Re: [PSUBS-MAILIST] Sub with arm

["D. Blake" <dblake@bright.net>]

Well, according to 'Pascal's' law, "In a closed system filled with a fluid,
the pressure will be the same in every part of that system."  The amount of
force psi applied by a 1-inch actuater will be equally transferred to a
1-inch slave in a closed circuit.  The amount of travel will also be the
same.
Notice here we refer to lbs. per square inch.  Both actuater, and slave have
the same per square inch of piston surface area.
According to 'Pascal's' law, if we increase the slave from 1-inch to 4-inch
surface area, we in turn multiply the advantage psi x4, but decrease the
travel x4.  Thank of it as a lever.  A 4-inch travel at 2-lb psi force
applied by a 1-inch actuater to a 4-inch slave will result in the 4-inch
slave having 8-psi force, but with only 1-inch travel.
Garage floor jacks reject the opposing force thru a check valve that allows
fluid to flow in one direction only, and so you have to release the valve to
lower the jack.
The manipulator arm Stan is suggesting has no such check valve to hinder the
flow of fluid to or from(although he could add one to the gripper part of
his design), and so the only limiting factor would be the ratio in terms of
amount of travel vs. desired force in psi.

TTYL,
BigDave

-----Original Message-----
From: Dan H. <machine@epix.net>
To: personal_submersibles@psubs.org <personal_submersibles@psubs.org>
Date: Saturday, May 12, 2001 9:41 PM
Subject: Re: [PSUBS-MAILIST] Sub with arm


>That's not exactly correct.  I'm sure this application will be using double
>acting cylinders.
>A double acting cylinder with a piston diameter of one inch probably has a
rod
>size of .250 to .375 inch.  It's the rod area that the water pressure will
be
>acting on.  At .375 dia. rod has an area of only .111 in.sq.  So at 45 ft.
>20psi, you really only have to overcome 2.2 pounds.
>
>Air is forgiving, but with cylinders filled with oil, you should use
identical
>cylinders, same piston diameter and same rod diameter, for actuator and
slave
>when you hook them in a closed loop.  Any mismatch in piston area verses
rod
>area RATIOS between actuator and slave would cause a closed loop system to
lock
>up. It's the area ratio that must be the same.
>
>Dan H.
>
>Marsee Skidmore wrote:
>
>> Stan,
>>
>> If I'm understanding your manipulator description correctly, you'll be
>> working against outside pressure. At 45 feet, that's around 20 psi
pushing
>> against each of your cylinders. A one inch diameter cylinder (for
example)
>> has an area of .8 in^2, so 20 x .8 = 16 lbs. Not impossible, but you may
get
>> more of a workout than you planned. Somebody already suggested using
smaller
>> diameter cylinders inside to obtain a mechanical advantage, and that may
do
>> the trick.
>>
>> What's the vacuum supposed to do?
>>
>> Joe
>> ----- Original Message -----
>> From: Stan Muller <smuller@iland.net>
>> To: <personal_submersibles@psubs.org>
>> Sent: Friday, May 11, 2001 10:31 PM
>> Subject: Re: [PSUBS-MAILIST] Sub with arm
>>
>> > Hi Dan H.
>> >    I had thought about the need for a stable platform from which to
work
>> > with the arm. This is the reason my arm will be mounted on the side of
>> > the sub, below the conning tower. Set up this way, the mass of the hull
>> > and tower will help prevent the boat from moving when a force is
applied
>> > to the arm. Initially I had thought to put it on the bow, but was
>> > concerned about the torque applied to the arm moving the boat.
>> >    > but than I have done some back yard,
>> > > picnic table, fish pond engineering myself a few times.
>> >    One thing I have found to be common among the backyard shade tree
>> > engineering types, Is they, as a group, tend to over engineer, usually
>> > ending up with a 300 % or better fudge factor. As the case in point, my
>> > hull; The tanks are 1/8th inch aluminum, I don't know what they were
>> > built for, but they have the manufacture ID tags on them showing that
>> > they were pressure tested to 175 lb per sq. in. over which I will lay a
>> > minimum of 1/2 inch of epoxyed fiberglass, (woven), and laid on the
bias
>> > of each preceding layer. Since the deepest dive we can make in our
local
>> > lake is 45 feet, and our operating depth will be no more than twenty
>> > feet, my buddy and partner in crime, made the suggestion that we use my
>> > two cylinder vacuum pump to draw a vacuum inside the hull of twenty to
>> > twenty five inches while the sub is down there. I am sure this is
>> > overkill, but that is what makes empirical engineering such fun. ;-)
>> > Just think of the bang and the fish kill if it implodes. ;-)
>> >
>> > Hi Phil,
>> >    Your arm, is just what I am trying to accomplish. My reason for
going
>> > the hydraulic route instead of the air was to have more control than
the
>> > on / off of an air set up. I will, however, incorporate the  weight
>> > reduction holes in mine, just so it will look cool.
>> > > The air manip worked well, could easily attach a lift line to an
>> outboard,
>> > > collect specimens into a screen tray, retrieve small object s
directly,
>> > > etc.
>> >    This is exactly what I plan on doing with mine, plus some sampling
>> > functions. Did you use the same "hand" for all your applications? I
>> > found it easier to have a "change hands" ability for different jobs
>> > rather than try to design one to do it all.
>> >
>> > Thank you, one and all, for your assistance, Stan, the shade tree
>> > mechanic that has survived, 'cause he's chicken!
>