#garfield Logs

May 07 2021

10:31 PM Tom_L: mmm
10:38 PM Tom_L: router must be on the fritz again
10:38 PM rue_shop1: hmm
10:38 PM rue_shop1: what was the last thing you got?
10:38 PM aandrew: oof, big ali order
10:38 PM aandrew: mind you $50 of the $97 shipping charge was for one particular item I really am willing ot pay DHL to get next week for
10:38 PM aandrew: the rest is nickel and dime shipping charges which I can't seem to get rid of
10:38 PM aandrew: rue_shop1: have you noticed that ali shipping prices to Canada have spiked again?
10:45 PM rue_mohr: there are aggragator people over there eh?
10:45 PM rue_mohr: yes, they been on a gradual rise
10:50 PM aandrew: ali is already one level of indirection, I can't imagine trying to introduce another level to aggregate shipping
11:00 PM aandrew: thought exercise: if you were going to design a pilot valve (just air, maybe 80ish psi, low volume), something easily machined and small, how would you go about it?
11:00 PM aandrew: I was originally thinking of something using a presto or shrader valve from a bicycle but the mechanical actuation would be trickier
11:01 PM aandrew: so then I started thinking about a channel cut in aluminum or plastic with a tiny bent piece of steel that I could pull on with a pcb coil or something
11:02 PM aandrew: you could make that bent piece of steel have a really wide paddle so the pcb trace coil dind' thave to be crazy
11:02 PM rue_mohr: hahah I been working on that for years
11:02 PM rue_mohr: have you seen how a washing machine valve works?
11:03 PM aandrew: yes, but it's enormous
11:03 PM rue_mohr: look how it works tho
11:04 PM rue_mohr: diaphram, differential area working against the flow
11:04 PM rue_mohr: solinoid pulls pin that opens hole to destroy difference and pressure takes over
11:05 PM rue_mohr: if you go with a small enough orifice, then you could probably just do a rubber stopper on a solinoid
11:05 PM aandrew: hm
11:05 PM rue_mohr: I'v not successfully machined anything yet
11:08 PM aandrew: the issue with the diaphraghm is that is an additonal piece
11:08 PM rue_mohr: solinoid core with a rubber end that plugs a pinhole?
11:08 PM aandrew: I'm thinking a bent piece of metal is easy to cut/stamp and bend in a press, and if you use an o-ring to seal it it's nothing fancy to hold air
11:09 PM aandrew: solenoid core is too big, I'm thinking flat, like total voume maybe 2" x 1" x 1"
11:09 PM rue_mohr: interesting
11:09 PM aandrew: just 1/8" NPT since it's a pilot valve
11:09 PM rue_mohr: we have a lot more tech in magnetic paths than we used to
11:10 PM aandrew: and at least in theory a big wide paddle means I should be able to pull on it sufficiently hard with a basic 4 layer PCB coil
11:10 PM rue_mohr: and rare earth magnets
11:10 PM rue_mohr: and flex pcbs
11:10 PM rue_mohr: ...
11:10 PM aandrew: basically think of a regular old PCB relay, but the too have a big coil
11:11 PM aandrew: I wonder if you can use an unshielded wide SMT inductor to make something similar
11:11 PM aandrew: smt air core with a ferrous slug maybe
11:13 PM rue_mohr: how big an orifice?
11:13 PM rue_mohr: 1mm?>
11:13 PM rue_mohr: less more?
11:14 PM aandrew: 2-2.5mm I'd think
11:14 PM rue_mohr: lets say 2.5mm
11:14 PM rue_mohr: zippo:/tmp# circle -d 2.5mm
11:14 PM rue_mohr: Radius is : 1.250000
11:14 PM rue_mohr: Diameter is: 2.500000
11:14 PM rue_mohr: Circumfrence is : 7.853981
11:14 PM rue_mohr: Area is : 4.908739
11:14 PM rue_mohr: Sphere area: 19.634954
11:14 PM rue_mohr: Sphere volume: 8.181231
11:14 PM rue_mohr: >> Area is : 4.908739<<
11:15 PM rue_mohr: zippo:/tmp# units 4.9087mm2 inch2
11:15 PM rue_mohr: * 0.0076085002
11:15 PM rue_mohr: zippo:/tmp# calc 80*0.0076085002
11:15 PM rue_mohr: 80*0.0076085002 -->> 0.60868
11:15 PM rue_mohr: .61 lbs of force
11:16 PM rue_mohr: zippo:/tmp# units .61lbs g
11:16 PM rue_mohr: * 276.69135
11:16 PM rue_mohr: say 300g
11:17 PM rue_mohr: fair bit
11:17 PM aandrew: hm
11:18 PM aandrew: but you can shape the metal actuator to get some mechanical advantage by adjusting the fulcrum
11:18 PM rue_mohr: I doubt a flex pcb and rare earth magnet could do that
11:19 PM rue_mohr: hmm
11:19 PM rue_mohr: at 80psi, you dont want the device to be too big
11:20 PM aandrew: yep and I have to calculate just how much flow I need to drive the main valve
11:20 PM aandrew: might be able to get away with a smaller oriface
11:29 PM rue_mohr: hmm, yea, me, a solution looking for a problem
11:33 PM aandrew: heh