Undergoing large project: go cart

[Ayrity]

Well I have sat around thinking about it long enough, and I finally have a place to build it so finally I am going to make my go cart/project car. I have acquired a 6HP vertical drive shaft mower engine. I may be able to get an 18HP one though, which would be better I think. I am planning on desiging and making my own frame, I have a friend with welding skills who will weld it all up for me, and help me bent the tubeing. I was thinking of using aluminium tubeing, and maybe bike frame parts, not sure about the wheels yet, but I think I will either find a used motorcycle tranny or make my own with pulleys and belts. I think ill use a differential on its side to transfer the power from the engine to the rear axle (since its a vertical shaft). at the very end I think ill use plywood foam board and fiberglass to make body panels, etc. but for right now I need to make the frame and make a final decision on the engine. Any help there? any program or website on frame and structural design? anyone have any hints or tips for me? would 6HP be enough for this kind of project and probably a 2 seater? or should I go for the 18HP engine? thanks everyone

 

[Danger]

Hi, Ayrity. Your choice of engine should depend upon how fast you want to go. I can forsee one problem with using a differential for your driveshaft. Unless you lock up the spider gears like in a Positrac or Sure-Grip unit, it will transfer the torque to the axle that isn't hooked up to the wheels.
Before starting with aluminum, make sure that your friend has the proper type of welder for it (Mig or Tig); a regular arc welder won't work on it. Also watch for dialectric corrosion if you're mixing aluminum and steel. You'll probably be fine with just a simple ladder-frame, but adding diagonal tubes to form triangular cells would be better. It sure wouldn't hurt to incorporate a padded roll cage and seatbelts as well, if you're going to be building up any high speed. In addition to the safety factor, a cage helps to stiffen the frame.

 

[Ayrity]

very good points. my bud has both kinds of welders, and i don't think ill be adding any steel, maybe for hinges or something later though. I want to have some speed, don't want to be passed by the little girl next door on her pink bike haha. i was thinking of maybe getting the hatchback from a car in the local junkyard and use that as my windshield and front slope of my car. perhaps even the door, open it up to get in and out, that way I don't have to mess with glass and sealing it etc. and if i pop out the tail lights, i can pop in some head lights right there too. any more ideas? oh and what i mean by the diff. is that use the part that normally comes from the tranny, and put a pulley on that from the engine, then have the power go out the two sides to the wheels like normal

 

[Averagesupernova]

If you start adding stuff like a hatchback for a windshield this thing is going to get heavy in a hurry.

 

[Ayrity]

this is true, which is why I am going to stick to light materials, like aluminium and fiberglass. ill strip down the hatchback to just the metal and glass. that and the engine and the driver will be the 3 heaviest things

 

[Danger]

I see what you mean about the differential, and it should work fine. If you're going to use one from a car, though, as opposed to from a garden tractor or something, it will also be pretty heavy. You'll need your welder pal to build some adapters as well, to mount go-kart type wheels on an auto axle.
Two things that we haven't addressed yet both involve stopping. You'll need a clutch of some kind (centrifugal, snowmobile torque converter, or just a moveable tension idler to decouple your belt drive). With the amount of mass that you'll have, you also should put a lot of care into the proper selection of brakes.

 

[Ayrity]

ya, brakes are on my mind, i was thinking perhaps I could scavange some calipers from the local junk yard, bu I am not sure yet. in any case, I was going to try to make the clutch along with a couple gear ratios. I was thinking that I could have the shaft off the engine have a small and large pulley wheel, and, a bit further back, have the shaft from the differential have 2 different sized wheels as well. I would use tensors to engage one or the other, or neither (there is the clutch). But the one thing I keep getting stuck on, is how do I prevent the belts from falling off the wheels when they are not tensed? anyone have any better ideas? I think more than 2 gears is unnecessary, although ill have to figure out some sort of way to calculate the ratios needed, maybe just trial and error.

 

[Danger]

I'll have to do some sketching about the belt problem. The simplest thing might be to just build a sheet metal 'pan' under each one to hold it up. The problem then would be to keep the unwanted one from intermittently grabbing a pulley by accident. What might be best, if we can figure out just how to do it, would be to build something like the deraillure (sp?) shifter on a bicycle. If you use 4 different sizes of pulleys (2 on each shaft), you could then have 4 ratios available (1-3; 2-4; 1-4; 2-3). Removing the belt completely from one end or the other would be 'neutral', and a separate clutch wouldn't be needed.

 

[Ayrity]

ya, that would be good, but a derailer for a belt might be a bit difficult, i was going to use a V belt because of the added traction, maybe if i use actual bik gears and parts? just mount it on its side? and maybe have one gear spin freely, that would give a neutral

 

[Danger]

I just remembered something that might be more practical. One of the presses where I used to do screen printing had a variable pulley on it. It was made of two separate sides spring-loaded together in a standard 'V' shape, and used a normal 'V' belt. Increasing the belt tension forced the belt farther in, which in turn forced the sides farther apart. It therefore decreased the effective diameter of the pulley. Maybe something like that could work in your situation.

 

[Cliff_J]

Get a salvage moped - it will have a centrifical clutch that engages automatically on its CVT (continously variable transmission) belt drive that is already designed to allow the ratio to change depending on RPM and load. The same idea is used in snowmobiles, some ATVs, and some cars (although the cars use metal belts instead of rubber).

 

[Danger]

Great idea, Cliff. I didn't know that they work that way. A right handy bit of information for future projects.

 

[Ayrity]

definetly, thanks very much. i think tomorrow I am going to try to make a mock-up of my frame with pvc pipe to see if i made any bad design ideas.

 

[Danger]

How about taking a few snapshots along the way and posting them here? It'll help us keep track of your progress.

 

[Ayrity]

sure, if you guys are interested i definately can do that, but be warned, I am a student and I am home on break right now so it might be slow going... back to some basic ideas, I think a CVT is the right choice for me, but there are SO MANY different types haha, if you can believe that. Some I can even see making for myself. here are the links for the few I am considering.

http://www.fallbrooktech.com/NuVinci.asp

http://www.mie.utoronto.ca/staff/projects/cleghorn/Images/mrco4a.gif

http://www.mie.utoronto.ca/staff/projects/cleghorn/Images/mrco4b.gif

 

[Ayrity]

ok so, transmission aside, i think i have my basic frame down, itll be a 2 seater, side by side. with the door in the front, doubling as the windshield, ill set it either on hydrolics (the kind in a hatchback not really ones) or ill have it slide up and down in a track. still working on getting an engine, I am thinking lik 15 to 20 HP, somewhere in there. now here is a question, I have seen these kits all over the internet for converting gas IC engines to work on propane, I think this could be a really cool addition to my project for not that much more time/money. I would much prefer tho to adapt the engine myself, and not buy a kit that has been marked up 800% haha. but i can't figure out how they work exactly. i was thinking maybe just cut the fuel line between the carb and the cylinder(s) and put a Y splitter with a valve in it then just hook up a line from a propane bottle. that way i could start it up on gas then switch over. do i need to do anything other than this? any ideas? thanks guys

 

[Cliff_J]

Ayrity - STOP!

You're playing with fire accelerants if you're going to mess with what you are talking about. This is highly dangerous, do you have an adequate firewall built into your design to prevent really bad things from happening? This is extremely unwise stuff to mess with, and not something to have a cavalier attitude about, this could be seriously bad.

On to the details, the whole point of the fuel delivery system is to properly mix the fuel/air so they are in the correct proportions for the engine to operate, if the mixture is incorrect the engine won't run or could even be destroyed. Even if the kit is only $5 worth of brass parts, the machining required to get that brass into the correct tolerance and design time to arrive at those numbers is going to be important. A gasoline carburator is not going to properly work with liquid or vapor propane and you haven't even mentioned a regulator to control the vapor pressure and so on. Those details are critically important.

Ignorance is dangerous! Be careful!

 

[Ayrity]

thank you for your care, but i am FAR away from screwing in a propane tank from any kind of engine. I may be ambitious but not stupid, haha. I am only trying to do research at this point. I know it will take a lot of planning, and this is where I am trying to get some secondary information. Like I have no idea what kind of regulator to use, I was thinking maybe some sort of vaccume valve? and i don't think it needs to be routed through the carb, because its already in gas form, but it still needs to be mixed with air obviously. so if anyone has any links to a good site, or something of that sort, that would be great. again cliff thanks for the concern!

 

[Danger]

I can't help you with links, but there are several factors involved with a conversion. My serious recommendation would be to visit an auto mechanic who does it a lot. There are kits available, but probably not for your type of engine. Some professional tinkering will be required. For starters, a dual-fuel carb is used, unless you want to stick strictly to one or the other. That will most likely have to be a modified unit made for a very small car or motorcycle, which will also need a custom manifold to attach it.
Propane heads are usually swapped in, because propane burns hotter than gas and also doesn't have the lubrication effect that even unleaded provides. You'll want hardened valves and seats, and might have to increase your fin area for an air-cooled engine.
The ignition timing is different for propane as well. Dual-fuel cars have it set half-way between the optimums for each, so you lose efficiency on both. Your cam timing might need to be changed too.
Lastly (for now), make sure that the tank you use is oriented properly. Some are made to work vertically, such as one for a BBQ, while automotive ones are generally horizontal to fit in the vehicle. It's very dangerous to put either one in the wrong way.

 

[dingpud]

Some good links to plans...may be helpful

Not sure if this is going to be of any help, but the following link sells kits for building go-cart and buggie type vehicles.

www.badlandbuggy.com

I've seen some of the projects under construction during a welding course that I took at a local community college. Buying a set of plans may be useful or give you some ideas.

Just a thought.

Best of luck.