To

Ron,

HA! - The ethafoam springs are not bouncy like steel springs. They are dampened like struts on a car. both spring and shock in one!

We do not see any noticeable movement effect standing or doing ground work next to ( within a meter) someone landing a throw or jumping up and down.... Just did a test with Jess!

I think our ethafoam springs are 4x4x3 but they were installed 4 high when we were in Toronto for the 2005 world masters tournament. My Gnome helpers installed the blocks (glued) instead of 3 high as I had planned. I even had left drawings for my Gnomes, come to find out, Gnomes can't read!

Here are the physical properties of the ethafoam:

Density 2.2

I don't really have a good feel if reducing the thickness would be better or worse?

Beyond the fact that if you leave the rest of the design the same... the block spacing, the osb plywood thickness, etc the same and only change the foam thickness, cutting the thickness in half will cut the deformation under load in half.

I think this would make a STIFFER FEELING floor system. How much? I don't know?...

If we look at the load on our floor system for loading:

Plywood weighs about .02 psi and we have 1 inch thick = .02 psi
Mats            1 mat is 40 pounds and 78.72 inch x 39.39 inch = 40#/3098 sq in=.013 psi

Players you can think of 2 players taking up 1/2 tatami max (39.39x39.39=1551Sq in )= 400#/1515=.26psi
                this is the real subjective part how much area is involved in a judoka landing on the mat or
                how many foam blocks are engaged in taking the fall impact force

So              = .3 psi total

Block           block spacing is such that a single block holds up about a 14 in dia. area = 150 sq in

load per block 150 sq in x ( .02+.013+.26 #/sq in ) = 44 #

Block area      3x3 = 9 sq in   44#/9sq in = 4.9 psi (pound per sq in)
                3x4 = 12 sq in 44#/12 sq in = 3.7 psi
                4x4 = 16 sq in   44#/16 sq in = 2.75 psi

So at 3x4:       3.7 psi and let's double it for impact??? we get 7.4 psi

My floor is 3x4x4 blocks and 3x4 is foot print ie block is 3x4 glued to plywood (osb)   my plan was to be 3 inch high and not 4 inch (gnomes! again)

Chart says      10% deflection at 7 psi and
                25% deflection at 9 psi ...

If you use 2 inch high
10% of 2 inches is 0.2 inch at 7psi
25% of 2 inches is 0.5 inch at 9 psi

if you use 4 inch high
10% of 4 inch is 0.4 inch at 7 psi
25% of 4 inch is 1.0 inch at 9 psi

Wild guess is we probably see .5 to 1.0 inch deflection in a block (floor assembly) at time of fall not counting the tatami deformation... Denver Dojo is a pretty comfortable mat surface without springy-bounce feel to it.

If I were to build another I would stick with the 4 inch height. I might go to 3 inch for a cost savings. I would even try 3x3x3 blocks!

Ron - Hope this helps!

Thanks,
Jim

At 08:49 AM 10/5/2006, you wrote:

Hi James sorry to bother you again about this dam sub floor but I have done some tests and I am leaning towards 4x4x2 (2 being the height ) cubes . I fear that 4 inches may make the mat too springy . and be moving while others are training near by , plus it have the cost . Where did you find the height of 4 inches and what are your thoughts of 2 inches ?. Since you may or may not know you are quickly becoming the judo sub floor exasperate of north America