Bicycle Powered Maize Mill
The Engineers Without Borders Malawi Team has been working with Kumponda, a small community in southeastern Africa since 2013. An initial assessment determined a lack of food security to be a major roadblock to the community’s success and well being. Since then, the team has been working to complete a bicycle powered maize mill to grind corn into flour. Corn flour is the key component in nsima, a staple of the Malawi diet. The completed bicycle powered mill would be more accessible, energy efficient, and affordable than the electric mill that is currently used. By building a mill that can be accessed so easily, the community members can spend less money grinding corn and spend their time on more valuable things than travel.
The values of Engineers Without Borders dictate that the project needed to be sustainable such that the community could take full ownership of the project and keep it going on their own once implementation is complete. This means that the project needs to be made with materials and manufacturing processes available in country so that the community will be able to make repairs as needed. This also means that information about the project and how it works needs to be passed on to the community so that they can take ownership of the project and have the knowledge to fix it themselves. The team also set out with the goal of designing the maize mill so that it can be replicated by other neighboring communities in the future.
This specific project was the result of the third implementation trip, which took place in December 2016 and was a continuation of the work of the two previous implementation trips, as well as work that the team had been doing back at Cal Poly in between trips.
The team traveled with the intentions of finding solutions for the issues faced on the last trip in September. The maize mill is still chain driven with several rollers of different groove depths to gradually produce smaller pieces of corn. The design of the basic components changed very little. Only slight adjustments were made to increase the efficiency of the design. These changes made a drastic impact to the amount of flour that was able to be produced and the quality that the team was able to achieve. The changes that were implemented were:
Tensioning Mechanism for Rollers
In the design, the rollers are held up by plates with holes for the axles. One roller is fixed while the other is placed in a slot so that the distance between the rollers can be adjusted. In order to get the rollers the correct distance from each other, they must be able to be adjusted to precision measurements. This is important so that the size of the corn will gradually decrease. The past system was created by moving a small plate to the desired location and tightening it with bolts. These bolts often slipped and caused the space between the rollers to widen during the passing of the maize.
Before the trip, the team designed a tensioning system that allowed for more precise adjustments and created a stronger hold to avoid slipping. The tensioner, uses bolts parallel to the plates to pull the small plate with tabs towards the fixed roller with each turn of the nut on the end. This new tensioner was very effective and allowed the rollers to get very close to each other and stay together throughout the entire pass.
Tensioning plates of bike stand
Similarly to the tensioning of the rollers, the team saw an issue with the bolts holding the bike in place. They slipped after a few minutes of riding the bike, causing the chain to fall off of the sprocket and causing someone to need to stop and fix it each time, slowing the entire milling process.
The team tackled this problem just like the rollers, with a tensioning system designed the same way. The tensioning system pulls the bike farther from the sprocket, keeping the chain taut and from falling off the sprocket.
Addition of bearings
The addition of bearings to the design are a huge reason that the system was able to produce flour. On the last trip the rollers spun eccentrically, causing a wavering of the gap and allowing some bigger particles to pass through the gap on one side of the rollers. This time, the bearings spun the rollers concentrically, allowing for a constant gap and a consistent particle size per pass. The team used self aligning flange mount bearings.
Blocking off of feeder
The team saw issues with the feeder because it allowed too much corn to flow through and ended up pushing full, unground kernels off of the top of the rollers rather than pushing them through the two rollers. This was a big problem for the yield and effected later passes with pieces of corn much larger than the majority of the corn, making it one of the primary goals to fix. Before the trip, the plan was to attach some material, possibly brushes or large metal washers, to block the flow of corn from the sides. After more in country testing and analyzing, the team determined that limiting the flow of corn was sufficient for getting all the kernels through the mill without any additional parts or materials to further complicate the design.
New stainless rollers
Throughout the trip the team acquired new smooth rollers made of stainless steel. Stainless is much more expensive than the other steel used, which is why the team has avoided using on the previous trip. However, they are also much smoother and can create even smaller particles of flour, making these rollers a great last pass for the mill.
Shafts
Another one of the changes to the design was the addition of shafts welded to the rollers. This adaption was necessary to be able to use the bearings. The travel team was only able to find basic bearing sizes (5 mm increments), which was an issue with the axles that were being used on the mill. The implemented solution was to weld 20 mm shafts into each roller so that they would fit in the bearings. This eliminated the changing of the rollers with set screws and instead the roller with its shaft was one piece that was completely removed from the mill when changing them out.
With the addition of the shafts came the need to change the entire axle. Unfortunately, changing the axle completely would require extensive remachining for the several parts that the axle runs through. Due to time constraints, the Malawi team decided to create an adapter connecting the old axle to the new shaft so that minimal machining was necessary. The adapter grips each axle with two set screws on each rod so that there will be minimal slip.
Strengthening of stand
The team also added some pieces of wood to the stand for structural support. These pieces allowed the stand to have minimal movement while the mill was running.
Results
The changes allowed us to achieve the correct flour consistency that the community needs to make nsima. However the yield was not high enough to make it feasible to use.
The values of Engineers Without Borders dictate that the project needed to be sustainable such that the community could take full ownership of the project and keep it going on their own once implementation is complete. This means that the project needs to be made with materials and manufacturing processes available in country so that the community will be able to make repairs as needed. This also means that information about the project and how it works needs to be passed on to the community so that they can take ownership of the project and have the knowledge to fix it themselves. The team also set out with the goal of designing the maize mill so that it can be replicated by other neighboring communities in the future.
This specific project was the result of the third implementation trip, which took place in December 2016 and was a continuation of the work of the two previous implementation trips, as well as work that the team had been doing back at Cal Poly in between trips.
The team traveled with the intentions of finding solutions for the issues faced on the last trip in September. The maize mill is still chain driven with several rollers of different groove depths to gradually produce smaller pieces of corn. The design of the basic components changed very little. Only slight adjustments were made to increase the efficiency of the design. These changes made a drastic impact to the amount of flour that was able to be produced and the quality that the team was able to achieve. The changes that were implemented were:
Tensioning Mechanism for Rollers
In the design, the rollers are held up by plates with holes for the axles. One roller is fixed while the other is placed in a slot so that the distance between the rollers can be adjusted. In order to get the rollers the correct distance from each other, they must be able to be adjusted to precision measurements. This is important so that the size of the corn will gradually decrease. The past system was created by moving a small plate to the desired location and tightening it with bolts. These bolts often slipped and caused the space between the rollers to widen during the passing of the maize.
Before the trip, the team designed a tensioning system that allowed for more precise adjustments and created a stronger hold to avoid slipping. The tensioner, uses bolts parallel to the plates to pull the small plate with tabs towards the fixed roller with each turn of the nut on the end. This new tensioner was very effective and allowed the rollers to get very close to each other and stay together throughout the entire pass.
Tensioning plates of bike stand
Similarly to the tensioning of the rollers, the team saw an issue with the bolts holding the bike in place. They slipped after a few minutes of riding the bike, causing the chain to fall off of the sprocket and causing someone to need to stop and fix it each time, slowing the entire milling process.
The team tackled this problem just like the rollers, with a tensioning system designed the same way. The tensioning system pulls the bike farther from the sprocket, keeping the chain taut and from falling off the sprocket.
Addition of bearings
The addition of bearings to the design are a huge reason that the system was able to produce flour. On the last trip the rollers spun eccentrically, causing a wavering of the gap and allowing some bigger particles to pass through the gap on one side of the rollers. This time, the bearings spun the rollers concentrically, allowing for a constant gap and a consistent particle size per pass. The team used self aligning flange mount bearings.
Blocking off of feeder
The team saw issues with the feeder because it allowed too much corn to flow through and ended up pushing full, unground kernels off of the top of the rollers rather than pushing them through the two rollers. This was a big problem for the yield and effected later passes with pieces of corn much larger than the majority of the corn, making it one of the primary goals to fix. Before the trip, the plan was to attach some material, possibly brushes or large metal washers, to block the flow of corn from the sides. After more in country testing and analyzing, the team determined that limiting the flow of corn was sufficient for getting all the kernels through the mill without any additional parts or materials to further complicate the design.
New stainless rollers
Throughout the trip the team acquired new smooth rollers made of stainless steel. Stainless is much more expensive than the other steel used, which is why the team has avoided using on the previous trip. However, they are also much smoother and can create even smaller particles of flour, making these rollers a great last pass for the mill.
Shafts
Another one of the changes to the design was the addition of shafts welded to the rollers. This adaption was necessary to be able to use the bearings. The travel team was only able to find basic bearing sizes (5 mm increments), which was an issue with the axles that were being used on the mill. The implemented solution was to weld 20 mm shafts into each roller so that they would fit in the bearings. This eliminated the changing of the rollers with set screws and instead the roller with its shaft was one piece that was completely removed from the mill when changing them out.
With the addition of the shafts came the need to change the entire axle. Unfortunately, changing the axle completely would require extensive remachining for the several parts that the axle runs through. Due to time constraints, the Malawi team decided to create an adapter connecting the old axle to the new shaft so that minimal machining was necessary. The adapter grips each axle with two set screws on each rod so that there will be minimal slip.
Strengthening of stand
The team also added some pieces of wood to the stand for structural support. These pieces allowed the stand to have minimal movement while the mill was running.
Results
The changes allowed us to achieve the correct flour consistency that the community needs to make nsima. However the yield was not high enough to make it feasible to use.
1 Teammate
