Hmm those are cheap, at $5 the old aerospace approach of a parallel/series high reliability network sounds like the cheapest way to prevent slow leaks. Draw 4 valves with two in series and two strings in parallel and no failure mode of any individual valve either stuck open or stuck closed can cause an overall mission fail. Another way to deal with slow leaks is a small intentional air leak on the top of the liquor bottle and trust your weight scale feedback because the output flow rate will be lower but how much lower will depend on the intentional air leak. So 10% of incoming air leaks out, well, thats OK if it prevents slow dribble.
WRT to quality valves if you have a slow leak in the air input valve, even just a drip per minute, you'll slowly drain the bottle while it sits there. A more complicated arrangement with more valves can vent the bottle when its not supposed to be pumping which helps.
Your scale idea is excellent and I've seen it done. If you're sufficiently motivated its a great platform to play with PID controllers or at least PD (not I) control theory.
For a literature search I've seen this kind of machine in make magazine maybe in the 00s or at least a couple years ago and in some 80s era home computer magazines. It fell out of favor in the 90s or maybe I wasn't paying attention.
Advanced systems put a slight vacuum on the delivery hose to prevent dribbling although there's obvious cross contamination fears. From memory this was part of the reason the "tip the whole bottle with a R/C servo" guy took that approach, side from being visually more stunning. I remember that guy writing about an air traffic control issue where you can't have the neck of two bottles in the same airspace simultaneously, so extra delay timing is critical, can't immediately drop one bottle at the same instant one is lifting up.
I also recall reading about a design involving "hit the wine-in-a-box button with a servo horn" although that had variable flow rate problems and splashing issues, which might be worked around.
The parallel/series approach sounds really interesting - I'll have to look at that. On the other hand, if you wanted to reduce valve count, you could even do charlie-plexing! Then you can get 2*sqrt(N) nice valves to control N bottles. That would be really cool. Now somebody's just got to build the 100 bottle bartending robot.
WRT to quality valves if you have a slow leak in the air input valve, even just a drip per minute, you'll slowly drain the bottle while it sits there. A more complicated arrangement with more valves can vent the bottle when its not supposed to be pumping which helps.
Your scale idea is excellent and I've seen it done. If you're sufficiently motivated its a great platform to play with PID controllers or at least PD (not I) control theory.
For a literature search I've seen this kind of machine in make magazine maybe in the 00s or at least a couple years ago and in some 80s era home computer magazines. It fell out of favor in the 90s or maybe I wasn't paying attention.
Advanced systems put a slight vacuum on the delivery hose to prevent dribbling although there's obvious cross contamination fears. From memory this was part of the reason the "tip the whole bottle with a R/C servo" guy took that approach, side from being visually more stunning. I remember that guy writing about an air traffic control issue where you can't have the neck of two bottles in the same airspace simultaneously, so extra delay timing is critical, can't immediately drop one bottle at the same instant one is lifting up.
I also recall reading about a design involving "hit the wine-in-a-box button with a servo horn" although that had variable flow rate problems and splashing issues, which might be worked around.