Designing my first build... Help!

[bread]

Hello everyone, I am brand new to this forum and this is my first post. I am not new however to the karting/fabrication hobby. I wanted to share with everyone my design (just made in sketchup). The plan is to build a 2 seater "go kart" with actual car wheels and tires. The chassis has a center beam of 3" square steel tubing, the subframe will be made out of 1" square steel tubing. I plan to build single wishbone suspension up front and no suspension in the rear. Pls look at the pics, they are attached. I was wondering if anybody had any advice when it comes to designing something of this size. Any thoughts or suggestions are welcome!!

Thanks

 

[jeeperjoel]

to spin up those big tires you're going to need alot of power, and low gear ratio, also the large diameter of tires will require a substantial braking system, 4 wheel disc? how big of wheels/tires are we talkin about, weight? a lot of energy will be stored in that large rotating mass, and will take a lot to put it there

 

[bread]

Thanks for replying so quickly, jeeper. The model does have some pretty wide tires. What is pictures is unfortunately not what will actually used. I plan to use 16" utility trailer tires, which tend to have a narrower shape about them. In terms of braking, which is also not pictured, I plan to do a single rear disk w/ caliper. I am going to use the 16hp duromax log splitter engine and I haven't really thought about gearing yet.

Thanks

 

[jeeperjoel]

gotcha, that will probably work fine, sorry, the pic was a little decieving, seems the frame will be based mostly off the center beam, i've worked with a lot of 3x3" square tubing and at .125 wall it flexes more than you would think (just as an example) if i was building a frame like that supporting the weight of 2 people i would use 3x6" .125 wall with the 6" vertical, for the main beam it's not all that heavy and won't bow nearly as much under weight, the other option would be upper tubing as well, if you're going to build basically a single level structure on a flat plane you'll fight bowing the whole way, the other part will be twisting and axle support, in the rear, i would run outer rails all the way to mount bearings on rear axle then tie into main beam behind it

 

[bread]

Again, thanks for the comment. You think the 3"x 6" is really necessary? The 3"x 3" I plan to use is .188" thick. Will that still be too thin? I also adjusted the design to add those additional axle struts. I've attached an image of that.

Thanks

 

[jeeperjoel]

you could get 2 people, put the 3x3 tube on 2x4's at distance of planned wheelbase, have them hop up and down a little on center and watch it flex, you will be suprised, with the .125 wall 3x6 you will not even gain all that much weight vs. the 3x3 .188.... even 3x5" .120 wall weighs in at 6.46 lbs/foot, vs. 3x3" .188 coming in at 6.87 lbs/foot, the flex advantage would be huge with taller tubing, i see no need to use 3/16 wall tube, thick and small won't be as good as thinner/taller/larger

 

[jeeperjoel]

my non-cad lol, this will better support rear axle, weight distribution, and add frame strength, remember these are just suggestions of what i'd do and not intended to put down your design in any way, the outer structure would be fine at 2", or 1 1/2" .125 wall square, or round tube, even 1 1/4" round would work

 

[tiremikejr]

I second this design by jeeper the rear flex will be exponentially less as well as more stable. the original would either bend axles with ease, or crack rear welds/ bend engine mounting plate.

 

[bread]

I'll change the drawing to have 3x6 tubing, thanks for the suggestion. Also, will the subframe be strong enough made out of just the 1" square tubing? You seem very knowledgeable about from construction.

Thank you for your comments and time

 

[jeeperjoel]

1" .125 wall could work, but i'd go bigger i'd personally use 1 1/2", 1" seems fine... till you're holding it, it's small, the 3x5" .120 wall tubing i reffered for weight reference could be a good pick too, i like that it's lightweight, and the 5" height should be plenty, a lot of this also depends on unspecified length of wheelbase, and weight of riders, 2 kids on a small cart wouldn't need nearly as much structure as 2 adults/grown people on a cart that fit them, being that you'll be using decent size wheels, and a big engine i assume this thing will need to be substancial... attached is a pic of where my project cart frame broke recently, both sides, and the gusset work i had to do to repair, it's frame was made from 1" thin wall 1/16" maybe tubing... 1 rider, 13 hp with slight mods, these frames take tons of stress while riding, this is? was? a yerf dog factory cart, and wasn't designed to take the stress i've been giving it lol

 

[bread]

Wow, thanks man you are a big help! You also appear to be an excellent welder! I listened to what you said, and changed the design. I have attached a picture of the car with the trailer wheels and a pic of the new rear half. I am still not sold that I can't use 1" tube for the subframe. I want to support two 150 lbs people easily. I see full go karts made out of the 1" steel that support lots of weight. Also, you wanted the wheelbase, its 83 in.

Thank you

 

[jeeperjoel]

why thank you sir! the design appears to be much stronger, i like it, i have some 1" square tube in the garage, but feel a pic won't do justice to just how small it is, i'll try anyway.... some random scraps, 1", and 1 1/2" 14 gauge.. a little under 1/8 wall roughly... 1" 14 gauge is 1.035 lb/ft, vs. the 1 1/2" 14 gauge at 1.599 lbs/ft, about 1/2 lbs/ft more for the 1 1/2" material, not too much of a weight gain for a lot of added strength

 

[bread]

Thanks for the pic, I have seen the 1" in home depot. I have priced out all the frame materials I will need at metals depot. 8 ft of the 3x6 and 48 ft of the 1 1/2 x 1 1/2 comes out to be $294 without shipping and my budget for this thing is $1100. Not too bad. Can I use 11 gauge for both the steels?

Still, even with the amount of gussets, that 1" tube won't be strong enough on this particular frame?

 

[jeeperjoel]

i had to look it up, and must correct myself, been welding on trucks for a while and not in fab shop dealing with gauges of metal, the 14 gauge is .083" where as 11 gauge would be .120"... still doesn't sound right for some reason... oh well, the 11 gauge would be a fine pick ... as far as the 1" goes it's all up to you, it will probably work fine, i just always tend to add a little extra, so my stuff doesn't break (hopefully! ) the last determining factor is how hard you plan on being on the cart, i go into it knowing i'm going to abuse it pretty good, if you just plan on cruising on the street, or mild dirt trails 1" shouldn't have any issues, if you plan on the cart leaving the ground, or think that could be a possibility, 1 1/2" for sure!

 

[bread]

Do you think the $1100 budget is reasonable? (I'm selling one of my boats)

 

[jeeperjoel]

spending 300 on frame.... maybe, all depends on were you get your stuff, and what you get, engine mods, extra's you'll end up wanting, building a rolling chassis, with engine could be accomplished i'm pretty sure, but it's the finishing touches that'll get you, i'm finding that out right now, i started with a 200$ rolling chassis more or less, cheaped out wherever i could not sacrificing quality, and have gone over that i'm sure.... wheels, tires, hubs, brakes, clutch or torque converter, chain, chainring, bearings, heim joints, steering wheel/column, seat, axle, spindles even the hardware (i use all grade 8)... the list goes on and on.. it adds up fast, and a lot will depend on how much of it you fab yourself

 

[OzFab]

It's been said before, "it's better to use larger thin wall material than smaller thick wall material"; the larger material will weigh less but it will be stronger, 14 gauge 1.5" SHS is plenty for the outriggers, 14 gauge 1" SHS for the seat supports...

Speaking of seat supports, I'd like to make a suggestion: There will be a lot of downward force on the outriggers; to alleviate this, I suggest you mount the outriggers to the upper side edge of the centre beam, then mount the seat supports to the lower edge; this will add some much needed support to the outriggers...

The reason karts can be made with lighter, smaller material is because they usually consist of two main rails which support each other; literally everything on this kart is mounted to a single main rail, making it much more vulnerable...

Just as an experiment, get yourself some square tube & weld up a small (about 18" long, 6" wide) rectangle; then put one end in a vice & try to twist the other end; report results...

Then take three pieces of tube & weld them in a t or cross shape, single beam with one shorter piece off each side; put the bare end in a vice & twist at the intersection; report results...

Again, not trying to rain on your parade, we're trying to make your design as safe & functional as possible...

 

[bread]

Thank you all for the advice, however I don't want to change my design from the last pictures uploaded. The center beam will be 3"x 6"and everything else will be 1 1/2"x 1 1/2" all 11 gauge.

Thank you fabroman for the experiment idea but I haven't the extra money to spend on little tests, that why I ask the forum.

You guys did not rain on my parade; I just wanted some design ideas and thats what I got!

When I get started with the project I will create a new thread with plenty of pictures and we can talk all along the way of the build. Sadly, this won't start until late January/early Feb.

Thank you so much guys for your ideas and suggestions and I want you to know that they will be considered!

 

[OzFab]

Thank you fabroman for the experiment idea but I haven't the extra money to spend on little tests, that why I ask the forum.

Well, just for the heck of it, I'll tell you what will happen:

With your bare hands, you will be able to twist the rectangle a little; with a 6' bar, you're more likely to damage the bar more than the frame; don't get me wrong, the rectangle frame will bend but, it will take some force to do it...

The cross will bend a lot easier because there's nothing to stop it bending/tristing/flexing...

 

[bread]

The cross will bend a lot easier because there's nothing to stop it bending/tristing/flexing...[/QUOTE]



Are you worried my frame design is not going to hold, even if I use the 1 1/2" steel tube?