Subsystem Build & Test
Table of Contents
Meeting Minutes From ReviewDownload
Team Vision for Subsystem Level Build & Test Phase
We focused on the three major subsystems during this phase.
- The Mechanical Subsystem
- The Electrical Subsystem
- The Software Subsystem
A description of each as well as the input/output diagrams for each can be seen below. For the working document including the input/output diagrams click here.
Mechanical SubsystemThe mechanical subsystem consists of the outer casings that enclose the electrical components both on the hand and off the hand. It also consists of the switch activators and the strings that run from them to the fingers. A major function of the mechanical subsystem is the ability for the device to be adjusted to the proper size for each user.
Electrical SubsystemThe main purpose of the electrical subsystem is to supply the hardware required for the software subsystem.The electrical subsystem consists of the printed circuit board that will go on the back of the hand.
Software SubsystemThe software subsystem serves to decipher the input from the user and turn it into meaningful output.
Test Results Summary
Mechanical Switch: Force Testing
- Test S22 23: Switch Activation Force
- The force recorded by the load cell was so small, that this method of testing was not a viable option to test the activation force. However, the activation force on the switch data sheet is listed as 1.47 N. This is the value that has been accepted by the team moving forward.
- Test S24: Switch Removal Force
- This test was performed to record the force required to remove the switch from the board or to break the switch. 11 trials were ran, with 3 of those using switches that had both the electrical and mechanical supports soldered. These switches showed superior strength. The results of the tests are summarized below in a table and graph. There is also an image of the test setup and end result.
- Additional Test: Finger Flexion Force
- An additional test was performed to determine the force of finger flexion. The graph below shows the force exerted by finger flexion. The large dip is where the subject is exerting as much effort as possible, which maxed out at 12 N. The following dips relate to a normal, comfortable finger flexion. This force was about 2 N.
- In this series of testing, we determined the activation force of the switch, force required to break the switch/connection and the force of finger flexion. These results are summarized in the table below. In conclusion, we have determined that these switches are appropriate for this design because the finger flexion force aligns with the actiavtion force, and the maximum finger flexion force is much smaller than the destruction force.
Switch SpacingThe PCB board was designed to fit the smallest 5% female hand. We tried out this spacing to ensure that the switch spacing is mechanically feasible. We found that for smaller hands, the strings will go straight to the fingers, where with larger hands the strings will be slightly angled out to the fingers. This angle can be adjusted by moving the device further back or forward on the hand. We also found that the thumb switch must be placed at a 45 degree angle in order for thumb flexion to activate the switch. After this basic testing, the PCB design was updated. Below are some images of the switch placement.
Base Design and Mock Up
The next thing that we completed this phase was to design and create a base that the PCB board would sit in to help strap to the user's hand. We began by gathering PCB dimensions from Nick, and then sketched a design around that. We ensured that we created holes for the velcro straps to fit through. We were able to 3D Print this design through the Constuct. Upon completion, we were able to cut a protoboard to about the dimensions of the PCB board and attach the switches to it with the appropriate spacing. Carolyn was then able to tie adjustable fisherman knots in order to have some adjustability in the strings. When we put it all together, we realized that the string must be almost perfectly parallel to the switch in order to activate. We shaved down "tracks" in the base in order to align the strings better. Below is a picture of the device to put together.
Electrical System: Switch PCBFollowing the test of the switch placement the PCB layout was adjusted to make sure the thumb switch was at an angle where it could be easily activated while worn on the hand. The switches were also spaced in a way so that they can fit the on a variety of hands, using hand measurements found online. A power button was also added to the design instead of a power switch as it can be more easily enclosed, and a vibe motor was added since it was found the the tactile feedback of the switches might not be felt as easily when pulling on the switches with string. The vib motor found was also much smaller than ones the team had found previously, making it ideal for a compact design. The PCBs have been ordered and are currently being fabricated.
Software System: Flowchart
The flowchart has been simplified and updated to account for a power switch as well as an action switch.
The adjustability of the cords that connect the switches to the fingers is critical to the success of the device for more than one user. Capturing this function remains one of the largest unknowns of the project at this time. During this phase we worked as a team to mitigate this risk.
One idea for making the string tension adjustable came from retractable headphones (see image below). To get a better idea of how this worked, we explored the patent for retractable cord reels for use with flat electric cable (Patent US7108216). This helped us understand the concept better and we learned that the way the cord is wrapped within the device is critical to functionality.
Once we understood the basic idea of how these devices worked, we designed a similar, but simplified part to test the idea. Instead of relying on a “braking” system to hold the cord at the desired tension, we used gear-like teeth to hold the cord in place. The user would lift the top piece, twist to coil or uncoil the cord, and then place the piece back in the locking position. This design was 3D printed and tested for functionality.
It was determined that although this design concept is viable, that it may be too complicated for our application. The design would also need to be made significantly smaller in order to fit five of these adjusters within the device.
This design came about as a plan for securing the strings that would be easier to implement. In this design the string can wrap around the center of the piece on the ring and the string would be secured using a slit and a knot in the string. This may not be as polished of a solution as would be desired in a final product, but for a proof of concept still provides a way to secure and adjust the strings.
Bill of Materials
- Reorganized part subsystems and part numbers
- Added electro-mechanical sub-system
- Renamed RCD to RCS (Resistor - Capacitor - Semiconductor)
- Added power switch
- Added diodes
- Added vibration motor & transistor
- Updated PCB vendors to OSH Park
- Updated order amount for power switch, motor, and switch PCB
Click here for the working document.
Risk and Problem Trackinghere for the working document. here for the working document.
Plans for next phase
Team Plan for Phase III
For the working document click here.
- Nick must solder the parts to the PCB before Jackie and Carolyn can ensure the PCB (with parts attached) fits properly into the 3D printed casing.
- Nicole must finish the adjustability design before any test plans can be completed.
Individual Plans for Phase III