Ultralight Plans and Construction PDF

Did you just design your very own teardrop or tiny trailer? Want to discuss it? Here's the place to post your design for discussion!

Postby angib » Fri Jul 17, 2009 10:58 am

I split the idea of a minimal, lightweight chassis into three steps:

1) If the body is going to be self-supporting, it needs to be well made. This doesn't mean heavy - it mostly means good quality joints that fit well and are glued and screwed or pinned.

2) Getting the axle load into the body is easy - all that's needed is to spread the point load from the axle over a decent length of wood. In the Ultralight PDF, this is done with the spring mount angles about 18" long that the HF trailer comes with. On my Ultralight chassis, the angles are 24" long.

3) Getting the hitch/tongue load into the trailer is a bit harder as the load is well outside the body, so it creates quite a bending moment in the tongue. For this I think the easiest solution is the Ultralight chassis that uses an angle A-frame where the back end of the A-frame members bolt to the front of the axle angles.

If you really want a single central tongue, then you need a body structure that's quite a bit more complex as it has to take the tongue loads in the middle of the floor. This needs reinforcing beams running across the floor which would ideally be a sandwich structure - for sure, just a single-skin unreinforced plywood floor is not enough. I reckon an oak 1x4 inside the floor sandwich at the front and back ends of the tongue would be enough, providing the tongue length inside the body is not much less than the tongue length forward of the body. The backing plates at the tongue fixing points are absolutely essential, otherwise the bolts will just pull out of the floor.

But this is getting sufficiently complex that it's less work to use the stronger A-frame chassis.

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Postby ai4kk » Wed Dec 23, 2009 4:15 pm

I wonder if motorcycle sidecar wheels would work or if the weight difference is even worth it?
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Postby angib » Thu Dec 24, 2009 3:59 pm

For light wheels, the choice is easy - 'ordinary' 4.80x8 trailer tyres/wheels which are just 11 pounds each (wheel and tyre).

Of course someone will now say that it is impossible to tow a trailer with such small wheels at any speed over any distance - though that will confuse the folks like Del who have done it.

If anyone wants a small light trailer, I'm just working on finishing the plan set for the Pico-Light - but, beware, I see I said I was working on this back in March, so my hobby delivery time promises aren't worth much.

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The weight estimate says 282 pounds ready to roll, so that ain't bad. The frame, without suspension and wheels, is 35 pounds.

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Postby dwgriff1 » Fri Dec 25, 2009 2:53 am

What would you use for an axle? Torflex 8?

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Postby Ageless » Fri Dec 25, 2009 3:04 am

In Late 2006; I ran a modified Apache tent trailer from here to Deming, NM and back with those small tires; not a problem. I did repack the bearings before the trip. It was a torsion axle.
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Postby angib » Fri Dec 25, 2009 7:30 am

dwgriff1 wrote:What would you use for an axle? Torflex 8?

Nope - a pair of Flexiride 425lb half-axles - that Dexter axle tube is just too heavy, plus it doesn't offer any mid-floor support like an axle tube built into the frame does.

Here's the chassis:

Image

I have a mate who used to regularly tow his racing dinghy up to about 100mph on 8" trailer wheels, carrying about the same total weight as this trailer. But that was before the days of widespread speed cameras....

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Postby vwbeamer » Wed Dec 30, 2009 5:51 pm

Now, we are getting some where. And the teardrop it self should be a light frame made of thin wall steel tubing, with an aluminum skin. Insulation 1/8 luan completes the walls and roof.

Course all of this is a waste of time for those towing with big cars, but I plan on towing with a small 4 cylinder diesel.
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Postby dwgriff1 » Wed Dec 30, 2009 8:10 pm

Indeed. Thanks Andrew.

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Postby Larry C » Mon Jan 04, 2010 8:11 pm

Hi All,
I'm new here. I really enjoy this thread and I hope it keeps going. I have always tried to buy and build light weight equipment, from backpacking, winter camping, bicycles, racing kayaks, and wooden kayak building. I want to incorporate this light weight passion in my Tear build. I like Andrews Ultra light frame design and I believe it would work great for my proposed 500# build. However, I am a realist and know getting a simple A frame licensed may be a problem.
I would like to know what you all, especially Andrew, think of this design built with aluminum square tubing. This one looks too long, but I think it could be shortened and keep the same shape. It looks like it has stub axles. BTW/ I pulled this from another post and don't know anything about its purpose. I just like the design and think it could work for my light weight build and may be easier to get licensed and let me sleep better.
I have a welder experienced in aluminum to do the welding. However, I am not entirely set with aluminum. If thin wall steel would be almost as light, I would consider that. I just want opinions on the design for an ultra light. Sorry for small image, I'm still learning how to post pics. I think If you go to my album its bigger if you click on it.
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http://www.tnttt.com/viewtopic.php?f=50&t=35852
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Postby angib » Tue Jan 05, 2010 7:05 pm

Image

That's very close to my Superleggera chassis, except it has a rear cross-member - which serves no real structural purpose, but may make some folk happier!

The design of the joint where the axle cross-member extensions meet the main rails is absolutely critical in this design, so it wouldn't be suitable for a novice welder - but that's not you, so no problem.

In my latest lightweight design, the steel tubes of the (admittedly minimal) chassis weigh 35lb but the suspension, wheels (tiny 8") and coupler weigh 60lb, so the potential saving from lighter frame tubes isn't great.

With aluminium you have to consider fatigue, so that you don't end up with a chassis that's good for 1,000 miles before it starts cracking. And designing for fatigue strength is difficult - I did learn once, but I've forgotten it now - plus getting the data for the particular aluminium you use often isn't easy. So I end up putting a big factor of safety on the strength of the aluminium and then it isn't all that light any more.

Manufacturers that build in aluminium will have a lot of experience on which to base their designs, so it's not a big problem for them to trim down the aluminium to the minimum. But for a homebuilder, it's tricky.

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Postby Larry C » Sat Jan 16, 2010 10:39 am

Andrew,
Thanks for comments/conserns about aluminum. I'm convinced, it will be steel. I like your new frame design. I would like to use it in my build. I want to use square tubing instead of angle iron that's in your ultralight design. In your new design, how does the use of half axles save much weight if there is still a cross member? wouldn't a Dexter 8 axle be similar in weight if it's tube is the rear cross member?
Here's some questions for all:
My tear will be an ultralight torsion box that is properly constructed. I want a strong tung, but my floor should be strong enough to just sit on the frame triangle without a full perimeter frame. My goal is 500-600# total weight build. 4.5' X8' or 5' x 8' trailer size.
What gage square tubing would be best for Andrews square tube triangle frame, using either half axles or a Dexter 8 axle?
I would prefer to use larger tires/wheels than 8 or12" Are there 13-14" aluminum trailer wheels that can save some weight or should I stay with 12" wheels to keep it light?
Thanks,
Larry
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http://www.tnttt.com/viewtopic.php?f=50&t=35852
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