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Mini Fabrication Mini Choppers, Mini Sandrails....Pint sized anything Fabrication


Mini Fabrication Mini Choppers, Mini Sandrails....Pint sized anything Fabrication

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  #1  
Old 07-02-2015, 07:38 PM
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JaysinSpaceman JaysinSpaceman is offline
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Mini-mini Buggy IRS axles?

Hey guys,

So my cousin has a China Inc dirt bike that he bought a few years back and the previous owner was supposed to "get the Title to him" and well, as you can guess, that never happened. At this point he doesn't want to go through the hassle of doing a "lost title" at DMV for a 200cc China Inc. dirt bike that isn't worth as much as my shirt. But it got me/us thinking about building a tiny Go Kart size off roader with the engine. 200cc, 15-16HP, five speed and electric start on a 48" +/- wheel base maybe 42-46" track (I'm thinking 1960's size) that would fit in the bed of a small pickup. Hell, maybe even source a few more engines (link to cheap engines) and have 3 or 4 we could race on his 80 or so acres. So there is the premise.

I have been thinking about it in the evenings and it definitely needs suspension at all four corners, maybe 4 to 6" travel, just enough to soak up some bumps to save the butt and back. The front is easy, little double A-arms (as long as will fit), a spindle and a spring and shock. The rear however, is another issue. The whole motor mounted to the swing arm thing like a lot of the cheap China karts is out, it's just a crap Idea, way too much unsprung weight and the motor gets beat to death. Swing arm with a jack shaft would work but it's not independent and that's a ton of bearings, chains and shafts and whatnot and all that stuff takes power to turn. I really like the Idea of IRS, super low unsprung weight, the bumps only affect the one wheel and it would just be trick on a tiny kart.

There seem to be a few ways to go about it, the first is the jack shaft with parallel trailing arms and chain drive down to the wheel. Like so...



Again lots of chains, shafts and bearings and it doesn't get any camber change,etc... But it would be OK.

Then there is a swing axle like old VWs used but again no camber control and a lot of possibility of wheel jacking in turns. (no picture because I think everyone knows what I'm talking about here). And you still need at least one CV or u-joint.

Then there is the trailing arms like they use on full size dune buggies which gives great travel but needs an axle shaft with a lot of plunge. This is a possibility but CV joints are $$$.



And of course the last is Double A-arm but again I am looking at CV joints and thinking this ain't gonna be cheap.



These images are all just yanked from a Google image search.

I would love to do a little version of one of the last two pictures but the CV axles are a huge stumbling point because of their Price $$$ and really with 15 +/- HP i think that all the ones I can find (like the type 1-4 or 930 CVs) that are easy to make attachment flanges for are way overkill strength wise and way too long. So I have been wondering about PTO type shafts and U-joints as they can be had for reasonable money and (on my tractor at least) they can take a hell of a beating. U-Joint. And a square bar and square tube slip-joint, like they do for long travel drive shafts. So has anybody built a little suspension like this? And what did you use for the axle shafts? Or does anyone have a source for small and cheap CV shafts?

Hell if nothing else this might just spark some conversation and get this forum moving again. And if you've got any pictures of your buggy or suspensions please post them up, everyone like pictures.

Thanx for any input you might have.
Jaysin
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Old 07-02-2015, 09:08 PM
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Brian1 Brian1 is offline
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I am currently in the middle of building one of these and I chose to go with the jackshaft and sprockets like your first picture. My current build is replacing an older buggy I had with a single u-joint per side and a swing style rear. I didn't like the camber change on it and it didn't have much travel either. It handled fine for what it was and was a ton of fun but it could have been better.

When I was making my build plans I was either going to use the old kart u-joints and add another with a slip PTO style shaft, build mini driveshafts using junkyard parts with 1310 yokes, use a car or VW CV shaft and hubs or find some stock take-off axles from a UTV. I finally settled on using a jackshaft because it turned out to be the cheapest option and provided an unlimited amount of travel (in theory).

When shopping for PTO style shafts the cost was adding up quick and wouldn't provide the angularity I wanted. The junkyard mini drive shafts would be heavy and big for the HP I was making. I seriously considered using 90's VW Jetta CV axles (cut, shortened and then sleeved) and wheel hubs and bearings since it was relatively cheap through eBay and/or rockauto but again the angularity was an issue.

I wanted a smooth belly (no big sprocket hanging down) and about 10" clearance at ride height under my buggy and that was the problem in getting the angularity needed with both CVs and small PTO sized U-joints while getting some down travel

I'm planning to start a build thread on here once I get a little farther along. I am using a 301cc engine, front a-arms with mini coilovers, fabricated front spindles, and rear trailing arms with a 1" jackshaft and mini coilovers. I am also using a Comet 40 series torque converter on the engine.
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Old 07-02-2015, 09:47 PM
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deaner deaner is offline
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It's almost always cheaper to use OEM parts. Chevy S10 4x4 front axles and hubs come to mind. They are cheap at the junk yard or Rockauto. They mount with a flange on the inner joint. A little over-kill, but you'll be ready for an engine upgrade. If you don't like the 5x4 3/4 wheel bolt pattern, Ford Ranger 4x4 front hubs will fit the S10 shafts for a 5x4 1/2 bolt pattern. Use wheels with as much back-spacing as you can find, to use the longest axles as possible, to get the most travel.
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Old 07-02-2015, 10:14 PM
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JaysinSpaceman JaysinSpaceman is offline
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Quote:
Originally Posted by Brian1 View Post
I'm planning to start a build thread on here once I get a little farther along. I am using a 301cc engine, front a-arms with mini coilovers, fabricated front spindles, and rear trailing arms with a 1" jackshaft and mini coilovers. I am also using a Comet 40 series torque converter on the engine.
Must start build thread!! Thanx for the great info. Would you happen to have any pictures? One of my thoughts was to go junk yarding for the smallest dive shafts that I could find and cut them down, then do a Jag style IRS where the axle is the upper control arm. I like multi use parts.

Quote:
Originally Posted by deaner View Post
It's almost always cheaper to use OEM parts. Chevy S10 4x4 front axles and hubs come to mind. They are cheap at the junk yard or Rockauto. They mount with a flange on the inner joint. A little over-kill, but you'll be ready for an engine upgrade. If you don't like the 5x4 3/4 wheel bolt pattern, Ford Ranger 4x4 front hubs will fit the S10 shafts for a 5x4 1/2 bolt pattern. Use wheels with as much back-spacing as you can find, to use the longest axles as possible, to get the most travel.
Yeah this has also crossed my mind too. And someone on a go kart forum had posted something about using late model VW CV axles because they bolt on at the inner end too and the hubs use a 4 on 100mm bolt pattern (if I remember correctly) which is apparently the same as most ATVs. Question, why use wheels with a lot of backspacing?

Thanx,
Jaysin
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Old 07-07-2015, 05:57 PM
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JaysinSpaceman JaysinSpaceman is offline
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OK. I did a bunch of looking at various off road karts, diy and manufactured, and I think that I am likely to go with a simple swing axle in the rear. It simplifies a whole bunch of stuff and while it doesn't offer adjustability and and the camber change isn't the greatest thing, we are talking about a tiny vehicle with maybe 6" wheel travel. There are several videos on youtube that show small buggies with swing axles in the rear and they all do just fine.

This one is a very nicely built buggy done by a fellow over on minibuggy.net

Rear suspension. Does great until his drive chain brakes at the end.

Overall

Since my design is even smaller I tink it will work well and be very cheap and easy to fabricate, which is important because I would like to build 3 or 4 of them so we can race!

But if you have better suggestions I will always take the input since I am still totally in the design stage.

ANOTHER DESIGN QUESTION

And since I am still designing bits, I am wondering if there is a DIY sort of way to make a Rack & Pinion steering system? I can find small racks for go karts in the neighborhood of $80 but with 3 or 4 to build I am thinking something less expensive might be in order. I was kind of thinking about a chain and sprocket DIY R&P, I can't really find any examples but basically a length of #35-40 chain welded to a length of bar stock in some sort of housing driven back and forth by a 10-12 tooth sprocket attached to the steering shaft. I'll try to draw something up if that doesn't make sense.

Keep the input coming. Thanx.
Jaysin
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  #6  
Old 07-07-2015, 06:31 PM
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TheBandit TheBandit is offline
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You know what they say... where there's a CNC plasma table, there's a guy who can make his own rack and pinion...

Search the google images for "ventilation rack and pinion" for some design ideas. I'm not sure how tight you could get the mesh / backlash on one of those, but perhaps it would work?

I think finding a used rack is your best bet.
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Old 07-07-2015, 06:56 PM
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I've seen a rack made with chain just like your talking about on MBN, but no idea where it is.

If the carts are light enough think about basic go kart style steering. It works on the Honda Pilot.

The problem with it though is bumpsteer. So also take a look at the Trophy kart steering, it combines a gokart style with a basic swingset setup. This way you can get your inner tie rods where you want them. I would think this could all easily be made out of sheetmetal.
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Old 07-08-2015, 07:29 AM
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Graham08 Graham08 is offline
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Originally Posted by bullnerd View Post
So also take a look at the Trophy kart steering, it combines a gokart style with a basic swingset setup. This way you can get your inner tie rods where you want them. I would think this could all easily be made out of sheetmetal.
I think this is a much better idea than trying to DIY a rack & pinion setup. Should be stiffer and have less slop than even a cheap commercially available R&P.

For your original question, I think any automotive half shaft/CV setup is going to be way overkill for the power level involved, but a brief look on Rock Auto showed that the majority of the options are less than convenient to attach to anything. I think you will be fine with a VW swing arm setup. I Googled Formula Vee rear suspension, and there a bunch of decent looking options for that basic design.

I don't think jacking will be as much of a concern for you because you're planning on running in the dirt. It becomes more of an issue as grip increases...but the FV guys go pretty quick and don't seem to have a huge problem with jacking.

Looks like a fun project!
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