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

--

In article , BR says...

All this just to have the ability to repeat the rotary motions in case a
particular fluid
pattern interests me.

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
==================================================

"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

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

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

In article
"BR" writes:

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.

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.

--
************************************************** ******************
Paul E. Bennett
Forth based HIDECS Consultancy .....http://www.amleth.demon.co.uk/
Mob: +44 (0)7811-639972 .........NOW AVAILABLE:- HIDECS COURSE......
Tel: +44 (0)1235-811095 .... see http://www.feabhas.com for details.
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
************************************************** ******************

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
"BR" wrote in message
...
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

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
"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

--

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

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.

--
************************************************** ******************
Paul E. Bennett
Forth based HIDECS Consultancy .....http://www.amleth.demon.co.uk/
Mob: +44 (0)7811-639972 .........NOW AVAILABLE:- HIDECS COURSE......
Tel: +44 (0)1235-811095 .... see http://www.feabhas.com for details.
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
************************************************** ******************

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.


"Tom Eastman" wrote in message
...
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

In article
"BR" writes:

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 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.

The stepping motor may work but I'm concerned with torque ripple
transmitted to the tank contents, although less thru a gear reduction.

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).

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.

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.

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....

Synchronisation might be your problem with this last idea.

--
************************************************** ******************
Paul E. Bennett
Forth based HIDECS Consultancy .....http://www.amleth.demon.co.uk/
Mob: +44 (0)7811-639972 .........NOW AVAILABLE:- HIDECS COURSE......
Tel: +44 (0)1235-811095 .... see http://www.feabhas.com for details.
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
************************************************** ******************

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.
--
D. Miller

"BR" wrote in message
...
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

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.

--
************************************************** ******************
Paul E. Bennett
Forth based HIDECS Consultancy .....http://www.amleth.demon.co.uk/
Mob: +44 (0)7811-639972 .........NOW AVAILABLE:- HIDECS COURSE......
Tel: +44 (0)1235-811095 .... see http://www.feabhas.com for details.
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
************************************************** ******************

"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.


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.

""Paul E. Bennett"" wrote in message
...
In article
"BR" writes:

[del]
The stepping motor may work but I'm concerned with torque ripple
transmitted to the tank contents, although less thru a gear reduction.

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).


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]

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....

Synchronisation might be your problem with this last idea.

That would be a problem.

Ben

--

"D.Miller" wrote in message
...
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.

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

--

[del]

"Walter Driedger" wrote in message
news:wcJdb.28429$O85.6295@pd7tw1no...
"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.


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.


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.

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.

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.


I'd really love to see some of the pictures.

Well, if anything interesting happens there'll be movies.

Ben

--


Walter.