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.
"Herman Family" /without_any_s/ wrote in message
...
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
"Stan Schaefer" wrote in message
om...
"BR" wrote in message
...
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:
http://www.kalliroscope.com/matisse/index.htm
click 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
www.surpluscenter.com 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:
http://www.etech4sale.com/commerce/c...roduct_id=1308
but 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
--
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 www.surpluscenter.com(now online!). Loads of goodies that you may
or may not need.
Stan