Solid rear axle suspension idea.

[chetcpo]

I was thinking last night what would be the easiest and cheapest way to make my crapola Ebay kart better. I would like to install a solid rear axle to have more than the current 1 wheel drive, and I also would like to have some rear suspension. (I'll address the front suspension some other time)

So here's what I came up with, let me know if you guys see any reason it won't work. I don't have any specifics on the plan per se, but I drew (poorly) a sketch of the concept in MS Paint to try and explain what I have in mind. I'll attach it below.

The plan is to make a rear subframe that will house the solid axle and bearings, and have a mounting point for the engine up above the axle with the chain running straight down to it. This subframe will then be attached to the rear of the kart by four links in a Satchell link arrangement. (with 1/2" rod ends)

What this will do is allow the engine to move up and down with the rear wheels as it goes over bumps and what not. Sure it will make the engine unsprung mass, but I doubt it will be a whole lot heavier than an IRS setup due to it's simplicity. Which is the goal. If you guys can't convince me it wont work I hope to build it for under $150 or so. Does that sound reasonable?

Oh and sorry again for my crappy MS Paint skills. I really need to learn CAD.

 

[Kaptain Krunch]

I cant really understand those pictures, but a simple rear swing arm would be very easy.

 

[chetcpo]

I cant really understand those pictures, but a simple rear swing arm would be very easy.

That's a good point. The above will function a bit like a swingarm only the two extra upper links will allow movement of one wheel up into bump/jounce while the other wheel is in droop. Some call it "articulation." A swingarm can't do that and thus won't conform to ground irregularities nearly as well. A swingarm would be cheaper to build, but not a whole lot easier.

Here's the kind of articulation I'm after: (well maybe not quite so much

On a side note, I remember seeing an online vendor that sold axle "kits" the came with all the bearings and brackets etc. you needed for one price instead of having to buy them all seperate. Can someone point me to them or another good place to buy the stuff I need for this? Thanks!

 

[chetcpo]

Here's another sketch of the same concept. Obviously it's not to scale since I drew it in Paint.

 

[Kaptain Krunch]

That makes a little more sense, kinda of overkill for a kids kart, but if you feel like doing it i say go for it.

 

[freakboy]

pretty much your doing a 4 link.

 

[chetcpo]

pretty much your doing a 4 link.

Yeah, more or less the Satchell link is an adaptation of the four link that moves the two upper (or two lower) link chassis attachment points inboard which eliminates the need for a panhard rod or watts link etc. to keep it from moving side to side.
You really can't tell on the bottom profile pic, but look at the first abomination of a sketch I posted and you can see the upper links are attached inboard.

Here's a decent pic of a Satchell link:

I really don't think it's overkill for a kids kart. The way I see it is they are essentially learning to drive with this thing and I want it to be a good tool for them. It shouldn't take too long or be too hard to make since I have all the tools and steel to fabricate it in the garage already left over from the last build.

I'm pretty confident that the principle of the rear suspension is sound and all, I was just a little worried that the engine might not run or might not run well getting vibrated and shook around at odd angles since it's essentially bolted to a suspension member.

 

[Doc Sprocket]

I think you're good to go! You're obviously doing your homework, and keeping the engine unsprung is the simplest, lightest, and cheapest means of attaining suspension while dodging potential driveline complication! No reason you can't make that work. As far as the engine being jostled goes, all I can say is that right now I have NO suspension (have plans, tho') and I pound the wee outta her offroad. I was getting jostled so bad, I was almost leaving the kart, so I had to install a seatbelt. Only once in all that banging around did my engine ever stall , and that was only because I was down to my last few ounces of fuel and it sucked air. Keep us posted on your build! Cheers- Chris

 

[chetcpo]

Thanks Chris! I appreciate the vote of confidence. I'm going to order all the live axle parts and will get started as soon as I have everything on hand. I had no idea kart bits were so expensive. I just added up the cost for the bare minimum I would need and it came to $260.

Oh well, it's cheaper than the therapy I need.

 

[Kenny_McCormic]

Worst case scenario with the vibration, a 2 stroke with the right carb will run in any position without a complaint.

 

[springer]

are you going to use little heim joints for the rod ends or just bolts or pins or something? if so, where are you going to get them? i wouldn't mind doing my susp like this. i have no need for it, but it will be different, thats for sure.

 

[Kaptain Krunch]

Thanks Chris! I appreciate the vote of confidence. I'm going to order all the live axle parts and will get started as soon as I have everything on hand. I had no idea kart bits were so expensive. I just added up the cost for the bare minimum I would need and it came to $260.

Oh well, it's cheaper than the therapy I need.

If you havent looked already, check out BMIkarts.com, really good deals on just about anything. I believe they have 1" axles as low as $25.

 

[Doc Sprocket]

It IS the therapy you need!!!
I've been playing around with some suspension plans myself. Your design is more costly and complex, but definately way high on the cool scale! I'm going a little more redneck, but it will function quite well. Cheers!

 

[chetcpo]

are you going to use little heim joints for the rod ends or just bolts or pins or something? if so, where are you going to get them? i wouldn't mind doing my susp like this. i have no need for it, but it will be different, thats for sure.

I usually buy from Midwest control, but their service can be wonky so verify stock (by phone) before you commit to buy.
For this project I was gonna buy these:
http://www.midwestcontrol.com/buy.php?item=438
Not bad at $4.50 each if you buy a min of 10.
And screw them into these:
http://www.midwestcontrol.com/buy.php?item=2072
about $2.50 if you buy a min of 10.
I still have a good bit of 1"OD .065 tube laying around to use them with.

On the car I built a few years back I bought all the rod ends and weld in bungs from QS components but it looks like their prices are higher for the weld in bungs now, although I did notice that they now stock tubing. Not bad prices overall and nice for one stop shopping:
http://qscomponents.com/

 

[springer]

ya, i found midwestcontrol, but your looking at $70 just for the rod ends. i was hoping you might be on a tighter budget, but i guess some things just aren't cheap.

 

[frederic]

If you want to go ultra cheap and you're building something that's adult sized... your local u-pull-it junkyard is bound to have many, many useful parts.

Most FWD cars have a "trailer" rear axle which is suspended by struts (bleah), a-arms (nice but complicated), or...... some variation of a 4-link. Taurus, Continentals, Sables, and many many imports.

Take all the rear bits and toss the trailer axle, and swap in a lightweight RWD import axle and do a little welding and you have a really cheap 4 or 5 link setup that can take any kind of power a kart engine is gonna toss at it.

And, you get integrated brakes.

 

[chetcpo]

If you want to go ultra cheap and you're building something that's adult sized... your local u-pull-it junkyard is bound to have many, many useful parts.

Most FWD cars have a "trailer" rear axle which is suspended by struts (bleah), a-arms (nice but complicated), or...... some variation of a 4-link. Taurus, Continentals, Sables, and many many imports.

Take all the rear bits and toss the trailer axle, and swap in a lightweight RWD import axle and do a little welding and you have a really cheap 4 or 5 link setup that can take any kind of power a kart engine is gonna toss at it.

And, you get integrated brakes.

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.


And Springer, just for you I have decided to go with poly bushed links instead of using pricier adjustable rod ends.

How does $25 sound? http://www.speedwaymotors.com/Rod-End-Bushing-Kit-1-2-Inch,1583.html

They won't allow the smooth long travel the rod ends would have, and they won't have the adjustability, but the kart shocks I was looking at only have 2" of compression travel so range of motion won't be an issue.

 

[springer]

ahh... $25 works alot better, but would this limit the amount of articulation? if so, wouldn't that kind of be a waste of the 4-link abilitiy? i have no experience in susp design, so diregard if this is impossible/impracticle. But, what if you used heims for the 2 lower links only to save on $$. Then instead of making the 2 upper links, just use the shocks to locate the axle and reduce side/side movement?

 

[T-man]

hay chet
go look at this link , this guy is doung the same thing but with a 5 point ... http://www.chickslovethecar.com/board/Topic60550-27-92.aspx

 

[newrider3]

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.