Manta Car Structural Help!

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MantaCamp
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Manta Car Structural Help!

Post by MantaCamp » Thu May 23, 2013 9:16 pm

Hello folks! We've done our fund raising, bought a chopped top pickup truck, and and just starting to get down to the design/build part of our manta ray vehicle!

Now the fun begins.....

We really are not engineers and while we have a general idea of what we're tryin to achieve, need some design advise for the specifics.

This is where we're at:

Narrowed it down to Lycra over PVC for the body of the manta
Have general dimensions, etc
Are trying to make modular wings that flap with a pulley system

The biggest issue is the skeleton and how it attaches to the vehicle. If anyone is willing to help with a design and share lessons let us know, we appreciate it kindly!

George Washington.

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Re: Manta Car Structural Help!

Post by Savannah » Thu May 23, 2013 9:19 pm

Hey George.

You might say where you're located, and/or reach out to your local regional group (if there is one) below, or search it out on Facebook.
http://regionals.burningman.com/

You might also try finding someone by searching or posting on The Spark:
http://spark.burningman.com/

Good luck!
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MantaCamp
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Re: Manta Car Structural Help!

Post by MantaCamp » Thu May 23, 2013 9:22 pm

Oh yes - thanks!

We're in Venice Beach.

And I'll post on "The Spark"

Already hit up the newsletter as well, and found a gaffer that's gonna up us with the lighting!

-Matt.

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Re: Manta Car Structural Help!

Post by Sync » Thu May 23, 2013 9:23 pm

Depends on if you need to disassemble it for transport. I just completed structural framing for my mutant using pvc. If you heat gun the ends of the pvc you can flatten and bend then as needed. This would allow you to attach the frame to the car using sheet metal screws. Drill through the car body/chassis first, then screw through the PVC to the car. Good luck.

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Re: Manta Car Structural Help!

Post by MantaCamp » Thu May 23, 2013 9:26 pm

Thanks Sync -

We do need to dissemble it for transport - would this change the advice above?

Thanks!

GW

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Re: Manta Car Structural Help!

Post by MantaCamp » Thu May 23, 2013 9:48 pm

Oh yeah - check out the sweet chassis we got for this sucker! It's gonna make a great art vehicle....
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Re: Manta Car Structural Help!

Post by Major Krash » Thu May 23, 2013 11:14 pm

first, will you be driving it to the Playa (street-worthy needed) or hauling it on a trailer (not needed to be street-worthy)? Where will you store it off season, and do they allow "art cars"?

you want to ideally attach the frame to the vehicle chassis. Think receiver hitches on a car (look up how they attach truck campers). You can even do this such that everything (but the receiver mount) can easily be removed (if needed). The vehicle body is just sheet metal, and not very strong to mount stuff to unless it is light and will not be carrying any people...the back of the truck can be built up using a "ladder rack" type construction (which also can be designed to be removed if needed). Nuts and bolts can be used, but should also use lock washers. Welding is stronger/safer, but cannot easily be taken apart unless great care is taken during design and construction. Paint all steel or it will rust (quickly).

If you plan on a 2nd level for people, consider modifying the suspension (depending how much weight you add overall, this may be needed anyways) - extra leaf springs can be added fairly simply which prevent bottoming out, etc. The upper deck must not extend beyond the wheelbase (unless you design for it) and should be inside it somewhat (to prevent tipping over). If you are just holding lightweight fabric, consider emt or pvc tubing to reduce weight (but ensure no one will try to climb on this by clever design). Plan for people trying to climb up to the 2nd floor from the outside (this is generally bad, especially if the vehicle is underway, but some idiot will try it at some point, so plan for it). Determine your max, capacity for the upper deck and stick to it (at least while under-way; while parked for the burn, it is possible to use vehicle jacks, positioned while everyone is off the vehicle such that when everyone gets on the vehicle sits on the jacks vs. the suspension, and it will be rock-steady with no tipping).

Consider your windload. A rough estimate is 50lbs per square foot. If you vehicle looks like a sail from the side, make those connections to the vehicle very strong (steel). If your covering is material that you can easily blow through, or has openings to allow air to pass, this figure can be reduced considerably.

Consider what will happen when (not if) some idiot on drugs tries to start (ie-steal) your vehicle (or at least turn everything on) when it is parked.
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Re: Manta Car Structural Help!

Post by MikeGyver » Thu May 23, 2013 11:22 pm

Obvious question that hasn't been asked yet, Do you have a Mutant Vehicle "Invitation"?
The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair.

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Re: Manta Car Structural Help!

Post by MantaCamp » Fri May 24, 2013 7:58 am

Mrpatatomoto wrote:Obvious question that hasn't been asked yet, Do you have a Mutant Vehicle "Invitation"?
Thanks for that question. We've been in touch with the DMV since January, are fully registered, and have been put on on the eplaya support page etc. So we're covered as far as that goes, but thanks for asking!

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Re: Manta Car Structural Help!

Post by MantaCamp » Fri May 24, 2013 8:05 am

Krash - thanks that's very helpful. We won't be doing a 2nd level but we do have "wings" so yes the wind is a major concern. I think wind slats is a great idea....

And thanks for the advise of "not connecting to the body." Definitely going to use the camper trailer pivots as connecting points!

We're not planing on driving it - it will be trailer hauled - but we will need to be able to take it apart as the wingspan will be too wide for the road, and the planned storage facility in the off season won't fit it fully built. I've attached a 3D rendering of what we're trying to do - it's pretty simple, the hardest part are the wind payload, and the wings which need to be modular to "flap" for a few reasons.

A. to get down the BRC streets
B. 'Cause it will look cool (like a manta ray swimming across the desert).
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Re: Manta Car Structural Help!

Post by Captain Goddammit » Fri May 24, 2013 9:08 am

The bed of that truck will come off with a few big bolts. If you need to keep the mechanics simple you can leave the cab but a sawzall will do wonders to remove more truck from your manta. The less "truck" the better, and lighter.
If you remove the doors, the doorjamb area where the hinges mounted is a good strong area to attach your stuff, you could even re-use the original bolts (or get longer same-thread ones.)
Without the bed, you could lay wood 4x4 posts sideways across the frame, or steel if you need that much "beef" but steel is really expensive these days. My hot tip on acquiring cheap or free steel lately is old bed frames. People give 'em away and they are often fairly stout steel angle-iron. If welding is out, you could drill a bunch of holes and bolt two pieces of steel bed frame together back-to-back to make a doubled-up stronger unit.
You can drill through the posts and through the top of the frame and bolt them on. If you need more strength but dont use steel, just use more wood. I suggest that cuz it's affordable, it works, and almost everyone can work with it if none of your group is a good welder.
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Re: Manta Car Structural Help!

Post by MantaCamp » Fri May 24, 2013 9:15 am

Thanks, that's extremely helpful!

That's a good starting point for us I think, take off the bed, use 4x4 posts, and the doorjamb to mount the wings.

We appreciate it kindly...

GeorgeWashington.

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Re: Manta Car Structural Help!

Post by MantaCamp » Fri May 24, 2013 9:52 am

Any advice on rigging to make moving/flapping wings would be greatly appreciated also. We've done some rough mockups that I'll attach. We're thinking of doing a sailboat style winch & pulley system with ropes to make the wings flap. The confusing part is how to do it in a way that the pvc will bend in segments from the joints/nodes that will exist.
We've also discussed a screen door hydraulic closer (that little piece at top of screen doors to keep it from slamming) as a release for the main part of the wing that is attached to the vehicle. The only problem with that is that I can't think of a good way to get a segmented wing flap with that. It would only be a stiff universal move, which could be boring.
Any suggestions would be great.
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Re: Manta Car Structural Help!

Post by trilobyte » Fri May 24, 2013 11:08 am

PVC could be dicey. A campmate used PVC to make himself a small chill dome a few years back (his was fabric covered, if I remember correctly), and by the second day it was in ruins. After a couple hours of exposure to the sun, the PVC heats up enough that the poles become a lot more flexible. I think he was using 1 inch PVC from his friendly neighborhood big box hardware joint, you may want to make sure you've got something bigger or with thicker walls on the pipe to avoid catastrophe, and bring along spare material in case you need to work out some fixes on the fly. Good luck!

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Re: Manta Car Structural Help!

Post by unjonharley » Fri May 24, 2013 11:41 am

I did some frame stuff a few years back.. I used cedar fence boards.. They are nice and light.. they were cut to 1 X3/4 inch.. Used door skin cut for gussets @ each joint.. We were building a mock helicopter.

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Re: Manta Car Structural Help!

Post by TomServo » Fri May 24, 2013 2:52 pm

Not advertising here..but maybe some solutions lie in this cheap toy?

http://www.discountpartysupplies.com/ro ... MgodYTYAqA
anything worth doing is worth overdoing..

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Re: Manta Car Structural Help!

Post by Major Krash » Fri May 24, 2013 8:23 pm

with wings like that you might be able to put a pulley at each wing tip then run a cable internally through (or under) the wings around each pulley. By pulling on that cable the wings would be pulled towards each other...how the cable is pulled, and how the tips are balanced so they stay in synch height-wise is an exercise left for the builder....but the hand idea, while more complicated, would avoid the possible hazard of a cable moving where it could catch someone....maybe pneumatics (or air hose that gets stiff when pressurized, and tries to straighten out, with springs or gravity holding it in the other position....
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Re: Manta Car Structural Help!

Post by unjonharley » Fri May 24, 2013 8:48 pm

How about the ray's wings moving up and down by an eccentric(wheel). One on ether side disguised as gills made of flexible fabric. Manta's do not move a lot making there way through the water.

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Re: Manta Car Structural Help!

Post by MikeGyver » Fri May 24, 2013 11:28 pm

As long as it is being hauled there and not driving it wont reach any high drive shaft speeds. So how about putting Cam Lobes or something on the drive shaft and 3-4 cables attached to the wings so as your driving the Lobes on the drive shaft tighten and release tension on the wings and they look like they are waving.
The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair.

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Re: Manta Car Structural Help!

Post by Captain Goddammit » Sat May 25, 2013 8:10 am

No good... that truck has about 4:1 reared gears, even at playa speed the driveshaft will be spinning too fast for flapping the wings unless it was a hummingbird. And too much engineering to make that actually work.
Even the wheels are probably rotating too fast to do something like that, the wings will flap too violently.
It needs to be geared way down to get a nice gentle flap that looks cool and doesn't tear itself apart.

I think if I were doing this I'd look at an old riding lawn mower. They can be had free if not running, sometimes even running.
They use a tiny pulley under the motor with a belt going to a big pulley at the transaxle at the rear, which gears them down even more than the little transmission they have does.
You could remove everything from the mower, the engine, hood, fenders, etc. leaving just the frame.
If you turned it on it's side (so the drive pulley system is in the same plane as the truck's driveshaft) and bolted it to the floor, you could drive it from a belt going to a pulley mounted on the driveshaft below.
If I had to do that without welding, I'd take off the driveshaft (just for small bolts, there are two little clamps on the rear u-joint) and find a pulley big enough to fit over the driveshaft - you'd have to cut/grind the hole in the middle until it's big enough to go on - and take it to a welding shop and have them weld it on for me. It would be super easy and cheap.

Those drive belts are just standard car fan belts, you can wrap a string around your pulleys and figure out how long a belt you need.
Either the mower chassis will have an idler pulley, or you can make your mounts adjustable (big bolts sticking up, first nut tightened down to hold them, then a second nut/washer threaded on under the mower chassis that you can adjust mounting height with - then another nut on top to tighten it all down) so that you can get the right tension on the belt. An idler pulley would probably be best.

The mower transaxle would allow you to shift to neutral so you could roll the vehicle without wing-flapping, and it would allow you to select gears to adjust the flap rate. You might have to play with pulley sizes to get it into the general range you want.


The transaxle would allow one rear wheel to spin independently of the other; you'd need to remove one rear wheel and bolt something else on the hub to lock one side in place, this could be as simple as a piece of plywood (attached solidly to your truck) with holes drilled to go on where the wheel was. Metal would probably be better though.
The other wheel would give you a place to mount a post to attach a pushrod - think about an old steam locomotive and how the pushrods attach to one point at outer edge of the drive wheels. Or you might rig up cables that pulls your wings up, letting gravity pull them down. Old bikes are a great source of parts to make such things from.
I think cables and pulleys would be the way to go.

There are other ways, but that's the one that comes to mind... I can think of better ways requiring a lot more advanced fabrication skills but that's what we're trying to avoid on this rig.
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