If you received a UAV (Unmanned Aerial Vehicle) or "drone" as a gift during the holidays, you may be wondering what else to do with it after you've gotten pretty good at flying your aircraft. We have some suggestions! We developed several lessons about UAVs that we've been trying out with middle school-aged students in an after-school program throughout the Fall of 2016. If you're interested in checking out some activities that add a bit of scientific investigation and engineering design to your drone-flying fun, you've come to the right place!
Once you've gotten pretty handy flying your new aircraft, what's next? Drones are in the news almost daily as companies unveil plans to have drones deliver small objects - everything from medicines to pizzas. How can someone decide whether a drone is up to the task of making such deliveries? You would need to know how large of a package or payload the drone could carry... is an extra large, thick-crust pizza just too much weight, or will it be OK as long as it is limited to three toppings? You also need to know how long the drone can stay in the air... can it get to the remote village 20 miles away with medical supplies and return to base on a single battery's charge or not?
Drones and Battery Life
You may already have a sense of about how long you can fly your UAV before the battery loses its charge. Our "UAV Performance Test: Battery Lifetime" activity walks you through testing how long your drone can stay in the air on a single charge. Not all batteries are created equal... how much difference in flight time is there from one battery to the next? In our tests with the batteries and UAVs we've been using, flight times have ranged from under 6 minutes to more than 9 minutes. These differences provide a great "teachable moment" to help your kids understand some simple concepts of statistics and variation in a practical and fun context. Does a given battery last about the same amount of time from one flight to the next, or does it vary a lot from one charge to the next? Does battery lifetime depend a lot on how actively you are flying - draining quickly when you are doing lots of maneuvers and lasting longer when you are mostly just hovering? How does air temperature affect battery duration... will batteries last longer on warmer spring or summer flights than they do now on cool winter days? A few scientific tests with a stopwatch can provide lots of insight into battery duration and how much (or how little!) it varies.
Drones and Payloads
You may already have an approximate sense of how long your aircraft can fly on a single battery charge. But how much weight can it carry? Besides taking photos and videos from novel perspectives (more on that below), a major use of drones is to deliver or retrieve an object. It is pretty obvious that a small drone cannot carry anything very large or heavy... but how large of an item could you carry on your drone? Our "UAV Performance Test: Carry a Payload" activity walks you through a series of tests to find out. You'll need to make some sort of a small "rig" on your aircraft to carry a weight... a fun little engineering design task with rubber bands, pipe cleaners, tape or whatever you choose. Make sure your rig stays clear of the drone's propellers! We used washers... the small metal circles with holes in the center... not the large machine next to the dryer in your laundry room (we don't expect drones to deliver large household appliances any time soon!)... as the weights in our experiments. Attach one washer to your UAV and rate how the added weight affects your aircraft's ability to take off and to hover. Add a second washer and fly again, noting how the increased weight affects your drone's performance. Keep adding washers, one at a time, until your UAV cannot lift off the ground.
Just like batteries, not all washers are the same. If you have a small postage scale, you can get a bit more rigorous by weighing the washers and/or the drone with the washers attached. We used some large washers (with a mass of about 15 grams each) in our initial tests, then worked with some smaller ones (with a mass of slightly less than 10 grams each) in our further experiments. Just as was the case with batteries, this variation illustrates the importance of statistical concepts... not all objects that "are supposed to be" identical are actually that much the same. The thickness and weight of the smaller washers, which were meant to be "the same", varied from about 6 grams to just over 9 grams in the random set of washers we used... so beware of assuming they are "standard" weights. We also found a lot of variation from one drone to another... one drone reached its weight limit with two large washers (about 30 grams), while another was still (barely!) able to take off with 6 of the smaller washers in tow... carrying a payload of nearly 60 grams.
You might also notice how the addition of a payload can dramatically affect the flight characteristics of your aircraft. The UAV becomes harder to control as more weight is added... tending to "pull" to one side or slowly spin one direction... or just generally becoming sluggish and hard to control. The design of your carrying rig can influence this a lot... setups that allow the weights to swing around in flight or that cause the weights to be off-center and out-of-balance can severely diminish your ability to control the UAV when airborne.
We also were reminded, as we developed this lesson, how our atmosphere plays a role in the flight characteristics of aircraft. I first flew the UAV model we used at a workshop in North Carolina. At the workshop, we did a few simple tests of the UAV's ability to lift a weight... and I was pleasantly surprised by the size of the payload it could lift. When I returned home to Colorado, I was disappointed to discover that the drone from the workshop was no longer performing as well. It didn't seem to be able to handle the sizes of payloads we had tried in North Carolina. What was going on? Was my drone a dud compared to others at the workshop? Was my memory of the payload size wrong (we hadn't actually weighed our payloads, so perhaps my estimates were mistaken)? Eventually, I got my brain in gear and realized that the air near sea level in North Carolina is a lot "thicker" (higher density and pressure) than the stuff we breathe here in Boulder at an elevation of more than a mile. The drone propellers just don't have as much "stuff" (thick air) to push against up here, so the aircraft cannot generate as much lift and hence can't carry as large of a payload.
Pick up an Object with the Drone
As we continued to develop ideas for scientific and engineering activities students could do with small drones, we began to realize that some sort of "deliver supplies" or "pick something up and bring it back" activity could be both fun and also a realistic representation of uses for UAVs in the "real world." We wondered: "How hard would it be to pick up or drop off something with our UAVs?" We started testing the "pick something up" part of the puzzle, to see whether it was a do-able challenge. My first attempts involved a physical hook made of lightweight wire dangling from the UAV's landing legs, and a similar wire loop extending above a small plastic block as the object to pick up. After running through three batteries without ever quite successfully hooking the payload... I got soooooo tantalizingly close several times... I realized that this was too hard and would likely be more frustrating than fun for most students. Back to the drawing board. Plan B was to use magnets... both in the drone's "sky hook" and in the payload to be retrieved. I used some of the powerful neodymium or rare earth magnets, figuring that they would snap together quite well if the sky hook got anywhere close to the payload. It turns out that even this version was very challenging to succeed with... but it worked well enough to make a good activity. We've tried "UAV Challenge: Retrieve a Payload" with several groups at this point, and in each case it was harder than people expected... but each group eventually succeeded, and had a lot of fun in the process. Each pickup attempt involves numerous close calls, with lots of emotional investment in the task and plenty of "A little to the left... almost! Oh so close!" and "Hooray we finally got it!"
The Disasterville Challenge
As we continued developing our UAV activities, we thought that it would be good to include a scenario that represented a possible "real world" use of UAVs. The battery test and carry payload test were a bit abstract and generic, using washers as a payload and such. In the Retrieve a Payload activity we drew a red cross on the payload, to vaguely indicate that it could be some sort of medical supplies. We decided that helping a town that had been struck by a disaster would make a good capstone activity for our series of UAV lessons.
We've seen some great videos of real-world uses of drones for making scientific observations... a team from National Geographic flew one into a volcano; Ocean Alliance uses drones to study whales up close.
The UAV model we chose to work with includes a small camera that delivers a video feed from the drone while it is in flight. We decided that an aerial survey of a town that had been damaged in a mock disaster would make a good final challenge. Disasterville was born! We assembled a scale-model town using wooden blocks and Lego Duplos and toy cars and figurines of people... and hid it behind a "mountain range", out of sight of the student pilots. Their task was to survey the town from the air and determine the extent of the damage.
We've run the Disasterville activity a few times now with different groups. It is a lot of fun... and the subject of the third and final post in our "So you have a new drone..." series of blogs.