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

[CosmicVoyager]

Greetings,

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

Thanks

 

[Andy Resnick]

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]

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]

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.