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-   -   How to calculate the RPMs needed to make a spincast lquid parabolic dish? (http://www.physicsforums.com/showthread.php?t=506874)

CosmicVoyager Jun14-11 10:08 AM

How to calculate the RPMs needed to make a spincast lquid parabolic dish?
 
Greetings,

Anyone know how to calculate the revolutions per minute needed to create a liquid parabola of given diameter and depth?

Thanks

Andy Resnick Jun14-11 12:32 PM

Re: How to calculate the RPMs needed to make a spincast lquid parabolic dish?
 
A good accounting can be found here:
http://en.wikipedia.org/wiki/Liquid_mirror

AFAIK, the main problem is getting a motor that can run at low constant speed without any high-frequency jitter.

CosmicVoyager Jun14-11 02:51 PM

Re: How to calculate the RPMs needed to make a spincast lquid parabolic dish?
 
Quote:

Quote by Andy Resnick (Post 3356555)
A good accounting can be found here:
http://en.wikipedia.org/wiki/Liquid_mirror

AFAIK, the main problem is getting a motor that can run at low constant speed without any high-frequency jitter.

If I have done the math correctly, it seems the wider the radius is the fewer RPMs that are needed? Is that correct? That is the opposite for what I was thinking.

Andy Resnick Jun15-11 08:12 AM

Re: How to calculate the RPMs needed to make a spincast lquid parabolic dish?
 
Quote:

Quote by CosmicVoyager (Post 3356797)
If I have done the math correctly, it seems the wider the radius is the fewer RPMs that are needed? Is that correct? That is the opposite for what I was thinking.

The larger the radius, the slower angular speed needed to generate the same profile... IIRC that's correct. Those large mirrors turn *very* slowly.


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