Ok.. so I got too much time on my hand even with the all the backyard projects my wife been giving me. I decided to design my own buggy and hopefully build it in the next 2 weeks so I can have it ready for DBBB. It's a very enthusiastic goal considering I haven't thought about how I will engineer the steering yet.

Criteria:

1) Must be unique ( single swing arm fork ) :singing:
2) Must use easy to obtain parts -- minimum fabrication
3) off the shelf tires and rims ( from ATV and gokarts)
4) super cheap!!
5) suspension -- optional , will add if I have time

Here's a quick sketch I made tonight.









So far, I've ordered:

1) bigfoot tires -Nanco 22x12x8
2) 8"x8" ATV rims with 4 on 4 bolt pattern
3) hubs to match rims
4) gokart spindle kit
5) steel tubings

things to figure out : seats

Since I am using a one piece rim , can I get away with not using inner tubes on my bigfoot tires???

looks cool, but how do you steer it?

haha.. still trying to figure that out. I guess I need to somehow rig up foot pegs that will connect tothe backside of the hub and wrap it around the other side. The idea is to still keep it functioning the same as a regular buggy. Since the hub is design with regular bearings that will allow a bolt all the way through, I can always go back to regular forks.

bummer ... I thought you had some trick idea how to make the single side swing arm work.

One option I thought about doing is keep the front fixed and have the back wheel turn!! It wouldnt' be too hard to accomplish with some linkage. Basically take a reverse trike with front wheel steering and turn it 180 degrees.

I will have a spindle in the front to allow the front wheel to turn. Just need to figure how to attach a foot peg system to control it.

Not to be a wet blanket, but the reverse trike could have some issues:

"Rear wheel steering can tend to be unstable because in turns the steering geometry tends to decrease the turn radius (oversteer), rather than increase it (understeer). A rear wheel steered automobile exhibits non-minimum phase behavior. It turns in the direction opposite of how it is initially steered. A rapid steering input will cause two accelerations, first in the direction that the wheel is steered, and then in the opposite direction: a "reverse response." This makes it harder to steer a rear wheel steered vehicle at high speed than a front wheel steered vehicle." (Wikipedia entry for "Steering")

Another concern is that you would have two spinning wheels.... possibly spinning very quickly. This would be happening just behind your line of sight in some cases. The possibilty of a body part or other obstruction coming into the path of rotation is too easy to imagine.

ATB,
Sam

Thanks for the info. I figure there's some good engineering mind out there. I guess it's back to front steering then!! I was thinking maybe a pedal right behind the front wheel that has a linkage to the steering arm off the spindle.

One foot peg option is to have a cap nut fasten onto the end of the spindle coming out of the hub and attach a foot peg to it. You will need to alimanate the dust cap and use a dust seal instead. This is the only downside I can see.
Of course this only helps with the right side peg. You still need to have a peg on the left where your steering spindle will be.
Move away from the problem for a short time and focus on something else. Then it will hit you like a ton of bricks and you'll wonder why you didn't think of it sooner.
Best of luck with the build.

Why didn't I think of that!! I actually already know how I'm gonna do the left side. I will have a bracket attached to the spindle itself like on a gokart and then attach a foot peg to that. On the right side, I forgot that the axle bolt goes all the way through. The hub has 5/8" bearings to accept a bolt so I can get pretty much any length. The way the hub is designed, you can use regular forks. The reason I want to make this design work is because it does not limit the tire width.

Take a look at blowkart steering , you might find a solution there.

I thouht blowkart steering is with the hands? It looks like they just lean the front wheel instead of actually turning it base on the angle of rake. I've never seen one in person so not really sure if you could apply their steering technology to such a wide tire like a bigfoot.

Spider most blowcarts are hand steer. But some may be foot steer.

I just talked to a buddy at work and we came up with an idea to extend the spindle/front axle so it protrudes to the left. I will need to turn the spindle bracket so it faces backward. I will also need to lower the front arms so that it is lower to clear the pegs. On the right side, an attachment to the bolt with some kind of extension nut like Rocfighter suggested. I will draw it up when I get home tonight. If this works, this will be a cool looking buggy!!

The Manta land sailer does have foot steering that may come in handy for you. google a pic of it and see what you think! The foot pads are mounted on a single bolt through the frame then has linkage that goes up to the fork! Looks relatively easy to duplicate!

Arrrh I knew I had one somewhere

Third from last photo....I think this is what you are trying to do

ptw,

the foot peg in that picture was close to what I wanted to do but it seems like every previous build have been to take the easy way out and have the pivot point behind the front wheel or use a rake angle that would cause the front wheel to lean over instead of actually turning. I want to keep the front wheel turning on teh same axis as it would with a regular fork setup.

well I found out the technical term of what I've been trying to describe. Implementing it is another story.

It's called Hub-center steering. It's use on some of the motorcycles out there. It can be use on single or dual side arms.





here's a little read up on it for you geeks out there.

http://en.wikipedia.org/wiki/Hub-center_steering

James Parker RADD.... Yahama Morpho..... thanks for the trip down memory lane....sigh.

ATB,
Sam

Here's some shots of some of Peter Lynn's early buggy steering systems:

Here's the other photo:

Morrie,

I can see why they went away from that. Doesn't look like it would work very well with the pivot point so far behind the wheel. Glad to know Peter Lynn was so creative back then. I know trying to do what I'm doing is crazy but you gotta try!! :singing:

I tried something similar to this a while back. The biggest problem you will run into is literally when running into things. Direct contact with something at even marginal speed can end in catastrophic results. This can happen in a variety of ways: running into what looked like a shallow gully, trying to ride up a bank that was a lot steeper than you first thought.


The fork design that has the pivot point right near the wheel could cause serious ankle injury as the impact forces quickly sheer the turning point sending the energy to the point of least resistance - your ankle. Along with that if the support structure is on a horizontal plane the wheel will contact the support structure every time you want to turn right.


This is the problem that I ran into - I had the monofork go to a headtube above the tire like most buggy forks- so that I could turn the front wheel on an axis above the wheel - giving the wheel a good rake angle in which to turn on. When I smashed my front end into a sand berm that I thought I could go over, all the stress from the impact went into the weak part of the fork - where the axle was welded to the fork support. Instantly the tire was bent back and rubbing against my down tube.


Here's a picture of it before I ruined it - it worked fine for about 6 or so outings - but 1 bad decision and my day was ruined.



If you only have a few weeks until you need the buggy - try not to be too flashy and tricky - just make something that works well - In the end it's all about how it feels, not how it looks. I would go with a traditional fork system and save yourself the frustration and hastle, besides building a regular fork isn't as easy as it seems. Good luck with the build - keep us updated with pics and ideas.

Flex,

Thanks for the insight. My pivot would actually be in the center of the hub. The hub has an offset so the pivot is slightly to the left of the centerline of the rim. I plan to have a slight camber to give it a kingpin angle that will create a turning point on the ground right in the center of the tire. I did wonder what would happen if you turn the wheel too much to one side.

I actually already have a ride.. just wanted to make one ready for DBBB to do show and tell...hahaa... Advice well taken on the regular fork. I have actually already planned for a regular fork as a backup and am already starting the welding on it. I figure this crazy fork will make my build more interesting.

As long as your down tube comes into a clamp and isn't welded to the frame - you can swap out any front end you build pretty easy. And yes the crazy fork will make your build more interesting.

OK.. Just got in from cutting and grinding in the garage so thought I make some buggy porn with Google Sketchup.

feel free to drool... :roll:

For the blokart type steering just move the handles down to where they become feetles.
Yea the steering radius may be a bit wide and its not intended for fat flat tires but it does satisfy the "KSS" rule. No insult intended. Building one myself right now. Good luck have fun!

No insult taken.. I'm an engineer myself so do understand the KISS principle. That's why I'm building a regular fork as a backup ;-)

With such a straight shot, wouldn't the front wheel turn anything that's on the beach into a seafood buffet for the pilot? Whatever you come up with a shield/mudguard will have to be factored into the swappable front end.

ATB,
Sam

Very sweet idea going with the mono.