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

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To calculate the RPMs needed for a spincast liquid parabolic dish, one must consider the diameter and depth of the dish. A key challenge is finding a motor capable of maintaining a low, constant speed without high-frequency jitter. It has been noted that a wider radius requires fewer RPMs to achieve the desired parabolic profile, which contrasts with initial assumptions. The larger the radius, the slower the angular speed needed to generate the same profile. Understanding these dynamics is crucial for successful implementation.
CosmicVoyager
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Greetings,

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

Thanks
 
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Andy Resnick said:
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.
 
CosmicVoyager said:
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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