EG's compost turner, part 2 of 4

Since the combined weight of the auger, gearbox, motor, and I-beam will be around 200 lbs., we're gonna need a relatively strong support system in place to hold the weight. I always like to beef things up a bit, because you never know if extra capacity will be needed later. So, 6"x6" posts will be concreted in the ground at all four corners, at a depth of about 18". Some cross pieces will be mounted across the top of the posts, which will keep the vertical posts from twisting - as well as giving me something to connect the monorail (steel I-beam) to. Here's a drawing for reference:

***Revision - the I-beam will not be mounted underneath a 6x6 as the picture suggests, but will span the distance alone. I just had to change that....sheesh. OCPD drives me crazy sometimes.

This entire structure will be connected by pretty large fasteners, because we certainly wouldn't want it to have movement in any direction. Now, let's talk about how pulleys can create a mechanical advantage.

To lift the weight off the ground as shown in the picture below, a person would have to exert a pulling force on the end of the rope that is equal to how much the object weighs. "Work"  is rated in ft. lbs, or newton meters - this one of which is depicted by the latter of the two. This setup has a mechanical advantage of "1", which can be multiplied by adding more pulleys. You can read all about Archimedes and how mechanical leverage works Here .

However, if the pulley is allowed to move upward as the rope is pulled, then the mechanical advantage is "2".

So, i'll go with a 4-pulley system, as in the picture below. It gives me an advantage of "4", which means only 1/4 of the force on the rope will be needed to move the same object. I can certainly appreciate that - because I have enough physical problems as it is.

Now, let's talk about gear reduction. Gears are used to reduce speed, change direction of motion, and multiply turning forces. My apparatus will utilize 2 of these : reduce speed and multiply force. Since a typical 4 pole electric motor turns at 1800 rpms, an auger turning that fast would probably (a) be dangerous, (b) be limited to the amount of horsepower applied to it, and (c) also make a huge mess! I'm sure Jude would enjoy compost flying everywhere, but I wouldn't! So, slower is better - and the added benefit of extra force is good, too! To get the reduced output speed of the gearbox, I simply took the motor nameplate rpms (1725) that will be driving it, then divide that number by the ratio of the gearbox (160:1)

1725 divided by 160 = 10.78 rpms will be applied to the auger

In the process, the torque of the output shaft has been multiplied as well. The formula used to find the torque value is : motor torque x gear ratio = torque

                          (1.5 ft.lbs.)   x    (160)    = 246 ft.lbs.

This is the actual force that will turn the auger, which will be doubled (by increasing motor horsepower) if not strong enough to get the job done. We'll just have to wait and see what happens, but I imagine it's gonna work pretty good.

Potential problems -
I can already think of 2-3 potential problems that might be encountered when this crazy contraption is turned on - which mainly involve the auger staying stationary as it drills down into each pile.

1. Bouncing (since the power unit is not rigidly connected to the overhead frame)
2. Walking (as Tom pointed out in the comment he left for part 1)
3. Some other unforseen problem

The only one that troubles me is bouncing, because there's not much that I can do about that. However, the possible "walking" issue is easily fixed, should it become an issue. The fact that it will turn at a slow speed will help matters - I can tell ya that much.

Anyway, part 3 will have current progress photos of the project, and the last post will be a video of it in action! WooHoo! I'll try to get part 3 posted in a few weeks, as it'll take 2-3 weekends to get the framework in place.

I picked up the 6x6 poplar posts today, and they must have weighed at least 300 lbs. each. When you order 6x6 posts 12 feet long from a sawmill, they are really 6" - not 5.5" like in the stores.Getting them unloaded and moved approximately 100 feet was pretty interesting - let me tell ya! It took some real ingenuity, and my son Chance helped me with them. I really don't know how i'll get them set into place, but an idea will pop into my head, I guarantee it. This will be the strongest outdoor structure I've ever built.....

Take care, and happy composting!

EG