Ways of dispensing fluid for drink-making machine

This has inspired me to make my own cocktail-making machine as my next Arduino project. I’ve seen several other DIY drink-mixing machines but the decent ones look super expensive to make. I think the most difficult part is going to be figuring out how to dispense/measure the liquids. I don’t have any experience with fluid control but I have a few ideas…

Pumps - get some cheap aquarium pumps with tubes that run in various alcohol bottles. But I’m guessing pumps don’t produce a constant volumetric flow rate so measuring the amount of alcohol dispensed might be tricky… Plus they’re noisy.

Solenoids - invert the liquor bottles with a tube running out of each one attached to a solenoid. Again, the flow rate is going to depend on how much liquid remains in each bottle so that’ll lead to inconsistent drinks. Plus I’m not sure there’s a good way to get a good seal while the bottles are inverted with nothing but a hose coming out of their neck.

Any ideas for a good, cost-effective way to do this?

Generally, this is done with a peristaltic (dosing or metering) pump.
Here’s an example.
You could also use stepper motors to drive a syringe, or use sensor to determine when a particular level was reached in a measuring container, then dump it.

How about an IV pump or an enteral feeding pump? Good accuracy, and eBay is full of them, starting at $20 or so.

or you can just order one of these

http://digitalbeverages.com/virtualbartender.htm

You could have a chamber that fills when a solenoid opens at the top (then closes when the chamber is filled), after which, another solenoid opens the bottom to drain the measured shot.

Or just use a single powerful solenoid to operate a conventional bar optic measure.

Awesome as it is, I’m not sure I’d like to spend $3500+ on this project… I’d rather spend that money on the booze. :wink:
I’m interested in the peristaltic pump idea – my ignorance about pumps prevented me from knowing there were ones capable of delivering essentially constant flow (guess I was only thinking about centrifugal-style pumps).

Now of course I could have a pump for each liquid but I’m thinking I could also have one pump and a bank of solenoids that only opens the flow to one liquid at a time. Thoughts on the either approach?

Would it be easier to get auto-dispensing spouts for each bottle and just tip them over with motors? I mean those spouts that dispense e.g. 15 ml every time you tip the bottle over.

You could have your bar bottles sitting on a scale and press a button to remove 1 oz or 2 oz whatever. About 5# of nitrogen pressurizing the bottles would give a nice gentle flow rate. It would require a hose and spicket for each whiskey.

In many ways that would be the easiest to do. Gravity fed systems have the problem of leaking valves. Pumps are complicated, and leave a lot of residue in the pumps and tubing after use. Pressure methods are complicated, potentially dangerous, and have the problem of leaks in valves and connections. There should be a way to put the bottles on a rotating rack that turns to select the one to pour, and then a single linear actuator tips the bottle to pour, then returns it to the upright position. The drawback might be that bottles that are nearly empty won’t dispense right.

There’s a lot of different approaches used at Barbot:

If you dig around, most of those bots have build blogs out there on the net.

For example, this one from my friends at Evil Mad Scientist Labs uses breast pumps:
http://www.evilmadscientist.com/2010/drink-making-unit/

You’ve just described the ‘solvent selection valve’ that can be found on many high performance liquid chromatographs. You can buy them from Rheodyne or Waters, among others.

They can be controlled by contact closure or RS-232.

Can you expand on pressurizing bottles? Obviously if I went this route I’d pour the liquors in bottles that can be safely pressurized but I’m not sure I understand the logistics of adding air pressure in bottles. Would I just have a hose in the liquid for extracting the fluid and another hose in the empty space in the top of the bottle to give it air pressure?