Hi I'm Jonathan and this is rad-head
Today I'm building this spinning water tank
that demonstrates the effects of the centrifugal force by creating this cool convex shape.
Let's start building
I started by making the tank itself.
I've cut some 4mm clear acrylic into two rectangles and four thin strips
that will make the edges of the tank.
I assembled the tank and held it together with spring clamps
once pleased with how everything aligned I fused the sides together with acrylic solvent.
Ideally I would have used a thinner solvent that will actually wick into the seam
but this is all I had.
I mixed a cup of water with a few drops of green food coloring for extra contrast
Once the tank has fully cured, I started filling it up.
First I marked the desired water level, which is half way up the tank
and used a syringe to fill it up to that line.
Now it's time to add the last piece of acrylic and seal this water tank for good.
There's no going back from this point.
This thin water tank needs to spin freely, but it has such a low moment of inertia
it won't hold a spin very well.
So I decided to make the tank holder from a heavy chunk of steel
that will make it spin much longer.
I milled a 12mm slot in the middle of the steel blank for the water tank to securely sit in.
machining steel always makes me think how crazy it is to cut a piece of steel
with just another piece of steel that is slightly harder.
The harder material always wins
I flipped the piece around and drilled an 8mm hole part way through.
Instead of using all the fancy gauges on the machine
I just marked the depth with a piece of blue tape.
I then gave it a couple of coats of white spray paint.
I've cut a piece of 8mm shaft to length with my angle grinder.
By the way I ended up using a 15cm long shaft and not 10 as you see me cut here.
Now it's time to make the base for this whole contraption.
I wanted something heavy that will easily support the rotating mass
so I decided to cast it out of concrete.
I still needed to somehow attach a couple of bearings to it in order for the tank to spin freely
and I decided to embed this 3d printed bearing holder in the concrete mold
which is just a plastic cereal bowl.
I prepped my work area before starting the messy part of the casting.
Giving it the final touch and let's mix some concrete.
I mixed the concrete following my grandma's famous recipe.
One part white cement.
Two parts sand.
One part plaster, which makes the concrete cure faster.
And grandma's secret ingredient
diluted PVA glue
I mixed the dry ingredients thoroughly and added the glue and some water
until I got to the consistency of gluten free oatmeal.
I carefully filled the mold using the stirring stick to push the concrete into every nook and cranny
I then used a power sander to vibrate out any air bubbles.
I noticed that the mold started rotating counterclockwise when vibrated.
It seems that no matter what I try, I can't seem to make it rotate clockwise.
I'll have to look deeper into this one.
If you have any ideas, feel free to comment.
I leveled the top part with a straight edge and now this needs to cure for 24 hours .
If you're impatient like me you can simply put it in the oven on high heat for 10 minutes.
I'm kidding of course.
Or am I?
Demolding the base reveals a very smooth surface
although I still had some bubbles on one side.
I was very pleased by how the bearing holder was integrated into the concrete.
I intentionally made the holes a little tight, so I lightly heated the part to get a really snug fit.
I assembled everything together, by first inserting the water tank into the steel holder
then I slipped a small piece of tube on the shaft to act as a stopper.
Now I can finally place the tank on top and give it a spin.
The tank spins freely and takes quite a long time to come to a rest
thanks to the extra mass of the steel holder
I played with different ways of spinning it, and found that I can reach very high speeds
by wrapping a string over the shaft and pulling it quickly.
You could calculate the RPM of the water tank by examining the obtained curve.
I plan to do exactly that including a pseudo rigorous analysis of the physics behind this demonstration
on my next video, so stay tuned.
Off camera I made two more water tanks.
The water level in these tanks reveal the full 3d surface created by the rotating liquid.
The cylinder gives a very clear view of this surface.
My original tank simply displays a cross section of it.
The cube however lacks the continuous rotational symmetry
and the edges are further apart than the faces
this gives it its unique look, however this is of course still the same surface
as with the other tanks.
That's all for this one, feel free to comment below
I'd love to know what you think about this project
As always, I have plans and 3d printable models over on my website
the link is in the description.
If you like my projects, and want to help me make more of them
consider supporting me on patreon
Until next time
Bye
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