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carcentric Samba Member
Joined: May 15, 2003 Posts: 78 Location: Seattle area (USA)
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Posted: Sun Jul 28, 2013 12:34 am Post subject: 1F2R vw trike frontend using bug suspension - workable? |
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If you see problems with the frontend below, please post.
If you suggest a solution for a problem, that's even better!
I'll be removing the Bug's framehead and front suspension from the pan, cutting the torsion beam apart, and reconfiguring one end into a single front wheel assembly that will use a standard size VW Bug wheel (typically, VW trikes use some sort of motorcycle forks frontend with a very narrow motorcycle wheel and tire).
The sketch above shows where the Bug torsion tubes are cut (just inside the base of the shock tower), a hefty rectangular tubing main support (green) that transfers the front wheel loads to the bug chassis via its front crossmember (pink), and a triangulating support tube (yellow, size and location to be determined) that ties the top of the shock tower to the front crossmember to reinforce the new structure.
Whichever end of the torsion beam is used, it will be turned around 'backwards.' Instead of trailing, the suspension links now lead - a method sometimes used to extend the wheelbase of fenderless volksrods. Since the torsion bar leaves will be removed, a coilover shock will carry what little weight there is in this design.
Either end of the VW beam would work as they are mirror images of each other. but to use a stock Bug speedometer, the driver side suspension must be used (that's where the speedo drive is). Speaking of speed: this is NOT intended to be a high performance frontend, just an inexpensive but workable one.
Thanks. _________________ M D "Doc" Nugent
Proprietor, http://www.carcentric.com |
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Derek Cobb Annoying
Joined: March 11, 2004 Posts: 2565
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Posted: Sun Jul 28, 2013 4:11 am Post subject: |
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You'll need to build in caster by tilting the whole shebang rearward, and I would suggest attaching your main support (green part in the rendering) to the remains of the torsion tubes, not the shock tower sheet metal. It's a lot more flimsy than the tubes. Your triangulating support isn't really triangulating. You'd need a third support member to complete the triangle and I would suggest adding at least that. Maybe make the main support more like a forward facing "V" braced to the lower tube, another "V" angled down to the upper tube with a flange between the two.
There will be tremendous torsional stress with the one support wheel being so far offset. It's going to want to twist that mount off like a mutha'. |
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carcentric Samba Member
Joined: May 15, 2003 Posts: 78 Location: Seattle area (USA)
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Posted: Sun Jul 28, 2013 7:46 am Post subject: |
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Derek Cobb wrote: |
You'll need to build in caster by tilting the whole shebang rearward, . . . |
About the same amount of caster as when it was on a bug? And - considering the whole assembly is now rotated backwards - is it the angle of the tube centers or the angle of the balljoints' centerlines that I should pay attention to? Those two are not the same angle in a b/j beam, correct?
Derek Cobb wrote: |
. . . and I would suggest attaching your main support (green part in the rendering) to the remains of the torsion tubes, not the shock tower sheet metal. It's a lot more flimsy than the tubes. . . . |
Hadn't checked the stock part thicknesses yet - makes sense, though to weld to the thickest parts. Also, what dimension of rectangular steel tubing would you use for the main support? Just seat of the pants, I'm leaning toward 3/16" wall 1.5"x6" rectangular.
Derek Cobb wrote: |
. . . Your triangulating support isn't really triangulating. You'd need a third support member to complete the triangle and I would suggest adding at least that. Maybe make the main support more like a forward facing "V" braced to the lower tube, another "V" angled down to the upper tube with a flange between the two.
There will be tremendous torsional stress with the one support wheel being so far offset. It's going to want to twist that mount off like a mutha'. |
This closer-to-scale drawing below (albeit using a l/p beam where I only have a b/j beam) shows there's not much room for V's between the outer ends of the crossmember and where the tire will be during right turns. I'm hoping that opportunities for triangulation will be more apparent when the main support is in place (in real life) - if I find opportunities, I'll use them.
I especially appreciate that each issue you identified came with a proposed solution . . . VERY helpful in shaping my design.
Finally, I'm thinking there's no advantage to a l/p beam over a b/j one in this application - do you agree?
_________________ M D "Doc" Nugent
Proprietor, http://www.carcentric.com |
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Derek Cobb Annoying
Joined: March 11, 2004 Posts: 2565
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Posted: Mon Jul 29, 2013 12:27 pm Post subject: |
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Your caster angle would be in reference to the ball joints, and I would probably start with the stock Bug angle plus leaning towards a slightly more positive setting. Taking the lower mounts from the farthest corners of the Napolean hat would help resist the twisting, and I suppose a brace from the top of the center tunnel to the upper tube "might" be enough support, but i'd need to find something with a little more structure if it were mine. Maybe a hoop going up from the ends of the Napolean hat, over the center tunnel with the upper braces to the upper torsion tube in the same basic design as the lower and an additional support going back a foot or so back from the hoop to the center tunnel.
I don't really see any advantage or liability in using L/P or B/J beam. Might be a bit more help if I knew what the car/trike/buggy might weigh and it's intended purpose. a one person, short wheelbase trike would need somewhat less engineering than a four seater, full bodied thing-a-ma-bob. |
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carcentric Samba Member
Joined: May 15, 2003 Posts: 78 Location: Seattle area (USA)
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Posted: Mon Jul 29, 2013 1:02 pm Post subject: |
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Derek Cobb wrote: |
. . . Might be a bit more help if I knew what the car/trike/buggy might weigh and it's intended purpose. a one person, short wheelbase trike would need somewhat less engineering than a four seater, full bodied thing-a-ma-bob. |
Except that the goal is under 1000 pounds, I can only list the 'ingredients' and let you estimate the weight: http://carcentric.com/DreiradPhaeton.htm
According to WA law, it'll be a motorcycle (see 2nd definition at the bottom of that page), but the look fits 'cyclecar' better.
The fiberglass body is an outer shell only (less than 50 pounds with the rear fenders) and the roof will be two layers of 1.5 oz mat over chicken wire with 1/2" conduit supports.
Here's a photochop:
I have three reasons for trying to devise a car wheel front end:
- so all three wheels will match with approximately equal tire contact patches,
- so I don't have to chop a hole in the hood for a motorcycle triple tree front end to stick through, and
- so I don't have to buy a motorcycle frame (or otherwise source a neck tube) to hang a bike frontend on.
Thanks for your input. _________________ M D "Doc" Nugent
Proprietor, http://www.carcentric.com |
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Derek Cobb Annoying
Joined: March 11, 2004 Posts: 2565
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Posted: Mon Jul 29, 2013 1:58 pm Post subject: |
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Four seater with that long of a wheelbase is going to need all the support you can engineer in. Even with the completed car weighing in at 1000 lbs (which is going to be a difficult goal to achieve), once you put four people in that thing you'll be damn close to a ton. Slam on the brakes on a sweeping turn at highway speed and there will be a shit-load of stress to deal with.
I think I'd get away from the idea of making it lightweight and build a laddered cage down the sides, use a hoop for the windscreen and tie it all together at the remains of the torsion tubes. Much like a sand rail. I'm not sure if you can find a coil-over that can handle all that weight without bottoming out, and I also question the strength of the single shock tower to support it all.
I don't mean to piss in your cornflakes, but this project would be asking one set of torsion arms to go way beyond their limitations. That's just my opinion though. I have been wrong many times before. |
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carcentric Samba Member
Joined: May 15, 2003 Posts: 78 Location: Seattle area (USA)
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Posted: Mon Jul 29, 2013 3:37 pm Post subject: |
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Derek Cobb wrote: |
. . . I think I'd get away from the idea of making it lightweight . . . . |
If it's not under 1000 pounds empty (including towbar), it's not useful to us at all as that's the max amount our motorhome can tow.
Not arguing with your conclusion, but here's my reasoning (attack it wherever you find it weak):
1. I think the donor bug was 1800 pounds empty as a car, and the only VW trike weight I've read was just under 800 pounds (Jerry Long's shown at http://carcentric.com/JerryLong-mirror-640.jpg).
2. With the VW chassis/drivetrain's severe rearward weight bias, wouldn't the front wheel only carry 15-20% of the total vehicle weight in a normal/coasting state? Seems like it'd be way under 33% (an equal share if the center of mass was near the center of the wheelbase).
3. I understand the coilover might need to be stronger than an offroad add-on, and the tower would definitely need to be reinforced, but the trike's weight with two adults and two kids should be no more than half the GVW of a bug sedan with full beam, 4th wheel/tire, metal body and fenders, bumpers, spare tire, jack, etc.
If it can't be done, though, I'd rather know that now than after I put a lot of time into it. _________________ M D "Doc" Nugent
Proprietor, http://www.carcentric.com |
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Derek Cobb Annoying
Joined: March 11, 2004 Posts: 2565
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Posted: Mon Jul 29, 2013 5:04 pm Post subject: |
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The biggest problem I see with the design is the offset nature of the trailing arms. The original car had a nice long beam to transferr all the stresses across the car. On your design all the stresses are concentrated on one point that's significantly away from the centerline. Your efforts don't need to be for nothing though. It could work if you can get it braced up enough, and if it just doesn't seem like it will be able to handle the stresses you could always chop it off and use a donor Motorcycle for your front suspension. You'd really only be out some fabrication time and a coil-over shock. |
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BL3Manx Samba Member
Joined: August 29, 2006 Posts: 6767 Location: Northern California
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Posted: Mon Jul 29, 2013 5:16 pm Post subject: |
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The triangulation support as you've drawn it in the top pictures would definitely interfere with the tire when its steered to the left.
A pair of asymmetric A-arms which point forward and sideways at about 45 degrees would be a lot better. The ball joints would be at the pointy end of the arm and they would pivot and swing vertically in bearings offset to one side of the front of the chassis. The asymmetric (even curved shape of the A-arms would provide clearance so the wheel could steer. They might even look like /_C-arms(except the diagonal brace would connect to the top of the C). The steering arm would need to come straight out sideways from the spindle, the opposite direction from the axle so that the steering box, also mounted on the front of the chassis would push forward to turn one direction and pull back to turn the other. The length of the tie rod would need to be the same as the distance from the center of the 4-arm pivot to the center of the balljoints, and run parallel to the A-arms to avoid bumpsteer.
Just as Derek said, you would definitely need caster for stability so the lower A-arm pivot bearings would need to be far enough forward of the upper to have at least 3 degrees caster, I'd guess. He's also right about how the force will want to twist the VW tunnel. It would need to be specifically redesigned to compensate with something like a truss (rail) frame.
These are Harley air shocks I mounted in a Miata front A-arm suspension. They're short enough and big enough for what you would need (and cheap used on ebay) and adjustable by air pressure. This is a single seat 2F/1R trike I've temporarily changed to a 4 wheeler to try out a different drive train.
Here's a crude sketch of the C-arm shape, ball joint at the top, pivot bearings at the bottom
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carcentric Samba Member
Joined: May 15, 2003 Posts: 78 Location: Seattle area (USA)
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Posted: Wed Jul 31, 2013 12:18 am Post subject: |
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BL3Manx wrote: |
. . . Here's a crude sketch of the C-arm shape, ball joint at the top, pivot bearings at the bottom
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Same as this?
_________________ M D "Doc" Nugent
Proprietor, http://www.carcentric.com |
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BL3Manx Samba Member
Joined: August 29, 2006 Posts: 6767 Location: Northern California
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Posted: Wed Jul 31, 2013 9:53 pm Post subject: |
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Wow, there it is. You can see the steering arm does come out on the other side and directly in line with the axle. I think it would have been feasible/better if he used a steering box or rack, instead of the handlebars. It appears the spring/shock is either lever action or maybe cantilever or maybe push/pull rod, can't tell from the pic. It probably gives a nice supple action and keeps everything tucked inside the chassis. That thing is super impressive. |
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Derek Cobb Annoying
Joined: March 11, 2004 Posts: 2565
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Posted: Thu Aug 01, 2013 4:27 am Post subject: |
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I would be very comfortable trucking my family around with this front suspension. This one gets my vote.
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BL3Manx Samba Member
Joined: August 29, 2006 Posts: 6767 Location: Northern California
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Posted: Fri Feb 21, 2014 8:37 am Post subject: |
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This thread has inspired me to see if I can fabricate a parallel leading arm front end using a modified VW balljoint spindle and modified upper trailing arms like the original poster suggested. However for it to work and be stable and steer predictably the ball joint locations must be changed in relation to each other and in relation to the wheel.
The goal is to have it act like a motorcycle fork(with a steering gearbox) but the steering pivot structure will be inside the wheel instead of sticking up above it.
I'm in the process now of cutting up and re-welding the spindle and making a jig so the ball joints will be in a vertical plane. Zero lateral inclination of the steering axis(not leaning to the side like a VW), is essential if a single wheel front end isn't going to pull to one side. On a VW each spindle does pull to one side, but the spindle on the opposite wheel balances the forces and together they increase stability. With a single front wheel that won't work.
Also, if you want the steering to have the same forces whether you turn left or right, the steering axis(ball joints) must be laterally centered within the wheel. If the ball joints are beside the wheel(like on a bug), the wheel will move in an arc forward and aft, instead of pivoting on its own vertical axis like a motorcycle wheel. I've got a narrow 16" aluminum space saver rim with huge negative offset which will center the steering axis and help take care of that.
I'll also ensure I have plenty of caster and trail for stability just the way its done on a bug by having the front beam mounted with the lower tube ahead of the upper tube.
Here are some pictures of the front end of a New Zealand V8 powered trike by Normanby Fabrications I'm using as the concept. The VW spindle is actually better than the one in the pics because it has the eccentric which can easily adjust for zero wheel camber (lean). I'll weld up the arms from steel tube similarly (but obviously not $$$ machined alloy), using upper VW trailing arms as cores.
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carcentric Samba Member
Joined: May 15, 2003 Posts: 78 Location: Seattle area (USA)
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Posted: Mon Aug 03, 2015 5:23 am Post subject: |
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Two years and several medical issues later, I've abandoned my OP idea of a dual arm front suspension.
What I intend to use now is a variation on the Robert Q. Riley Trimuter front end. The only ground I'll be breaking is to use a round tube right under the motorcycle neck (because it's easier to drill at an angle through a round). Here's a graphic of Riley's system:
I'm thinking a driver's side Super Beetle knuckle/spindle/brake will work.
The project has changed somewhat, too. Details at http://www.carcentric.com/Les.htm _________________ M D "Doc" Nugent
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BL3Manx Samba Member
Joined: August 29, 2006 Posts: 6767 Location: Northern California
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Posted: Sun Aug 09, 2015 10:36 am Post subject: |
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I'm going in the same direction now, planning to build a single sided leading arm fork which mounts a VW brake. However instead of trying to modify and adapt stock VW parts for the axle I went with an aftermarket combo spud and mounting plate. It will be very easy to weld to the leading arm. I need to space it out about an inch so that the tire and brake backing plate clear the leading arm. I plan to just use a VW drum brake for simplicity, at least at first, but an aftermarket disc would also be fairly easy to mount but I'm not sure you want that powerful of a brake up front on a trike.
In the 70s the Tri-Vette was a fairly successful VW based trike with a very similar design. They were tandem seat and also very stable
This is an earlier version of R. Q.'s front end. I like the way he's reused the VW steering box by flipping it and turning the Pittman arm 90 degrees
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carcentric Samba Member
Joined: May 15, 2003 Posts: 78 Location: Seattle area (USA)
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Posted: Thu Aug 13, 2015 11:52 am Post subject: |
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This (not to scale) sketch shows the mods I'll be making to the Trimuter-style frontend:
- Top crosspiece in the fork is round tubing because it will be easier for me to drill for attachment to the neck stem than square tubing would be. Indexing the crosspiece to the square tubing fork sides will happen during welding.
- The right side fork tube will be extended forward enough for two m/c coilovers rather than one car coilover. Since they are different distances from the hinge point, there will be a progressive, softer ride quality, but the main reason is I have m/c parts from the suzuki and no car coilovers.
_________________ M D "Doc" Nugent
Proprietor, http://www.carcentric.com |
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BL3Manx Samba Member
Joined: August 29, 2006 Posts: 6767 Location: Northern California
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Posted: Fri Aug 14, 2015 2:33 pm Post subject: |
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Here's the link for the combo spuds and stepped backing plate. You can't weld the step backing plate directly to the leading suspension arm. You need to space it out about an inch so that the tire and brake backing plate clear the leading arm.
I plan to just use a VW drum brake for simplicity, but an aftermarket disc would also be fairly easy to mount but I'm not sure I want that powerful of a brake up front on a rear engine 1F/2R trike.
http://www.kartek.com/Product/298/Stepped-Combo-Spindle-Spuds.aspx |
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carcentric Samba Member
Joined: May 15, 2003 Posts: 78 Location: Seattle area (USA)
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Posted: Fri Aug 14, 2015 2:55 pm Post subject: |
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BL3Manx wrote: |
. . . I plan to just use a VW drum brake for simplicity, . . . |
I have a spare SuperB DS strut/brake, but no loose DS Bug front brakes, and I'm told a Kartek-type spud/plate for the SuperB is not available. Are any of the SuperB brake innards usable with the Kartek Bug spud/plate or do I need to buy a whole DS Bug front brake?
Don't forget to post a pic or two when you start building yours. And BTW, what size (and wall thickness) tubing are you using for the fork and leading link? _________________ M D "Doc" Nugent
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BL3Manx Samba Member
Joined: August 29, 2006 Posts: 6767 Location: Northern California
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jaxdream Samba Member
Joined: August 12, 2014 Posts: 31 Location: North Central Tennessee
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Posted: Thu Aug 27, 2015 8:53 pm Post subject: |
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I have looked at the trike thing , although this idea would work , you just have to decide which side you want to have your back to on the road shoulder to change a flat tire on ( open side of the front fork arrangement ) . I personally would want the open side facing the right as opposed to the left as the pics propose( except that rocket sled trike with the double front wheel / tire ) . YMMV ...
Jack |
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