassis (resisting rotation of the rocker), and that will control axle-bounce at that end of the car (ie. this would be instead of a separate coil spring at axle centre). Doing same at front and rear gives body heave and pitch control.
Edit: Note that:
1. When the axle rolls wrt chassis, there is no movement of the Mumford rockers wrt chassis (ie. they could be welded solid to the chassis).
2. When the axle bounces (=heaves) wrt chassis, both rockers rotate equal amounts but in opposite directions wrt chassis (ie. they act as if they are two gears in mesh).
All this is proof that a picture is truly worth a thousand words!
Z
So you could have a heave/pitch spring attached to both mumford rockers....
Z,
I was just suggesting the Zumford Link as a lateral control of front and rear beam and z bar interconenction in one clever Chapmanesque device and not as a complete form of beam location. I was also looking to use said mechanism to tie into some sort of rotary damper to tie inline with the Mumford rocker pivot(s) such as a cush drive works on a motorcycle in order to eliminate any need for hydraulic dampers. A rotary way that a F500 achieves linearly. I realize that front and rear beam would still be unconstrained longitudinally. I started with "how do i z bar a double beam" without other layout concerns as my first "wouldn't it be cool if". I was under the impression that two z bars were needed but now if I understand correctly we only need one.
I started drawing and found there there are a couple driver/engine placement combinations in reference to wheelbase along with many different beam and beam control. Some of which were quite innovative and packaged neatly such as the one that places the rear beam 2.5 inches rearward of the main roll hoop while the engine lays underneath the drivers legs. This led me to have questions regarding these linkage arrangments along with what would be an ideal canvas to work with to later add aero.
I dig your concept but would like to explore some other possible methods to achieve the same effect. That being a double beam car with aero but with the addition of suspension interconnection to reduce expensive componentry and more effective platform for aero.
Please review these statements to make sure my understanding is correct. Assume A/B=1 for these and that lever arm A and B connect to the middle of the beams.
1) A beam connects each end pair together so only one z bar(as opposed to two in an IFS/IRS car)is needed because rotation of chassis to one beam is equally and oppositely reacted by the other beam to keep the chassis level. If I lift up on the LF by 1 unit then RF,LR,RR will push down by 1/4 unit which will effectively make a heave of 1/4 unit? ***One wheel lift skew effect***
2) A single spring/damper setup on the end pair beam will affect only the compression of that beam so the spring/damper on the rear is for acceleration squat and the front is for braking dive. Without these, if i lift up on LF and RF by 1 unit then LR,RR will push down by 1 unit which will effectively make a pitch/dive of 1 unit? ***End pair pitch effect without spring/damper***
3) A beam connects each end pair together so only one z bar(as opposed to two in an IFS/IRS car)is needed because rotation of chassis to one beam is equally and oppositely reacted by the other beam to keep the chassis level. If I lift up on LF,LR by 1 unit then RF,RR will push down by 1 unit which will effectively make a roll of 0 degrees? ***Side pair compression roll effect***
I read you correction. So if I ran a single z bar with lever arms that attached to a the beams in the center and run a spring/damper at each end again attached to the beams in the center I would be able to control all spring and dampening through the centerline of the car (spring damper mounts and torsion bar bushing mounts) and have my suspension interconnected? I like the symmetry and ease of this. Would there be any other good reason to run more than one z bar to pullrods coming off of ends of the beams. Beam bending from spring forces? Your comments of mumford rockers not doing anything in roll confuses me. You can see it move with one wheel bump (roll) in this video...
http://www.youtube.com/watch?v=jIiEV0DILBw
I am rather unfamiliar with aero requirements and wonder how that effects the freedom of design if the intent it to eventually put a single piece aero tray that has been claimed to offed the most downforce. Both designs have the minimum wheelbase of 60" and a track of 48" One has the beam axle 2.5" behind the main roll hoop plane and the other is 15". The crossbar for the main roll hoop is 1" ODx 24 inches wide and currently 3 inches to tube centerline from the ground (2.5" ground clearance) The rules madate how far the tunnels of the diffuser can go behind the rear axle. I have no idea the hows and why of how fast the tunnels grow but I was wondering if you or anyone could comment if that it doesnt leave enough room for future tray design versus the less choked up rear axle centerline.
Rob,
As I said, a picture is truly worth a thousand words, and a simple sketching facility here would make all this much easier. http://fsae.com/groupee_common/emoti...n_rolleyes.gif
Nevertheless, let's start with the Mumford link, as shown in your link above. This has;
1. The "chassis".
2. "Two rockers" pivoting about longitudinal axles fixed to the chassis.
3. A "central link" connecting the two rockers, such that the rockers always rotate equal and opposite amounts wrt the chassis. Looking at this a different way, instead of this central link, each rocker could have gear teeth near the car centreline that mesh with the teeth of the other rocker. Structurally, the central link is probably better than teeth (less backlash, etc.), but for understanding it might be easier to imagine the two rockers as "geared" together.
3. "Two diagonal-links" going from the rockers out to the beam-axle ends.
4. The "beam-axle".
You say "Your comments of mumford rockers not doing anything in roll confuses me. You can see it move with one wheel bump (roll) in this video..."
What you are seeing is indeed "one wheel bump". But, importantly, the left-wheel-only-bump of say 2" equals axle-bounce of 1" (ie. both wheels up 1") plus axle-roll of 1" (ie. left up 1" and right down 1"). So what that video is showing is the rockers moving as a result of the axle-bounce of 1" (ie. the height the centre of the axle is moving wrt chassis).
To further clarify this (hopefully???), imagine the rockers welded solid to the chassis. Now there is a four-bar linkage consisting of the chassis, two diagonal-links, and the beam-axle. The beam-axle and chassis can only move wrt each other by rotating about the "Instant Centre" found at the intersection of the two diagonal-link centrelines (these being "n-lines", or lines of "no relative motion"). This IC is thus the "Kinematic Roll Centre" (for this simplified 2-D analysis).
So "no rocker motion" = "pure roll".
Now imagine the axle moving in pure bounce (both wheels up or down equal amounts). The diagonal-links pull equally on their respective rockers, and the rockers rotate equal amounts but in opposite directions ('cos geared together).
So if you want to provide a spring that controls ONLY axle-bounce, you can do so by resisting this rocker rotation. This could be your "some sort of rotary damper to tie inline with the Mumford rocker pivot(s) such as a cush drive works on a motorcycle", or any other arrangement that resists the rotation of the rockers. Note that you only have to control one rocker, because they are both linked together, but providing a torsion spring to both rockers spreads the load structurally, and may be neater (?).
All the above only refers to one end of the car (ie. front OR rear). But if you provide such an arrangement (ie. Mumford link with spring controlled rockers) to both ends of the car (F AND R), then you have control of body heave and pitch. This is similar to the "Z-Bar Sketch" top-left WITHOUT the two side "centre-pivot-leafsprings". So the "sprung-rocker-MLs" replace the "coils-at-beam-centres", plus providing lateral control, and perhaps being better structurally because less "beam bending".
BUT, you must still control the body's roll mode, without adding twist stiffness!
A single centreline Z-bar connected to the beam centres would ONLY add body heave stiffness/control. When I said "you only need one of these" (connected to the ML rockers) I meant that one bar adds heave stiffness, and the second just adds even more heave stiffness. Importantly, neither adds any roll stiffness/control (in fact, they add NO stiffness to ANY other mode).
So, YOU STILL NEED TWO LONGITUDINAL Z-BARS with their ends connected to the outer end of the beams (say, via short vertical links). These give body heave and roll control. The extra heave control is not really needed, but to get independent control of ONLY the roll mode takes a different mechanism, possibly more complicated.
There are other solutions possible (eg. "Balanced Suspension", which gives simple and completely independent control of all modes) but that is another very long (!) story, and not really necessary for the smooth tracks of FSAE and F500.
~~~~~o0o~~~~~
You say, "I realize that front and rear beam would still be unconstrained longitudinally."
Yes. But if (?) you want to use something like the side-pair Centre-Pivot-Leafsprings (= body heave/roll Z-bars) in the Z-Bar sketch (top-left), then these can be used for longitudinal control. Braking torque reaction of the axles would also be needed, but even this could be incorporated into the side-pair CPLs.
In fact, that top-left sketch, with peg-and-slots for lateral beam control, has a lot of potential for a very simple, smooth track, short wheelbase racecar.
~~~~~o0o~~~~~
You ask, "I am rather unfamiliar with aero requirements...
I have no idea the hows and why of how fast the tunnels grow but I was wondering if you or anyone could comment if that it doesnt leave enough room for future tray design versus the less choked up rear axle centerline."
From my point of view, tunnels are NOT necessary. A completely flat floor will work IF you "drive" it right. That is, a separate "flap", or "wing", or "aero surface", at the right distance from the rear edge of a flat floor will work just fine (like each wing on the Twin Beam Wing sketch). Similar "aero devices" at the front and side edges of the floor will make it work even better! This requires some original thinking, but there are huge gains possible. http://fsae.com/groupee_common/emoticons/icon_smile.gif
One aero requirement that should be met (I guess?) is that the aero surfaces should remain a reasonably constant distance from the road. Since the road is likely to have some small "twist" in it, I reckon it may be beneficial to let the periphery of the rectangular aero-undertray also twist with the road surface.
The Twin Beam Wing does this, in the sense that the two beam-wings follow any twist in the road. Likewise, the top-left Z-Bar sketch does this, if the aero-undertray periphery is fixed to the two beams and two side-pair CPLs.
(Edit:
Also, the top-right "Z-Bar" sketches (p4) show how the undertray can be divided into five rigid pieces and still conform well to a twisting road. The floor of the chassis forms the central diamond shaped piece, and four triangular corner pieces pivot off the edges of the central diamond to complete the rectangular undertray. The pivots (ie. hinges between diamond and corner pieces) can be low friction, so the whole undertray is very flexible and adds no twist stiffness to the suspension. This also makes accident repairs easier - just replace the damaged corner.
End Edit)
~~~~~o0o~~~~~
Apologies for all the capitals, but this forum definitely needs a simple sketching facility!
Z
All,
A lot of what is being posted about interconnecting corners in varying manners has already been or is being done. However, it's being done hydraulically. Think UWA.
TestDriver,
"Already been done"?
Let's not forget the "world's cheapest car", the Citroen 2CV, designed in the 1930s with very effective mechanical side-pair interconnection.
I am sure motorsport will catch up one day.....
(Not sure about Detroit. http://fsae.com/groupee_common/emoti...on_biggrin.gif)
Z
Z,
I'n not getting something here. You say "A single centreline Z-bar connected to the beam centres would ONLY add body heave stiffness/control." and "So, YOU STILL NEED TWO LONGITUDINAL Z-BARS with their ends connected to the outer end of the beams (say, via short vertical links). These give body heave and roll control. The extra heave control is not really needed..."
Let's say that the front axle bounces by 1" the rear goes down by 1". This to mu understanding represents a pitch motion (heave would be the other way round). When the front axle bounces by 1" the Z-bar would like to push the rear axle down by equal amount (if A=B). So how a Z-bar connecting front and rear axles contributes to heave/pitch stiffness? Am I missing something here?
As I see it we have two separate issues to be resolved:
1st is axle location both longitudinal and lateral.
2nd is control body movements. If you can incorporate lateral control to motion control or something, you end up with fewer parts->lighter. The real issue to me right now is which modes you want to control, why and how.
On a beam axle car I would not bother having some roll and pitch, as they do not affect tire path or tire loads that much. It might be upsetting for the driver a little, but I think that those modes should not be (very) stiff, they could be left somewhat soft.
The same applies with warp mode (as soft as it gets) and bounce (stiff enough for the chassis not to bottom out hard on axles; maybe rubber bumpstops?). Actually the only movement I would like to limit somehow is single wheel bump. Any thoughts on this?