Welcome to Socolofsky Farms
Colorado-raised all natural Pork and Lamb
from the foothills of the Rocky Mountains
In-Vessel Composter
» Page 4: The Drive Mechanism
Page 5: Parts and Materials List
The Drive Mechanism
This is the part where the story starts to break down a bit. The drive mechanism only sort of works. Improvements are on the way, but we can consider this page a review of what doesn't really work that well.
The overall goal is to rotate the compost vessel at about one revolution every 5 to 10 seconds. No need to go very fast, in fact slower is better and easier on the machinery. We decided to make the drive unit powered by the hydraulics on my skid loader. An electric motor was an option, but protecting it from weather could be challenging, and getting electricity to it could be challenging as well. Plus, I did not attempt to calculate the power required to turn the drum. A hydraulic motor is strong compared to its size, and since we handle manure with our skid loader anyway, it will be readily at hand when we're working with the composter. Plus, since the composter is designed to be carried around by the skid loader, a hydraulic drive made sense. The front hydraulic ports on my skid loader (a 1997 Case 1845C) are variable-speed, so I purchased the slowest drive motor I could (1100 rpm), hoping I could drive it slowly enough so as not to need a gearbox to reduce the speed. This appears to be possible.
The power is transmitted to the drum by using a direct-driven go-kart wheel. The shaft on the hydraulic motor is 1" diameter, with a 1/4" x 1/8" keyway. A go-kart hub with the same bore was available, as was a 4" go-kart wheel to fit the hub. A 4.10/3.50 x 4 studded go-kart tire completes the drive. The drive motor is mounted on a bracket made out of a 1' piece of 6" x 6" x 3/8" angle iron with holes drilled to accomodate the shaft, motor mounting bolts, and bolts to mount the bracket to the composter frame.
As mentioned in the Introduction, the casters that support the drum are placed around the circumference of the drum to let the drum rest on the drive wheel. In addition, the support bracket is adjustable up and down, to allow more or less pressure between the drive wheel and the drum. Adjustment is via nuts above and below the mounting bracket.
The studs that support the bracket are welded to the frame. First, holes were drilled through both the top and bottom of the beam to allow the studs to pass through the box beam. The studs were then welded to the bottom of the beam section from the bottom, and then tack welded to the top surface of the beam section. Being welded, in essence, through the beam, gives the mounting studs as much strength as possible. The studs themselves were cut from 1/2" all-thread and provide about 4" of vertical adjustment. The drive wheel is adjusted so that, when the drum is empty, the tire holds the drum off one of the casters on one end about 1/4". When loaded, the drum compresses the tire and rests on the casters.
So far, so good. When the drum was empty, the drive worked perfectly. The skid loader control provided enough variable speed control so as to allow the drum to rotate slowly.
Then we loaded the drum about 1/3 full and tried again. Even only 1/3 full, there is enough weight in the bottom of the drum to create significant inertia and the drive tire begins to spin against the drum surface before the drum can get all the way around. The hydraulic drive is reversible, and by working it back and forth, the drum will rock back and forth about 2/3 of the way around, but will not go around completely.
As far as composting goes, the rocking back and forth appears to provide enough mixing to keep the composting action alive. But to get the drum to go all the way around, it's back to the drawing board.
Design attempt number two involves parts currently on order. It's of course significantly more expensive than design attempt number one, but should have greater potential to rotate the drum completely around. The new drive will use a PowerTwist Plus V-Belt from Fenner Drives. The drive wheel and tire will be replaced with a pulley. The belt will extend completely around the drum with the pulley below the drum - about 14 feet in total length. The adjustment bolts on the motor mounting bracket will be used to lower the pulley, providing tension on the belt. At least this is the latest theory. I will update this site with results once we've tried this new drive mechanism. In the meantime we'll resort to rocking our compost back and forth.
For a parts list, go to Page 5: Parts and Materials List