Here is what it looks like with a 3 inch inner tube and socket
head metric 10 mm bolts. I think this is an improvement but
we can still test what we have. This is a minor change in the
over all scheme of things.
Paul Lamar
That works too. My thought was to extend the three "paddles". By
extending the paddles, there is more space for the silicone.
FWIW - From looking at the welded up assy, I don't see how this little
assy will be able to absorb 350 hp.
Mark
Two ways to get HP. Torque or RPM.
The rotary is RPM. Lets say it generates 350 HP at 7500 RPM.
What is the torque?
HP = T X RPM /5252
350 = T X RPM / 5252
350 X 5252 / 7500 = T = 245 foot pounds.
3000 inch pounds. Divided by 5 inch diameter = 600 pounds total force.
3 rubber lumps 200 pounds per rubber lump.
One inch high by 1.4 inches is 1.4 square inch.
142 psi.
It is hard to quantize rubber for compressive strength because it expands in other
directions 90 degrees to the load.
The tear strength is 580 pounds per square in or about 4 MegPas.
Cut 4 pieces 1 inch by 1 inch. One square inch. Stack them up on the floor. 3/8th of an
inch thick roughly. Best to glue them together with red RTV and let it cure for 24 hours.
Put the heal of your shoe on the rubber stack and balance with on foot.
See if it springs back to shape.
Paul Lamar
Paul,
If this thing is bigger than 5" and 5" is actually the distance to the
center of the paddles, ignore this. I didn't want to go back and dig up
dimensions.
You should only take credit for the diameter to the center (or so) of your
metal paddles if you want a closer estimate of the force reacted by the
rubber. Using the 5" diameter of the outside of the pipe assumes all of
the force is reacted by the rubber at the outside edge, which isn't the
case.
Josh
Yes Josh I know :) It is six inch OD and three inch ID.
Paul Lamar
Here is another test Mark.
Get a 3 pound sledge and see if you can beat that silicone rubber into
submission.
Paul Lamar
Sounds like a fun test. I'll give it a try today after work.
How about "bunching" of the plies? As I cut them initially, the force will
be applied to the edges of the plies of silicone. Should I cut some new
ones and stack them like a loaf of bread so that all the force is
applied across the faces, or does it even matter?
Mark
Don't bother glue those together and see how it goes.
Paul Lamar
Mark, I had this old tube of clear silicone RTV lying
around. It had solidified in the tube. So I pealed off the covering
and performed the 3 pound hammer test.
Here is the video.
Paul Lamar
That looks like it should do the trick. Maybe we should assemble it with liquid RTV and
let it cure, then test it. The rtv would help hold it together.
Mark
--
It is all the same stuff. You can get it in clear or red.
The red is supposedly higher tenp.
Smack what you got :) You can't hurt it.
Paul Lamar
Mark,
Pep Boys has some silicone hose in three different sizes per package.
1/8 3/16 and 1/4. About 27 feet of it.
Cut lengths to about 1 inch long and insert them in the mold to provide voids.
Paul Lamar
Paul,
I cut the wooden spacers today and did a fit-check. I only have enough silicone sheet cut
for one section at this time, so that's what you'll see in the pictures. Next step is to
drill holes in the spacers for the bolts, and to drill the #10 bolt holes in the spline
piece, but that will require me to remove the psru from the a/c. I don't really want to
do that right now as I have my BFR due soon and could use some practice beforehand.
Also, I need to cut more silicone. The bunch in the pictures is 9 layers, so I'll need to
cut 18 more. Not sure if I have enough material on hand.
Then I need to bond the silicone pieces together an let them cure. The Texas sun should
handle that task nicely.
Mark
I am not ready to come down there anyway yet.
Maybe in a week or two.
I am having a heck of a time finding socket head 10 mm bolts 1.0 (threads per mm) 17 or 18
mm long (grip Length).
We need these to go with a 3 inch diameter center steel tube.
I am getting to the point where I recommend drilling to a 29/64 (.4531) and tapping with
a 1/2 20 fine thread tap.
5/8th of an inch long.
At least we can buy socket head screws in that size.
If your building a heavy duty engine this is what you do with the tension bolts.
Paul Lamar
Would Kevlar fabric (layers on any axis)improve the buffer modules performance? With a
pour your own, you get lots of options. Even vac. bagging of mold.
C. Smith
I think it would stiffen it too much.
With that chunk of curred pure clear that I have the 3 pound sledge hammer had no effect
on it.
I suspect we will wind up with a lot of void in the bumper.
Short pieces of silicone rubber hose surrounded with curred silicone liquid.
Paul Lamar
Paul,
You mentioned "the devil in the details" - One thing I have not seen addressed (did I miss
it somehow) is how to balance this damper. At 6000+ RPM, this is a big concern. I know
if it is built perfectly, it will naturally be in balance, however, we do not live in a
perfect world and slight differences in manufacturing could cause some serious vibrations
at higher rpm.
Norm
Six inches of sheet metal and silicone rubber is not much compare to
two 9 pound rotors spinning around on the eccentric shaft with counter
weights. The outer DOM tube weighs only 11 ounces.
The coupling parts are machined. The machined back plate fits inside
the outer section of DOM tube which is intrinsically accurate. DOM stands
for Drawn Through a Mandrill. The inner assembly is trued up on a lathe
after tack welding. There is little opportunity for imbalance to
occur. Everything is piloted on everything else.
However if balance is suspect a rig would have to be made
in order to balance it. This could be an engine assembled with out
rotors or counter weights and spun up.
IMHO not worth it due to the small percentage of the
total rotating mass.
Paul Lamar