Any experience with piston systems?
 

Do you have any experience with piston systems, home-made or prebuilt ones?

Do you have to cope with increase of pressure inside the WTC? Doesn't it cause or air the grease to exit when filling the ballast and then the water to enter the WTC when venting?

I'm thinking of making one with a syringe, a motor and a screw.

RE: Any experience with piston systems?
 

Usually the piston type is its own self contained tank. The lead screw draws the piston tword the bulk head compressing the air inside the container, not in the WTC. There are usually two rocker switches as well to stop the piston tank from moving to far out or in.

RE: Any experience with piston systems?
 

"Usually the piston type is its own self contained tank. The lead screw draws the piston tword the bulk head compressing the air inside the container, not in the WTC."

Not true. You're thinking the R-RCABS system which uses a bladder. The piston type system pressurizes the entire WTC since it's difficult to seal up the back side of the piston. Also, the RCABS type system creates a vacuum inside the WTC whereas the piston type creates pressure.

Skip Asay

RE: Any experience with piston systems?
 

Tha bladder system sounds interesting. Is it some kind of an air closed-circuit? On surface, the bladder is full of air, then to dive you pump air out of the bladder to a pressurized bottle, the shrinking bladder creates a vacuum and water enter the ballast tank (where the bladder is). To surface again, you release the pressurized air from the bottle again into the bladder, which expands and expels the water out.

Is that right? WHAT ARE THOSE BLADDERS MADE OF?

RE: Any experience with piston systems?
 

Thanks for the correction Skip. Didnt know you ventured over here.

The rubber bladder is usually a blood pressure cuff I believe.
If you want more info I would check out. www.subcommittee.com the guy who invented the system (big Dave) is over there and there is a good amount of archived info you can get with the search button.

RE: Any experience with piston systems?
 

as for syringe systems, I'm building a new one after
operating a first one with succes for over 3 years.

this version features a more coarse thread than the first, causing the piston to move faster (well, okay, less slow).
It requires limit-switches, which I have not yet tinkered out for this version.

it is 60ml (2 oz, I'm told) "big" meaning it can lift 60 grams out of the water

http://www.modelbouwforum.nl/forums/...8e69747826.jpg

RE: Any experience with piston systems?
 

Great! The servo is a nice motor-and-gear box system already available (you just have to quit the electronics, better don't make the receiver draw a great current!, and the tip that limits the turning).

BUT, can it handle the forces involved here?

As for the limit switches, 2 diodes and two push type switches will work: you need to solder every diode pins to the switch pins, in parallel, so when one switch is open (the piston reached that limit), the curren can only run through "its" diode, which must be soldered the correct way. So the piston can only run in one direcion, the opposite one.

Please see the drawing, maybe not pretty accurate, but something like that.
Regards
Robert

RE: Any experience with piston systems?
 

I use my limit switches to short the potmeter signal wire to ground or it's positive lead. that is the same as when ou would yank the potmeter to it's extremes. That way you do not have to switch big currents. and you can leave out the diodes.

as for force : the previous version ued asmaller servo and during development destroyed my wtc. it pushed it apart.
do not underestimate the gear ratio of the thread/nut combo.

as said, the price is relative slow movement. each servo full turn (servo was modified to do multiple turns) will advance the piston
about a millimeter. that's about 1/25 of an inch. the thread is M5.

RE: Any experience with piston systems?
 

RAALST: I still can't figure it out how it (your syringe system) works: according to the picture, could you please how the components work?

THANKS
Regards
Robert

RE: Any experience with piston systems?
 

ok, the servo potmeter is fixed in the middle so that if your stick (on the transmitter) in is the middle,
the servo does not move.

as soon as you move the stick up or down, the servo starts turning in some direction and it keeps on turning as ong as the stick is held
out of the centrer position. the servo was modified to be able to rotate freely. that is also why the potmeter is outside the servo package.

the servo turns the threaded rod.

The white thing on the tube that is the piston arm is basically a nut. it moves along the threaded rod when the servo turns.
each servo turn means the nut moves a millimeter.

the threaded rod disappears into the hollow tube piston arm.

switches must be added to make sure the servo stops when the piston reaches the extreme ends of the syringe.

(shameless plug mode on) If you really want to know all, I have written an article about such a setup in the next SubCommittee Report,
available to members of the Subcommittee.