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Old 11-19-2001, 02:40 AM   #1 (permalink)
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why would this not work? (susp.)

i have been thinking of a 1/4 eliptic setup and have an idea on a link setup for it. what i need is a susp. guru to tell me if it'll work and if not why? so what i was thinking was a link setup which basically looks like a big "A". the two legs would be attached to the axles on the outer ends but instead of joints they would be hard mounted to the tubes. the two legs would go up and come together to a crossmember somewhere below the x-case output. there they would uses a big joint that would only allow up and down movemen (i.e. like a joint used on heavey equipment) and where they hoint connected to the "A" it would allow the "A" to pivot side to side either on a piviot or a threaded shaft. i hope i am describing this clear enough. anyway this would be the only link for the rear suspension. you would not need anything else. no panhard bar because the big forward joint would not allow side to side play. would this work?
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Old 11-19-2001, 03:15 AM   #2 (permalink)
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whats gonna keep it from going side to side? a joint that only allows up and down movement would have so much stress on it on a side hill or any time the tire is getting pushed from the side, and then you add all the leverage from the link. I think you would have some serious strength issues. also it seems like there would be an awful lot of stress on the mounts to the axle tube from the rotational force.
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Old 11-19-2001, 03:27 AM   #3 (permalink)
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well the joint would have to be big like one from some sort of heavey eqipment rig. as for the rotational forces on the axle i'm not too worried. look at the scorpions. they use a hard mount on the axle end and i have never heard of a problem there.
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Old 11-19-2001, 05:30 AM   #4 (permalink)
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give it a shot then. do you have any pics of the suspension on a scorpion? I knida want to see how theyre setup
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Old 11-19-2001, 08:01 AM   #5 (permalink)
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sounds interesting just a couple things though.
1. if you mount the A to the top of the axle housing the other end must go on top of the t-case. if on the bottom then clearance problems.
2. a panhard bar does not limit travel but a single joint is going to have alot of stress on it. that stress might be reduced with a panhard bar from the top of the housing to the frame rail.

I think you should try it and see how well it works.
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Old 11-19-2001, 09:57 AM   #6 (permalink)
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Q #1: What is keeping the axle from axle wrap? The mounted "A" arm being hard mounted? And how are you attaching the 1/4 spring pack? Is there going to be a pivot on the axle too for the pack?

Q#2: What type of heavy equipment mount are you talking about? Remember, some of them are allowed to pivot due to the way the "axle" is mounted. SO again, what type of mount. better yet, from what "earth" mover?

Q#3: Have you considered using a pivot "plate" for the top of the "A" above the t-case for some lateral movement? It would not be hard to make stops but relieve some (A LOT) of the stress that will occur?
Maybe draw a picture that way we are not guessing at what you are thinking and we can give btter advice
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Old 11-19-2001, 10:41 AM   #7 (permalink)
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I believe that is how ths Scorpion suspension is designed. He had to add a second air spring to compensate for the massive leverage on chassis. The rear of the rig is leveraged up under acceleration. (anyone with personal experience with the scorpion please correct me if I'm wrong). Without getting too far into the physics of it, it has to do with how the roatational forces of the rear axle leverage on the chassis in relation to the c/g of the vehicle. A three or four link setup allows that leverage to moved further forward on the chassis to make the the vehicle much more driveable. Given that, and the fact fact that you are placing a huge load on a single joint, it creates more problems than it solves.
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Old 11-19-2001, 11:01 AM   #8 (permalink)
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on that note

I've seen a suspension setup called a "davids star". It's two arms opposite each other. the point of one A meets at the axle housing. This prevents side to side motion but allows up and down.

The other A point mounts like you said, on a crossmember forward of the axle. This allows up and down and keeps the axle from pivoting forward and reverse on the other A point. I've actually seen it move and it's amazing!! but the project vehicle wasn't done and so I only saw it move in the shop.

This guy actually had the engine counter balanced with the rear axle. Literally the whole engine and trany moved with the axle. Technically the idea was awsome. It was a desert racer he was building. The idea was, the faster you go, the more weight the suspension "assumes" because of the upward velocity of going over a bump, faster. By balancing the rear axle and making it "weightless, you could hydralicly or pneumaticly increase or decrease the amount of down force on the rear axle as speed increased.

The guy got about 1/2 into and then just let it sit. Would've been awsome though!! He runs a towing place outside Barstow, CA. He's a bit eccentric though. Ok this post is long enough. Sorry
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Old 11-19-2001, 12:25 PM   #9 (permalink)
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Re: on that note

Quote:
Originally posted by sfazr2

This guy actually had the engine counter balanced with the rear axle. Literally the whole engine and trany moved with the axle. Technically the idea was awsome. It was a desert racer he was building. The idea was, the faster you go, the more weight the suspension "assumes" because of the upward velocity of going over a bump, faster. By balancing the rear axle and making it "weightless, you could hydralicly or pneumaticly increase or decrease the amount of down force on the rear axle as speed increased.
I can sorta see how he thought that might work, but it wouldn't. He's just adding the (huge) inertia of the engine and tranny into the suspension equation. Every time you'd hit a bump, not only the axle would have to move (up), but the engine and tranny with it (down). As you went faster, it would only get worse...

As for the original post, I think there would be WAY too much side to side leverage on the main joint. A pan-hard bar would probably solve that problem though...
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Old 11-19-2001, 04:21 PM   #10 (permalink)
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Since everyone is saying that you'll need a panhard anyway (and I agree) why not ust do a traditional radius arm suspension like a box bronco had?

Two arms hard-monted to the axle (no play in any direction) come forward of the rear axle and could be monted to the frame with rod ends - allowing twist, vertical, and lateral travel.

Then add a panhard rod to control lateral forces. Done.
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