DYI Tensahedron Hammock Stand

[jeff-oh]

Hey "we're both right" is better than the "we're both wrong" that I'm always afraid of!

OK one more question (for anyone really): I agree with the calc of the 47.6 degree side-view angle. If this angle (equivalent to the hang angle) was more like 30 degrees (by lengthening ridgeline, for instance)... would less bending stress be imparted to the poles? And perhaps less stress overall, as 30 degrees is the angle that minimizes the force of the loaded hammock pulling on each apex?

Or... perhaps "tensahedron magic" causes 30 degrees to NOT be the angle at which the hang & the tensahedron stabilizes? (Definitely over my head here physics-wise, my college science requirements were all satisfied by calculus and statistics)

I don't often let tensahedron magic do its thing; I'm often setting up a tensahedron stand in the mostly dark on a Boy Scout campout and haven't had time to do too much experimenting. But I'd like to understand the theoretically "force minimizing" angle in order to help construct bomb-proof (well, scout-proof) tensahedrons, which will usually have fixed or nearly fixed apexes. Mainly in order to avoid moms asking "what does it mean when my son came home and said he tacoed his tensa?"

Thanks!

Several different things going on here. The beauty of the tensa, is there are no bending forces. All tension (compression). Also nothing is magical about 30 degrees. There are Two different loading areas you are looking at. Hammock suspension loading into the Apex and stand loading to handle that hammock load. the minimal suspension load is a 90 degree hang. i.e. straight over head. then suspension load is 1/2 hammock load. as you spread the the suspension points apart the suspension load increases sinusoidal. (i.e. fancy word for increases slowly at first then very quickly.
(suspension load = 1/2 hammock load / sine (angle))
at 90 degrees: sin(90)=1 thus suspension load for 200 lbs = 1/2 * 200 / 1 = 100 lbs.
at 30 degrees: Sin (30)= .5 thus suspension load for 200 lab hammock load = 1/2 * 200/ .5 = 200.
As suspension gets flatter then suspension load increases extremely rapidly.
At 10 deg. angle suspension load ~= 3X hammock load. 1/2 *200 / .173 = 575 lbs

The second half is reacting that load out. No matter what the suspension angle is, the vertical component is 1/2 hammock load (or 100 lbs in our case) always. Again the smallest pole load would be a vertical pole. Then the pole compression load would = 1/2 hammock load regardless of the suspension angle. The guy line load would react out the horizontal load. (assumed horz. guy line) This is why Turtle dog stands have a pyramid style support. (among other design features that help react the side loads.) The load in the pole thus increases with angularity off vertical. The Tensa magic is that when the poles meet in the middle they self react out the side loads and as a system only needs to react out the vertical hammock load to the ground. however the system is unstable and will fall over. (thus the two end tension lines). The load in the poles continues to increase as the angle decreases. The load in the poles also increases as the splay angle increases.

edited as I though about this a little more. The side load reaction does cause compression in the poles. This compression load in the poles is minimized by aligning the poles with the suspension angle so they provide equal and opposite lines of force. This is independent of the suspension angle. i.e. 25, 30, or 35 degrees the loads will change but the pole loads will be minimal for that case if they match the suspension angle. The off set of the suspension and the pole angle will increase the pole compression load. Bigger offset bigger load.

Then the design issue comes down to how high off the ground do you want you hammock to hang and getting.

Hope that helps. Fun discussion

[CaptainGravity]

...
How that helps. Fun discussion

Mmm... thanks... need to chew on that

[UncleMJM]

We would be happy to Uncle Mike, just let me know when your tribe can come over and we'll get 'er done. The conduit is $28 per stand and we can get it locally at Winkley's just down the road. Bring the Amsteel, fid and some Shiner and let's build some Tensahedrons!

That would be awesome sir! I'll check with my social calendar coordinator and see what we can do!

[Buckaroo]

I have looked thru this thread a few times , is there any discussion about a ridgeline permanently fixed to the Tetrahedron stand ?

I just built a stand out of some 1.250 aluminum tubes with .062 wall that a friend gave me that I think he bought at menards. I have taken a nap in it and it seems to work great but I am only using the ridgeline from the hammock at this time.

I think I am going to like this stand as its lighter and simpler than the turtle dog stand I was using

Are there any down sides to a tetrahedron stand besides learning how to get in and out without getting Tacoed ?

[Watertooner]

A permanent (and adjustable) ridgeline for a tensahedron stand is useful when you want to replicate a certain configuration over and over with minimal fiddling.

One might say that the weight of the tensahedron stand is a downside, but it really wasn't designed to solve ultra light backpacking issues. Everything has downsides, but folks are finding that these stands have enough upsides that they are worth the investment.

[jeff-oh]

A SLR on the stand should also be used if you hammock does not have a SLR. The flexibility of the stand with only the hammock fabric holding the apexes makes getting in and out more unstable than needed. It can be done, but may feel too "wobbly" for some. This also makes getting the end tension lines set harder.

If you use tension lines on both ends then you should never taco or have to worry about taco-ing. IMHO it was a marketing mistake to release the product without tethers on both ends. As LD stated the PR/ perception problem is something they now have to live through. Case in point "Are there any down sides to a tetrahedron stand besides learning how to get in and out without getting Tacoed ?"

Downsides to the stand. 1) The stand is unstable and will shift with the user moving in the hammock and while getting in in out. Properly tethered this will not lead to any issues, but it may make some people nervous until they get used to it. The shifting may also lead to pole banging (noise issue). I do not have that with the bolted joint, however, I did notice it on some videos.
2) The commercial stand is a little finicky to set up. with all the threading of the poles and setting the lines up etc. (This is a result of how well it packs down, and better ways to set up may be developed over time.)
3) The DYI stand does not break down and it long (8') to store or transport. Top rail DYI designs do have oles that break down, however they are bulkier than the EMT poles... but at 4' you can put them in a car.
4) Until the apexes are connected, it is a little wonky to set up. not really a big deal, but I've had to go back and forth a few times.

Bottom line no real drawbacks on this design, Biggest sacrifice is the inherent instability (note using as engineering term, not how it feels) of the design, but I feel that is also one of it's strengths and is the magic of the Tensahedron design.

[fivefreds]

I have looked thru this thread a few times , is there any discussion about a ridgeline permanently fixed to the Tetrahedron stand ?

I just built a stand out of some 1.250 aluminum tubes with .062 wall that a friend gave me that I think he bought at menards. I have taken a nap in it and it seems to work great but I am only using the ridgeline from the hammock at this time.

I think I am going to like this stand as its lighter and simpler than the turtle dog stand I was using

Are there any down sides to a tetrahedron stand besides learning how to get in and out without getting Tacoed ?

My first build didn't include a stand ridgeline, but I've since added one to build #1 & included one in build #2. In addition to making it easier to replicate a "dialed-in" hang, it also makes setup much less finicky.

The very first stand I made was based on the tarps.com connectors, there's another thread on that design here. I played with the tarps.com stand & the tensa stand side-by-side for a while, and ultimately favored the tensa design.

Sometimes I still set up the tarps.com stand with short legs & hang a couple of kiddie hammocks on it for the grandkids/nieces&nephews.

[CaptainGravity]

Several different things going on here. The beauty of the tensa, is there are no bending forces. All tension (compression). Also nothing is magical about 30 degrees. There are Two different loading areas you are looking at. Hammock suspension loading into the Apex and stand loading to handle that hammock load. the minimal suspension load is a 90 degree hang. i.e. straight over head. then suspension load is 1/2 hammock load. as you spread the the suspension points apart the suspension load increases sinusoidal. (i.e. fancy word for increases slowly at first then very quickly.
(suspension load = 1/2 hammock load / sine (angle))
at 90 degrees: sin(90)=1 thus suspension load for 200 lbs = 1/2 * 200 / 1 = 100 lbs.
at 30 degrees: Sin (30)= .5 thus suspension load for 200 lab hammock load = 1/2 * 200/ .5 = 200.
As suspension gets flatter then suspension load increases extremely rapidly.
At 10 deg. angle suspension load ~= 3X hammock load. 1/2 *200 / .173 = 575 lbs

The second half is reacting that load out. No matter what the suspension angle is, the vertical component is 1/2 hammock load (or 100 lbs in our case) always. Again the smallest pole load would be a vertical pole. Then the pole compression load would = 1/2 hammock load regardless of the suspension angle. The guy line load would react out the horizontal load. (assumed horz. guy line) This is why Turtle dog stands have a pyramid style support. (among other design features that help react the side loads.) The load in the pole thus increases with angularity off vertical. The Tensa magic is that when the poles meet in the middle they self react out the side loads and as a system only needs to react out the vertical hammock load to the ground. however the system is unstable and will fall over. (thus the two end tension lines). The load in the poles continues to increase as the angle decreases. The load in the poles also increases as the splay angle increases.

edited as I though about this a little more. The side load reaction does cause compression in the poles. This compression load in the poles is minimized by aligning the poles with the suspension angle so they provide equal and opposite lines of force. This is independent of the suspension angle. i.e. 25, 30, or 35 degrees the loads will change but the pole loads will be minimal for that case if they match the suspension angle. The off set of the suspension and the pole angle will increase the pole compression load. Bigger offset bigger load.

Then the design issue comes down to how high off the ground do you want you hammock to hang and getting.

Hope that helps. Fun discussion

Yes the addition helps a lot.

I think you just said (paraphrasing):
* When side angle of poles = hang angle, compression on poles due to hammock suspension forces is minimized.

So... this might be a dumb question... but there's nothing (mathematically) optimal about a 30 degree hang angle, is there? The hammock suspension forces aren't minimized at 30 degrees.

[Latherdome]

Yes the addition helps a lot.

I think you just said (paraphrasing):
* When side angle of poles = hang angle, compression on poles due to hammock suspension forces is minimized.

So... this might be a dumb question... but there's nothing (mathematically) optimal about a 30 degree hang angle, is there? The hammock suspension forces aren't minimized at 30 degrees.

Suspension forces are minimized straight up and down. The forces increase as the suspension angle gets more shallow. 45° is less stressful than 30°. Check how the suspension line tension changes with angle here: http://theultimatehang.com/hammock-hang-calculator/

[Rat]

I have a (semi) permanent ridge line on mine. I built it with a UCR so I can adjust the ridgeline easily for longer or shorter hammocks to maximize the strut angle for each. Plus, this is my first one so I wanted to make it easily adjustable to find what length worked best; but I will make them all this way, it's so easy.