Solid rear axle suspension idea.

[chetcpo]

If you use bushings instead of heims, you'll end up with an overly complicated, heavy, expensive swing arm. The heim joints are what allow articulation of the suspension; the links have to be able to twist.

I respectfully disagree. It will be less complicated, lighter,(less metal, no weld in bungs etc.) ummm, can't really argue with the expensive part, and it definitely won't be a swingarm. You are right it won't work as smoothly, the resistance it requires to twist the bushing around the bolt will have to be overcome, but it won't "bind" in the classical sense of the word.

Bushings are used in this manner everyday, and while they don't allow "twist" as easy as would a heim, they do allow plenty of it as long as the links are properly located.

see

I promise a youtube video of me articulating the suspension by hand prior to installing the shocks and driving it. If I'm wrong about this you will at least be able to relish me doing it in a public forum live before your eyes. If I get the bushings out of the box and they're hard as granite, I reserve the right to eat my words, drop back and punt and use the heims.

And T-man. That guy's just using an old school traditional four link with a panhard rod in a totally wacky location at an equally wacky angle that makes it look similar to the other links. Same principle though as your regular horizontal panhard rod.

 

[frederic]

That would certainly work, but I'm trying to keep this as lightweight as possible since whatever I come up with is going to have the weight of the engine in addition to it's own weight.

Fair enough, was thinking with that degree of articulation, you might be pounding on it harder than the average kart builder.

I have a lot of experience building serious off-road trucks, solid axle as well as IFS/IRS, and the one thing you must consider for wild articulation is longer suspension links. Shorter links obviously limit travel but also can cause the axle to move forward and back more, which adds to the the angles of your u-joints as well as can cause tires to rub on things if the area is tight, as I imagine would be the case in a kart since they're... um... smaller

This is one of the reasons why I particularly liked to build out crewcabs.... I could weld up one big mount for the front and rear arms to the brackets, essentially in the middle of the truck. This lessoned suspension artifacts which helped give better handling and steering capabilities.

It's very hard to turn straight when one wheel lurches forward moreso than the opposite wheel, in effect causing a turn.

This may not matter on a kart but I mention it just in case you're not intending to put around slowly.

 

[chetcpo]

<snip>
This may not matter on a kart but I mention it just in case you're not intending to put around slowly.

I actually am believe it or not. This thing is for my 6 year old to drive.

And I don't expect or really desire wild articulation. The cheap shocks I want to use only have 2" of compression so if I mount them 2 feet apart, with one at full extension and one at full droop the angle will only be 5 degrees. So to acheive that, the poly bushes have to allow only 2.5 degrees of twist each.

If the range of articulation is totally impressive without the shocks mounted I may invest in some longer travel shocks.

 

[chetcpo]

If you use bushings instead of heims, you'll end up with an overly complicated, heavy, expensive swing arm. The heim joints are what allow articulation of the suspension; the links have to be able to twist.

OK, here's living proof I can admit when I'm wrong. The links wont twist with those bushings I pointed to earlier in this thread as substitutes for heims. I got them yesterday and they are nylon, and thus hard as stone, and thus useless for the intended application. I figured they were poly which has some compliance to it, but these have very very little if any. So I'll be ordering the heims one Monday from Midwest Control.

The bushings aren't totally useless though. They will make excellent chassis mounted suspension pivots for the double A arm design I plan on working on after I get this first kart sorted.

So in a nutshell, my apologies to newrider... you were right.

 

[chetcpo]

OK, so some parts have come in and I've had a little bit of time to play in the garage since my last post. So far I have the basis for my rear axle frame built, now I just need to locate the engine proper, and the brake caliper, and then of course mount the links. Then I have to hack all of the other crap off the back of the other kart. At this point I'm seriously considering just building another chassis and leaving this one be in all it's one wheel drive glory.

Pics provided below. As pictured with the engine and all attached it weighs only 67lbs., and more than you might think of that comes just from the axle itself and the heavy sprocket and brake rotor. I'm curious if anyone sees any red flags. I frankly have no idea what I'm doing so it wouldn't suprise me a bit if someone pointed out a major flaw in this design. (minor flaws are expected)

It should be easier for folks to see where I'm headed now that you can see actual parts rather than a really bad MS Paint drawing.

On a related note I scored a complete Yerf-dog Spiderbox front end off Ebay for $50 plus S&H.

 

[joshpit2003]

there is a wealth of info on 4-link suspensions. If thats what you are going with I'd suggest you read these 4 articles and also download the link-calulator... the important thing would be your anti-squat... having 100% means your links will keep the cart from "sqating" under acceleration, but that also means that if you hit obsticles under power your links will be taking a lot of the load. Having 0% anti-squat would mean that your links will be neutral, not taking any load under acceleration, your cart will "squat" under acceleration and when you hit obsticles your shocks/springs will take ALL of the load...making for a smoother ride over a bumpy surface.

your positioning of the links will determin how much anti-squat you will have... I'd suggest something like 0 - 25% for a go kart application. for some of the low-speed crawlers its nice to have 100% while others swear by 0%, but in general you want low anti-squat #s for higher speed applications (so your shocks/springs can do all the work).

here are the articles:

Give yourself a good amount of time to read them (1-2 hours).
4-Link Part 1: (introduction)

http://www.4wheeloffroad.com/techarticles/suspension/131_0306_four_link_suspension_part_1/index.html

4-Link Part 2: (geometry)

http://www.4wheeloffroad.com/techarticles/suspension/131_0307_four_link_suspension_part_2/index.html

--------------------------------------------------------

Link-Basics Part 1

http://www.off-roadweb.com/tech/0908or_multi_link_suspension_system_technology/index.html

Link-Basics Part 2

http://www.off-roadweb.com/tech/0909or_front_suspension_technology_link_basics_part_2/index.html

---------------------------------------------------------

Drag-Link & Track-Bar Harmony:

http://www.off-roadweb.com/tech/0809or_off_road_unlimted_crossover_steering_kit_install/index.html

"Links to Proper Travel":

http://www.off-roadweb.com/tech/0012or_multi_link_suspension_sytems_links_proper_travel/index.html

 

[chetcpo]

Thanks for the links, and yes I plan on using antisquat geometry. I've already done the reading and calculations elsewhere but I will certainly have a look.

I think it's hard to say the exact percentage of AS on a kart with any consistancy, especially with the engine unsprung since the center of gravity location will depend almost completely on the weight of the driver and passenger and how far forward or back they have the seat slid. I'm going to aim for 100% with couple 50lb kids up close to the wheel for starters and see where that puts it.

This uncertainty is why I plan to make the amount of antisquat adjustable by providing alternate locations (extra bolt holes in an enlarged bracket higher and lower) of the lower chassis links on the Satchell link setup.

 

[joshpit2003]

just keep in mind that 100% = bumby ride and greater forces on your links. (when under power)
there is a nice Pirate4x4 topic about antisquat... and basically the top guys agree that the desert-racers like baja 1000 trucks typically have close to 0%. and i would think that your cart will be more of a desert racer type than a rockcrawling type.

 

[rgvkid]

looking good! You'll definitly have to triangulate 2 of the links unless you want to make a panhard bar. or just make it a 2 link with a panhard bar.

The only thing i don't like about mounting the engine on the swing arm or axle is that the engine will get knocked around with the axle. Rather then mounting it on the frame and adding the extar weight so the shocks work better. To bad chains don't flex and stay on the sprocket better.


Great find on the heims. I wonder how much is added on the shipping. I have been pricing around and i can't find anything less then $14-15 for both economy 1/2 heim and boss. About $15 also for the Poly bushing kits for 1/2 ID and 1.25OD. That sucks that the bushing pakage you got was Nylon. That would have been a steal if they were Poly. I think i'll get the nylon kit also for some arms or swing arm setup. Let us know how dealing with Midwest works out for you.

What size tubing fits around the Bushings? Is it 1.5 or 1.25"?

One more thing, I would probably go with at least .090 tubing rather then .060. Better for strength and easier welding without being to heavy. How about using a coupling as a boss?

Good luck, and thanks for the thread and updates.