Mount and Reservoir Discussion

[Toasterboy]

Ok, so I programmed the arduino to fire the injector 20 times a second and hold it open 80 ms each pulse. Wired up the pump, and connected the hydraulics with surgical tubing (and zip ties, after the hoses popped off the first time) =) Using regular water for now.

Latex tubing expands in such a way that it provides approximately constant pressure, apparently. (people use variations of it to power homemade cps supersoakers).

#1 Wow, the clicking from the relay I bought is annoying... it's a lot louder than the injector, which is quiet.

#2 It basically works.... fired it up and the injector pulses water at what appears to be the programmed rate. Dispensing volume and pressure unknown, but it's pretty quick... maybe approaching the rating of the injector, which is 300cc per minute.

#3 Need to solve pressure regulation before it makes sense to do any measuring... the pump I bought is adding pressure to the system faster than it leaves the injector, and that's with an undersized power supply. I might have gotten a pump that's too beefy (500 ml/ minute and 40psi). Clearly need to get some kind of pressure sensor, and shut off the pump when pressure is above target level, and probably control the current too. The latex tubing can only handle so much volume before it expands (and that's destructive, it can only handle that a few times).

#4 I didn't have the right arduino pin cables, so I jury rigged with bits of wire and alligator clips. It works, but if water leaks it's going to short out and potentially electrocute me. Need to get the right bits and bobs and re-arrange the parts so as to minimize mixing water and electricity.

#5 The jets from the injector come out with a good bit of force. Looks like some of the nozzles on the used injector I got are clogged... will need to get some brake cleaner and try to salvage the clogged ones.

But yeah, it basically works, and it's pretty clear that it will be able to adjust dispensing rate to match a given container. (above some minimum drop size, which depends on the pressure, and physical characteristics of the injector).

Yay, fun!

[Toasterboy]

Here's a video of the proof of concept injector setup:


It is configured to open the injector for 80ms, and close it for 50ms. That works out to ~7.69 pulses per second (not 20). After the video I did another test and measured it dispensing ~100ml in ~91 seconds. I don't think that it's operating at full capacity yet though.

That works out to ~0.14ml per pulse. (which is about 1/2 micron per pulse z level rise in a ~2'x2' container) Also, the dispense rate would be ~4000ml/hour with this setup, which is about twice as fast as the siphon dripper. Haven't played with varying the open/close durations yet.

I suppose the next steps are to research and select a pressure sensor, and figure out a better tubing solution, so it will take a while before I'll be able to proceed. I'm also pretty sure that the latex tubing isn't sufficient to run at the right pressure.... suspect it's well below 40psi currently and will perform better at higher pressure. I used latex initially because it fails gracefully, and pops like a balloon rather than exploding on overpressure.

It seems pretty clear that this concept can provide some pretty fine control over volume dispensing and timing though.

[3dspider]

You might try some braided vinyl tubing. The stuff I have is rated for 250 psi.

[Toasterboy]

Yeah, that's what I have in mind to try after I get a sensor (and probably an emergency release valve). Will the braided stuff hold around 100psi with barb connectors and zip ties? Rather not have the connections pop off under pressure.

[3dspider]

I usually use barbed fittings and worm gear hose clamps. I'm not sure if zip ties will provide enough pressure.