When understanding the electrical component of the opening and closing mechanism, it is important to understand the entire flow of the system that is being worked on. There are multiple components to consider at the current point: power supply, servos, microcontroller and the user interface (UI).
The servos have already been installed and electrically are fairly easy to understand. They have 3 wires that contain positive (Red/Orange), negative (Black/Brown), and signal(White). The 9 gram servos that I am using are powered by 5 volts therefore I must be able to supply this power to all 6 servos. What I ended up doing to simplify the process was by creating a power board that combined all the the positive and all of the negative leads from my servos. Therefore, I can just supply a single 5 volt supply to the 6 servos. I will then have to add signals to all the my servos and in theory, half of them will be using a certain set of code while the other half will be using a ‘mirror’ of that code.
Microcontroller + Button + Lights
For my microcontroller, I wanted to use an Arduino compatible controller since I’m already familiar with their IDE as well as their wiring. I had some Arduino Micros laying around so I decided to use them. The micros must be supplied with a power supply ranging from 5V-12V through the VIN. This will be supplied by my main battery which will be explained in a later section of this entry.
I had decided to have 2 different pwm signals (the main and the mirror version of the code) that will go to their respective servos on the gauntlet. Using pins 9 and 10, I wired up the servos into pairs, 2 for pin 9 an 2 for pin 10. These signal wires will be used later in the programing aspect of the function. These signal wires were wired onto the servos through an adafruit servo shield (explained later in the power section).
The next thing I must consider is how I would be activating the opening/closing mechanism and I decided to use a simple pushbutton. When I press down on the button (high), the mechanism will open, and vice-versa. This button was was first soldered onto a smaller perfboard since I wanted more real estate to work with for my wiring. My plan for the button was based on the basic Arduino project of a button that turns on a light therefore I would need to add a pulldown resistor (10k) to make sure there is no floating variable. I wired this button according to the basic example sketch provided by Arduino and placed the input onto pin 3 on the Pro Mini. I placed this button on an area of the gauntlet where my left thumb can comfortably press it.
Another small detail that I thought would look cool in my opening/closing mechanism would be adding blue LED strips on the inside of the gauntlet. These LED strips are RGB that run off of 12 volt however I only needed the blue and not at full brightness. Therefore, I simply powered it using the battery which will be explained in the power section of this entry. Since I wanted these LEDs to be powered by a power source while still using the Arduino as an electrical switch, I decided that I would need to use a transistor. The only transistor that I had laying around that I knew would work was a 2N3904 (a common NPN bipolar junction transistor). I wired the base to pin 6 of the Pro Mini therefore acting as an electrical switch. I wired the collector to the positive power supply of the battery and the emitter to the positive lead of the LED strips. Since I had two strips, I wired the strips in parallel with each other. I then wired the negatives of the LED strips to the battery.
When deciding my power supply for the entire project, I decided that the best option would be using a lithion-polymer battery, lipo for short. There are different voltages and capacities for these kinds of batteries and I already had some prior experience since I used to make my own RC planes. The best lipo that I decided to use was a 2 cell (7.2 Volt) 1000 mAh battery since I was considering its power and size. It is compact and small enough not to be too heavy and make an impact while still powering plenty of power for the opening/closing mechanism while being able to power other functions for later on.
The aspects of the project that uses power directly from the battery would be the Arduino Pro Mini VIN and the LED strips. In order to safely and effectively power the 9 gram servos, I have to bring the voltage of the battery down to a constant 5 volts. I did this by buying a voltage converter (buck converter) which takes in any voltage between 4.5-40V and drops it to a constant 5 volts at 2 amps. This output power then went into an Adafruit servo shield since I was in a time crunch. With previous experience, I’ve had trouble using a raw 5 volt supply to a servo without any stuttering and jittering. However, I knew that the power that the servo shield filters for the servos will work flawlessly. Therefore, after converting the battery voltage down to 5V, it then went through the servo shield before ultimately entering the servos. It was at this servo shield that the servo signal lines were wired on from the Arduino PWM outputs.