I recently landed a small contract to build 25 compost bins for schools in Accra, Ghana. The budget is limited so I needed to have something simple but interactive and safe around kids and public spaces.
Here is the design brief I wrote for the proposal.
Scope of Project:
Provide 25 schools with a compost system taking into consideration aesthetics, tactile use, and proximity to children and public.
Design Requirements:d
• Pleasing to the eyes
• Low or no smell
• Low maintenance and easy to use
• Very little brown waste
• Safe for around children and public
• Does not create an attraction for pests
• Provides some sort of interaction for kids to aid in education
Proposed System:
The pictured design will be adapted to local building materials (not my picture so not including it on this blurt). Using the 33 gallon blue plastic shipping barrel with the screw on top, and bamboo using rope lashings to create the A frame.
Yesterday I went to where my garden is as I have stock piled some materials there, the first barrels and some bamboo sticks. There is also some room to work there. I used my truck bucket as my saw horses and did the rest of the construction in as small slice of shade on the ground.
Below are the build pictures of the prototype. I will already make some changes for production but this at least allowed me to get most of the measurements of things so I can make production a lot simpler and add a helping hand to do all the cutting of the bamboo for instance. I will also use a lag bolt or metal wire to bind the top of the A frame. As I know that rope lashings can be very durable it will be a learning curve for me to learn to do them well and tight. Finding the right natural rope here is difficult also. I may change from the equal width sides too, and rather than having them staggered have one side nest into the the the other side a the top of the A frame. All that is left is to add a few ventilation holes and this tumbler is ready to go.
I like the vertical tumbler design also. Most that can be purchased and a lot of DIY designs have it horizontal. But then you have to add flaps to the inside to carry the material around and make a door on the side and reinforce it. That seems like a lot of unnecessary work when one good flip of this will aerate everything in this bin, the top is easily opened to put materials in, and you can use it to pour into a wheel barrow.
First step was to cut a hole in the side of the container with a hole saw. This was done a little above the center of gravity line so it would remain upright when empty and easy to load.
Test fit of an axle.
Looking at the lengths and angles of the A frame.
I lashed the top of the poles with a Japanese square lashing, I learned from youtube.
The cross piece I used a smaller piece of bamboo and used the hole saw to make a hole in the bigger piece of bamboo to put it in. I then drilled a hole through both of the bamboo at the joint and drove a split bamboo spike through the hole holding it very securely in place. The whole structure became ridged at this point.
Nails will rust over time and also split the bamboo.
Here is the whole system mocked up without any of the horizontal supports for it to be laterally stable.
To tie the two A frames together I needed to add some cross pieces. I added 2 on each side so it would not move from side to side. I once again cute two holes into each leg and put smaller bamboo in the holes to bridge to the other leg.
I then assembled everything and got it as square as possible. I then drilled holes and used some more bamboo pegs to fit it all together. In the production pieces I may use clue and the pegs. But it all came out very sold. Below are the images of the almost finished compost bin. I just need to wash out the barrel well and add some vent holes. I am thinking I dont need too many because the rotating motion will be the main aeration I just need to be able to have to air to be able to turn over in the empty part of the barrel.
All pictures and video were shot with an Infinix Smart 3 Plus phone