Calcualting Motor Torque

I am looking for a motor that meets the following requirements: Spin about a 50 gallon tank filled with liquid Tank of about Diameter 12 in, height 16 in
The motor needs to start the tank from sitting still and spin it for about 20 minutes at a decent speed **the process is being used to separate one mixture into 2 liquids
I have been looking at gear motors, torque motors ect...but I am unsure how to determine what motor to use. When looking at gear motors - How should I calculate the startup torque? (been using I*Alpha is this correct? I got about 25 in-lbs) and the constant torque required once it it spinning? ??
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@umich.edu wrote:

You're spinning a liquid. If the drum has no internal vanes, The liquid will come up to its speed with much delay. The starting torque -- friction aside -- will be little more than for an empty drum.
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You could obtain a worst-case answer of the torque during the pullout period by assuming that the drum and contents are solid. The result will be somewhat greater than the case where the fluid slips, but is that an issue? If you design with too small small a margin you're likely to find that the setup lacks grunt, at least at times.
Without knowing much about your application, it looks like the pullout torque requirement would be a lot higher than the running torque if your mechanics are good, so sizing for pullout is probably going to be OK.
This also depends on your drive type. Fixed frequency AC induction motors aren't happy for long at speeds significantly below their synchronous speed, so if you're considering such a drive you'll need to ensure that it can pull out fast enough. There's plenty of information on the web on motor protection.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@umich.edu wrote:

Eh? You're describing an 8 gallon tank.
How quickly does the thing need to spin up? What sort of bearing drag do you expect? What do you define as "a decent speed" -- all of these things make a significant difference in your answer.
--

Tim Wescott
Wescott Design Services
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Tim Wescott wrote:
...

I feel silly for not picking up on that. 36*16*pi/231 = 7 5/6 gallons. That comes out to about 65 pounds; just over a cubic foot.
...
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jerry Avins wrote:

When I started working at my Dad's shop one of my jobs involved rolling 55 gallon drums around. I couldn't tell you just how big they are in inches, but I can close my eyes and see one, and feel just how much heft it takes to tip a full one up on it's rim to roll it around.
--

Tim Wescott
Wescott Design Services
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Tim Wescott wrote:

Have you ever dealt with one filled with CCl_4. That stuff is *dense*. About 1.6 * water.
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.