To-Do List

This is our to-do list as of November 30th:

- Construct arm extension module
- Modify motor and gear ratios of tape dispenser
- Construct bin blocking cover and its fastenings
- Construct linking arm between the two modules
- Actuate bin blocking cover and linking arm
- Test completed machine

The list is in order of anticipated completion. Our schedule has been updated for this week as well; we're simply working all days this week. There isn't much left to do now besides manufacturing. With our machine design completely defined, we should finish manufacturing smoothly and on time.

Week of November 22nd

We successfully finished our MCM last week. The tape dispenser module was able to retract the tape smoothly, but it had a few small issues extending the tape. This is expected since the tape measure has a built in retraction spring; it is going to take more torque to pull the tape out than to push it in. Fortunately, this issue is easily solved by adding another gearbox to the planetary motor. We could also increase the gear ratio between the motor and the wheel axle to improve the torque even more.

During manufacturing, we learned a helpful technique when dealing with low accuracy tolerances. We were trying to mount the motor onto the module. Rather than drill all four holes at once onto the baseplate, we drilled only one hole. We mounted the motor onto the one hole and marked all the other holes from there. Drilling holes with this method will decrease inaccuracy when using rough tools such as a hand drill.

With this module complete, our next step is the arm extension module. We are approximately 40% done with our machine.

Week of November 15th

Last week, we began manufacturing work on the pieces of our MCM. We created a handful of brackets out of our aluminum L-piece, a few support columns out of our aluminum tube stock, and a drilled base plate out of our plywood plate.

We learned two important things from our initial manufacturing process, the first being tool accuracy. Different tools are capable of different ranges of accuracy. When we cut our support columns from the tube stock, we used a band saw. The band saw isn't a very accurate tool and created un-squared support columns as a result. To fix this problem, we finished off the support columns with a mill. The mill is more accurate than the bandsaw and was able to shave the support columns to a proper 90 degree square. We could have used a sander instead of the mill, but it isn't a very accurate tool like the bandsaw.

The second thing we learned was tool resolution. When we worked on the brackets and support columns, we noticed that the tool sometimes removed more material than we thought it would. For example, a drill bit of diameter 1/4" sometimes made a slightly bigger hole or the width of the bandsaw blade might throw measurements off. We had to carefully account for the tool resolution to avoid problems such as inaccuracy or error propagation. For drilling, the reaming process can be used. For cutting, use of bandsaw (cut slightly longer than needed) followed by use of mill can be used.

Week of November 8th

Last week our main goal was getting through the motor lab. We accomplished this, but we were not able to get to the shop to start manufacturing. Gotta step it up this week! We tweaked the design for our MCM slightly, practiced using the band saw, got our CAD files ready for the laser cutter, and scheduled time to use the water jet cutter. We are well on our way to creating three unique parts!

Week of November 1st

Last week was spent on developing our MCM. We created a CAD model, relevant drawings, gear ratio analysis, bill of materials, and manufacturing plan. Our MCM is a relatively uncomplicated machine to design, but it had to have very good dimensional accuracy. The machine is responsible for dispensing the tape measure; if any measurement was off too much the tape measure would deploy incorrectly.

The gear ratio analysis we did for the MCM was helpful as well. First, we defined a maximum tape measure extension / retraction rate. From there, we worked through different gear sizes and numbers of gearboxes to figure out the required ratio. Eventually, we were able to design a setup that provided the required extension / retraction rate as well as being able to fit within the size restrictions.