Rear axle articulation

Just like a 4x4 mower, the concept of a 4 linked front and rear mower is about the same cool factor for me. I've thought about it for a while, and while a swing-arm is definably a workable concept, i havn't thought of a solid plan for a 4 linked (or leaf sprung) rear axle. The problems would be how it would handle, how to run shifting linkage, and how to run a belt. I cant really think of to many designs for something like that, vertical and horizontal input axles. But having rear suspension and be able to flex as much as you want sounds so good.

So anyone have any ideas on how this could work? Anyone think of this too? It would be a good design for a low speed project.

The trick is controlling your belt at the pivot points, and keeping the belt locked into the pulley grove while leaving enough room for it to slacken while clutched. I'm thinking inline skate wheels could be employed for belt retainers, and plastic pvc pipe on a rod for the pivot joints

Linkages, ( like shifter) should also should be aligned with heim joints at the pivot points to prevent binding or bump shift. The clutch itself should be positioned in the non flex area of the drive train. The other way to do this is to use rear swing arms, and centrally locate the transaxle (like redneck computer geek did on his hydro build) you could use a live axle with mimimal flex (chain) or belt drive it for more flexability, but more chance for slippage. Independent axles (stub axles) on a trailing arm suspension (imagine 2 dirtbikes side by side) would give the most independent flex, but would need an anti sway bar arrangement for stability.

There are ways and ways, it depends on how deep ya wanna go

Push / pull system for the gearshift. - Bikecycle brake wire's.

Build a frame for the transaxle, so it can be linked easy to the links or frame shocks, do the belt drive as you go along. If you want standard clutch I would make a jackshaft, and do the clutching on the non-articulating part.

Thunder beat me to it- forget the mechanical shift linkage, go with a cable system. Personally, I wouldn't use bicycle brake cable, I don't think it would hold up in the long run. Something a little heavier is in order. I think I would use a Morse cable system. A good place to start might be a shortened outboard motor shifter cable system.

As for the rest- Getting a little articulation out of such a setup probably wouldn't be TOO hard (whilst keeping the belt in place). Getting a LOT of articulation would probably be a whole other ballgame. Shaft drive really is the way to go with this. However- as a proof-of-concept, I'd like to see it done.

RAGBs and ujoints.

gimme a hand with the lexicon..... RAGB?

Right Angle Gear Box. Generally used to describe any gear box that transmits power through 90°.

Yea, I was think what Doug said, maybe 700 to a golf kart axle. You can probably make a driveshaft from a PTO shaft from TSC

Imagine my chagrin (grin) I use 'em all the time, just never clicked that that was what you were referin to

Expanding on LW's suggestion: For the clutching, it might serve to have a jackshaft with the clutch on the motor side and a belt that is always "on" with a spring tensioner for the transaxle side.

I was thinking this setup would be have like a 10mph at most. No sway bars, just let it flex as much as the driveshaft andgles and clearances would allow. Proballt limit straps. Like FF's craftsman crawler but alot better.

redlinemotorsportts wrote:

I was thinking this setup would be have like a 10mph at most. No sway bars, just let it flex as much as the driveshaft andgles and clearances would allow. Proballt limit straps. Like FF's craftsman crawler but alot better.

So get a T output gearbox? probably some in your junkjard.

What If you left the stock transaxle, in whatever tractor this would be done to, where it is. Replace rear wheels with light motorcycle chain sprockets so you can run chains to each rear wheel. Make swing arms to hold some hubs and attach them to a pivot point either behind the transaxle or over/under it depending on where you want everything to end up. The springs of your choice would have to hold the weight of the tractor on the swing arms of course. If you really wanted to make things simple, since you are talking about only going at slow speed. You could use front rims and spindles from a junk mower for the rear bearings. Just weld the sprockets and rear wheels you want to use to the small "front" rims. Torch off one side of the rim if you want to save weight. Weld you a arms to the spindles. The pivot point could just be pipe sleeved over another pipe. A little grease and it would work good enough for slow to moderate speeds. I think it could be made half way light if you didn't make all the parts real overly beefy. You could probably substitute the a arms for leaf springs somehow too as long as they didn't move sideways enough to knock the chain off. It wouldn't have to be as lenghtened out as in the picture if you either moved the transaxle forward or just kept everything tucked in close to the trans. Of course you have to figure it so the chain doesn't tighten up when it moves, but that shouldn't be a big deal.

It would be a good idea but I think keeping the chain tensioned would be harder then you think. Ifs would be nice for high speed but the setup you drawed up wouldn't do as well rock crawling. But it still is rear suspension I just see the chain skipping sproket gears a lot.

You could keep the chain snug with a follower with a spring. Then you wouldn't need anything to be adjustable as far as moving the wheels or anything. Just like a dirt bike. They just use a block of plastic and a spring.

redlinemotorsportts wrote:

It would be a good idea but I think keeping the chain tensioned would be harder then you think. Ifs would be nice for high speed but the setup you drawed up wouldn't do as well rock crawling. But it still is rear suspension I just see the chain skipping sproket gears a lot.

The chain wont get slack & tight, since you would build the axle pivot and a sprocket on the same line. Look at T-mans latest videos to see what we mean.

absolutely correct. Having the sprocket on the same pivot axle as the swing arm maintains the same chain tension throughout the swing of the pivoting arm. The bad thing about the chain is that when the arms articulate, the sprockets will twist in relation to each other... this tends to throw chains. This is why I would go with belts over chains despite the slippage problems... I have run belts with a horizontal to vertical twist with little problem

Lawren Wimberly wrote:

absolutely correct. Having the sprocket on the same pivot axle as the swing arm maintains the same chain tension throughout the swing of the pivoting arm. The bad thing about the chain is that when the arms articulate, the sprockets will twist in relation to each other... this tends to throw chains. This is why I would go with belts over chains despite the slippage problems... I have run belts with a horizontal to vertical twist with little problem

Yeah I would run a small portion with belt, and like i said in an earlier post. "Then use that portion of belt to do the clutching on also." And have chain to the wheel still.

I was going off of mr.'s drawing witch wasn't a swing arm.

I drew up a 4 linked front and rear with a 700 and a driveshaft. I like the design, so I might build something for the 2nd annual build off comp.

I like Mr. Mods' drawing. The trick with that setup would be to get the transaxle sprocket as close to the swingarm (s) pivot (s) as possible to eliminate chain tension problems. The japanse dirt bike manufacturers figured this out in the late 70's. Before that, they ran spring loaded chain tensioners that only really work under power and let the chain slack when off the gas.

When I first started my allis build I made a swing arm for the rear, it works off of the principal that yall talkin about.

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The front short axle is a jack shaft / rear pivot point. ( if you look on one of my allis pics from the side you can still see the mounts on the frame for this). But basically the mount on the frame accept some more flanged bearings, the short front axle slides through those bearings then in just like the pic.  Locking collars hold the axle in place and from falling out.  That allows for the short front axle to be spun freely in either direction while allowing the swing arm to flex up and down.  The long axle is for the wheels and tires And yes I was going to cut that shorter.

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In the middle of the front section of the swing arm was were the sprocket would go to tie that axle to the motor.

Exactly!

I was not talking about a swing arm when I made the thread, it was about two axis of piviot, just like a truck axle.

A truck axle that's on leaf springs? That mechanism pretty much works like two independent swingarms. That is, if the shackles are in back, the other end of the leaf spring is just a big trailing link, like a swingarm. (we know it flexes, but that really just changes the yoke angle under torque. That's what ladder bars and traction bars "snubbers" are for). Did I lose anyone?