Rotary tank - how to build?

I'm doing some casual experimentation at home and would like suggestions on
building a
rotary tank to study fluid motion. I have many questions and probably could have
gotten a
few of them answered on my own but what the heck. I have no experience in
metalwork,
though I have experimented with brushed DC motors and PWM controllers.
Kalliroscope is a type of rheoscopic fluid used to study fluid motion.
For example:
formatting link
on Kalliroscopes / Revolving Kalliroscopes
A circular tank about 6-8" diameter by 3-4" deep, is mounted to a shaft
supported
by a suitable bearing block assembly. It will be filled with water and
kalliroscope or
other particulate matter, driven by a PC controlled reversible DC motor. The
tank could be
a cylinder, but prefer a hemiphere. The problem is finding a hemiphere that can
be mounted
accurately to a shaft. Perhaps a metal spinning co. might have some leftover I
could work
with, however haven't yet asked around. If I had to have one built, what would
be the ~
cost of a hemiphere, aluminum or stainless steel, 6" dia x 3" height with an
additional
1" height vertical wall section, with a boss or mating surface at the bottom
that would
allow accurate placement on a flange or shaft? I imagine the less TIR, the more
expensive.
Wall thickness can be whatever is necessary given it only has to contain water.
If it's
stainless steel then it can be similar to a kitchen mixing bowl. Max speed is
around 200
rpm or whatever that doesn't cause the water to be thrown out of the tank.
Coupling the motor to the tank. Should it be belt driven, or direct using a
flexible
coupler? Thinking of low speed DC servo motors in the ~300-550 rpm range at
formatting link
and perhaps they can be direct coupled? Or should I
consider a
higher rpm motor and reduce the speed thru a belt drive? Since tank rotation
will be
reversed frequently, I'm concerned with backlash of a coupler. I've seen zero
backlash
couplers but would then have to adapt shaft sizes, unless there are some
available with
different sizes on each end. But I guess it depends on what the motor shaft and
tank shaft
diameters happen to be. Now if I had one of those 7x12's...
Another thought (though seems insane) was using something like this:
formatting link
the max rpm was I believe 63 rpm for this model. Other models go to about
220 rpm or
so but were not on sale. However I'm not at all familiar with servo actuators,
and if it
would be worth it/too much trouble to adapt. The controller is expensive. Seems
like
overkill at 25 lbs. and they refer to it as compact, which kinda strikes me
funny. Of
course what am I thinking - I'm talking about a 6" diameter tank on my desktop.
Will a
servo actuator of that type allow for programming a smooth change in velocity
without much
trouble? What other smaller servos with bearings suitable for direct mounting
would be
reasonable for this application? A surplus servo and controller would be ideal
but I need
help in finding the right one that won't cost an arm. Having one that can take
the tank
directly would save a lot of work.
All this just to have the ability to repeat the rotary motions in case a
particular fluid
pattern interests me.
I appreciate your help.
Ben
Reply to
BR
Loading thread data ...
Oops - I mean hemisphere. Where did the "s" go...
Reply to
BR
I built a setup like this years ago, we used a large custom built rectangular tank, and there were various types of paddles run by a Bodine variable speed motor, which oscillated vertically up and down.
The fish-flake solution (that what the visualization fluid is actually made of, BTW) was used to watch the flow dynamics for various paddle shapes and speeds.
Later they fitted a laser doppler velocimeter to the setup to get three-axis velocity profiles.
Jim
================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================
Reply to
jim rozen
have gotten a
tank could be
can be mounted
could work
more expensive.
and tank shaft
220 rpm or
without much
but I need
particular fluid
Sounds like another application for the ubiquitous DC treadmill motor and controller. With the one I've got, I'd definitely gear it down or use a jackshaft to reduce the speed, top speed is around 6000 rpm. See
formatting link
(now online!). Loads of goodies that you may or may not need.
Stan
Reply to
Stan Schaefer
How would a metal wok do for this? They are relatively cheap, readily available, and the right shape. Tack weld a shaft to the bottom, and spin it to your heart's content.
Michael
could have gotten a
The tank could be
that can be mounted
leftover I could work
would be the ~
with an additional
bottom that would
the more expensive.
water. If it's
speed is around 200
available with
shaft and tank shaft
about 220 rpm or
actuators, and if it
velocity without much
ideal but I need
can take the tank
particular fluid
Reply to
Herman Family
Must be a hemisphere with height = dia/2. A stainless steel mixing bowl has the correct shape (except small flat on the bottom), but trying to spin it by hand while floating in water makes it difficult to fine tune. If the spin is off center, especially when trying to reverse rotation, the bowl wobbles and there's no control. Only one attempt was successful in producing an especially interesting pattern in the bowl consisting of water and a measured amount of baking soda . So I'm trying to figure a way to gain some control in the process, and it needs to be precise. If it were possible to obtain a direct drive DC servo with a bearing for direct mounting of the tank, capable of fine resolution over a 0-200 rpm range, that would ease the project considerably. Of course the one I mentioned before shown at etech4sale was overkill and happened to be too slow. Something smaller would do. Otherwise there's bearing blocks, pulleys, whatever. Positional accuracy isn't needed. Only change in velocity.
Reply to
BR
Make yourself a wooden mould for the bowl shape, a wooden ring and make the bowl in fibre-glass. The wooden ring would form the basis for the shaft attachment. Keep application of the fibre-glass and resin even around the shape. A rotating flat table (with suitable clamps) and a sander held at a fixed point will assist in making the outside smooth (the inner would be smooth from the mould form).
On the drive side, a stepper motor (at least 100 steps per rev) with worm drive gearing to the base gear wheel would provide a quite smooth rotation which you have total control over. The drive electronics would be quite simple.
Reply to
Paul E. Bennett
There are also salad bowls which are round bottomed. I would not have tried to do precise control with the wok by just spinning it by hand. Tack weld a rod to the center of the bottom. Put some bearings on the rod so it spins around the rod axis.
Michael
while floating in
consisting of water
gain some control
resolution over a
accuracy isn't
controllers.
formatting link
> > > but the max rpm was I believe 63 rpm for this model. Other models go to
Reply to
Herman Family
Perhaps you could use a servo motor from an old 51/4" floppy drive. These are build on an aluminium frame and have good bearing. There is also a hub to mount the bowl to. Some old turn tables used servo motors also.
Tom
could have gotten a
The tank could be
that can be mounted
leftover I could work
more expensive.
shaft and tank shaft
about 220 rpm or
velocity without much
ideal but I need
particular fluid
Reply to
Tom Eastman
Your idea sounds like a good one except I'm not sure I'll make it with little runout. I made some spherical speaker enclosures using a rounter mounted on a turntable setup, but don't have that anymore. Though it may cost some, a metal spinner could make the tank. They'll make it more precisely in terms of TIR than anything I could do.
The stepping motor may work but I'm concerned with torque ripple transmitted to the tank contents, although less thru a gear reduction. It's unfortunate that servodisc motors are so expensive since they have no cogging and are brushed dc motors. Well, it's just like anything - it'll take some experimenting to see what effects things like cogging have on the contents. Perhaps it won't be a problem due to its mass, just like platters used for record turntables. I'm just a bit paranoid about building this contraption, because it's then a lot of trial and error for a certain pattern. The only other possibility is using say, three small motors with rubber tires around the circumfrence to turn a mixing bowl floating in a larger bowl of water. Just thinking out loud....
""Paul E. Bennett"" wrote in message
smooth
Reply to
BR
Now that's a thought. I do have a 5-1/4 floppy drive. Will it have enough torque to handle what I described? There's a lot of reversing going on.
Reply to
BR
The fibreglass bowl was an idea to keep it light but strong. Naturally some thought needs to go into the design details. However, if you know a metal spinner who could do your task to your satisfaction then that is an option to explore.
Having done quite a bit of work with stepper motors over the past couple of years (very special application where we were concerned with the potential for forming striations within an extrusion process) we found that having a large number of steps per revolution of the stepper motor means that you have already minimised the ripple factor. Our motor drives a linear translator which advances 5mm for every rev. Our current motor is 400 steps per rev and the mechanical output in the extrusion process is very smooth (couldn't see the steps in the extrusion force measurement at close magnification).
You can only try. I noticed that someone mentioned disc drives as a source of stepper motors. Old hard drives are aslo quite good if the use stepper motors in them for head movement or as the main drive. I know I have obtained a couple of quite good motors that way which had 160 steps per rev at reasonable torque.
Synchronisation might be your problem with this last idea.
Reply to
Paul E. Bennett
You might be able to obtain an assembly with allowable run out by welding an over sized shaft as accuratey as possible to the bottom of your bowl. The end of the shaft to be welded to the bowl should be milled square, so the bowl will have best chance of being perpendicular to axis of the shaft. To eliminate any offset between shaft and bowl axes, place the weldment in a 4 jaw chuck on a lathe. Adjust 4 jaw chuck till you reduce runout at bowl edge to an acceptable level. You can now turn the shaft down to your bearing size and the axis of the bowl should coincide with the new shaft axis.
As an alternative you might design a coupling element to use between bowl and shaft that can adjust offset and tilt. It could be as simple as a long oversized collar with 8 set screws. Kind of like a Chrismas tree stand.
Reply to
D.Miller
could have gotten a
Don't sweat the small stuff.. For example, you had mentioned: i) The small flat in the bottom of a mixing bowl. This would have very little impact on your results. Get on with your stuff and don't worry about perfection until everything else is working perfectly. ii) Back lash in the speed reducer. That will have no effect at all except to introduce a very tiny time delay in your direction reversals. Again, first make it work; then perfect it.
I did some very primitive experiments along these line using a phonographic turntable. It worked fine. Try borrowing an AC signal generator and driving a turntable with one of these. The variable frequency together with the 78/33/45 gearing would give a pretty good range. 16 RPM versions also exist. I would not recommend welding to the bottom of the bowl. I suspect you will waste a lot of time trying to adjust it and it will never be quite good enough.
I'd really love to see some of the pictures.
Walter.
Reply to
Walter Driedger
[del]
I may try a stepper, but already ordered a small surplus Servodisc motor. It's shaft will take a 7.5 lb axial load, and the tank (decided on 5" dia) will weigh under 2 lbs, so it won't wear out any time soon. The Servodisc has zero cogging, and through the point of reversal the torque would be smooth.
[del]
That would be a problem.
Ben
Reply to
BR
I'm hoping, that at a reasonable cost, a metal spinner could make the tank with a 3/8" shaft at the bottom. Then have an adapter made to fit the motor shaft. Since I already ordered a motor, the adapter will have to fit an 8mm dia. shaft. Just in case the motor doesn't work out, I'll just have to try another. Appreciate your suggestions. I'm trying to get this thing together as simply as possible. I was going to use an additional bearing and flexible coupler between the tank and motor in fear the motor bearings wouldn't support it, however I later learned that the particular motor I ordered will take up to a 7.5 lb axial load, and a 5" dia hemi filled with water will be well under that.
Ben
Reply to
BR
You don't know how much time I've wasted thinking about results before getting them. :-) The motor won't need a speed reducer since it's a Kollmorgen Servodisc (found surplus recently), which has zero cogging and can turn as slow as 1 rpm, perhaps even slower. The speeds in the experiment would range between 0 to 150 rpm or a little faster, but certainly slower than centrifugated water all over the place.
it > will never be quite good enough.
No welding. A metal spinner should be able to provide a shaft at the bottom of the hemisphere for mounting. It will be direct coupled to the motor shaft with an adapter.
Well, if anything interesting happens there'll be movies.
Ben
Reply to
BR

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