Critical Module:
One of our biggest concerns with our current bicycle-powered blender designs is that it is unclear what our detachable, back-wheel stand will be able to support. We need to design a stand that will be stable and adaptable to the potentially wide diversity of bike designs present in Nicaragua. Thus, for our critical module, we measured 20 bikes on campus to get a better idea of what our stand design should be able to support. Our hope was that the bikes present on Wellesley’s campus would be more diverse than the array of bikes that would typically be found in Nicaragua, and therefore our stand design could safely support those found in Nicaragua. To do this, we measured the circumference of the chain stay (where the stand will attach), the distance from the middle of the rear wheel to the top of the rear rack, and the width between the left and right chain stays that straddle the wheel on 20 bikes around the Wellesley College campus.
We then took the average value and standard deviation for each of these measurements, which is summarized in the graph below:
Figure 1. Bike measurements from Wellesley College for critical module. The value for the chain stay circumference, represented as a mean + standard deviation, was 6.5 + .8 cm. The value for the distance from the rear rack to the middle of the rear wheel, represented as a mean + standard deviation, was 8.5 + 1.8 cm. The mean value (+ standard deviation) for the width between the left and right chain stays was 9.6 + .5 cm.
Based on these measurements, we can conclude that our bike stand should have clamps that can attach to the chain stays with a circumference of anywhere between about 5.5 cm to 7.5 cm. Furthermore, the mechanism by which we clamp the stand to the chain stays should be able to accommodate a width of about 9 to 10 cm. In terms of the blender attachment, the length of the wheel and axle attachment to the blender should be between 7 to 10 cm. Our critical module measurements demonstrated to us that we will need to design a stand that can make slight adjustments to different types of bikes, though accounting for these deviations should be doable with the design we are considering. We now have a much better understanding of standard bike dimensions which will be particularly useful as we move forward into the construction phase of our project.
Updated Schedule:
Bike Blender
- make a physical prototype (Jambo): start on 4/8, continue work on 4/11
- implement blender on bike(s): by 4/18
- test blender and revise costs: 4/18 or 4/21
Bike Stand
- draw design and communicate with Estuardo about constructing a bike stand 4/8
- provide this design and materials list to Grupo Fenix 4/8
Bike Anatomy:
The blender attachment will sit atop a rear rack (over the rear wheel). The rack will attach to the 5-sprocket block on the rear hub. The bicycle stand will attach to the chain stay above the frame of the bicycle. The variation that we are most concerned with is the difference in the circumference of the chain stay, the width between the left and right chain stay and the distance from the rear rack to top of the tire.
Communications with Grupo Fenix:
Last week, we were able to have a conversation with a member of the staff of Grupo Fenix. In this conversation, we had a number of our initial questions answered about the project, which are summarized in our previous post. Today, we will hopefully be talking to members of the youth group that has worked on the bicycle powered blender. The questions we plan on asking are as follows:
1. What are the biggest problems with your current design?
2. Do you have photos/other documentation of the design?
3. What design specifications/elements are most important to you?
4. Is it very difficult or expensive to purchase a rear rack for a bicycle?
5. Are there a wide variety of bikes in Nicaragua? What factors vary the most?
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