Monday, March 27, 2017

Week 9

     This week, we gathered all of the parts we needed to assemble our second prototype (revision 2). We then went to the shop to press-fit the pin and various components (bearings, gears, etc) into the "arm" portion of the newly designed brace. This can be seen in the pictures below.






All of the pictures above show the second prototype being assembled. The pin fits through two holes in the "arm" and holds one of the brass weights, a gear, and bearings. The vise was used to press-fit the entire assembly together. 

     The final assembly, with the motor casing attached is shown below. (The lid is not placed on the box to show the fit of the assembly.
 

     During the week we also tried to test the system. We went to Dr. Kim's lab and used the force plate again, with the user standing on the force plate while wearing the system. However, the test was conducted the Friday before spring break, when Isaac (the normal wearer) was gone. Kimberli wore the brace during testing, and there was still quite a bit of wiggle that we had hoped to eliminate with the double-mass system. It was unclear whether the design did not address the issue as well as hoped, or if the wiggle was produced because the brace did not fit well on Kimberli. (The brace was custom-designed for Isaac's foot, and was significantly larger than Kimberli's.) This is one thing that needs to be double checked after break when all of the group members return.
     Another problem was experienced during testing. The upper mass hit the lower gear when it spun. We will either need to add a bit of clearance or file down the lower gear to reduce this problem.It was also found that the upper gear sometimes became out of alignment, so that the gears were not always opposite of each other. Both of these problems are likely due to the fact that the bearings (on the pin) are somewhat loose and will need to be glued to the brace to reduce movement.

As can be seen, the brace sits much lower on the foot/ankle as it was big on Kimberli's leg. (Isaac was not available for testing.)

Video of one of the tests performed while standing on the force plate.


Thursday, March 16, 2017

Week 8

     This week we ordered another LiPo battery for the motor, as the previous one died from being plugged in for too long to the low- voltage checker. We also received the stock brass we had ordered and used the CNC machine to mill out our second brass weight. (We had tried to do this last week, but the stock came loose and we were unable to use it.)

We now have two of the brass weights that are this size (Revision 2). 

     The rest of the week each person worked on his or her Broader Impacts essay that was due at the beginning of Week 9. These were individual assignments and consisted of a 1,500 paper that discussed the social, economic, safety, and environmental implications of the project in both a local and global context.

Monday, March 6, 2017

Week 7

     During class this week, we presented our midterm presentation. This included a summary of what has been up to this point, as well as future testing and actions to be taken. Our presentation was slightly different than most other groups', as we will not have as much testing to do (since we are unable to take our project to space or perform bed-rest studies). Therefore, much of our presentation focused on the redesign that we are working on, and how it will be incorporated into the current prototype. Further details about the redesign may be seen below and in the previous blog post. An example of one of our slides may be seen in the image below.

This is one of the slides that was included in our midterm presentation.
     The rest of the week, we ordered parts that will be used in our redesign, such as pins (for holding one of the brass weights) and ball bearings. The redesign consists of two brass masses spinning in opposite directions. These will be spun by the motor and a gear system, and held in place by a large "arm" on the leg brace. The reasoning behind this is that the opposite spin should cancel out the forces (and thus the wiggle) around the leg. This would result in force only being transmitted along the z-directions, or along the bones of the leg. (The CAD images for this overall system may be seen in the previous week's blog post.)
     Isaac also worked on the MasterCAM for milling the second set of brass weights this week. Dr. Hekman agreed to meet with us and help us use the CNC machine in Bourns Lab again. We were using the same piece of brass stock before, as the remaining brass was just long enough to machine our new parts.
     We experienced an issue during milling however, where one end of the brass stock was not supported as well as we had believed it to be. This left one end free to move around during milling, which caused one of the new brass weights to be cut incorrectly and unusable for our purposes. We were able to cut one of the new weights out successfully (see the image below), but will need to purchase more brass in order to mill the second one. (One advantage to buying new brass stock, however, is that we can get the thickness that we want, rather than having to face off a large portion of the brass.)

The successful brass weight that was created. This part was easier to mill than the original, since the entire piece was the same height.
     We also sent our redesigned leg brace (with the large arm to support the gears) to Josh Park for 3D printing. The leg brace finished printing successfully late during the week, but we were not able to test anything as we are missing the second brass weight. The motor casing had also been sent to Josh for printing, but will not be available until next week. Additionally, the gears for the redesign were 3D printed from SLS nylon from an outside source (Jake's parents), which should be stronger than if they were made out of PLA (as is the leg brace). These may be seen in the images below. 

The redesigned portion of the leg brace. The large "arm" will hold/guide the two spinning masses. 
The gears to be used in the redesign.