Thursday, September 10, 2015

Quick update on the shuttle prototype

Got back from the burn and have been working on the shuttle prototype; had some good time to think about it while I was at TTITD.  Here's was the first version of the shuttle:

It used a pair of circular brackets, made from pieces from previous prototypes (I always get a bit teary-eyed when I cut up an old prototype to make a new one, but the cycle goes round-and-round.)  This was elegant, but it tended to rotate while passing through the sheath, so I had to scrap it.  The current version looks like this:

It's strapped to a couple of pieces of shelf bracket, and I've laid an aluminum rail down on the bottom of the sheath (not shown.)  I didn't film my first experiment, but the result was interesting: it worked well, once.  But it's unreliable because of poor circulation of air to the interior of the sheath.  This is an issue I've seen a lot.  I'm starting to think it might be a major issue with a number of my prototypes.  I can either pump air in (I bought a Shraeder-to1/4" NPT adapter so I can use a car tire as a compressed air source) or open up the sheath a bit.  Haven't exactly decided which.  But a quick test with just using a fan to blow air into the sheath improved it a lot.  Unfortunately the viton came out of the compression fitting after that.  Making sure the compression fitting is secure will be tricky.  In the original shuttle design above, I used a barbed hose fitting with some copper tubing soldered on to make it fit right, and ziptied it in place.  While I think this is actually more secure than the compression fitting, it's not as "legal" according to BMOrg rules.  Getting this approved will require working with them on the design, but for the prototype either is fine.

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