# VG Paper Blog

#### Doing the Math: Holland Beater Building

I found that there are really no places or sites with exact plans for building a Hollander Beater, until I get this done. It was up to me to figure out all the mechanics and ratios.

So I decided that I was going to build a beater that uses 2 lb. (minimum) of dry material. A good amount of water would be 10 - 12 gallons of water. So how big does the tub need to be to contain that volume?

V = L*W*H

Volume ends up in Cubic Inches. There is 231 cubic inches in 1 US Gallon.
For Example: A tub that is 42.25" that is 13.5" wide and 6" tall = 3422.25 cubic inches = 14.81493 gallons. So you have to start some where and adjust things as you go. The reason I chose some of these values was based on materials that I had. 42.25" is the largest space I had to store the beater. I could only find (afford) an 18" keyed stainless steel shaft so that limited the width (I found a bigger one later). The Hollander ended up being _____" tall.

Next is figuring out pulley sizes to figure out how to get 400/500 rpm out of a motor that is either 1725 RPM or 3450 RPM. I thought that a motor for a swamp cooler would be good and that is what speeds they run at.
d1 n1 = d2 n2    (single belt transmission - one drive pulley & one driven pulley)

d1 = driving pulley diameter (inch, mm)
n1 = revolutions of driving pulley (rpm)
d2 = driven pulley diameter (inch, mm)
n2 = revolutions of driven pulley (rpm)
The first equation can be transformed to express the:
Revolution of Driven Pulley
n2 = d1 n1/d2
Revolution of Driver Pulley
n1 = d2 n2/d1
Diameter of Driven Pulley
d2 = d1 n1/n2
Diameter of Driver Pulley
d1 = d2 n2/n1

So if you know that the motor turns at 1725 rpm and the motor comes with a 3.5" pulley (standard on an evaporative cooler motor), you have one side of the equation. 3.5"*1725 rpm = 6037.5. You also know you want the drum spinning between 440 and 500 rpm. 6037.5 / 440 = 13.72" d2 (driven pulley). The closest pulley size is 14".

Finding the Angle/Degrees
If you are going to put a certain amount of blades/bars on a drum, what angle or degree are the blades/bars placed?