Frame
I know I want to mimic the dimensions of the Honda frame, yet stretch it a little to fit a taller person. Lurking around the pilot forums, I figure the length would have to be stretched at least six to eight inches, maybe even twelve.
At the same time - we may have to stretch the back end to get proper room for the engine and drivetrain. because the Hondas used single-cyilinder engines, I may need to widen the frame slightly to accommodate a two-stroke twin. I
would have to check to see if the roof height is fine. Most of the ROPS
I have seen on bulldozers and other heavy equipment gives you around 2
feet of headroom when sitting in the seat.
(Idea - Put the engine and transmission on a single mount - if the frame is wide enough, the whole power unit can be removed with a engine hoist!)
The steel tubing on the Honda is around 1 1/4" and about 15 gauge. I would probably want to go up to 13 gauge, as that would make the frame more bend resistant. I'll have to talk to my dad about what kind of steel I should use.
Engine
After a little research, I have determined the 440 Rotax is from a late seventies Ski-Doo Everest. The engine is supposed to output around 80 horsepower, and is reputed to be one of the more reliable snowmobile motors made by Rotax. The air cooled motors are not mentioned as much as the later liquid-cooled models, but parts are supposed to be easily acquired and inexpensive to boot. The motor does not have a carburetor, but my dad does have a large-bore Mikuni sitting around from his dirt-biking days that might work.
For air filtration, the simplest would be to grab a airbox off a Geo metro or Suzuki Sprint. While not normally intended for heavy dust conditions, they are usually designed with the best filtration intentions; the paper filters are inexpensive to replace; and the external air inlets on the airbox usually allow a hose or snorkel to be attached, allowing for a precleaner to be installed.
Fuel System
If the frame is stretched sideways, I might be able to squeeze a fuel tank alongside the engine like the original Honda had. This would mean the use of a fuel pump, but it should be pretty trivial to implement. Honda does not appear to have a very big fuel capacity, which would be an issue - I may need to consider how I would add an extra fuel tank.
Electrical
The new information I found about the engine indicates I have a 12 volt system, so that calms that concern. I don't have a rating for the generator, but considering the snowmobile had a 75 watt headlight, I'm going to guess around 100 watts. That gives me about 8 amps to work with for lighting.
I will probably need to use LED lights to get the lighting configuration I want. They are a little more expensive than regular sealed beam lights, but also consume half the power of an equivalent sealed-beam.
Instrumentation might be neat to build. I would probably go electronic
(I am taking courses in electronic engineering!), but would stick with
simplicity - engine heat, tach and a speedo, for instance.
It might be possible to retrofit the motor with an electric start - It looks like Rotax just throws a ring gear behind the clutch and mounts the starter beside the motor. That method makes it almost look like an afterthought than intentional - Yamaha's snowmobile motors by comparison have it on the flywheel.
Drivetrain
I think I'll find a FL350 odyssey transmission. While parts for it may be getting harder to find, it is probably the most inexpensive gearbox option for what I want. The average selling price for an FL350 gearbox on eBay is around $700usd; a knockoff of the RPM gearbox is available for $900usd. compare that to the +$2000 the RPM goes for.
Another option would be to use a reversing snowmobile chaincase (Around $300usd), but two other things come in: Complexity and Ratios. The Odyssey transmission is around 10:1; the RPM is 9:1, and the snowmobile chaincase is around 4:1. To get this gearing down, I would need to add a chain drive to a "Spool" - a shaft that connects the two rear wheels together. While this may be okay, it introduces a whole range of issues in both construction and maintenance that I hope to avoid with the enclosed gearbox.
Operator compartment
If this buggy is going to be a rocket that can be thrown around by a nutcase, I'm going to need some pretty serious safety gear. a four or five point seatbelt is mandatory, and some consider a suspension seat important for high speed off-road travel.
Since my main intended use is high-speed, long distance travel of logging roads, I'm going to have to put a bit more money into driver comfort. I might go for a more expensive seat, and consider a windscreen.
Wrist restraints will be needed to keep the hand from flailing about during a crash, and I should probably consider some form of padding for the leg area. I might also consider a "Doughnut" to put around my neck to help prevent whiplash.
Of course, a helmet is mandatory. Why bother with all the safety gear if you plan to get a fatal head injury?
Body
I do happen to have a set of rear fenders off a ATC200 that would be perfect for the rear end. The front fenders would have to come off a racing quad to get the proper kind of profile.
For the front "foot tub", however, I would be better off molding fiberglass into the shape I want. Some simple carpentry would get me a mold that would match the shape I want to lay out the fiberglass cloth.
Suspension
The main hurtle I have is the rear suspension - Partly because of the drive axle limiting it's travel, but because of the different setups the Honda uses.
For the FL350 Odyssey, they use a "Trailing Arm" suspension on all four corners. The FL400 Pilot uses A-Arm suspension up front and "Multi-Link" suspension on the back.
There is nothing wrong with trailing arm suspension - the original VW Dune buggies used it and is still common on dune buggies. The linkages are very compact and so heavily built that they are very sturdy. The only drawback is that it provides limited articulation on rough ground, which can affect handling.
A-Arm suspension allows for camber adjustment of the wheel as it moves within it's travel, which allows for improved handling at high speed. This is offset by the fact that the arms are somewhat fragile, and will get damaged during crashes.
Multi-Link suspension takes A-Arm suspension a little further. By adding more stabilizing links to the wheel bearing, suspension become easier to tune, while making the vehicle easier to handle. But here is the rub - It is also more difficult to design.
It is extremely hard to know just how the suspension will work without Computer modelling, and would need to be tuned precisely to the design - meaning changes to the frame that affect how the suspension mounts would also affect how the suspension moves as well. I don't think this would be an issue - it just means I will need to learn how to work with 3D Cad design and modeling. Solidworks, Here I come!
For the Shocks, the Rear shock on the Honda are 20 inches long, the fronts are regular 13.5" shock. I do have a set of shocks that I could use for the front, but the rear looks to be a bit harder to find - initial research indicates the rear shocks off a Polaris RZR UTV might work, but I'm looking at around 500 bucks or more for a pair.
Controls
The steering wheel is going to be the biggest PITA, as the hondas are the only buggies that used a hands-only control scheme. The biggest issue is the brakes, but I think I have an Idea of what I can do, though.
The FL350 and FL400 have hydraulic brakes - the 350 used two cables going down the steering column to work a central master cylinder. Since this setup was difficult to bleed, The FL400 moved the master cylinders to the steering wheel itself, using what I believe are modified motorcycle rear brake master cylinders. The FL400 brake cylinders are very expensive and a complete steering wheel commands a premium - We are talking about >$500 here.
The main issue is what I can use as a substitute for my own steering wheel. I cannot use regular front brake cyilinders as I doubt they would work sideways. Then I read of how One person on MBN came upon a solution while trying to improve the brake system on his adapted buggy - Street bike brake cylinders.
Probably because of the large slant of streetbike handlebars, the reservoirs on them are now often detached and mounted alongside the levers at an angle. This is perfect, as I can mount the reservoirs along the top of the steering wheel and not have to worry about the cylinder sucking air or even how to load it with brake fluid. Best of all - generic cylinders are available rather inexpensively on ebay.
