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Author Topic: #715 - Speed Demon  (Read 25361 times)
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Peter Jack
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« Reply #15 on: August 01, 2012, 12:47:15 AM »

I would think that using the two in that configuration would prevent chassis roll. Interesting theory and I'd like to know why they'd want to do that.

My choice would probably have been some sort of Watts link configuration but I'm sure this one has been well thought out.

Pete
« Last Edit: August 01, 2012, 12:49:53 AM by Peter Jack » Logged
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« Reply #16 on: August 01, 2012, 06:25:28 AM »

The four trailing links by themselves would be weak in resisting side to side motion (sort of like a cardboard box with no top and bottom) and twisting of the box they form, they have no diagonals to resist deformation sideways. It looks to me that the Y bars provide that lateral and torsional stiffness against the rear end shifting side to side, and any twisting of the box formed by the four trailing arms.

It would be easier to see with a couple of oblique views.

The trailing bars appear also to not be exactly parallel, different center distance on the front than the rear, I assume to manage U-joint angles of the drive line as the differential rises and falls as the suspension deflects.

Larry
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« Reply #17 on: August 01, 2012, 11:42:50 AM »

Look at the way the Ack Attack controlled lateral movement of the swing arm.

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« Reply #18 on: August 01, 2012, 12:06:01 PM »

Quote
Look at the way the Ack Attack controlled lateral movement of the swing arm.

You talking about the rear piece that goes around the back of the tire?
Things are packed in so tight on the Ack Attack it is a bit difficult to see what does what unless you really stick your head in there and examine things.

Larry


* ack_attack_rear_suspension_DSC_5204.jpg (243.38 KB, 1509x1060 - viewed 425 times.)
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« Reply #19 on: August 01, 2012, 06:12:05 PM »

In a Drag Race 4 link rear end the single A Arm normally controls Lateral movement.

This Double A Arm 4 Link looks to me like it keeps the wheels parallel while allowing the diff to rotate around the vertical plane for the pinion/tailshaft angle and the horizontal plane so wheels can follow the uneven surface. Binding should not be a problem due to the small suspension travel. That is cool cheers

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Seldom Seen Slim
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« Reply #20 on: August 03, 2012, 09:41:35 PM »

We're in a motel with crappy internet, so look here tomorrow for an update on the suspension for the Speed Demon.  Ron called to say that I missed posting the text that explains some of the questions.  And today he sent a few bits on the new 7-speed trans - which stuff I'll post tomorrow while we're going down the road to Wendover.  Right here the service is so slow that if I waited to do it -- I'd never get to sleep.  (Nancy, quit doing that to me evil evil)

I'll get you the information in the morning.
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Jon E. Wennerberg
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« Reply #21 on: August 04, 2012, 12:09:11 PM »

Here are the three photos that Ron Main sent - showing the details of the new 7-speed transmission for the #715 Speed Demon.  You probably remember tha they'd had long-term problems with tearing up the driveline when shifting - too much engine inertia, too much torque at the shift, and so on.  This will give them smaller ratio changes too, they sure hope, minimise the shocks.  And it'll give George something to play with as he drives the car up and down the salt.







Next I'll try to get the text/details on the suspension pictures I put up here a few days ago.  Just trying to be helpful, folks.

Nah, I can't do it - at least from the front seat of the pickup.  It's mostly text, with a few thumbnails, and I can't get it to come out in a copyable form.  If one of youse guys think you can post it I'd be happy to send you the entire email and let you tell me how to do it - or, hey, have you post it here.  If nothing else --- www.maxwellindustries.com is a site that's offered up in the explanation.

Be in touch if you can help.  Thanks.  I might not have the'puter on since we're bouncing along in ND right now, but I'll check it now and then.
« Last Edit: August 04, 2012, 12:28:03 PM by Seldom Seen Slim » Logged

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Rex Schimmer
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« Reply #22 on: August 04, 2012, 02:37:38 PM »

The amount of shock that is felt by the diff and tires is related to the stiffness of the gear box and the drive shaft and a good look at the drive shaft certainly says that it is stiff. Shock loading can be many number of times higher than calculate max torque based upon engine output and you only have to stress one component of the drive train one time above its yield or tensile strength and it will fail. One of the ways to attenuate the shock of shifting is to make one of the links compliant in torsion. Back when the original Doug Nash 5 speeds were built they made a street model that had a "quill" shaft that ran through the counter shaft gear. It was splined to the input gear and then ran the length of the counter shaft gear and was splined to it at the far end. The diameter of this shaft was calculated to provide a certain amount of torsional "spring" which greatly reduced the shock that was transmitted to the drive gears. The quill shaft idea was also used by Leo Goosen and other engine designers that adapted roots style blowers to their race engines, the shaft reduced the maximum shock seen by the drive gears and made the whole thing live. Typical shaft material would be 4340 or better yet M300 and heat treated to around 200,000+ psi yield strength then shot peened and polished. Shouldn't be a problem for this team (dollar wise) and it looks like you might be able to do something in the drive shaft although in the counter shaft gear would require a smaller shaft.

Just a thought, nothing is new.

Rex
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« Reply #23 on: August 04, 2012, 05:58:55 PM »

Here's the info from Ron Main via SSS .......... enjoy  cheers

SUSPENSION

First of all, if the racing surface was smooth and flat, we wouldn’t need any. But unlike drag racing Bonneville sometimes is more like off-road racing. There is only one way to go fast. The drive wheels movement must be dampened by the coil/shocks and stay on the track surface for maximum traction. The 1st 400 mph wheel-driven car had full suspension. The “Turbinator” world’s fastest wheel-driven car had full suspension both ends. All the total movement we had on the Demon was .250. I believe we need a minimum of .500.  Also if there is room for a lower wish bone it will help, with our lateral movement. After watching the Replay films of our rear end almost jumping out of car on a ruff track even though we had a upper top fuel wishbone suspension and a huge (1.75)track bar. I ask Steve Watt if we could design twin wishbone suspension as proposed on the Bloodhound SST. As far as I know this is the first racecar with this suspension. [Speed Demon_Ferguson Rear End_Maxwell Gemini I Suspension.jpg]

Shock absorbers absorb . . . shock. Damper is a better word. Take the shocks off of your car and drive around. A small bump sets off a reaction that goes on a long time. The shock on the streamliner helps damp out those reactions. [Traction without suspension at Bonneville.jpg]

Bloodhound SSC references:

Construction is about to begin on the Bloodhound Supersonic Car (SSC) after three years of aerodynamic research and modeling. A prototype Eurojet EJ200 jet engine used in the development of the Eurofighter Typhoon will be used for initial acceleration. A hybrid rocket using a combination of solid and liquid propellant will combine with the jet engine to create 212 kN (47,500 lbs) of thrust and reach 1,000 MPH in 42 seconds.

This is a neat way to keep the package as small as possible – after all, Brian Coombs has to fit in 2 wheels, 2 uprights with 2 sets of bearings, 2 brake packs and 2 sets of double wishbone suspension into the nose of the Car – so it’s pretty tight in there.

http://www.bloodhoundssc.com/car/suspension.cfm


* Speed Demon_Ferguson Rear End_Maxwell Gemini I Suspension.jpg (68.18 KB, 749x589 - viewed 244 times.)

* Traction without suspension at Bonneville.jpg (17.01 KB, 533x400 - viewed 234 times.)
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« Reply #24 on: August 04, 2012, 06:47:03 PM »

Having been somewhat alarmed by the configuration of the rear suspension as depicted heretofore in this thread, I inspected and conversed with Steve Watt regarding it.

First of all, the “wishbone” configuration bears no relationship whatsoever to that proposed for the Bloodhound, which is basically a conventional double A-arm suspension with pullrods--similar to most open wheel race cars.

Secondly, the 1.75” “track bar” is, in fact, a 1.75” anti-roll bar, which is mounted in the large, bronze bushed holes gusseted into the frame above the axle.  This item is the primary method of resisting the axle input shaft torque.  Although not shown in the above photos, Steve says it will be in place when in use--which is a good thing, since the wishbone single Heim joints, loaded in bending, are likely not up to the job without it.

The intended function of the upper and lower “wishbones” is to provide lateral location of the axle.  However, as configured they will also share, to some degree, the anti-roll function, which is worrisome.
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« Reply #25 on: August 04, 2012, 07:48:30 PM »

Hi Woody

Do you know what car left those skipping black tire marks, looks a little spooky too like in a big right drift wow!!

In 68' i helped install a Henen-Froude dyno and we used a solid shaft made by Donovan with Rasappa u joints , after seeing the standard type drive shaft i was wondering if a splined solid shaft would be better and like Rex says it would give a little to help reduce the big bang with each shift.

Don
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« Reply #26 on: August 04, 2012, 07:49:22 PM »

Thanx to the other "Interested" poster for speaking up, especially from his past posts indicating a strong physics background.

Having bit of practical experience  in live axle suspensions, I too was puzzled by the arrangement.

Looks like a lot of common pickup points could have been chosen and think there may be OVERKILL in what they're doing. Hopefully, no  hingebind.

I'da talked to Roger Lamb

No matter what, I wish the truly dedicated team great success!
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« Reply #27 on: August 04, 2012, 07:57:03 PM »

The tire marks were from the end of Tom Burklands run,Ray the Rat took the picture.
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« Reply #28 on: August 04, 2012, 09:49:21 PM »

Thanks Glen, Don
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« Reply #29 on: August 05, 2012, 01:44:59 AM »

>DND asked "i was wondering if a splined solid shaft would be better and like Rex says it would give a little to >help reduce the big bang with each shift".

I wondered the same thing . At .6 Gs of acceleration my 1 3/8" x 26" streamliner driveshaft twists 4.2 deg .

The formula for degrees of torsional deflection is : ft lb x length (in) divided by (dia cubed x 1642).
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