Robotic Hand

For my third milestone, I completed the base project: a 3D printed hand controlled by a separate glove. In the finished project, when a user bends a finger on the glove the corresponding finger on the hand will bend in real time. For example, if the user bends their index finger the hand will also bend the index finger. First, I sewed the flex sensors onto the fingers of the glove as seen in the image above. In my project, the ring finger and the pinky share a servo, so only one of them needs to have the flex sensors attached. I used the same Arduino and breadboard from milestone 1 and kept the servos and flex sensors attached to the breadboard through the use of jumper cables. The Arduino has the same code as it did in milestone 1, which I got from dschurman on this instructables page While working on this milestone, I had a lot of mechanical issues. One example is when I shorted out an Arduino by plugging in the battery wrong. One non-mechanical issue that I had was that when the fingers on the glove were straight the fingers in the hand would bend, and when the fingers on the glove would bend the fingers on the hand would straighten themselves. I fixed this by changing the map function of the servos so they would turn from 180 to 0 instead of 0 to 180. I changed the code from:
pos1 = constrain(pos1, 0, 180); int pos2 = map(flex2, 400, 700, 0, 180);

to

pos1 = constrain(pos1, 0, 180); int pos2 = map(flex2, 400, 700, 180, 0); In Arduino, the map function takes in an input and scales it through the input range then the output range and then gives out an output. For example, in this project the input is the flex sensor value and the input range is based on resistance of the flex sensor. The actual input is the ADC value of the flex sensor. ADC stands for analog digital conversion and is used to convert the analog voltage in the pins to a digital number. This is useful because it can change the analog signal into a digital one without changing the value. ADC is used in this project by changing the flex data in the analog pins from an analog value to a digital value that the servos can understand. The amount of flex sensor voltage is put through the input range and scaled to the output range which is what position the servos will turn to. Learn more about ADC and Arduino analog pins here. The servos are the output of the function and after the flex sensor bends the servos will move to a position between 0 and 180. The flex sensors were mapped into a range between 400 and 700 because those are the values where the fingers were fully open or closed. Although I had a lot of issues with getting this project to work, one thing that I enjoyed while doing this milestone was finally getting everything to work properly after days of trying.

For my second milestone, I constructed the hand and connected the string and servos to the hand. As I said in my first milestone, servos are small motors where you command exactly how far to rotate. The servos are attached to strings that go through each of the fingers. This milestone was completely mechanical, so as of right now I do not have any power going to the servos, so they cannot pull the fingers. I had a lot of challanges with this part because the strings need to be in the perfect position where they are not being pulled too much or too little otherwise it will not pull the fingers. To get to this point I had a lot of issues with putting every part together. First, I screwed together the fingers and had a lot of difficulty getting the screw to fit into the holes. To get the screw in I had to drill and file the holes to the right sizes. I later realized that I used the wrong screws which made the fingers too stiff. After I had the whole hand together, I started to put the string through each finger. Since the hand was 3D printed there were a lot of small pieces of plastic in the string holes that I had to drill to get the string through. Once I had string going through each of the fingers and all the right screws, I saw that the string was too thick for it to bend the fingers. I then changed the strings, but they were too thin and were not able to pull the fingers. I changed the string one more time and then it was (finally!) the right size. The strings would slip through the fingers so I used hot glue on the tips of the finger to stop them. In figure 1 you can see the correct strings going through the fingers and some of the glue on top to hold them down. Next I attached the string to the servo heads and pulled them to see if they could pull the fingers down. First I tried looping the string through the servos but they would just slip through. Next I tried to tie them, but my knots kept coming loose. Then I tried to keep the string on the servos with hot glue, but the strings would pull off the glue. Finally, I used crimp tubes to hold the strings securely. In figure 2 you can see the servos attached to the arm and the strings attached to the servos heads with crimp tubing. Now the fingers were able to move, but there was still a lot of friction between the different parts of the fingers. To make the movements more fluid I filed down parts of the fingers. Now the servos can pull the strings and the fingers well.One thing that I learned from this milestone is to test pieces of a larger project one at a time and check for issues instead of doing everything at once and finding out it does not work. The idea of doing one thing at a time would have been useful when I was testing out the screws, strings, and how well the strings are connected to the servos.