Why Have a Suspension

In my line of work I get to play with many different tractors & equipment built to go through "off road" terrain. The majority of the tractors I play with have a single pivot front end with the rear end being ridged mount. In watching the newer built buggies & rock rigs most seem to lean towards minimal compression & are using center limiting straps to limit "unloading". This in essence gives them a center pivot suspension. Keep in mind as we go through this that this is for a slow speed rock rig only. What is rattling around in my demented brain is a center pivot mounted front & rear ends. Thinking this through, the rig would have great clearance with no control arms to slide on. Both front & rear would be center pivot with sway bars & shocks to center & control the rig over the axles. It should make the rig extremely predictable in steep climbs with no front end unloading & anitisquat BS to worry about. Decent should be cool with no front end diving. No axle wrap to worry about either. I would do this with portal axles or maybe even go full hydro drive & build hyd. motor housings out of tubing that will be rolled into arches to give added clearance. The only down side I can see is it could get ruff riding at any speed, but with the tires at 5 psi how bad could it be. I know this is way out of the box & don't know is I'll ever get the balls to actually try it, but the idea has intrigued me for a while now. I'll let you guys chew on that for a while & see what you spit out.

Matt

Take a look at the bright yellow Willys in the latest FourWheeler TTC. It uses an sliding center pivot kind of like you are describing.

The big problems I see with hydro is that it's heavy and expensive. And you'll have fun building up a pump and reservoir setup that won't spill, can breath, and won't suck air into the pump. My Dad & brother have (what's left anyway) of an FMC nut shaker. Full hydraulics, with 110+ gallons of reservoir for counterweight, a 20gpm Cofeyville pump driven by a Ford 300 inch I6, Spicer trans and axle. It doesn't get as much torque to the ground as you think it would.

The hyd. wouldn't be a problem for me to whip up. I see the system would be just trading weight. I can't see it being heavier than the componants it would eliminate, but this is a side issue. I'm more interested in the suspension aspect. What are the downsides that anybody can think of other than the ride being a little ruff.

Matt

FarmerMatt said:

The hyd. wouldn't be a problem for me to whip up. I see the system would be just trading weight. I can't see it being heavier than the componants it would eliminate, but this is a side issue. I'm more interested in the suspension aspect. What are the downsides that anybody can think of other than the ride being a little ruff.

Matt

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Steep inclines combined with off camber.

I'd think that would be where the new buggies still rely on articulation, no?

If the front and rear where on a pivot wouldnt there have to be some sort of spring keeping the corners of the rig up? As you stated on a tractor, the rear doesnt move and its just the front axle that articulates under the "body" of the tractor. How would that be solved?

As for the bumps, why not make the cab float on the frame like a semi truck does with airbages under the cab attached to the frame. Semis have been around for ever and they seem to work for the truckers driving down the interstate everyday.

AARON

Matt.....

your harvest time is nearing to a close.....long winter right?

begin building!!!!!

ChiXJeff said:

FMC nut shaker

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Torque is the main reason it wont work.No matter what side/or rotation you use it will want to lift one of the corners(front or rear).

If the front and rear where on a pivot wouldnt there have to be some sort of spring keeping the corners of the rig up? As you stated on a tractor, the rear doesnt move and its just the front axle that articulates under the "body" of the tractor. How would that be solved?

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Sway bars & shocks. Basically you'll just need enough bar to keep the rig centered over the pivots & however stiffer you want it to counteract body roll in off camber situations.

As for the bumps, why not make the cab float on the frame like a semi truck does with airbages under the cab attached to the frame. Semis have been around for ever and they seem to work for the truckers driving down the interstate everyday.

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The center pivot mount could be tied into a sub frame using spring eye bushings or something like that, but I'd rather keep it more simplified than having an air bag system suspending the body that may open a whole different bag of worms. Keep in mind that the fastest this rig would probably is is 25-30mph.

FMC nut shaker

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Almond tree shaker. Many of these are full hydro driven meaning there is literally a hyhro motor on each driven wheel rather than having an axle shaft & differential. Some have hydro motors attached to a transmission that drives a standard differential. Our old OMC shakers used dana 70 differentials & would strip the teeth off the R&P. We'd have to rebuild 2 or 3 of them a year. If that's not torque than I don't know what is. Although they are using 7:17 gears.

Torque is the main reason it wont work.No matter what side/or rotation you use it will want to lift one of the corners(front or rear).

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I'd like to here more about this. The only time a tire gets lifted on the front of any of my tractors is when we have a huge implement hanging on the back. Why would torque lift a tire in this situation? I know the TJ's have a problem with the short wheelbase & short arms transfering torque from side to side, but thats more a function of the suspension transfering it. In this imaginary setup there realy is no suspension although the swaybars could effect this I guess??

Matt

Sorry,It was earlier this afternoon when I originally started reading this thread.I was thinking of a single pivot point in the frame(articulated knuckle).Now I understand what you meant,it sounds interesting but what about front-to-back "torque",thats what a suspension really does,keeps all wheels working equally!

As far as the ride is concerned, it shouldn't be a big problem. I drive large forklifts at work all the time. They have no suspension and 100 PSI in the tires. An air seat should be all that you would really need. The fastest of these lifts probably gets up to 25 or 30 mph. The ride gets a little rough after 8 hours, but it isn't too bad. I say build it.

Thousands of Hondas in Fresno run around with no suspention, If they can do it why can't you? I even see them bouncing down the freeway at 85 mph on 35 series tires. I say if your kidneys can handle it, go for it.

FarmerMatt said:

The hyd. wouldn't be a problem for me to whip up. I see the system would be just trading weight. I can't see it being heavier than the componants it would eliminate, but this is a side issue. I'm more interested in the suspension aspect. What are the downsides that anybody can think of other than the ride being a little ruff.

Matt

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You, have trouble with a hydraulic system? Naw, never happen. In your line of work, you HAVE to know something about hydraulics. And you've probably got just about everything you need except maybe a couple of motors in your spare parts racks.

Sure, if you run individual motors at each wheel, that's going to be lighter than an axle. Don't forget you're going to need a bunch of oil in a reservoir, and probably a radiator as well.

On a side note, I've spent the last 20 minutes looking for a picture of a nut shaker, and I've found 2 thumbnails, neither one of which is very good. Basically, it's a low slung vehicle with flotation style tires with a long boom and hydraulic claw hanging off the front. It grabs on to the base of the tree, and shakes the whole thing (hence the name.)

The nut shakers that Matt has experience with are built a LOT heavier than the cherry shakers I've used because nut trees are huge compared to cherries. Taking the teeth off a D70 ring? Wow. The major issue we had with the FMC was the brakes sucked, and the parking brake was more of a suggestion.

The new rigs are tricycles, each wheel has it's own hydraulic motor, with inclined plane canvases. 2 good operators can harvest about two and a half trees per minute, in excess of 100,000 lbs. per day pretty easily.

EDIT: Ha! http://www.fdocitrus.com/fig6.htm Okay, this isn't an FMC. But it gives you a pretty good idea of what a nut shaker looks like.

Matt, you and I have been pondering the same thing it seems. If you eliminate the need for a differential in the middle of the axle housing it sure does make fabricating the perfect suspension a lot easier. Ponder this....

Take a wishbone, similar to Beezil's latest creation, and run the tip of it through the center of the axle housing(just for picturing purposes imagine the shaft on Beez's wishbone going into the pinion shaft hole in the housing and being secured). With one "link" you have now located the axle side to side, back and forth and rotationally. Now let the top of the axle compress an airbag against a crossmember on the frame of the buggy. There are two major problems with this design.

1) Creating a wishbone strong enough to do ALL the locating of the axle, the biggest one I would think, would be pushing one side of the axle back and the other forward, if you catch my drift.

2) You can't possibly have a differential with the wishbone going into the center of the housing.

In your idea, you wouldn't have the airbag or need any of what I just described, but I think that with the airbag design, you eliminate the problem of trying to make the ride bearable. I think my idea is somewhat of a combination of yours and typical suspension setups. My inspiration was the Wiggins Marina Bull forklifts that I used to work around. Front axle solid mounted, rear/steer axle pivot mounted. Anyway, just my .02

Ary

Here's another oddball thought.

Anybody remember how the front suspension is set up on a Morgan roadster? Independent front that slides on a vertical rail.

If you're running independent hydro motors, run a long coilover shock with the wheel travel on a vertical rail.

This is the machine we use in the trees for those not familure with nut shakers. Full hydro drive with a 110 hp cummins diesel motor complete with AC & stereo. Weighs is at a ground shaking 11,400 lbs. We have 2 of these. We have four of the late 70's modle OMC monoboom shakers. 2 of these new ones replaced 4 of the old...
http://www.orchard-rite.com/nutshaker/rowshaker.cfm



I'm curious as to how a swaybar would react with this type of axle retainment. As tension is applied to a swaybar with a normal suspension it actually pulls the entire suspension down or up depending on compression or droop in any given situation. With what I'm talking about doing the swaybar wouldn't have that lee way. Any of you suspension guru's out there have any comments? Hello Alyn, Mr. Stevens, or anybody out their that knows anything about suspension dynamics.

Matt

I think it would be fun to be sitting in the tree when one of those things came up on it. Also, I'd be drunk.

Did someone say "Nut Shaker"??

Interesting thread.

Rev

Beezil, come on up to the farm next July when Dad & Steve are shaking cherries. Nobody quite believes me when I tell them what happens, or how fast. That nut shaker of Matt's is gonna run even faster, it doesn't have a catch frame to deal with.

Den, I saw a clip for the Monster Garage episode. I decided that I really didn't want to bother watching it. More or less, they've built a Shockwave shaker from about 1972. Seriously, that's going to be one of the easier projects. The hardest part would be getting enough hydraulic power to run the head, and counterweighting the front.

Someplace at home, I do have some digital video on a VCD. May have to try and dig it up again. None of my PCs has a DVD decoder, but my player might take it.

BTW, Matt....... how many trees/minute?

What about Nitrogen gas pressurized shocks. They should be enough to keep the rig level and would eleminate the need for the sway bar. My experience in racing is that when the force of a turn pushes up on one wheel, the sway bar lifts the other side of the suspension thereby lowering the car. All of these are in very small amounts. I don’t think that a sway bar will be able to handle the axle travel that you are suggesting. If the forces are high enough the sway bar would bend or snap.