I am going to help them design a mash rake. I looked at the local 7bbl brew pubs rake today and have a basic paddle configuration but have not had any luck finding any info on the HP rating and rpm needed. Would a 1hp motor reduced down to about 20 rpms have enough torque to dough in the mash?
I am not familiar with brewpups, my answer is based on conventional breweries.
Standard mash rakes are not used for mixing only to cut the grain bed to help during lautering.
You need a mash mixer with 20-40 RPM.
Keep in mind the function of the mixer is to mix the grain not just rotating it.
To calculate the impeller power you need the power number for the type of impeller you are using (supplied my manufacturer) or use the standard values.
Mr Google can help.
To do the calculation you need the mixer RPM, fluid specific gravity, mixer plates diameter and power number or experiment.
Currently I am looking for my old info, I am very rusty on this subject..
My 200 liter mash mixer with adjustable blade angle and supported on both ends.
146 lb-in, 26 RPM motor