Alright here is a video demonstrating a solenoid raising a 25.5 cm x 16.5 cm x 4 cm object in salt water. This will lower the large (27.4 liter) container's "resin" (actually dish soap here, I don't have resin) about one mm. If more than a mm is desired then the object could be more than 4 cm thick. Since the object is roughly the same density as the salt water, a pretty small solenoid could in theory change the water level of an enormous amount of water if desired.



How it works is the object sinks to the bottom displaces salt water and resin. The top layer (which is the fresh water) isn't really displaced since the object is only 16.5 cm tall. When the solenoid is powered it pulls the object up about one cm. This then causes less salt water to be displaced, which in turn lowers the resin level. Then the solenoid is not powered anymore and the resin goes back up.

The object in this case is just a few sheets of plastic glued together filled with salt water. Therefore I didn't use anything that costs much at all.

In the video two problems can be seen, but I think this is good because it points out two things to watch out for. First is that the object jerks up from momentum wildly, then down a bit when the solenoid is powered. Then when not powered it goes back to normal. This is because I had wire (versus something rigid) connect the solenoid to the object as you can see in this photo.

solenoidtoobjectwithwire.jpg

The second issue is that the liquid sloshes around. There are a couple things to address this. First had I set things better and the object didn't swing around wildly and just went up and down the liquids wouldn't slosh. Second a sheet of plastic can isolate the object from the rest of the container if the sheet is placed to form a wall between the solenoid connected object and the object being printed. It is necessary to leave a hole in the bottom of this wall though so that the salt water level can change. This would also address a possible issue in that the solenoid connected object would screw up the resin as it moves. That said I'm not sure if the wall is necessary, but if it is it's just a matter of gluing one properly sized sheet of plastic.

Let me know if anyone has any questions or concerns! I would have had this a few days ago but the solenoid I ordered the first time had the plunger missing. That's like ordering a bike and it having no wheels. Not sure how they screwed that up! haha