[SML] Extremely low profile air caster?

[Jon Lagerquist]

My question is what is moving this? Is it a 87 pound stage management
intern or a 5HP winch? We pull a lot of pallets across stage with motors
in a wide range of sizes. In the "very thin" world a piece of ply with
Teflon tape on the bottom works pretty well. A steel angle down into a
track with UHMW on the bottom works really well. The primary challenge
is smoothly overcoming the static friction, unless you make it so
slippery that you do not want to stand on it. Because the static
friction will typically be more than the sliding friction you want to
minimize the stretch in your cable, which translates into a larger
diameter cable.

If the character has the balance skills you could have the track ramp up
and bring a dog up under their foot and they cable cable surf backwards.


On 10/12/2018 2:23 PM, Rick Clever via Stagecraft wrote:
> This sounds almost like a hovercraft. Maybe look in to their 
> construction and see if it can be adapted. On Thu, Oct 4, 2018 at 
> 9:03 AM Joe Dunfee via Stagecraft <stagecraft at theatrical.net> wrote:
>> 
>> I was in a rehearsal, when at the end of a dream sequence, the 
>> director asked the character to "float" away as the dream faded. He
>> said ideally, she would just move backwards, without walking. But
>> he just asked her to walk backwards smoothly.
>> 
>> That got me wondering if it was possible to do.  In this case, the
>>  actress is actually starting out kneeling, so she can simply stay
>>  kneeling, so she is well braced if a platform pulls her.
>> However, to not look like she is on a platform, the platform would
>> need to be very low profile.
>> 
>> I 1st though of just dragging a piece of 1/4" ply, or linoleum, 
>> perhaps with Teflon on the underside if really necessary.
>> 
>> Then, I thought of air casters.  The commercial heavy-duty ones are
>> designed with what looks like a bicycle inner tube.  But, they also
>> tend to lift the platform a few inches as the "inner tube" 
>> inflates. Then, I thought of the standard air-puck that is used to 
>> demonstrate Bernoulli's principal, when the moving air creates a 
>> lower pressure, so the puck actually adheres to the table surface. 
>> The flowing air also reduces friction to near zero.  So, the air 
>> puck is both levitated, and also held down.
>> 
>> Those air pucks have nothing more than just a flat surface on the 
>> underside. So, they are very low profile.  But, a quick test using 
>> a large wood circle was unsuccessful. Though, the air pressure for 
>> the number of square inches should have lifted the disk. But so 
>> there are other issues. I imagine the air pressure needs to 
>> overcome the weight of the disk by the surface area of the air 
>> inlet.  But, even lifting the disk a bit to help the process
>> didn't get it to float.
>> 
>> My air source was a very old CPAP machine (that helps people
>> breath at night).  It provides up to 0.26 PSI at a pretty high flow
>> rate, and most importantly, is very quiet. Newer ones all have
>> security built in, so that it takes a password to set the pressure.
>> So, I am looking for a reasonably affordable source for just the
>> fans, so I won't have to scavenge for them.  Note that these are
>> brushless, so they would need a motor controller.
>> 
>> Any air-puck experts out there?  I am sure a lot of people in 
>> theater would love to see an extremely low profile air-caster.
>> 
>> -Joe
>> 
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-- 
Jon Lagerquist
--