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    Newbie Brainstorming A Buggy Design
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    First off i would like to say hello everyone. I have been looking at this forum for some time now and finally decided to make a post. I'm a college student aiming for a degree in Mechanical Engineering Technology and have access to SolidWorks, ProE, and AutoCAD.

    Anyways I want to start designing a buggy and I'm looking for a little direction. My general idea of a perfect buggy would be something that can hold two 6ft plus guys, sprint across wide open Montana at 70mph chasing down coyotes, and have a cargo rack to hold enough for a weekend in the boonies. So a baja style car in general but it would never see the sand. Rough and rocky hills and deep steep sided coulees would be it's playground. There's not many buggies in Montana, and I have never rode in anything but utv's and don't know what to aim for. I feel the rorty shotgun II is along the lines of what I'm after. Buying plans, where is the fun in that?

    Just a fore warning I'm about to ask a million question so for the faint of heart and easily irritated I would turn back now. From what I have read on here I need to pick a wheel and tire and work in from there, so what tire and wheel size should I start with? My general idea is that 20" of travel would be necessary and I would lean towards A arm front and trailing arm rear suspension. I don't want a monster buggy I want a minibuggy, so what width, length, weight tolerances should I be looking for? Why does everyone use expensive CV joints? I understand that they are tough, but I have seen some cheap u joints last a long time on 1080 pto shafts turning some tight angles running some big equipment. Also with a a u joint setup axle plunge is easily compensated for with a somewhat inexpensive split axle you can get at any implement dealership. Another thing I've been looking into is reverse. There has to be some inline reverse gearbox for industrial or agriculture use that doesn't cost $1500-$2500 dollars. For the price of the rpm gearbox I could probably rip a hydraulic pump and motor off some old farm equipment to create a disengage able low speed four wheel drive system. I'm a redneck if you haven't figured that out yet. I also have a wrecked 1987 honda hurricane 1000 for a power plant and hope to reuse what I can from it. Ive done a fair amount of reading on axial scrub, scrub, KPI, ackerman, bumpsteer, camber, castor, rake, and etc. It's a complicated compromise of give and take. I'm sure full realization of this headache will not be apparent till I'm sitting in front of solid works

    Travel should be aimed at 60% compression 40% droop, 3-4" ground clearance at full bump, axial scrub 1/2-3/4", from tire center, lower inner a arm mount at same height as spindle centerline at ride height,2 deg. neg. camber at ride height, 10 deg. rake and castor, I'm I correct in aiming for numbers to start?

    Im just ranting at this point and coming to the realization of not having any clue what I'm trying to accomplish. There is a million more questions and ideas but I'll reserve them for later. All feedback is appreciated but please have mercy on me.
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    Re: Newbie Brainstorming A Buggy Design
    #2
    Senior Member
    Join Date
    Sep 2013
    Location
    Australia, Gold Coast and Sydney
    Posts
    729
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    Firstly, read, read more, look at other buggies, get an idea of what you want. Copy aspects of things you like from other buggies. If you try and reinvent the wheel for a first buggy, it is almost bound for failure (no offence).

    20" is monster travel for a minibuggy. Its not achievable, but it will come at an expense, costly shocks, driveline, etc.

    I think you are starting in the wrong place. Figure out "how much can I afford", and work your way in from there rather than wheel size.

    U joints last a long time on machinery as they are used as intended. ie, slow revolutions with big torque. On a buggy, reverse that, high revs, low torque, big travel angles, and they don't last too well. Almost all the big travel buggies use CV's, and the only one I know of using Uni's uses them for their big travel, but replaces them regularly.

    As for suspension design, here is an EXCELENT thread that puts it all into persepective:
    How to Design Front Suspension

    You can go into as much or as little detail as you want with suspension design... its a black art and maths helps but knowing what numbers to aim for is where the art lies.

    As for a design approach, design the suspension and driveline, then the cage. Doing it the other way you compromise everything for something that looks cooler.

    The edge products just released a starter motor reverse for one of their buggies. I am installing something simlar (but not from them) on mine. You can download the lazercut files for about $5 so it could be an option for a cheap reverse. Mind you, a lot of people complain about the starter reverse setups so they are far from ideal... more a way to go backwards than an actual reverse gear.
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    Re: Newbie Brainstorming A Buggy Design
    #3
    Senior Member
    Join Date
    Dec 2014
    Location
    Airdrie, Alberta
    Posts
    202
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    Definitely agree on determining a budget that you will be working with... and then accept the fact that you will go well beyond it lol.

    In addition to what Hambam said, one of the first things you should plan for is your powerplant/drivetrain and if you want to have 4 wheel drive, or if 2wd good enough for you. Your powerplant will play a large part in what rear axle set up is sufficient... 40hp and you have alot of options... jump up to over 100hp and you have to put some serious thought in to strength and components (Speaking from experience here lol). Then once you have your engine and rear axle figured out, choose if you want to use rear A-Arms or a Trailing Arm suspension. Once that's done the rest of the buggy will sort itself out. Front suspension, steering, seating, etc. then all of that will dictate the basis for you cage design.

    I started with the frame and thankfully I didn't get too far. I found a great deal on a 140hp engine and now I have to scrap the frame as it is too small for the engine.
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    Re: Newbie Brainstorming A Buggy Design
    #4
    Millenium Member rgvkid's Avatar
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    Jan 2009
    Location
    Los Angeles
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    2,119
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    Sounds like your on the right track when it comes to Cad capabilities, so that will cut a lot of time on R&D.

    Your knowledge if Scrub, KPI, and camber angles sounds about right on. The suspension Gurus on here will chime in when you get to that point.

    As for U-joints. Yes you can get a lot of the plunge issues out of the way with a U-joint setup, but they aren't as bullet proof as you'd think. The main problem with them is use of them on Trailing Arms and possible binding on the slip. The problems that a lot of people have, mainly 50+HP, is not the driveshaft or U-joint it self, it's the trans or Gearbox. When the slip isn't greased enough, or it plunges too fast and binds, then it will push the output shaft on the gearbox or trans inwards and out of the opposite side. This causes a lot of problems with gear boxes or transmissions.
    I'm using u-joints on my setup but it's only about 45HP and it uses all of 4inch slip to get a true 15inches travel. It flies through the whoops at 50mph, but I have to make sure I grease the joint every trip.

    20inches is probably way more then you would need or want. I'm sure a lot of your terrain will be crawling boulders and rough ruts. So I'd stick to 16-18", so that your arms aren't super wide.

    If your not planning on hitting long desert roads with lots of Whoops and jumps, I'd suggest looking into A-Arm rear setup or even a 4 link setup with a straight axle like Mr. brackets buggy. If you go with A-Arms in the rear you can use U-joints and have almost 0 plunge.
    A-Arms will also give you more clearance from hanging up on rocks and boulders as compared to a Trailing arm setup.

    When you weigh out the pros and cons of a $1500-$2500 gearbox with reverse, you think twice about that price being considered expensive. You'll spend more time and labor figuring out a cheaper solution, and you may still not get around some of the ground clearance issues or gear ratio options, like a sproket setup that hangs a few inches below the frame and you lose actual ground clearance.

    Just my 2cents.
    Last edited by rgvkid; 01-29-2015 at 10:35 PM.
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    Re: Newbie Brainstorming A Buggy Design
    #5
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    Thanks for the replies everyone! So it looks like my first step should be to pull the engine from the bike and get all the measurements to draw it up. As I said before I have never road in a buggy. The closest thing to a buggy i have rode in is a stock polaris rzr xp900, and it left me wanting more as far as it's ability to soak up bumps/jumps at speed. But after looking at the rorty r16 shotgun again and seeing it's 87" wide, maybe 20" travel is more than I need. As far as the budget goes I am pretty lucky to have the access to the equipment both at school and work to build pretty much anything I can dream up. I understand certain aspects such as shocks and reverse/differential are just plain expensive and that's that, but I would really like to try save in places such as in the spindles, hubs, brakes, and axle by utilizing components not originally intended for buggies (since buggy components are a niche market and they charge whatever they want). I already have a running engine so that's a good start right. Which brings me back to my U-joint argument. Lets say a buggy has 28" tires, this would produce 720 revolutions of the axle a mile, so at 60mph we have an axle rpm of 720. On most farm equipment we run pto rpm's around 1000 on a lot of equipment behind tractors with 800 lb-ft of torque. I can't say I have ever brought a protractor out to measure the angles some of them are running but unless I'm really underestimating something i feel they should work well. Especially if as someone mentioned I go with a arm rear suspension and work towards zero plunge. I could see how the slip axle could put side load on bearings cause they can get pretty sticky. Thanks again guys!
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