This is an extremely rough primitive MK2 design for a water sprayer. a motor spins a cam lobe which strikes the sprayer trigger and, well it sprays water - I'm uploading by request from Reddit but please understand this is a very rough first go, it works perfectly but just yeah, understand it's very much a first shot. 

1) For the part that holds the bottle just design your own for whatever bottle and bolt it to the body, you might have to zip cut some of that clamps plastic off to clear the motor depending on your model. 

2)  For spacing the cam and gear on the axle I just used some washers I had but you could just print some.

3) I didn't put any keepers on the end of the crankshaft as it seems to not need one, it's ran multiple nights now and hasn't had an issue. 

4) The wood under it was just to prop it up as I wasn't sure what height was needed, depending on your spray bottle you'll need to print your own riser. 

5) I used crazy glue to fuse the cam lobe and gear to the crankshaft, my next model will use a keyed crank shaft but this seems to work fine too. 

6) body spacers are used to space out both body shells

7) Everything but the crankshaft is PLA, crankshaft is PETG but you could just use threaded rod or something if you wanted. 

8)Print two body shells but be sure to mirror the second*

I have this hooked up to a P.I.R motion sensor that keeps my adorable but pesky cats off the counter.

The motor is some cheap generic stock gear motor sold at Princess auto, harbour freight and all over the internet →  https://www.mpja.com/12-24VDC-19_45-RPM-Gearhead-Motor-with-Wheel-Used/productinfo/17971%20MD/     I just cut the plastic wheel part off with a cut off wheel and put the “Spur gear 30 teeth” on it.

You can use any motor you want, you'll just need one with some decent torque and modify the file in Fusion and gear ratio's

Video of it's first test run
https://imgur.com/a/OQCp2fc