Day Three: Flipping Out

Note: This is a series of articles in which we document our attempt to build an autonomous drone for the Sparkfun AVC.  The previous post is here.

Any project in which a lot of learning takes place will inevitably experience setbacks.  But those kinds of projects are where the real fun happens, so days like this are a great experience for the aspiring engineers on the team.  If failures can teach you more than successes, then we surely learned a lot during day three.  After all the highs of day two, day three was packed with... challenges.

We experienced all kinds of problems from the small to the large, from 3D printer filament tangles to a major crash that has put our main copter out of commission.  Be sure to check out the video below, but I think what this means is that the easy part is over and now we're on to the real engineering portion of this project!

Ball Drop Brainstorming

We started the day by brainstorming ideas for tennis ball dropping.  The simplest thing that we thought might work was a passive drop where we put the ball in a container and attempt to tip or flip the copter to cause it to drop.  For testing this "passive" drop, we chose a tall cup to ensure the ball misses the propellers on the way out.  Unfortunately, we couldn't tip the copter enough to cause the ball to fall out.  Flipping the copter didn't do any better either since the copter accelerates through the whole flip and the ball stays pressed to the bottom of the cup.

On the bright side, we did get some practice at acrobatic flying, so that was fun.  We tried both manual and autonomous flips, which gave us the opportunity to learn how to trigger an autonomous flip command from our transmitter.

The other idea we pursued was an active drop using a servo motor to release the ball.  We modeled the parts in Creo for printing on the 3D printer and we created a quick Arduino-controlled test circuit to test the mechanism.  Thanks to filament tangles and other challenges, this part of the project got a little bogged down today.  The final parts didn't finish printing until about 2 AM, so we'll have to test the active drop tomorrow.

A Few Wins and a Big Loss

In a day filled with nagging little problems, we did manage to get a few other things accomplished.  Sondra and Matt did some more research on getting the autopilot to talk to the vision system.  Alex successfully re-flashed the Jetson board with the latest version of the OS.  The re-flashing process was giving us problems, so it was nice to finally get that to work.

The day's largest setback occurred during a nighttime test flight of yet another passive drop design.  The copter was handling a little strangely but we decided to go forward with the test anyway.  We lost control of the copter during a flip and it crashed from a height of about 30 feet straight into concrete.  The DJI air frame is tough, but it couldn't withstand that impact and we broke one of the motor arms and both the upper and lower boards.

Fortunately, we had initially ordered a F450 quadcopter for this project.  When we decided to try onboard vision processing with the Jetson board, the extra weight led to the switch to the larger F550 air frame.  Alex and Matt were able to quickly transfer all the components to the smaller quadcopter and we managed to get it flying before we called it a day.

I guess the good news is that we'll be able to use the quadcopter to continue prototyping our active ball drop mechanism while we wait for replacements for our damaged hexcopter parts.

Next: Day Four