Major Project: Hexacopter Drone

(The fifth in our student blog series, written by Sam in 11th Grade, is followed by the teacher’s two updates on the project, so please read all the way down! Flight tests were finally successful, as students and teacher alike learned the hard realities of “going back to the drawing board!”)

While we don’t plan on taking him to the sun, Icarus was the name we selected for our massive hexacopter drone. With a 31-inch diameter, and the theoretical ability to lift almost two pounds on top of its own five-pound weight, it is operating at the higher end of recreational drone constraints. Most commercially available drones today feature only four propellers, and a mass of around one pound.

Early sketches of the design, with design priorities listed on the side

When we were designing “Thiccarus” we decided to push the boundaries with the materials we had available. A hexacopter design, as opposed to a more common quadcopter (a standard recreational design with four propellers), gave us more lift power and stability with a trade off on speed and maneuverability. To reduce weight and maintain strength Thiccarus would be constructed with 3D printed body parts and carbon fiber struts connecting them. However, when we were brainstorming, we decided that our drone’s primary function would be cargo delivery (despite my suggestions to make it into a fishing drone or a laser-toting drone with a search and destroy mission).

Pedro, Nolan, and Joshua tear apart
old quadcopter drones from two years
ago–fare thee well!

We came up with our design, then our constraints and requirements. After this, we split into design teams, each headed by ”captains.” After the protective shrouds around each propeller and control center base were decided upon, we set to starting a joint Onshape project. Onshape is our 3D design platform of choice for this project. Each team member was assigned one component of Thiccarus to design, and it came together well in a collaborative fashion. Each member of the design team is able to see in real time how their part will integrate with the other parts, which is incredibly helpful.

The eight students work concurrently on the drone CAD model,
with each one instantly able to see how their component fits into
the broader scope

The hexacopter design emerges!

The largest and most difficult piece to print: the central electronics
platform; five or six attempts at printing were required

Icarus is currently in the printing stage, and when it is fully constructed, it will be mounted with two cameras feeding to a battery powered LCD screen. Steered by the controller, it will be capable of flying high and low to deliver small payloads.

(Sam’s article was written in early October. After a delay in printing production due to some technical difficulties, the entire drone was finally fully assembled and taken for some early test flights. And now the update—which gets a little technical…)
After many hours of printing and assembly…

Sam, Ben, and Todd carefully attach
the motors and batteries and other
electronic components

The 8th Period engineering class proudly marched their huge drone out to the Providence soccer pitch. Gentle (and safe!) power-ups in the classroom had proved troublesome, with erratic behavior being immediately apparent. The drone was very touchy, and tended to spin around and roll to one side. Cutting the throttle from even six inches of altitude caused the aircraft to fall with a ungraceful “thump”, with small 3D-printed pieces occasionally breaking off.

Alena gave an insightful suggestion that we could take it outside and stretch out a big sheet of fabric to catch the drone as it fell. This would allow us to try to gain more altitude—and more time to evaluate its behavior and get it under manual control. The soft fall into the fabric would certainly keep both drone and students completely safe! As an added bonus, we would look comically like cartoon fire-fighters.

The group heads outside to try an initial flight: safety goggles on!

And look like cartoon fire-fighters we did! The plan worked rather well, except for Ben slipping accidentally in a mud patch on the field in his zeal for saving the drone. With the extra flight altitude and time, we learned that the machine wanted to spin on its vertical axis—absolutely out of control. Where it should have lifted gingerly into the air and hovered obediently, it was a veritable whirling dervish, and the group could not even agree on their recollection of whether it had spun clockwise or counter-clockwise!

It may look like the class is flinging it into the air—we promise
it is actually flying!

In a typical situation like this, the pilot should be able to add in some “yaw” trim. This means that the controller is set to always provide a little bit extra of yaw control, intended to counteract whatever is naturally happening and make everything balance out again. But adding yaw trim in either direction just didn’t change anything, and after one particularly wild spin the drone fell outside of the fabric and broke one of its 3D-printed propeller shrouds.

See that tilt to one side? About three seconds later Thiccarus
successfully escaped our circle of friendship!
Back to the drawing board…

  1. It is possible that the flight controller—the 1-inch small box that houses gyroscopes and inputs and outputs and magnetometers and so on—is just misbehaving or badly calibrated. But after several recalibrations and trying an alternate one that we had in stock, there was no improvement. Check.
  2. Is Thiccarus just way too “thicc”? Maybe. We could have designed more aggressively, and perhaps brought him down to 2 kg even (4.4 lb). But the specs say that each motor should be able to create up to 550 grams of thrust. With six motors in total, that’s 3.3 kg of thrust available (7.3 lb). And it’s definitely getting off the ground, even with the thrust output turned down for safety. So: check.
  3. It is possible that one or more motors are just misbehaving or getting bad signals. Tiny, threadlike wires carry the commands between the different components, and we have run into problems of this nature before. But replacing one bad cable fixed that, and simple individual motor bench tests show snappy, responsive motors that will blow your papers away from across the room.

When all else fails, Google it. Apparently, when your drone experiences untrimmable yaw, it is likely the result of not having set all motors perfectly level. In other words, one or more propellers might not be perfectly flat relative to the ground, but tilted slightly to one side. And yes, this is quite noticeable on poor old Thiccarus once you look for it. Fortunately, it can be easily solved by readjusting the four screws that hold each motor down, and putting a little “shim” on one side to nudge it up to level.

This is actually an interesting application of standard high school trigonometry. If a thrust vector is pointing straight up to sky, well and good. This is what the flight controller is banking on for its power distribution calculations. But if a motor is tipped to one side by even two or three degrees (barely perceptible to the eye), the aircraft will experience a mysterious lateral force equal to the thrust times the sine of the angle. If the motor is generating a healthy 500 grams of thrust (a little over a pound), three degrees of tilt creates 26 grams of sideways thrust (500sin3°). Small but significant—and the flight controller is not accounting for it.

Maddening: yes. Fixable: absolutely. The motors will be checked and adjusted, and Thiccarus will be bandaged up and flown again. It is also very likely that a Mark II design will surface in the second semester, with higher tolerances for motor angles accounted for from the very beginning and a lighter airframe. Less airframe weight means longer flight times, a more responsive drone, and a greater possible payload.

Providence Engineering Academy: carry on!

(Our final update for this story on the 19th of November.  Spoiler alert: it’s a happy ending!)


As promised, the motors were checked and adjusted. Ben and Mr. Meadth stayed after school and carefully placed pieces of card under this or that side of the motors to shim them up, bringing them as close as possible to vertical. Three motors were in need of adjustment, but none of them were out of line by more than about two or three degrees.

The drone was powered up, with high hopes… but the end result was exactly the same. Thiccarus wanted to flip over to the side and rotate faster and faster, and nothing could persuade him otherwise. Forget flying too close to the sun—Thiccarus couldn’t even get off the ground!

And then…

And then

Mr. Meadth had his flash of inspiration, and it all came down to this image:

The source of all problems.

This diagram shows the initial wiring and setup instructions from the flight controller. A certain teacher thought he had carefully followed the diagram; unfortunately, he had set the actual propeller directions all opposite. For example, propeller 1 was supposed to be rotating clockwise, but it had been set up to be counter-clockwise.

What’s the big deal, you ask? Well, while having everything opposite would still be balanced to some degree, the flight controller uses the spinning propellers to control its yaw. Say the craft wants to yaw to the left, it chooses a propeller to spin faster to the right (like propeller 1), and Newton’s Law of Reactions takes over. If it wants to yaw to the right, it might choose a left-spinning propeller to do that (like propeller 2). But since each and every one was backwards, the corrective actions it tried to take were in every case making the situation worse. If it started drifting left, it would end up spinning more left—a classic vicious circle if ever there was one.

A quick click of a checkbox in the computer and that was solved. All propellers: backwards. Oops.

Propellers… spinning the correct way!

You know you’re doing something
right when you’re looking at the bottom
of the drone

This portable outdoor screen receives
video input from two onboard cameras

Today marks another successful series of flights. We currently get about ten minutes of air time with two fully charged batteries. Three students plus teacher have been brave enough to fly around a little bit. No major accidents—perhaps a leg snapping off here or there with a rough landing!

Lessons learned:

  1. Persistence pays off. If this is a thing that can be done, then you can do it. Just get out there and keep troubleshooting until you work it out.
  2. This is a new era of high school education. To collaborate on a CAD model, 3D print it, order the electronics, and create a hovering 2.2 kg monstrosity in the space of three months is just not something a school could have done in-house ten years ago. Truly these are amazing times!
  3. These students are capable. With the right leadership and direction, they know how to think and problem solve and calculate and design. They will go far.
The story ends here, but keep an eye out for Mark II! We just can’t resist. There are already so many things that could be optimized (chiefly, stronger airframe and lighter weight). Lighter weight means more air time, so bring it on! Look out for Son of Thiccarus in the second semester, and until then, stay posted.

Searching for Solutions: Search and Rescue Robot Challenge

(Our latest blog article comes courtesy of Joshua in the 10th Grade.  Thanks, Josh!)

In the event of an emergency, robots may be called upon to enter into areas which have been devastated by natural disaster. The thirteen students from the Foundations of Engineering II class split up into four groups to build such robots, and testing came after eight weeks of work and dedication!

The original CAD model of the obstacle course, constructed
over several weeks by our indefatigable teaching assistants,
seniors Josh and Claire
The testing included nine phases (any of which could be skipped) all while carrying a payload. The teams would go through two gates of different sizes, over a gravel pit, up onto platforms of varying heights of 50 and 100 mm, push a block with the mass of one kilogram, go across a chasm, and make their way up a 45° incline. At the end of the run, the robot would be required to drop off the payload. The driver for each team would first do this routine while watching from nearby, and then once again using only a first-person camera view.
Davis gets his team’s robot up onto the 50 mm platform with
no worries at all
The first robot to test was the “Trapezoidal Tank”. This robot was built by Nolan, Davis, and Alan. They felt ready for the first trial of the course, but decided to skip the 45° incline. Everything ran smoothly until the payload drop at the very end. They realized something was wrong.

The payload mechanism’s motor came unplugged!

Davis, the driver, thought up an idea. The payload was resting on top of the robot. What if he just flipped the whole robot over? Using the tank’s “tail”, he flipped the robot up onto its end and delivered the payload.

Although not able to climb the full 45 degree slope, with a slight
modification the Trapezoidal Tank was make it at 40 degrees
A moment of pure glory! Davis upends the entire robot and performs
the obligatory victory dance!
On the camera-only run, the course was successfully completed again with only one obstacle skipped.

Caleb taking things in his stride, as the long-legged robot effortlessly
clambers over the gravel pit obstacle
Caleb attempts to steer by camera only–
no easy feat! 
Pushing the one-kilogram block away, the package waiting to be
delivered is clearly seen on the right-hand side of the robot
This complex (and squeaky) maneuver involves a series of
high-torque gymnastic activities

Next up was “Daddy Long Legs,” a robot with motorized wheels attached to extended legs. It was built by Caleb, Sydney, and Zach. Caleb, the driver, slowly completed the run, also skipping the very difficult 45° incline. On the camera-only trial, the robot was not able to place the payload in the designated area.

Anaconda brings its bulk to bear on a one-kilogram block of wood
This monster robot leaps 100 mm platforms with
a single bound!

Next was “Anaconda”, built by Sam P., Isaiah, and Pedro. It’s most notable feature? The robot’s tracks could rotate all the way around to point in the opposite direction. Sam P. took the wheel, and on his first run, he only skipped the smaller gate. On the camera-only run, he made it through the same obstacles without any issues.

James steers the Iron Horse through both gates and up onto
the 100 mm platform
Finally, the “Iron Horse” entered. This robot was built by Sam K., James, Joshua, and Kaitlyn. The design was simple yet effective. However, the extra mechanism they had added to their robot at the last minute broke! It was designed to help them get up onto the two platforms. Fortunately, there was enough power available for it to slowly assist with the obstacle it was built for.
Charging over the gravel pit with a huge ground clearance
Shortly after, that extra mechanism fell off and so did the payload. In a lengthy and complicated series of maneuvers, James used the one-kilogram block to push the payload over into the designated area.
End of the road: the Iron Horse capsizes while trying to free its
jammed package (the small yellow catch was supposed to release
and allow the hinged door to fall)
On the camera-only run, the Iron Horse’s payload wouldn’t release. James used the gravel pit to try to get the payload to come loose, but the robot flipped over. He attempted to flip the robot back over, but it tipped over on its side instead. This run was incomplete.

The lesson to be learned for these four groups? Each problem can be solved in many different ways, but some are more effective than others. In every problem you encounter, consider those many solutions and then choose the most effective one.

Providence Students at the MIT Enterprise Forum

Last Wednesday, Mr. Alker and three students (Josh, Wade, and Caleb) spent the evening hearing from top professionals in their respective arenas at the MIT Enterprise Forum of the Central Coast. The topic for the evening was “The Future of Digital Imaging & Camera Technology”. The program featured Nicholas Weissman (Founder & Director, Vacationland Studios), Russ Mead (VP of Engineering, SEEK THERMAL Infrared Imaging), and Dr. Edward Clift (Co-Author, “Digital Futures and the City of Today).
Left to right: Mr. Alker, Josh, Wade, Caleb, and the students’
sponsor, Ms. Horton

The students enjoyed hearing about the topics: a very practical cinematography presentation by Nicholas Weissman, an introduction to the infrared industry by Russ Mead, and a challenging and thoughtful presentation from Dr. Clift about how imagery is shaping modern forms of communication. After the presentation, students mingled with local leading architects and entrepreneurs.

We want to especially thank Kristi Horton of the Education Committee who invited the students to participate and sponsored their attendance. We look forward to continuing our relationship with the MIT Enterprise Forum and the rich and engaging programs they offer.