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Summer blog - update every few days with new findings.
Today I worked on making more fabric but using the kevlar thread instead, since it is thinner and could potentially allow us to make thinner rolling diaphragms. However, we first had to spool the kevlar thread onto a bar that would fit the sewing machine. We did this by putting the bar on an electric drill and letting it twist. I realized that the kevlar allowed me to do straighter and better stitches because it was really thin and a little more rigid. However, when the time came to put this fabric inside the mold, it fit too tightly. We then went to cast the rolling diaphragms and I got to cast them myself with the help of alex.
On Friday I went and worked on post processing the 3D prints for new molds. I learned about the different types of resin baths and the UV cure oven and how the different resins need to be cured differently. Alex also came up with the idea of cutting our own pattern into the silinylon. However, I did not get the chance to cut it myself because there was a long line at the prl due to a summer camp.
On Thursday we went to the prl to try and make a railing to feed the fabric perfectly straight on the sewing machine and have parallel lines to prevent bulging on the rolling diaphragm. I used the laser cutter to cut rails and bars to hold the fabric taught. Then alex also taught me how to cut the silinylon for the other type of rolling diaphragms that seems to be working. After we came back we realized that our cast of the kevlar mold with the paper did not come out well because it was only cast on one side and it peeled off. The silicone did also not cure with the new molds.
On Tuesday, I worked on different ways to make the fabric for the rolling diaphragm. We finally got the water soluble paper so I tried gluing the kevlar in parallel strips with the new jig I had made. The kevlar looked really parallel and seemed to look well. We also tried printing straight lines on the dissolvable paper and sewing onto it. However, we realized that this did not work to well because the stitches on the mesh became to loose when the paper was dissolved. After this Alex showed me the proper process to cast the silicone meshes. We also then assembled as a lab the new cupboard/stand for the 3D printer.
Today while Alex was out, I worked with Wilson on finally deciding the shape for the new climbing hand. After some brainstorming we decided to make the climbing hand look more like a bear claw but still remain two-sided. With one side having a granular jamming palm with 3 spiky fingers (like the ones in the old hand) and the other side having three ice axe like structures.
After working with Wilson, I then worked on learning about arduino, to help Alex with a device to push the two parts of the casting mold for the silicone together while it is being degassed. I learned about bread boards and how to code the motors to do different things. I also worked on CADing a container for the casting molds that would hold them in place while the two molds are being pushed together.
On Thursday I spent most of the morning redesigning the brush for the sewing of the kevlar. I redesigned it so that both sides and can be used and we can maximize the production of the fabric and minimize waste. This was definitely a learning experience as I got to use solid works and become more familiar with the different features like doing mirroring of of a plane. I found OnShape to be really useful for continuing to work on my pieces at home and I am slowly becoming more familiar with it. The new design is shown in the image below.
After Wilson came in, I started working on sanding down the new prototype for casting the silicone casing for the particle jamming hand. There had been issues with bubbles and casting before so I tried to sand it as smoothly as possible. When I was sanding the mold Mark taught me some tips for casting urethane. Degassing the mold to get rid of some air bubbles before casting is a good step and so is turning the vacuum on and off because the urethane might boil.
After sanding the mold, I had to drill holes for dowel pins in the mold. This turned out to be challenging because they had to be at exactly 20 degrees so that all the spikes are inserted at the same angle. To drill these tiny holes we had to turn the drilling machine at a 20 degree angle, which reduced the human error of having to tilt the mold at exactly 20 degrees. I also had to use a really tiny 1mm drill bit.
However, the job was not done with just drilling the holes for the dowel pins. We also had to make some calculations for the length of the dowel pins in the mold and find a way to cut them all at the same length. We tried snipping them at exactly 15.43mm every time but this was not very accurate and we failed. I then thought of using a block of wood that was exactly that length and drill holes into them where we could put the dowel pins in and then cut the remainder. Although it required several iterations to make this process successful and efficient by the end we improved it so that cutting 20 dowel pins only took a couple minutes rather than an hour.
Although I spent most of the morning on Friday continuing to design the brush for the fabric of the rolling diaphragm, the rest of the day was spent on doing lab cleanup.
On Monday, I spent more time looking at the grasping mechanisms of the bear as well as other animals like pangolins. I constructed a foam core model to see how the bear grasped onto things. It turns out that it is the long claws that allow the bear to better climb up things. After finishing up with my bear claw I helped Capella in cleaning parts that she had printed in the objet printer. It turned out to be really time consuming and they had to be carefully done so as to not ruin the sizing for the press fit.
After Wilson came in on Monday we picked up the test tubes from the TLTL with our urethane samples. As mentioned earlier, we had poured urethane at two different times into each of these tubes, varying the times when we poured the urethane for the second time. After opening the tubes up we realized that it wasn't the curing time between the pours that affected the bonding between the urethane layers. So probably it was the demolding spray in between the layers that affected the bond.
On Tuesday, I worked with Alex on trying to make different fibers for the rolling diaphragm. After talking with Mark we thought of different ideas to better weave the fabric for the rolling diaphragm. One of the ideas that came up was using a brush to weave the kevlar fibers perpendicular to each other onto the mesh and then cast it. Sewing them in the sewing machine was not working so perfectly because the fibers did not always get sewn perfectly perpendicular to each other. Therefore, using the comb and doing it by hand might work best. We also needed to find a way to keep the Kevlar fibers together before casting them since this seem to be an issue. Alex had already made a prototype of a brush from before so I spent the rest of the day using that prototype to find different ways to sew the kevlar onto the mesh.
Day 2 & 3
On day 2 I started working with Wilson on the climbing robot. He started by explaining his vision of how the robot hand would look like, with one side having a particle jamming pad and the other having an Ice pick like side to cling onto holds. After explaining how the hand worked, I practiced prototyping it with legos and rubber band.
After prototyping, we went to the TLTL to do some urethane curing testing. I learned how to cast the urethane used for the pad and use the degassing machine. The particle jamming pad when manufactured at two different times and put together has not been curing together properly so we tried to figure out at what times the urethane best cures together. We therefore poured some urethane in multiple tubes and then poured more urethane at multiple time intervals.
The next day, I started looking the human hand articulation to look at grasp. I was inspired by the sticky bot to use push and pull wires to articulate the hand as well as a paper on the DLR hand (http://journals.sagepub.com/doi/pdf/10.1177/0278364912459209). However, although my prototype articulated properly, it enabled me to see how the human hand may not be the most optimal mechanism for a climbing robot. It also has many degrees of freedom with twisting and bending movements, which are useful for pinching and grasping things but may not be necessary for climbing. Therefore, I started looking at the pangolin and bear claw as a sources of inspiration. After looking at a paper on bear claws and human feet (https://www.fws.gov/lab/idnotes/idg11_bearhumanfeet.pdf) , I learned that bear paws and human feet are very similar in structural anatomy and the main difference is the presence of claws. However, I have decided to make a foam core prototype to better understand how the bear paw works, which I am currently working on. I think it may be interesting to have articulated bear claws for the climbing hand combined with a particule jamming pad on where the paw pad would be on a bear as opposed to having them on opposite ends of the hand.
After doing some prototyping and readings, I worked on putting together the prototype for Wilson's claw. I drew and cut some rods and a handle for the claw and then we put together the 3D printed structure at the TLTL where I got to work with the band saw and power drill.
After the clean up today, we also did some brainstorming on how to best put the hooks into the silicone molds because currently sometimes the urethane breaks. It was really interesting looking at how to improve the molds and the ideas the came about, including perhaps using a fluid based gripper instead of particle jamming or using a twisting fibre that allows claws to come together around a rock. I am currently reading papers on particle jamming to find a coarse yet smaller particle than coffee to improve the gripping.
Today I helped Stephanie with improving the pulley system in the SuperSCAMP. The string kept on slipping off the pulley and therefore the legs of the SCAMP did not move. At first I thought of using silicone to increase the coefficient of friction between the pulley and the string but as the pulley rotated, the string rubbed the silicone off and eventually the string would slip again. I then started designing a pulley with grooves, on solid works, to prevent the string from slipping but before I printed it, Prof.Cutkosky suggested using the same pulleys we had but instead wrapping the string around several times as this would increase the friction exponentially.
As I tried to do this, I quickly encountered some challenges, the string we were using was too thick and did not fit without overlap around the pulley twice and the pulley was V-shaped allowing the strings to become tangled more easily. Moreover, the string was not feeding in tangentially so this made the string slip off the pulley. To fix this I changed to using thinner strings and tested Kevlar and Spectre fibre, which despite being smoother did not slip when they were turned around the pulley twice. To allow the strings to come in tangentially to the pulley, I used bolt nuts and glued them to the frame. However, this did not work as the string had to feed tangential both horizontally (on the sides of the pulley) and outwards (in the direction of the face of the pulley). I then modified this to be made out of a other pieces which were longer and would allow proper alignment. This improved the feeding of the string into the pulley but did not prevent the strings from getting tangled. Therefore, tomorrow, I will try and design an wider pulley that is not v shaped and spirals to prevent the strings from getting tangled and see how it works.