Sunday, February 4, 2018

Probe nose progress

A major disadvantage of our current probe design is that it's hard to put together. To get an idea of the messiness, see this video (sorry about the expletive but the process is frustrating).

So I'm now working on a new probe nose that will integrate all the plumbing and the static probe mount into one unit. To make it easy to 3D print (and with an eye towards future injection molding or machining), it's in several layers, with the plumbing routed as a series of grooves. The layers will get bonded together and sealed. The 1/8" OD vinyl hoses will get bonded directly into the manifold.

This is the stackup looking from the front:

and this is what it looks like from the rear:

the parts need to be cleaned up in some cases -- some holes need to be chased to exactly 1/8"; the mounting holes in the nose need to be tapped to 6-32; and the exterior holes in the nose need to be drilled out carefully so they have a nice clean edge rather than the 3D printed blobby shape.

Since this is a bit of a mockup, I'm using a fairly large nozzle (0.3mm) and layer thickness (0.2mm); the nose, in particular, could probably do with a far more fine printing resolution.

The static probe attaches into the bottom of one of the layers, with a groove in the tube to pass the pressure through:

The longer term plan is to secure it with a 1/16" diameter by 1/4" long dowel pin through the whole subassembly before mating to the other layers.

This then is what you end up with, with all the tubes coming out in nice convenient locations:

and the slot secures the PCB so the whole thing can go into the housing as a unit:

Now note that instead of the temporary machine screws you see here, the plan is to use four 6-32 threaded rods that go the full length of the probe and clamp everything together axially.

I've also ordered some (expensive!) 1/16" wall thickness, 2" OD polycarbonate tubing for the housing, as the 1/8" wall thickness stuff I've been using so far is just way too heavy and clunky.

This design is fully compatible with our current board using the Fio V3 (though it may require some creativity in mounting the Fio lower down, to clear the threaded rods). Our longer-term plans include an integrated electronics unit, without the Fio as a daughterboard, which should be even easier to work around. I'm hoping that the switch to the newer-style board can happen with simply a shorter housing, by keeping the same basic form factor (1.5" wide PCB).

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