The TurtleDog stand

[Dynamystic]

Well I finally made myself a turtledog stand. It works well for showing off my new rainfly design.






https://www.hammockforums.net/forum/...ad.php?t=79534

[gmcttr]

...Any comments and/or suggestions?

Yes...one important suggestion.

One of the design features of the tripod/ridgepole stands is to have the hammock suspension attached as close as possible to the suspension holding the pole...preferably to the outside. This minimizes the bending forces applied to the ridgepole.

Move the stands a bit closer and move the straps holding the ridgepole just inside of the hammock suspension. This will allow the forces involved to bow the ridgepole up just enough to offset it's own weight. The way you have it will bow it downward enough to collapse some ridgepoles, although the mast may be strong enough to take it.

[thekid]

There it is again the magical two pole TDS( 3rd pic down)

[skree]

^^^
gmcttr: thank you.

^^
thekid: I seen that, too.

sliver:

That pipe ridgepole looks dicey to me.

2.50" schedule 40 pipe, 144 inches, steel:

• 2.875" O.D.
• 0.203" wall thickness
• 922.08 lb. force applied (arbitrary number, here)

Deflection: 20.000865 inches.

Increase pipe length to 168 inches (14 feet):

Deflection: 31.76", 922.08 lb. force applied.

I used 'Solid Round Tube Beams Deflection Calculator'
from
http://easycalculation.com/mechanica...tube-beams.php
aka
http://tinyurl.com/solid-tube-calc

and took 2.875" (not 2.50" I.D.) to be the correct input for this calculator.

I haven't verified this calculator.

----------------

Looks like the cube of the length drives deflection!

----------------

Deflection = (length^3 * force) / (3 * E * MI)

So, if you shorten it from 14 feet to 10.5 feet, for example:

2.50" schedule 40 pipe, 126 inches, steel:

• 2.875" O.D.
• 0.203" wall thickness
• 922.08 lb. force applied

Deflection: 13.4 inches.


. . .


Note: I'm supposing a deflection of just 6" of 12' of this pipe will
create a permanent bend, from an applied force of just 277 lb, supplied at the center, when the beam (pipe) is supported only on the ends. I don't have a good reference yet.


I may be way outside reality on this. A little knowledge is a dangerous toy.


Here are the numbers I'm (wildly) supposing:

L=144 D=2.875 W.T.=0.203 F=277 lb.

Deflection: 6 inches
Bending Stress: 37,487.4 psi

A 92 lb. person, accelerating themselves to 3x their weight (by jumping up, and grabbing on) should be able to do this.

L=144 D=2.875 W.T.=0.203 F=332.2287 lb.

Deflection: 7.20638 inches
Bending Stress: 44,961.69 psi

310 MPa (megapascals) = 44,961.6987 psi (pounds per square inch)

A500 steel, grade A, UNS K03000
tensile strength: 310 MPa
yield strength: 230 MPa

See:

• http://en.wikipedia.org/wiki/Bending
• http://en.wikipedia.org/wiki/Deflection_(engineering)
• http://en.wikipedia.org/wiki/A500_steel
• Classical Mechanics at askthephysicist.com

These guys sound like they might know something:

http://www.homebuiltairplanes.com/fo...-strength.html
aka
http://tinyurl.com/aero-stress-bent

[gmcttr]

...from an applied force of just 277 lb, supplied at the center, when the beam (pipe) is supported only on the ends. ...

I'm not sure what you're thinking, but we are not applying force downward at the center of the ridgepole. It is being put into compression as straight through the center of it's lengthwise axis as possible. That's why connecting the hammock as close as possible to the ridgepole hangers is important. If you get more than an inch or two of deflection in a 16' pole, you are not making the connections in the correct locations.

[Floridahanger]

The calculators for other applications are not constructed to perform calculations for a TDS or other style of load bearing connections.

I'm not sure what you're thinking, but we are not applying force downward at the center of the ridgepole. It is being put into compression as straight through the center of it's lengthwise axis as possible. That's why connecting the hammock as close as possible to the ridgepole hangers is important. If you get more than an inch or two of deflection in a 16' pole, you are not making the connections in the correct locations.

Thanks, gmcttr. This is important to note.

The calculations have been made by trial and error, corrected by engineers in the hammock community and applied to the specific construction designs for transfering horizontal load forces to vertical load forces. In doing so, the connections from the TDS to the load bearing crossbar, to the hammock suspension, down across and under the load(me and/you), back and up the other side of hammock suspension to the load bearing crossbar and finally to the other TDS is specifically taylored for keeping the TDS freestanding and the crossbar as straight as possible by removing the stresses that contort and weaken the bar.

Babble talk for keep it simple and connect everything in a vertical line.

Happy hanging.

[hppyfngy]

Dang!

When I get to a screen in a few days I sure look forward to catching up on what you folks are talking about!

HFG In da woods.

[olddog]

Was wondering where you had been on this discussion.

[sliver]

The Aluminum windsurfing mast I used will hold over 600 lbs of compression. Modern windsurfing sails use a 3-pulley block and tackle system to tension them.

I had a steel chain link fence rail but it was pretty heavy compared to the Al mast. According to my calculations, I am putting a max of about 432 lbs of compression on it.

[sliver]

Good call on the location of the ridge pole - hang point. I'll try reversing them so the ridge pole straps are inboard of the hammock hang point (prussic).

I have my doubts about the way I rigged my tarp over the top of the pole. When I did that I wasn't thinking about rain. I was thinking about the added structural strength I'd get if it snowed. Now I'm thinking I probably should have hung my tarp under it if rain is a possibility.

Any experience/thoughts on that?