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  1. #1

    Question Handy NoGround DIY

    Dear hammockers,

    I am currently sourcing material for building a DIY version of a stand using the principle of the handy hammock and NoGround poles.* While it's easy to obtain cord and truss poles, finding suitable main poles is difficult.
    For truss poles I can get DAC Featherlite of 8,05mm, 9mm or 10,25mm diameter. Any recommendations? (Question 1)

    For the main poles I am still searching:
    -Handy Hammock might use ~20mm "aircraft" aluminium. Exact details aren't available. At least the hammock attachment ring is of 20mm inner diameter (1).
    -Raftingtigger uses Easton .742" (18,85mm) poles. These are aluminium 7075 T9. Wall thickness should be .032″ meaning .81mm. Ultimate tensile strength should be 96,000(PSI) (2).

    Easton poles are difficult to obtain in the EU, so my goal is to substitute them. Several Tent manufacturers offer tarp poles having dimensions and materials that might be similar to Easton poles.

    1:Hilleberg tarp pole: Seems to use DAC DA17 of (up to) 19,5mm; Price: ~70
    2:LuxeOutdoor: Aluminium 7001 T9, weakest part of the pole is 16mm, wall thickness is 1mm; Price: ~40
    3:Wechsel tarp pole: Aluminium 6061-T9, weakest part is 19mm, wall thickness is 1mm; Price: ~30

    There are other manufacturers like Tatonka and MSR, mostly not offering details on type of alloy, wall thickness and even diameters of the pole.

    Now I would like to calculate which of these poles might be suited for the purpose. (Questions 2) Is there anyone able to help me with this task? I couldn't really find which measurements (e.g. surface, lateral surface...) might be of interest for calculating the strength of such poles.
    The system should hold at least 125kg (1 person + luggage).


    Thanks in advance for any suggestions and help towards the topic. Of course recommendations of other material are highly appreciated, as long as it's easily available around here (Germany, EU).

    Best regards

    JotEm


    *reasons for not using said systems:
    Handy Hammock:
    -Low ground clearance
    -Too short for connecting a tarp
    -pole sections too long (max. 55 cm)

    NoGround:
    -shipping and taxes (to EU)
    -availability of spare parts (no Easton stuff in EU)
    -(no hiking poles needed)

    Sources:
    (1)https://theultimatehang.com/2012/12/...-stand-review/
    (2)tentpoletechnologies.com/?p=614

  2. #2
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    I looked into the same thing and am having trouble finding a financially feasible pole that is light enough and strong enough that breaks down into 2 feet pieces for a portable (perhaps even hikable) turtledog stand. I am running into the same issues as you. I found carbon fiber poles but the cost is outrageous... I would probably end up spending 500 bucks on materials before figuring out how to attach them to a hinge even. I may need to look into the aircraft aluminum option, but not sure that would be light enough for backpacking.


    Sent from my iPhone using Tapatalk

  3. #3
    I stopped thinking about the turtledog stand as soon as I first found the Handy Hammock. The amount of parts needed just simply asks for more weight in whatever configuration you might build it. So I always thought of it as a car camping option. Since I want to be able to fit the stand into carry-on luggage such a stand isn't an option.
    I found that using the Hilleberg poles the cost would nearly rise to the price of NoGround poles including shipping and our beloved 19% VAT (well, still not including customs...). I also thought about buying and modifying the Handy Hammock system to hold a tarp but the portability issue would stand by.

  4. #4
    Senior Member
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    Look up he Yobo hammock stand, it is currently on kikstarter. Looks pretty promising


    Sent from my iPhone using Tapatalk

  5. #5
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    I'll try to dust off my engineering degree to give you a hand with this (and hopefully keep your butt off the ground). Take this advice with caution, as it does not replace a thorough analysis of your own.


    Quote Originally Posted by JotEm View Post
    Now I would like to calculate which of these poles might be suited for the purpose. (Questions 2) Is there anyone able to help me with this task? I couldn't really find which measurements (e.g. surface, lateral surface...) might be of interest for calculating the strength of such poles.
    The design of these stands places a compressive load on the poles, which will cause the pole to fail by buckling. This failure mode is typically not dependent on the tensile strength (or even the compressive strength) of the material; it is dependent on the geometry of the pole and the elastic (Young's) modulus of the material. For slender (long, thin) members, Euler's formula is applicable to calculate the critical buckling load (Pcr, the load at which the member fails).




    It should be noted that any perforations in the tubing (i.e. adjustment holes) can significantly reduce the critical buckling load.


    It should be noted that the length of the member is a second order factor in the denominator of this equation. So doubling the length of the pole reduces the maximum load by 4 times. Because of this, it is apparent that the supporting trusses are CRITICAL to the structural integrity of these stands. Although they introduce a slight preload on the poles, the truss sleeve halfway down the pole modifies the end conditions, which significantly increases the allowable load. You can give yourself an idea of this effect by using the attached spreadsheet. You could also use it to size poles for this application, but I have provided it as a reference only and would recommend further analysis before proceeding.


    Quote Originally Posted by JotEm View Post
    For the main poles I am still searching:
    -Handy Hammock might use ~20mm "aircraft" aluminium. Exact details aren't available. At least the hammock attachment ring is of 20mm inner diameter (1).
    -Raftingtigger uses Easton .742" (18,85mm) poles. These are aluminium 7075 T9. Wall thickness should be .032″ meaning .81mm. Ultimate tensile strength should be 96,000(PSI) (2).

    Easton poles are difficult to obtain in the EU, so my goal is to substitute them. Several Tent manufacturers offer tarp poles having dimensions and materials that might be similar to Easton poles.
    I'm not convinced that any of these specific poles are adequate for this application, even if they are reinforced with truss lines. I've included some failure load estimates for a 125 kg hammock weight using vertical poles of length 2 m and a safety factor of 8.

    Quote Originally Posted by JotEm View Post
    1:Hilleberg tarp pole: Seems to use DAC DA17 of (up to) 19,5mm; Price: ~70
    I'm unable to find details on the DAC DA17 poles (although this source says they are Al 7001-T6), but unless you are willing to accept a low factor of safety, they seem under-rated for this application. Assumed 25 mm OD and 2 mm thickness. Estimated failure load: 98 kg.

    Quote Originally Posted by JotEm View Post
    2:LuxeOutdoor: Aluminium 7001 T9, weakest part of the pole is 16mm, wall thickness is 1mm; Price: ~40
    Much too thin for this load. Estimated failure load: 14 kg.

    Quote Originally Posted by JotEm View Post
    3:Wechsel tarp pole: Aluminium 6061-T9, weakest part is 19mm, wall thickness is 1mm; Price: ~30
    Still too thin. Estimated failure load: 23 kg.





    It looks to me that you would be safe with ~25 mm OD poles with about 4 mm thickness. If you have access to a swage tool, the connection would lend the pole a little stiffness when assembled.


    Calculator:
    NoGround Pole Strength Analysis.xlsx

  6. #6
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    Texas towers sells aluminum tubing in a wide range of sizes, up to 2.5" diameter. Looks like it's all .058" wall.

  7. #7
    Than you so much for all your replies, especially to Vermonster for the in depth mathematics towards the topic. Sorry for responding so late, I was mainly busy with my new job.
    I calculated a bit with the given values. I set the pole length to 157cm, roughly equalling the length of noground poles. Estimated failure load would be 42kg using AL 7075-T6, 18,8mm diam., 0,81mm wall. That leads me to the question whether there is such a huge difference between AL 7075-T6 and AL 7075-T9. Otherwise the noground poles shouldn't work the way they are. Any idea why they still do?

    Thank you so much for all your work.

    Best regards

    JotEm

  8. #8
    New Member
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    From what I've read, T9 is a stronger temper than T6. I hadn't been ab;e to include it in the materials list, though, since I couldn't find data about how strong it actually is.



    My thoughts are that the nested pole design stiffens the pole significantly. When you think about it, the nested portions are essentially 18.8 mm diameter, but 1.62 mm wall thickness. This changes a few assumptions I made in the calculations.

    I also used a very conservative SF, which lowers the estimate a lot. For the 42 kg calculated, you wouldn't expect the aluminum to bend until the weight in the hammock is about 250 kg. Since you (hopefully) won't be hanging somewhere you could die if you fell, it would probably be ok to accept a lower safety factor.
    Last edited by Vermonster; 07-03-2017 at 08:23.

  9. #9
    New Member
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    I can also try to make a better estimate tomorrow. Might be a fun engineering problem.

  10. #10
    A new estimate would be amazing. In the above mentioned link to the HandyHammock review by Derek Hansen, I found that it uses AL 7075-T6. While the measurements remain unknown it still shows that the material suits the purpose at a diameter of about 20mm.
    The difference between T6 and T9 seems to be, that the latter is work hardened, making it stiffer but more brittle than T6.
    I agree, that the nested portions should add to the strength, although the "single walled" parts would then be the "weak link in the chain". Knowing the effect would be interesting.

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