MYOG CF Tent Poles

[Roger Caffin]

You know, if you bought a small DC motor from ebay ($3), a spare drone propellor from ebay ($3), and a little DC panel meter from ebay (<$3), stuck the motor and propeller on the end of a long pole stuck out the FRONT of your car, with the meter back in the car where you could read it, you could make your own windspeed monitor. Calibrated off your car speedo. Best done with an assistant of course so you don’t crash while trying to write down the readings. Um – you would need a battery for the meter as well, but they draw very little power.

Cheers

[Sam Farrington]

Roger, et al; Did you mention wall thickness, or did I miss it.  A good example of how it effects stiffness is a comparison of Easton .340 dia. flexible poles, with .344 dia.  While the .344 has a larger diameter, it is more flexible (and less strong) because it has a thinner wall than the .340.  As was earlier noted, the wall thickness and dia. are coded on the Easton alloy tubes and provide both the outer diameter and wall thickness in 64ths of an inch.

After much break-testing, the lightest and strongest flexible carbon poles I found were Gold Tip 75/95 Expedition Hunters, and I’ve used them on a wedge tent for years and never had a break.  The company states they are formed of multiple layers of carbon layup, but is not clear about whether they are different orientations of wrapped carbon fabric or if they are filament wound.  Cabelas has made similar claims about the layering of their carbon arrow shafts, but I found they break much more readily.  Since the Gold Tips tested better than anything else tried, it did not matter whether they were wrapped or wound.

At that time, the principle providers of carbon tube online were Rockwest, Clearwater and DragonPlate, some of which sold filament wound tubing in various diameters and wall thicknesses, but at very high prices, far more than the market would bear for backpacking tents.  Today, however, I see from JCH’s experience, and from browsing on line, there are a lot more providers, including those that provide the filament wound.

The Gold Tips I use weigh just under a quarter oz per running foot.  So the weights and lengths JCH provides for larger diameters poles that are rigid are pretty good, I think.  It’s useful to know about new sources, like Hao Zhong and others, in the search for the lightest and strongest carbon tubes for tent poles.  But one surprise was a high-end carbon trekking pole that was exceedingly flexible compared with an inexpensive carbon pole with alloy in the lower sections that was stiffer and more user friendly and has never failed.  Such things become apparent with an opportunity to use the gear for a while.  While the forums are enjoyable, I miss the many articles on BPL that evaluated products in depth.

[Roger Caffin]

Did you mention wall thickness, or did I miss it.
As long as the tube does not collapse, the wall thickness is not super-relevat. The formula for bending moment is
k*(OD^4-WT^4)/OD
In effect, for thin walls, OD^3. I was wrong when I claimed OD^4 – sorry about that.

My understanding is that the E344 is slightly stronger than the E340: about 91% wrt E355 compared to 88%. The E355 is the classic tent pole. However, the strength/weight ratio is 1.216 vs 0.956 in favour of the E344. Hum – all other things being equal. Caveat: this is data from many years ago when I was building tents. But I don’t see why it would change.
All 3 of these are 7075 T9. Only Easton can make T9 it seems.

There is also the ill-fated 7178 alloy which was briefly sold by Easton. Stronger, but it did seriously work-harden after a number of pitchings (ie bendings), and then it snapped. This happened to me in the Pyrenees. I repaired the pole once, but it happened again.

Cheers

[Sam Farrington]

Roger, if break tests are any measure, the Easton .340 is much stronger than the higher diameter .344.  So keep the .340’s that you bent for your pack frame.  The .344’s will not survive the rigors of packing.  BTW, I got an Aussie Shepherd as a companion for my Shetland Sheep dog.  The Aussie is crazy nuts, and is driving the Shelty and me toward the same fate.  The groomer says the Aussies are all “headstrong.”  If that is true, I hope it only applies to  dogs.

[Roger Caffin]

Hi Sam

Break tests is something I have not done. Calibrated deflection tests, yes for sure. But something which has a higher stiffness can break sooner when the wall thickness is smaller.
Comment: I try to stay within the ‘deflection’ zone!

‘Headstrong’? Yeah, well, funny about that. :)

There WAS a track under all those vines – somewhere. Sue just stood back and let me at it, then strolled through.

Cheers

[Roger Caffin]

Roger says diameter to the 4th power.
Roger was wrong. To the 3rd power.

Cheers (with blushes)

[Jerry Adams]

wind meters are pretty cheap, like “Proster Handheld Anemometer Wind Speed Meter Thermomoter Wind Detector Gauge Airflow Meter for Outdoor Sailing Surfing Shooting Fishing Hunting” on amazon is $17.  I’m sure cheaper on ebay or alibaba or whatever.

I have “Brunton ADC Wind Atmospheric Data Center” for $60, a little better quality.  And I like how it displays time, date, day of week, temperature.  Back light when you push a button.  The temperature sensor is calibrated so it says “32 F” at freezing temp.

[Jerry Adams]

But Roger’s project of making your own wind meter for $9 looks like a worthy project : )

[Stumphges]

I got a $13 one off Amazon and while it seems nice, sticking it out the window has it reading 5-7 mph less than my speedometer. If it’s consistently off by that much, well, it could still work, but…not gonna cut it.

[Roger Caffin]

Just sticking it out of the car window will NOT work. The air in contact with the car surface is at zero velocity relative to the car. 5-7 mph error is not bad here.

Try putting it on a 10′ pole sticking out IN FRONT of the car. Get into the air flow before it is upset by the car. Chuckle: you may need binoculars to read it when it is that far away.

But yes, this does mean that taking a reading with the unit only a few feet above the ground will NOT give you the real wind speed as measured 10′ above the ground. On the other hand, it may tell you the wind speed at the height of your tent.

Cheers

[Stumphges]

Thanks, Roger. I’d wondered about that. Maybe it is accurate. I can use my new carbon poles to hold it in front of the car. I frequently use cell camera images blown up in place of magnifying glass; will work also as monocular:)

[Eric Blanche]

I have bought multiple times from the chinese vendor described in the original post. I have found the OD diameters to be inconsistent and have had to sand down some of them. With that said, i am perfectly happy with the performance of the tubes. My poles of two sections are very similar to Bob Moulder’s and have literally fell onto them flexing considerably without cracking or any other compromise to the tubes.

[Sam Farrington]

Why bother with a wind meter when you can just strap a solo tent on the cartop.  Then just check the speedometer as you go.  Best to do this in large city parking lots when the mall is closed so you don’t have to look out for traffic.

[Sam Farrington]

Roger, glad to see you are getting out there.  We have a trail here called the North Slide on a mountain called Tripyramid.  The brush is used to hold in order to keep from falling off while climbing.  Don’t recommend descents.

Sometime ago, posted the whole breaktest setup with photos, so won’t bore you.  The tubes were stuck into a very snugly fitting reinforced hole in the wall, then a 100 pound fishing scale with a good handle was affixed to the pole around 6 inches from the wall and the handle pulled slowly downward.  The scale showed the pressure in pounds when the pole broke, always at the wall as you might expect.  The better poles consistently broke at higher pressures.

Daryl and Daryl then posted an arguably more scientific setup from a now defunct website.  But was satisfied with mine for purposes of comparisons.  The poster of that setup concluded that external ferrules made the poles more break prone than internal ones.  However, the tube samples were not held at the break points snugly enough to keep them from flattening somewhat and breaking more easily.  External ferrules help to address that problem.

Eventually the fishing scale sprung a spring and was thrown out.

[Roger Caffin]

Why bother with a wind meter when you can just strap a solo tent on the cartop.
Because the wind speed across the top of the car will NOT match what the speedo is showing. The car distorts the airflow badly. That is why wind tunnels are so large: to get away from the skin effect from stationary surfaces. In this case the car roof is ‘stationary’ relative to the tent.

Cheers

[Sam Farrington]

Hi Roger,

Yes, you made that point in your previous post on this thread.  But I was only having some fun.  Even with the tent separated from the car top by a roof rack, it would be hard to find a place to legally do this without risking the wrath of law enforcement.  An abandoned airport maybe? Empty mall in the middle of  the night with a full moon?  Doesn’t sound promising.

 

[Author]

Posts