A project log for BIRTHA - Pneumatic RV antenna mast

Telescopic cellular antenna mast, extended and retracted with air using a collapsible garden hose.

Daren SchwenkeDaren Schwenke 10/03/2018 at 21:273 Comments

5 months, it stopped working apparently.  Won't extend anymore.

I don't know what is wrong yet as I'm about 1000 miles from it, but I suspect the rubber tube has failed as it is the 'weak link' in this system.   

I'll be back in the same state again with it in a week or so and then I can give a full post-mortem.

<EDIT> Post mortem.

The hose failed at the attachment point on the top.  This caused the rubber to snap down and collect at the bottom, which prevented the mast from retracting fully.  That was rather inconvenient...  

I removed the hose and held it up when we needed to extend it with the pin holes originally designed for this.

Since I'm now back to a single length of mast anyway, I've decided to go simple and use threaded rod and a DC motor.

That build is in progress.



Morning.Star wrote 12/10/2018 at 07:29 point

Just a thought, Daren.

You're using air to expand the hose, right? Its probably a bit late, but I'd have tried hydraulics before a screw thread. The reason for this is, air is compressible and water/oil is not. In a straight lift there shouldnt be any difference, but if the mast fouled as it rose, the pressure would build and split the hose. Its meshed to prevent that so the only thing it could do was blow an end out.

A hydraulic system is more likely to overcome the fouling without breaking because the pressure only ever equals the resistance and doesnt build. In other words, that system would likely break in a different place, overcome the fouling and move rather than blow out a union.

It looks like the coupling came apart, that hose is intact... ;-)

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Daren Schwenke wrote 12/10/2018 at 17:32 point

Correct on all points.  

Air was just easier as it drives the brakes/suspension system already. Technically I have hydraulics also for the leveling/slides, but the hose breaks down with oil. Ask me how I figured that out... 

It has always broken at the coupling point. It took me a couple times to get the compression fitting just right so it didn't leak and didn't fail immediately.  Two raised areas, two different compressions.  Squishy balooning hose is hard to work with.

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Morning.Star wrote 12/11/2018 at 08:17 point

Oh dear. You've been having fun with that hose :-)

Vegetable oil? That shouldnt affect silicone hose, which I'm guessing that is. And yeah, it doesnt respond well to being crushed either and compression fittings tear real easy.

If you're still up for experimentation, I'd try soldering an olive ring to the fitting, sliding the hose over that and then binding it with thick wire, a good couple of inches of it to secure the hose above the olive, which also rounds off the end of the fitting nicely. Those screwclips bite the hose, and circlips wont hold strongly enough - a binding is somewhere in between. :-)

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