All-Wheel-Drive Go-Kart!

[Smurph]

Scratch that, I'm going to put CV joints in up front. I want this to perform rather well. I've found a pair on ebay from a 1989 saab for $50, and they have a u-joint end on one end, and the cv joint on the other. This will work perfectly. I'll most likely go grab some from a junk yard, though.

 

[Smurph]

Got the differential locked in place, and then put the axles in there. I went ahead and drew the u-joints in there inside the spindle, though they will be CV joints. The image shows the wheels turned.

Does this help explain my ideas for the front?

 

[theo]

If you arn't using suspension you might be able to get away without the inboard u joints

 

[Smurph]

If you arn't using suspension you might be able to get away without the inboard u joints

I don't feel like tackling suspension right now, but I would like to expand to that later on.

 

[Smurph]

Honestly. A car's differential will probably be the cheapest option. I'll be able to find a used one off some old stock wrecked car for next to nothing. And I need 3 of these. The ring and pinion gears are going to be hard to come across. I'd like to get as close to 1:1 ratio as I can.

Also, theo, by the looks of most CV joints, they'll have u-joint connectors on one end. And they will determine my kart's width.


Put the steering linkage in there, it works right. I also edited the differential to look a little better. Its hard to tell, and almost of no importance, but the spindles are smaller, too, and it has a slightly lowered center of gravity than before.

 

[Smurph]

Though the width (and ultimately the length, as well) of my kart may be altered by the dimensions of the differentials and CV joints I collect as well as other things, I have it mocked up right now as about 30.5" between the centers of the front wheels (assuming 6" wide tires). With that width, I'm going to shoot for about 40" between front and rear axles when the wheels are pointed straight.

On the kart in the basement, there are some wheels with slicks on them. The back wheels are a little bigger--It's a 1-seater. The tires are about as old as I am (22) and almost definitely need to be replaced. I would want something closer to the ones on the awd twin-engine found in that pic.

Anyone know what kind of tires those are?

Calculations on speed right now:
A CR 250 engine makes its power at 8500rpm. I believe I multiplied it properly after finding its 6th gear ratio, and came up with a 9700rpm sprocket speed and I used that to calculate, and hoping I get 1:1 ring/pinion gears. I have found a 35 tooth sprocket with a pretty wide opening to use as my drive sprocket, I have also found a 14 tooth sprocket to use on the transmission output. This calculated with 8" tires to go 92mph. Assuming that drag and weight will take 25% of my power (random guess), that will still leave me running about 70mph.

Got a little more done on my design. I have the wheel base set up, and the rear end put in. The wheels I drew up were 6"wide x 8" diameter


If built exactly like that, it's got a 2.203" ground clearance.


There's the full drivetrain. It even functions properly within this program (Inventor 2008).
The front/back differentials wont be centered, and will be facing opposite ways. My kart will look very similar to this, not exactly. But this does show the functionality I want my kart to have as far as the drive train goes. I took a wheel off to more easily see underneath unobstructed.

 

[TOO FAST]

Makes sense now. Keep us informed - this is pretty cool project

 

[anderkart]

I have found a 35 tooth sprocket

Driver sprockets for a Honda CR250 are the much larger/stronger 520 chain size. They seem to be commonly avalible in 12 to 16 teeth models.

 

[Smurph]

Driver sprockets for a Honda CR250 are the much larger/stronger 520 chain size. They seem to be commonly avalible in 12 to 16 teeth models.

We might have some terminology mixed up here. I've found a 35 tooth sprocket to put on the axle (or middle differential in my case). And I'll be attaching a 14-16 tooth sprocket to the engine.

 

[freakboy]

What size engine are you looking to use?

 

[Smurph]

im thinking about a 250cc 2 stroke

Mostly because of how much smaller they are, keeps my weight and size down.

I've been thinking about making the center drive shaft run parallel to the rear drive shaft. I don't know if I want to spend a couple hundred dollars on pinion gears that are going to kill my speed. If I do this, I'll put sprockets on both sides of the shaft. I'll still have a differential between front and back, but I'll run the power via chain. This will probably save a lot of weight, like someone mentioned before. I just didn't think about this option.

Any ideas?

 

[anderkart]

10-4 Smurph, I misread what you meant there.

 

[Rickracer]

... If I do this, I'll put sprockets on both sides of the shaft. I'll still have a differential between front and back, but I'll run the power via chain....Any ideas?

How/where would you put the center diff? Maybe on a jackshaft somewhere in the middle? Where will you mount the motor?

 

[Smurph]

How/where would you put the center diff? Maybe on a jackshaft somewhere in the middle? Where will you mount the motor?

Right now, all of these dimensions (and there are TONS of dimensions on that project) are approximate. The only thing I'm mostly sure about at this point is the axles will most likely be an inch thick. My huge hurdle is that I don't currently know how to weld, but I'm trying to save up for a welder so I can learn. I also am having the hardest time finding a welder at all (which is why I'm trying to purchase one). I even have a good friend who is wanting to practice welding (was planned to be the welder as per my ideas), but between us, we can't find someone who'd let us use theirs--or anyone with a welder at all.

I also don't have any of the crucial parts. The actual size and shape of the differentials I get ahold of will determine where they will need to be mounted for things to all line up. The actual CV joint I get might determine how wide my kart ends up being, unless they're just too wide or too narrow that I'd have to cut them or extend them. I don't have any clue what the dimensions are on a 250cc 2stroke engine. If anyone could just get me the dimensions of a box that it barely fits in, would be a lot of help in the design phase.

Lots of things will be decided in the garage rather than the office. I'm drawing up more of a "best-case-scenario"/Optimal type drawing. I did calculate a 40" between front and rear wheel centers, and 35" between the centers of the front wheels, which, according to ackerman steering geometry principles, would require the front steering control arms to be at a 66.37degree angle. I'll try to stick to my wheelbase more than anything. I want it to be close to square, but the width will be no less than 3/4 the length. I'll make the steering control arms adjustable, so I can use it to learn more about ackerman steering principles as they apply to performance later on.



That is what it might look like without the chain, if I were to use chain drive. The more I think about it, The more I like the idea.

Good news, it looks like I'm going to get away with about $25-$30 per differential.

I also might not ever put any suspension on it. It can't make too big of a difference on pavement. Which, theo, you're right. I bet it would be easier to go without the u-joints.

I've done some calculations via the program to find the mass of the frame should be around 25lbs. This is very hard to be accurate with. But is probably within 5lbs.

Anyone think it'd be outrageous to think that I could have a 100lb cart?
If so, scaling top speeds claimed by others on the internet that have bikes with 250cc two-stroke engines, I should be able to do 80.

 

[Rickracer]

Well, since I have a 250 2 stroke kart going together, and if thing go as planned, it will be hitting the 1/8 mile dragstrip this weekend, I might have some factual data for ya,

 

[Smurph]

I just found out that SCCA has a shfiter kart class (a purpose for this, at last!) with a 125cc limit. I wonder if they have a 2wd restriction? If so, too bad. If not, I have a bloody fast kart that I can use in large empty parking lots.

So I think I'm gonna go down to 125cc... I won't turn down a good deal on a 250 tho. We'll see when I get to the engine part.

 

[brendonv]

Wouldnt it be really hard to turn on the road with 4wd?

 

[Smurph]

Wouldnt it be really hard to turn on the road with 4wd?

actually, awd ought to increase my lateral g tolerance just a bit. Because I'm using 3 differentials, power can be distributed to which ever wheel is getting the least traction which will allow all wheels to move at the speed they need to. For instance, when turning left, your right wheels (outer) spins a little more than the left (inner) wheels. The differential will allow for both wheels to receive power, but allow one to move faster than the other as necessary.

The middle differential will be driven by the engine and will [via chains] turn the front/rear differentials. It will turn the front/rear differentials more or less depending on which one is easiest. The front/rear differentials will both do the same thing: distributing the power they are given between the left and right wheels where necessary.

If I held 3 wheels still, and had one wheel free to spin, it would be the only one spinning. All of the power would go to it, but it would work..

I have had some good luck finding differentials. I'm just looking for the carrier with inner gears, and have found some old ones for pretty cheap. Finally got some parts on the way! I still am buying differentials if ya have some lying around.


That's what I'm looking for.

 

[modelengineer]

However, if one wheel starts to slip then all the power will go to that wheel, since you're not using LSD's.

That's a neat looking little diff!

 

[Smurph]

However, if one wheel starts to slip then all the power will go to that wheel, since you're not using LSD's.

That's a neat looking little diff!

Yeah, I was thinking today of ways to easily lock it that can be just as easily un-done so that I can have essentially a live axle in the back when I want it. I'm planning on just being able to whip around on the pavement as I wish, so I would want 4wheel traction as often as I can. I'll play around with everything when I get it together

That differential is out of a 1975 cadillac. I think they said DeVille. I might be wrong on the model... Either way, I want it. It looks pretty small, and I can definitely get a sprocket on that.