<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>Thanks Steve,</div><div id="AppleMailSignature">I thought there might be a solenoid valve that gave a good variable control over</div><div id="AppleMailSignature">the flow.</div><div id="AppleMailSignature">I did experiment quite a bit with linear actuators, but thought pneumatics might</div><div id="AppleMailSignature">be a lot simpler. The commercial deep sea linear actuators are oil filled & use </div><div id="AppleMailSignature">brushless motors. As I found out, the small brushed motors don't run so well in</div><div id="AppleMailSignature">oil. They have external oil reservoirs to compensate for the piston movement &</div><div id="AppleMailSignature">an overpressure. Can always re-look at them.</div><div id="AppleMailSignature">Cheers Alan</div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature"><br>Sent from my iPad</div><div><br>On 17/03/2018, at 3:58 PM, Stephen Fordyce via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:<br><br></div><blockquote type="cite"><div><div dir="auto">Hi Alan,<div dir="auto">I've done a little with pneumatic cylinders and I think it will be very difficult to achieve any kind of accurate positioning. Pneumatic is fine if you only need a cylinder to be fully extended or retracted (as is used for industrial automation) but anything mid way is likely to need a complicated feedback/control system.</div><div dir="auto"><br></div><div dir="auto">Even considering as a perfect system, if you have varying force/load, to avoid movement you must have an equally varying pressure in the cylinder. Increasing pressure in the cylinder doesn't help because you then need to increase pressure in the opposite side and then the tendency to resist a disturbing force is not much different anyway. (And if using a single rod cylinder, the pressures in each end need to be different to achieve the same force due to area of the piston) Throw in real world considerations of static friction and dynamic friction and it's harder again to reach and hold a desired position.</div><div dir="auto"><br></div><div dir="auto">I'm a bit surprised you haven't already ordered a cheap pneumatic cylinder for some concept testing :). That should give you a feel pretty quickly if it's doable or not.</div><div dir="auto"><br></div><div dir="auto">Cheers,</div><div dir="auto">Steve Fordyce</div></div><div class="gmail_extra"><br><div class="gmail_quote">On 17 Mar 2018 7:27 am, "Alan via Personal_Submersibles" <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Have thought a lot about pneumatic manipulators.<br>
Hank has commented several times that they are too "spongy".<br>
If you had pressure relief valves or similar in the system set at something<br>
like 30 psi, so there was always a minimum of 30 psi either side of the piston;<br>
would this make it a lot less "spongey".<br>
You would now need to put an extra 30psi in to get the same force.<br>
It would mean more air, but it is not likely you would be using the manipulator<br>
every dive, & it would be a small quantity compared with blowing a ballast tank.<br>
Has this been done before?<br>
Cheers Alan<br>
<br>
<br>
<br>
Sent from my iPad<br>
<br>
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