The cycle of increased battery capacity and payload
On October 5th, the class heard a lecture from Thomas, a professor at Old Dominion University and an advisor to the project. In this presentation, we came to understand some of the basic physics and electrical engineering concepts that are key to the success our work. For instance, we discussed payload integration–a payload being anything that the UAV has to carry. Thomas explained that when any payload is added to a UAV, the drone both alters its center of gravity and gets caught in cycle of ever-increasing weight and battery size. Our team found this to be an important consideration, particularly because we’ve discussed moving on to larger power source. We’ve illustrated the cycle to the right.
The most important concept we explored during the class, however, was that of pulse width modulation (PWM) in relation to electronic speed controllers (ESCs). While that sounds complex, trust me Mom it’s not that bad. So, the best analogy to illustrate PWM is by considering touching your finger to a hot pan (not literally please). The pan has a consistent heat, but if we touch our finger to it for only a split second we will not feel it. However, if we allow ourselves to touch or “read” the heat a bit longer we will begin feeling it. Like how our finger can only be on or off the pan, the voltage of the pulse can either be absolute minimum (0v) or absolute maximum (let’s call it 5v). However, our ability to read the pulse at different durations is what allows us to reach outputs between 0v and 5v. This “reading” duration occurs between 1 millisecond and 2 milliseconds with 1 being zero output and 2 being maximum output (2ms is the max because at this duration you’re reading the entire pulse). So, let’s say we wanted to achieve an output of 2.5v (half of the max output). We would do this by reading the pulse for exactly 1.5ms (half the duration of the pulse). Ok, but where does the ESC fit into this function? An ESC is what actually controls the PWM for an electric motor like the one we’re using on our UAV.
This GIF shows the motor spinning at a power we set in Arduino, after speaking with the ESC
The physical setup of our experiment
After the presentation, we engaged a mini-project geared at getting us accustomed with ESCs, motors, and controlling throttle output with coding. The physical setup look something like the figure on the left. We had a propeller arm attached to a moving arm on a hinge. When the propeller was on, it would send the arm downwards onto a digital scale that would then read the force in grams. Using code in Arduino, we told the ESC to read the PWM for different durations of time. The longer we told the ESC to read, the more force the propeller would cause. This activity illustrates how we can use arduino coding to change the thrust of the propeller.
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