Designing a very simple gravity powered cart

Status
Not open for further replies.

saturnv7890

New member
Messages
22
Reaction score
0
Hey everyone, I'm new here, and I've been doing a ton of search around on the forum, and it seems all of you are very knowledgeable, and although this is a "go kart" forum for powered go karts, this is the same idea, just without a motor. I hope to learn a lot from you guys.

Goal:

Just like the title says, my friends and I are building carts to race down hills varying between simple straight hills that require all-out speed to tight curvy roads that require good handling.

My goal is to create something that handles well and will speed along the straights nicely. Above all else, the design must be very simple to make. I only have access to basic woodworking tools and hand tools. So yes, this will be made out of wood, with a few metal parts that don't require welding. I live in a condo complex, and I only have a small car port with no electrical outlets to work in. I'll be able to take it to my friends house with a few more tools (no metal-working tools) occasionally.


Design:

So I figure to create a fast cart, you would need the least amount of force pushing against you with drag and wheel friction. I think I'll order some pillow blocks, and get decent tires, and that will decrease friction as much as possible.

With drag, it may be a little more complicated. I'll probably want a good amount of foot room, and a very low ground clearance to keep myself very low. And I'd want to fashion some sort of body. What is the easiest way to make this? Would it be easy to make it out of fiberglass? I don't have much experience with fiberglass, but seeing as it won't be structural, and doesn't have to look pretty, I may be up for it.

Now for handling, obviously the steering would have to have a pivot for both wheels, instead of a simple single pivot design, which will slightly complicate the building process. And I assume it will also need a shorter wheelbase. Another issue is going to be grip through corners. I'd want to be able to take a corner as fast as possible, but it doesn't take a genius to know that the faster and tighter a turn, the more the cart will want to be pulled sideways. So we would want to somehow design the weight distribution to somehow push down on the tires through a corner thus increasing the force of friction, ideas?

Above all else, it must be simple to build.

Material:

What sort of materials should I build it with? I don't have a tight budget, but I'd like to keep it reasonable. I live in amerce, if that makes a difference.

Should I build it out of wood, or could I bolt together a metal frame? I realize this might weaken it considerably, but it's not a motor-powered cart, just a downhill racer.

I'd appreciate any ideas! (and I thank anyone who reads this whole post)

Also, I'll also be working on a design on keycreator over the next few days so you can let me know what you think of it.
 

modelengineer

Lord of the noise
Messages
1,609
Reaction score
2
Location
Sydney, Australia
Easiest way by far is to make it steerable with your feet, and have hand operated brakes. Very easy to do in wood. I had a "billy kart" which is what they're called over here which wooped everyone elses. It was absolutely fantastic. The secret is good bearings and hard, or high pressure, tyres to reduce rolling resistance. You probably won't go fast enough for aerodynamics to actually make a difference so I'd just forget about it all together. Once the thing is finished if you end up going over 50mph then you can put a fiberglass body on it.

Then we made the bus which could hold 4 ppl in a line, the front person steering and the back person had the brakes. Very dangerous but also very quick.
 

saturnv7890

New member
Messages
22
Reaction score
0
Easiest way by far is to make it steerable with your feet, and have hand operated brakes. Very easy to do in wood. I had a "billy kart" which is what they're called over here which wooped everyone elses. It was absolutely fantastic. The secret is good bearings and hard, or high pressure, tyres to reduce rolling resistance. You probably won't go fast enough for aerodynamics to actually make a difference so I'd just forget about it all together. Once the thing is finished if you end up going over 50mph then you can put a fiberglass body on it.

Then we made the bus which could hold 4 ppl in a line, the front person steering and the back person had the brakes. Very dangerous but also very quick.

Would you recommend I get 4 of these?
http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_21987_21987

and then pass an axle (maybe a threaded rod?) through and attach it to hard wheels with some locking nuts?

and of course, on something like this?



How does that handle on curves though?
 

Rickracer

RM250 Race Kart Driver
Messages
673
Reaction score
2
Location
Kissimmee Fl.
Pillow blocks will have considerably more friction than a good quality bearing. I'd do the foot steering (locked) front axle with free rolling wheels and hub mounted bearings, same in the rear, but with brakes on each rear wheel. I'd build a "canoe shaped" body just for the aero. :cool:
 

kfosburg

New member
Messages
19
Reaction score
0
Agreed... aero is a non-issue. Concentrate on something that you can actually drive - it's generally the loose nut behind the wheel that makes the most different in any form of racing. Keep it simple and have fun. If I were making it out of wood, I'd use mostly 4x4 lumber (not pressure treated) with a bunch of big lag bolts and a beach chair. You could build it with just a hand saw and drill.

Karl
 

Rickracer

RM250 Race Kart Driver
Messages
673
Reaction score
2
Location
Kissimmee Fl.
I just checked out the video in the other thread, those karts are MOVING. Aero is DEFINITELY one of the keys to winning. I'd plan on some "real" race kart wheels/slicks 5" x 5" wheels and 4.50 slicks, and regular race kart hubs and bearings. Your axles can be regular 5/8" cold rolled steel. Your brakes can be either hydraulic or mechanical discs or even a pair of band brakes, and I'd recommend NOT to use a live axle in the rear (too much scrub in the turns with no power), so you will need brakes on both rear wheels, and they need to apply evenly, so hydraulics would be the best way to go. I would try to mount the steering axle on a pivot with bearings so it will turn smoothly and freely. :cool:
 

saturnv7890

New member
Messages
22
Reaction score
0
I just checked out the video in the other thread, those karts are MOVING. Aero is DEFINITELY one of the keys to winning. I'd plan on some "real" race kart wheels/slicks 5" x 5" wheels and 4.50 slicks, and regular race kart hubs and bearings. Your axles can be regular 5/8" cold rolled steel. Your brakes can be either hydraulic or mechanical discs or even a pair of band brakes, and I'd recommend NOT to use a live axle in the rear (too much scrub in the turns with no power), so you will need brakes on both rear wheels, and they need to apply evenly, so hydraulics would be the best way to go. I would try to mount the steering axle on a pivot with bearings so it will turn smoothly and freely. :cool:

Thanks for the input!

How hard is it to learn to weld? I'm really considering buying a MIG welder off craigslist and welding a nicer chassis together.

How difficult would it be to learn to weld, and then weld a fairly quality frame?

Also, what other tools would be necessary, and what kind of space? I might be able to do it on my back porch near an electrical outlet, or run a very loonng extension cord to my car port...

so for the wheels, I'm assume i'd get four of these (or would I want to get bigger ones for the back and smaller for the front?):
http://www.northerntool.com/webapp/...tDisplay?storeId=6970&productId=34770&R=34770

and then 4 of these (or different diameters..)
http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200331476_200331476

and 4 of these, bolted on to the chassis one way or another...
http://www.northerntool.com/webapp/...isplay?storeId=6970&productId=531385&R=531385

And to attach the brakes, would I get 4 longer bolts for the hubs, get spacers, and attach the disc to one end of the long bolts?

Also, are the disc brakes at northern tool any good?
 

modelengineer

Lord of the noise
Messages
1,609
Reaction score
2
Location
Sydney, Australia
With a MIG, and someone to help you get the settings right, you should be a pro in less than 2 hours welding. It's really like a metal glue gun when it's set up right.
 

Rickracer

RM250 Race Kart Driver
Messages
673
Reaction score
2
Location
Kissimmee Fl.
I'm talking about hubs like these:



You can find them, and the wheels and tires, used, here: http://karting.4cycle.com/forumdisplay.php?f=57 . I've bought A LOT of the stuff for my kart off those classifieds, most recently 4 nearly new Dunlop soft compound racing slicks (for my RM 250 powered race kart), with about 95% rubber still on them, virtually new, for like $60. That's about $250 worth of tires. I see nice aluminum wheels going for $10~$15 each all the time, sometimes with slicks on them. :cool:
 

saturnv7890

New member
Messages
22
Reaction score
0
Well, after realizing how quickly this project has become complicated and expensive, I've decided that, at least for the first one, I'm gonna keep it really cheap and simple.

This is what I'm going for, only, without those brakes... I'll try and find a way to make them out of wood.


Where should I buy the wheels? I don't wanna spend too much on them... like $25 max for the whole set. Is home depot good for this kind of stuff?

And what is a simple and cost-effective way of mounting the wheels onto the 2x4's?
I'll be using simple tools and materials from a hardware store (i.e. home depot)
 

Kaptain Krunch

Pro Junk Collector
Messages
4,636
Reaction score
4
Location
vermont
Many people have tried and failed with those harbor freight tires, there very weak. You better off with a some front tires off a race kart.
 

saturnv7890

New member
Messages
22
Reaction score
0
How will navigating the curvy roads with single pivot steering be?

And it just feels silly to spend over 30 dollars on tires for a little project like this
 

porsche930dude

New member
Messages
906
Reaction score
29
Location
Upstate, NY
i had a cart like that made by boy scouts when i was a kid it worked great and lasted along time even pulling it through the woods with our gokart. It just had solid rubber wheels. the brake was a leaver between the drivers legs that you pull up twourd yourself at the other end just scraped the ground and had an old bicycle tire section nailed to the bottom. it worked fine
 

kfosburg

New member
Messages
19
Reaction score
0
To mount your wheels, I would use 4x4 instead of 2x4. Drill a 9/16" hole dead center in it about 4" deep (careful to keep it parallel!) . Then, just thread a 5/8" lag bolt into it exposing just enough of the smooth shank for your wheel using washers as necessary for clearance. Minimize any cantilever of the bolt to keep it stronger. Depends a little on how many times you will race this as to how well this will stand up, but it should be plenty strong unless you are a really big guy. Check for loosening after each run!

YMMV,

Karl


Karl
 

porsche930dude

New member
Messages
906
Reaction score
29
Location
Upstate, NY
mine had full length threaded rod for axle shafts. you can get that stuff pretty cheap from the hardware store. and that will also reinforce the 2x4 so a 4x4 isnt nessesary
 
Status
Not open for further replies.
Top