Back to the Basics - Chassis, Engine, and Suspension

[Jonas]

Hey guys-

I know this is a very broad title, but I've got a lot to learn. I'm looking to build a kart/buggy cross, some kind of one-seater to cruise around in my fields with. However, I'm still really new to this, so any help is appreciated.

Chassis/Frame: From what I gather, these tend to be custom built to fit the driver. Is this true? I'm a slightly shorter than average male (5'9"), so it would seem that it would be fairly easy to find a prebuilt one. However, if I build my own, what design features does one look for in a frame? Just a simple rectangle, or is there reason behind the "fancy" flairs and bends that some have?

Engine: I've heard that somewhere between about 4-8HP is the sweetspot for karts, but given that I'll be doing some off-road hill climbing, it would seem logical to air on the higher end of the scale. I know that this topic has its own topic section, but I'm just looking to clear up the basics before I get into detail.

Suspension: I still can't visualize how a suspension system and steering can go together. It seems like when the shock absorbers compress, the tie rod would no longer be in a straight line outward, but would rather be a radiant of a circle. This would imply that hitting a bump would affect the steering because the tie rod would effectively be traveling a couple degrees around the circle, making the total distance from its origin (at the kart's center) to the suspension shorter. Is this at all true?

Thank you so much for any answers you can provide. I'm still really new to all this.

~Jonas

 

[fowler]

firstly how serious do u want to go
or more importantly whats your budget

u have 6.5hp yard karts that go just fine over rough ground and up grassy slopes at a good 30 mph
they are a few $100
then u get 100 grand trophy trucks thatll do any speed over any terrain

ill go with the more common end for this site
u are wanting somthing like a big yard kart or small superlite buggy

maybe look into the edge buggies and the spider karts
http://www.edge.au.com/
http://www.spidercarts.com/go-kart-plans.html

you are right the frame is usually custom built
it can be like my first buggy of just make it up as u go
or u can buy plans off the above sites

engine
yes 6 to 8 hp is common
but for an off road kart with some go u can run a 13hp
for the transmission u can run a 40 series torque converter
a t/c gives u good low down power and good top speed
it operates like an automatic car (in a wide view of things)
so its just accelerate and go

suspension
well hell i could write u a good essay on this but lucky for all of us someone else already has
read this
http://www.diygokarts.com/vb/showthread.php?t=11760

as for the tie rods
u must make the pivot points of the tei rod align with the pivot points on the suspension arms
but for an off road kart this is less important
as long as the geometry is close then thats good
firstly
your geometry is set up to be crorrect when the buggy is sitting at normal stance wheels straight ahead
as soon as the suspension starts to articulate or u turn the wheels some points go way out
also driving on dirt and grass is slippery so less focus is on perfect steering geometry and more on just keeping grip
although really bad setup steering will cause u to lose grip as well

so tell us what sort of kart u want and your budget
and we can go from there

oh and what sort of environment are u in?
a snow mobile is no goo in sand and a drag car is no good on forest trials

 

[Jonas]

Thanks for the quick reply. I've got a decent budget - since it's technically a school project, my parents are willing to help, so I won't need to be too skimpy. I think I could work them for maybe $400, and add another $300 of my own. But to be honest, I really don't know what the typical budget for one of these things is, so those numbers could change.

I love the look of the Edge Barracuda! I think I would definitely be going for something more along those lines than those of the Spidercarts. I'm in northern Vermont, but I won't be using this in the winter, so it'll be handling summer conditions only. My main driving area is a pretty rough field (lots of rocks, ruts, tall grass and hills,) as well as our gravel driveway. That's why I'm thinking the suspension is a must.

 

[landuse]

What type of fabrication skills do you have? Can you weld?

 

[fowler]

To do a barracuda properly u need 10 grand

Locally they go for 22

Look into the sidewinder
It is far simpler to build
Still full suspension and in America u should be able to build one inside your budget

The biggest cost is usually engine

 

[exenos]

If you want cheap power I'd suggest finding a small sled engine in the 250-300cc range since your in Vermont. That way you get the cvt with it.

If your budget is $700 I'd pretend that I only have $500 to spend. That way you have a better chance of staying under budget. ( Wish I had done this)

 

[Jonas]

Thanks for the responses. Yeah, I definitely wouldn't be building a full kit Barracuda. Right now, I don't have any fabrication skills, but I know someone who can teach me welding pretty well. I like the idea of the sidewinder.

In terms if buggy engines, what kind of horsepower is typical? I'm gathering that they're pretty significantly bigger than those of the traditional small go kart. What do you guys think about getting a manual transmission? I haven't looked into them that much, but they don't seem very common in buggies or karts. However, it seems like having one would be a lot of fun.

 

[exenos]

Some of the chuggies are only 9 hp, It really all depends on your performance expectations and how large your buggy is. Take a look at Djeeper's deathtrap. It only has a 18hp twin with a cvt on it and its more than fast enough.

 

[OzFab]

Ok, I'm being lazy, I haven't read the entire thread but, I get the gist so, my apologies if I repeat anything:

Chassis/Frame: From what I gather, these tend to be custom built to fit the driver. Is this true? I'm a slightly shorter than average male (5'9"), so it would seem that it would be fairly easy to find a prebuilt one. However, if I build my own, what design features does one look for in a frame? Just a simple rectangle, or is there reason behind the "fancy" flairs and bends that some have?

A custom built frame has the advantage of having exactly what you want where you want it; 9 times out of 10, when someone buys a prebuilt frame or plans, they change something, it may be miniscule but, it's a change...

Sometimes, the bends or "flairs" are a design feature & are done that way to be more pleasing to the eye, sometimes they're just "fancy flairs"

Engine: I've heard that somewhere between about 4-8HP is the sweetspot for karts, but given that I'll be doing some off-road hill climbing, it would seem logical to air on the higher end of the scale. I know that this topic has its own topic section, but I'm just looking to clear up the basics before I get into detail.

IMO, the main reason 4-8hp is preferable is due to budget. Once you hit 9hp, the PTO shaft of an industrial engine goes up to 1" & clutches to fit them are considerable more expensive ($30 as opposed to $100 for a cent clutch or $150 as opposed to $350 for a torque converter.

Another affordable option is a motorbike engine; they have the advantages of an internal clutch & a 4 or 5 speed gearbox plus you don't need to go too big to exceed 9hp (a 150cc 4 stroke typically has 11-15hp)

Suspension: I still can't visualize how a suspension system and steering can go together. It seems like when the shock absorbers compress, the tie rod would no longer be in a straight line outward, but would rather be a radiant of a circle. This would imply that hitting a bump would affect the steering because the tie rod would effectively be traveling a couple degrees around the circle, making the total distance from its origin (at the kart's center) to the suspension shorter. Is this at all true?

As long as the tierods follow the same line as the A arms you won't have a problem...