Model Forum / Radio Controlled / Air Models / February 2007

The message <12t3gj37ltm5l21@news.supernews.com>
from "Martin X. Moleski, SJ" <moleski@canisius.edu> contains these words:

A small geared motor working a push-pull rack and pinnion connected to
the plnnger of a 4 ml syringe which in turn feeds two 2 ml syringes
would give ample power to raise or lower a couple of u/c legs weighing a
couple of ounces each,  you have a ready made high pressure piston and
cylinder with a syringe which cost about 10c each and hydraulics are
much more effective than air pressure as it is positive with no lag from
the need to compress first before anything happens.
Fluid is heavier than air but you only need about 10 ml of it and you
can do away with your air bottle, valve and other gear so weight for
weight it is comparable if not slightly lighter overall,  size for size
a hydraulic ram will produce much more power than a pneumatic ram
because once you have a cylinder full of fluid you have 100% positive
pressure unlike airwhere you have to force in more and more to get a
rise in power both being dependant on the source of pressure of course.
To me some jobs on models could be powered by hydraulics instead of
servos and you can feed a hydraulic line where you may not even be able
to get a snake to go, if you need two wing servos for instance for your
ailerons why not a central hydraulic feed to two rams which would fit
into the wings much easier requiring much less space and be lighter  and
also not need wiring looms and such.
If an undercarriage leg needs one ram and lot of air to raise it then
another to lower it (unless it acts by gravity) you can replace this
with one slave cylinder that works under vacuum to raise and compression
to lower as it is a sealed system, all we would be doing is copying the
full sized practice I suppose,

                                       regards,                       Terry

The message <fe6dnX1Ol6xylk_YnZ2dneKdnZypnZ2d@brightview.com>
from "David Williams" <newsreply@remove-me.dandcwilliams.com> contains
these words:

Nice bit of kit David and proves it works but cant understand why they
have a fluid bag and exhaust system when it would work with a closed
recirculator system, means using a double acting piston so the fluid
under pressure pushes the piston down the tube and the oil behind it
which is unpressured back to the sealed tank, when the valve changes it
works in reverse and the pressure changes sides etc causing the piston
to go up the tube again pushing the unpressured fluid back to the tank.
There are a number of ways to do it but what you need is as few joints
and seals as possible and keep it simple to keep the weight down, using
small bore polypropylene pipe instead of steel or copper and engineering
plastics where possible,

                                       regards,                    Terry