This is a video of me explaining my three projects at BlueStamp’s parents night and thoroughly discussing and displaying my prosthetic hand, breaking down the three steps I took to get it to where it is now to my fellow BSE engineers and their parents:
Here is a link to the youtube page in the event that this video does not work: http://youtu.be/w6tOH3bciCc
I have had a fantastic two years at BlueStamp. That is due mostly to the wonderful and committed instructors that I have had. They have taught me and encouraged me through every step of my amazing experience and, along with Dave and Robin (the co-founders of BSE), have made my time at BlueStamp an incredibly enjoyable one. Being a second year student at BlueStamp, I was eager to share the knowledge I acquired last year with this year’s BSE students. While I did frequently give advice and input, especially when approached, I certainly learned a great deal from my fellow young engineers. The comfortable feeling of entering my “second home” that I experienced last year continued to this year as well. My main project this year centered around mechanical engineering, therefore finally giving me a deeper understanding of each of the three aspects of this profession that I love the most: mechanical engineering (this year), electrical engineering (both years) and programming (mostly last year). Along with the resources, experience and professionalism that BlueStamp offers comes, in my opinion, the most important aspect of the program — the engineers of the future. It was evident to me that all of my fellow BSE students had at least one thing in common — an aspiration for greatness. It is not very often that you can forge a life-long friendship over the course of 6 weeks and I have done so on multiple occasions over the past two years (12 weeks) at BlueStamp.
Prosthetic Hand – Final Blog Post (within BlueStamp)
Within BlueStamp, I have successfully put together a digital watch and gram piano as well as built the mechanical structure of a prosthetic hand with limited yet successful functionality. BlueStamp has been amazing for me this year. Being that I am a returning student, I naturally must try and compare this year’s experience to last year’s. However, they are vastly different in so many respects. Unlike last year, my project this year mostly consisted of mechanical work. As a result of that, most of the problems I encountered this year are problems I have never before faced. Also contrary to last year, I decided to work on a student defined project (SDP) that was not one of the possible options given by BlueStamp. There is one thing, however, that remained the same between the two years — the level of difficulty and amount of time put in. While I did progress in many fields from last year to this one, I look at the similarity in struggle as a testament to my wanting to push myself to work on a project that is mostly outside of my comfort zone.
My main project, the hand, can mostly be broken down into three steps. The first step was 3D printing all of the parts and assembling them without even basic functionality from a mechanical or electrical standpoint. The second part consisted of threading the tendons into the fingers and creating an electrical trigger to control the motors within said fingers. This step therefore implements both the mechanical and electrical aspect of the prosthetic hand. The third and final step revolves around implementing the thumb component and putting the entire hand together in a way that makes it aesthetically pleasing.
My prosthetic hand consists of five fingers, four of which having 3 joints and the thumb having two joints with the ability to rotate its angle as well. The design of the spool within the finger allows for the motor to pull on the tendon around a pulley system, moving the wire parallel to the way the finger bends. The thumb’s rotation requires a servo, which can only rotate up to 180 degrees (or at least the one I am using). When one of my servos shorted out in an attempt to manually reverse its polarity, I decided to bring the servo home and open it up to learn a little bit about the inner workings of this device. What I learned is that the wires from the servo hook up directly to a printed circuit board (PCB) inside and from there, it goes to a direct current (DC) motor which is limited in rotation due to the gears inside. It was therefore evident to me that the reason the current stops at a PCB first is to allow the Arduino to upload code, outputting a Pulse Width Modulated signal (PWM) of variable widths, into the servo and give it instructions on where and how fast to move by using a rotary variable resistor (potentiometer) — which tells the PCB how many degrees from zero the output shaft has rotated. I managed to disconnect the motor from the PCB in the servo and it still worked, teaching me that the PCB must have been the only electrical component effected by my short. So basically, I learned that a servo is just a overly complicated DC motor.
I can rotate the servo using an Arduino Uno and the code that uploads into it. There are three sockets in the servo that attach to the Arduino. There is power, ground, and signal. The signal aspect of the servo is what allows the Arduino code to tell the DC motor inside to turn in either direction by either rotating in the positive or negative degrees, since the servo is unable change directions by alternating the flow of the current (by opening it, I learned this is because it is hooked up to the PCB rather than directly to the motor). My trigger for the rest of the motors can do exactly what the servo cannot. Since the wires are attached directly to the motors, by creating a trigger that alternated the flow of the current, I can shift the direction of the motor — which converts the electrical energy into mechanical energy.
Here is a video of me talking about my overall project and demonstrating it at its fully functional form:
Here is a link to the youtube page in the event that this video does not work: http://youtu.be/MjqysDatVJk
This is my initial code that only controls the servo of the thumb by using an Arduino: https://gist.github.com/RCTank/7dd0e00781c5e84bde12
Here is the Bill of Materials (BOM) list for my prosthetic hand within BlueStamp (note that this list can change later on — higher up — on this website): https://docs.google.com/spreadsheets/d/1OFBBSrXLsQUtT583zTGsqwGYliZUhkTHyp3Yrvd3dYg/edit?usp=sharing
Here are the electrical schematics for the initial phase of my project within BlueStamp, where five DC motors are powered by an electrical trigger and one servo is powered by an Arduino Uno:
Prosthetic Hand – Second Milestone
My second milestone proved to be very challenging yet productive in the overall scheme of my project. I have accomplished the majority of my mechanical work in the weeks leading up to this milestone. I threaded the tendons (fishing wire) through the finger structure, placed the motors into their holsters, created an electrical trigger for the motors, and designed the schematics for said trigger. While these steps might not seem too challenging, and I did not anticipate them to be when I began, they certainly require a lot of patience and determination.
My fingers use a pulley system in which the fishing wire wraps around the spool, which is around the motor axle, and goes down and around grooved ball bearings and into the different sides of the finger. The tendon wraps around two of these pulley systems and then reconnect at the finger tip. A spring is used to increase slack and relieve the tension on the wire as it goes through the tensioners. The fingers are set up in this way because the motor rotates perpendicular to the push and pull of the tendons. Therefore, the spool allows the wire to be fed into a pulley system that moves parallel with this process.
The electrical trigger I designed for my fingers is another huge part of my project within the realm of BlueStamp. While I will be using an Arduino to control the hand down the road, I built this trigger for both the learning experience as well as showing that my fingers can move at its most basic form. I designed two triggers in this process. The first one hooks up voltage to one switch and ground to the to the other and then connected both switches to both sides of the motor, allowing me to turn the motor in either direction by turning both switches one way or the other. Then, I decided that it would be more efficient if I found a way to only need to hit one switch to turn the motor one way and one to turn it the other. Therefore, I used two double pole, single throw switches (DPST), which means that the circuit can be completed through the switch at two poles but they both attach simultaneously. They allow the current to flow through one of the the poles, into the motor and out the other side where it can flow back through the other pole of the same switch. Then, to control the other switch, the poles of the two respective switches are attached to the opposite pole to allow for a reverse of the previous current flow, changing the direction of the motor. Then, I attached the motors in parallel to each other, the positive pole to all the positives and the negative pole to all the negatives for each motor, to allow all the motors to use the 6 volts from the battery source.
In the process, I ran into many problems with my hand structure and a few problems with my trigger as well. The tendons kept unwrapping from the spool and the overall construction was a rather long and, at times, tedious process. At one point during the process of making an efficient and functional electrical trigger, the two ends of both of my switches switch were not isolated; rather, they made an electrical connection. That is significant because the two ends of a switch should only have a connection when the bridge is manually closed (by pressing the button). Therefore, by not isolating the two ends, I was allowing current flow directly into the battery. This shorted out my circuit and burned the battery. Also, for the battery, I did not have a battery case that allowed for 4 AA batteries and so I used two 3 AA battery cases and attached the two in series with 3 batteries in one and 1 in the other.
Here is a video of me discussing my experience with electrical circuitry and the way my hand works to this point:
Here is a link to the youtube page in the event that this video does not work: http://youtu.be/dn2QOtETFqg
Prosthetic Hand – First Milestone
For my first milestone, I have assembled the major components of a prosthetic hand without attachment or current functionality. This milestone, however is one of great importance to my project. Aside from completing a ton of hard mechanical work and working through a multitude of obstacles, reaching this milestone allows me to observe the individual parts and their components. This will prove to be critical, as after I have put the hand together per following Joel’s instruction, I will need to manipulate the 3D components and lock some of them in place as well as allow them to move slightly differently. This is because ultimately, the goal of my project, within my limited time at BlueStamp, is to create the structure of a hand that will eventually be able to efficiently write with a pen or pencil.
My prosthetic hand parts feature four fingers that consist of three joints each and then one finger (the thumb) with two joints. All of the parts are 3D printed and put together via mostly screws, ball bearings, and dowels. The thumb has a servo in it to allow for side rotation across the base of the hand. There is the main structure, featuring the palm and back of the hand with room in the middle to place the motors which will ultimately be the direct source of control. The ball bearings, with dowels in them, serve as joints in all of the fingers.
I ran into many difficulties in my first real mechanical engineering experience. Working with 3D printing can be frustrating when extreme precision is necessary because printing even the smallest part, if it require high resolution, can take twice as long. Also, many of the 3D printed parts used had issues. The fit was often too tight and the design was slightly altered in an attempt to turn a model into reality due to the lack of incredible precision when working with a 3D printer. The ball bearings more than anything else required much attention. Fitting the 3mm dowels through even smaller holes required the use of many power tools, a hammer, and many hours.
Here is a video of me discussing my first mechanical engineering experience and the various pieces of my prosthetic hand:
Here is a link to the youtube page in the event that this video does not work: http://youtu.be/xvUFjwIGn0k
Second “Starter” Project -Gram Piano
For my second “starter” project, I built the Gram Piano. While waiting for some parts to arrive for my main project, I did not want to waste any time and so I decided to build and learn about another project. This mini piano outputs different frequencies as it can switch between three octaves using a potentiometer, which is a variable resistor. The printed circuit board (PCB) uses pulse width modulation (PWM), a type of digital signal, to determine which of the three octaves will be outputted to the speaker. The sounds will consist of the three octaves alone because the signal being received is digital as oppose to analog. While analog uses sine waves, allowing for a more varying frequency, digital signals do not. The pre-programmed notes are outputted from the ATMega328P AVR Microcontroller and the stored up electrons are released in a current from the capacitors, which have electric fields between two conductors and can act as batteries, to the many resistors all over the PCB, which limit this current. There are two light emitting diodes (LED’s), which allow current to only flow in one direction, on the PCB. One of the LED’s signals that power is being put into the system by two AA 1.5 V batteries, which have voltaic cells and acids inside them that produce a current flow from the anode to the cathode, while the other LED gives the status of the PCB. If the button is pressed, therefore playing the pre-programmed song, the status LED will light up until the song has ended or the button has been pressed again. This mini piano comes equipped with both keys and key sharps. All of the keys on the piano use capacitive sensing. It takes human body capacitance, the electrical energy stored in the human body – which is capable of acting as a conductor, and it inputs this electrical charge. The capacitive sensors pick up this human dielectric, an insulator that can be polarized by an applied electric field. One side of the insulator in the PCB is coated with conductive material. When the human finger, a conductor, touches the uncoated surface, a capacitor is formed by the two electrically isolated conductors that connected and energy is released into a current that goes through a resistor and into its proper place on the ATMega328 microcontroller, which then knows the button that was pressed. It uses this information, as well as the octave generated by the switch, to output the proper note to the speaker. To make your own piano, you can visit this website:
Here is a video of me displaying my Gram Piano and explaining how it works:
Here is a link to the youtube page in the event that this video does not work: http://youtu.be/_rmIWx2unTI
Starter Project – Digital Watch
Hi, my name is Scott. For my starter project, I made a BigTime digital watch. The watch uses an ATMega328 microcontroller as the main source of control on the Printed Circuit Board (PCB). The clock source uses a 32 kilohertz (kHz) crystal to generate the frequency of a 16-bit counter with a pre-programmed code. The crystal has a set natural frequency and when the voltage inputs to it, the crystal produces an oscillated wave which the ATMega micro controller can pick up and use as a reference to produce the correct time. The watch has a 4-digit 7-segment LED display, which is triggered by pressing the button on the side. A CR2032 coin cell powers the watch. Two 0.1 Microfarad (μF) capacitors are used to store energy electrostatically in an electric field on the circuit. A 10k ohm resistor is used to implement electrical resistance, thereby limiting the current flow, to the LED display. This is because Light Emitting Diodes do not require much energy to run, and too much current could result in burning the diode. The button on the PCB inputs to the ATMega328 and, subsequently, to the 32-kilohertz crystal, which – after going through capacitors and a resistor – outputs to the LED display.
After soldering all of the pieces onto the PCB, the acrylic pieces are screwed around it and the strap of the watch is inserted through slits on either end. Clicking the button will light up the LED display and show the time. To change the time, press and hold down on the button until the time is incremented to the correct positions. To make your own watch, you can visit this website:
Here is a video of me displaying my watch and explaining the way it works:
Here is a link to the youtube page in the event that this video does not work: http://youtu.be/xc9EX_h8zuM
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.