The air pressure that is needed depends on how large the pads are, how heavy
the load is, and how smooth the floor is. The floor smoothness and the
condition of the pad skirt's bottom surface significantly affects the volume
of air that is needed. Of course, some air has to leak out to provide the
air bearing function, but the less air escaping from under the pads, the
less dust will be blown around. I always sweep my floor before using them,
but I don't make it perfectly clean. Sometimes I'll see some dust being
blown around on the floor but I never get major dust clouds in the room from
them. I guess it really all depends on how good the skirt to floor seal is.
They used a vacuum cleaner to inflate the cheaply made pads in the link,
which is high air volume and very little pressure, probably only a few psi.
I use my shop compressed air system, a 3/8 line to supply line my regulator
bank and 1/4 inch lines from the regulators to each pad. My air system has
an 80 gal tank and 18 cfm compressor and I've never run out of enough air to
run them, but if I was to run a pad over an 1/8 inch crack in the floor, the
pad would collapse. I can sometimes crank up the pressure (and thus the
volume) to a collapsed pad to get over small defects, but it's best to make
sure that the floor doesn't have any significant voids in it where you are
going to be using the pads. We used bondo and duct tape as a temporary floor
fix to get the pads to work over some bad spots in the floor when I was
using the commercial pads to move the robots, but rough floors can be a
major problem. Floor defects can easily damage the rubber skirt seals on the
pads as well as pose the significant air leak problems. To lift an 800 lb
table saw with 3 - 8 inch diameter pads on a tile floor you probably will
only need about 2 or 3 psi. I rarely move my tools with my pads any more as
my present shop is relatively small and tool locations are stable. Lately,
they seem to just get used for moving big clumsy projects where it is very
inconvenient to try to move them around with dollys, etc. or sometimes when
I'm the only one in the shop and I want to move something myself. Once the
pads are in place under a project I usually leave them there until the
project is finished, so it can be moved or turned around for the convenience
of getting to the other side, etc.
I didn't mention in the previous note that I have been adding a small circle
of 1/2" plywood in the center of my pads to take the load off the rubber
skirt material when the pads are not inflated. I found that this helps to
protect the rubber should a side force (bump) be applied while the pads are
deflated. They can easily tear if a load is on the rubber alone and the load
is pushed sideways. With the plywood in the center the weight of the load is
on it and not on the rubber.
What risks? When the air's not on it's a piece of plywood sitting on
the floor. When the air is on either it lifts or it doesn't. If it
doesn't then you've wasted what, ten bucks? If it does, how high is
it going to lift? 1/8 of an inch would be quite a lot.
Kill the air and down it goes. If it's going real fast _then_ it may
Actually, the answer is "No" it doesn't require an increased amount of
pressure to stop it. When I was playing with it at the woodworking show with
a sizable tablesaw on it, I was able to manoeuvre and stop or change
directions quite easily. So much so, that my wheelchair was only slightly
prone to rolling away when I was moving it around.
Momentum is the word.
It's easy to get something moving when it's on an air bearing, but there is
so little friction that it wants to keep moving at whatever speed you get it
up to. Instead of the normal friction slowdown that we are accustomed to,
you will need to supply very nearly the same force to stop it as you did
getting it moving. We are so accustomed to friction slowing and stoping
things that we move our bodies aren't really prepared to have to supply this
much negative force to stop something once it's started moving. After a few
minutes of pushing and pulling we quickly adjust to it, but the first
experience with a relatively heavy object on an air bearing (like 1-2 tons)
can be a bit of a surprise and an almost certain crash. I almost pushed a
3600 pound robot through a wall with my first experience. I got it stopped
in time, but nearly got pinned in the process.
Nice to see somebody engineer this out to an affordable level. The
tech, as you know, is old hat. I seen those used when moving 100 ton
presses. Here's a supplier:
What I did not want to do, is rain on anybody's parade. But the blow-
up dust is a huge issue, as mentioned in here already.
The nice thing about the whole concept is that it easily done by the
little guys on the cheap.
I see guys move skids of granite cut-offs all the time. Whole sheets
of granite moved on pucks, home-made from 3/4" UHMW, where air
pressure is applied to move the piece, and then flipped over with a 3-
way valve to vacuum to hold while machining.
Their problem is water flying all over the place.
To make your own? I was thinking small inner tubes... wheel-barrow/
lawn-tractor style. Cut them along the external and internal
circumference... maybe, if small enough, leave them whole and
perforate them on one side? Insert them in a channel routed out of a
slab (doubled) of MDF with a bowl bit and a circle cutter? Maybe a
bicycle inner tube stretched into a rectangular slot with rounded
corners? The inlet is already on the tube...even...
Come ON PEOPLE!! We're a smart bunch here. One groove for the tube,
one groove outside that tubed perimeter for the shop vac? I want ideas
on my desk by night fall. hehehehe
Can't answer that. The time and effort I'd need running around to get the
parts and assemble one to my satisfaction would be put to better use my just
doing my job the equivalent amount of hours and buying the General version.
Guess which one I'd choose?
If you look closely at the General hoverpad you will find that it's really
many small hoverpads on a big sheet. Making one big one will give you
stability problems. Multiple small ones like 3 or maybe 4 on one common
sheet will give you the stability of the General's version.
Actually, my pads have a sort of manifold made into them. I groove one sheet
of 3/4 ply and then sandwich/glue it on top of another piece to allow me to
have the air inlet enter along the middle of one edge. I epoxy any voids in
the plywood groove and also epoxy a quick connect air line fitting into the
hole (bored out to fit) in the edge. It's positioned so that nothing
interferes with the flat top surface. That way the pad will fit under
anything. To be sure of a good glue-up of the two sheet joint and have no
leakage I make sure that I run an unbroken bead of glue all the way around
the groove area so that it seals real well when put together. Then I hold
the sheets together with clamps followed by screws "until the glue dries".
Of course, the screws remain when the clamps are removed. If you were making
several small pads on a large sheet, manifolding between them this way may
not be such a good idea. Maybe you could sandwich a piece of pipe in the
groove to minimize the possibility of leakage.
I have never made a multi pad assembly. All my pads have been single and
each one has had it's own air line from it's own regulator, so I can feed
each one and control it separately. I don't know how they would respond if
they were all manifolded together.
That's the difference then. For some things I like to build them from
scratch like setting up and organizing a workshop, but other things I like
them to just be there for use. The HoverPad would fall into that category as
far as I'm concerned. I'd just want to use it and not worry about saving a
few dollars building one. It's unlikely I'd be saving any time, so building
one from scratch is just not a consideration.
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