Thursday, February 1, 2018

More probe designs

Now that I have a 3D printer at my disposal, I'm thinking about ways to streamline the probe design.

One thing that Jeremy and I have talked about is removing the Fio V3 and integrating the Atmel chip that runs our Arduino code, along with the battery charging circuitry and other utilities, directly into the board. This will eliminate the bulky daughterboard that gets in our way.

But meanwhile, it should be possible to print all the components myself now. With an 0.3mm nozzle and 0.1mm layers, here is a 3/4" half-sphere with holes I printed to try things out:


This looks pretty acceptable. The one thing I should do is make the holes a little smaller, then chase them with a 1/8" drill bit, to ensure they are sharp-edged and consistent. But otherwise, this is a pretty good start.

My currently brewing design involves the probe nose and a "manifold" which can both be either 3D printed, or subtractively manufactured by machining:



The manifold also holds the static tube, which can either be bonded into place or secured with a 1/16" dowel pin match drilled into it after if is assembled.

According to my quick experiments with a hammer and a piece of wood, a 1/4" OD by 1/16" wall aluminum tube is trivial to bend to a 90 degree angle without kinking it. To plug the end of the static tube, I tap the inside, drive a screw into it with Loc-Tite, then chuck it in a drill and round off the end with a file. I will try to blog this process sometime. There's no rocket science there.

That leaves the connections for the 1/8" OD by 1/16" ID PVC hose we use to connect the sensors. So far we've been using various little barbed hose fittings that look sort of like this:


They typically have a 10-32 thread. This is actually pretty bulky, and I wondered if there was an easier way. Jeremy suggested maybe just gluing the hose directly into the PLA. I tried that on a piece of scrap, using regular CA glue and roughening the PVC hose a little bit before bonding. The results were excellent -- those hoses were not going anywhere!


I plan to use the Loctite Plastics Bonding System for this but, given the good results with just plain hardware store CA, I expect this will be pretty reliable!





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