Background: Every year Fort Worth Academy (FWA) participates in an Egg Drop project for the 5th grade class. The 5th graders attempt to build a shoe box filled with materials or contraptions to protect a raw egg and the entire box is dropped from a height. It's a traditional science experiment. The twist by FWA is that a team of 3rd graders organizes and host the event. The 3rd grade team learns to organize a project, fund-raise and manage the event.
This year the 3rd grade project team wanted to do something a little different. They wanted to use Drones somehow in this years event. They approached me in December 2014 for help with the project. Through several iterations of high level concepts and alternate options the 3rd graders insisted on drones but instead of dropping contraptions the drone would be dropping the eggs and the 5th graders would build contraptions to attempt to catch the eggs.
I don't have a drone and didn't have any experience working with them but I helped the team develop their concept and expectations. The team understood the complexity of the project and that there was no off-the-shelf solution available. They determined that lifting and dropping an egg with a drone would be considered a success. In February 2015 the team of 3rd graders "hired" me as an engineering consultant to deliver a solution to drop eggs from drones.
In need of a drone and pilot willing to work with me I reached out to the North Texas Drone Users Group for help. Nick McCarthy responded with enthusiasm and volunteered his drone and expertise. Together we developed two methods of dropping eggs from drones, met the 3rd Grade Teams deliverable requirements and had a ton of fun!
*Cheesy announcer voice*Here is how you too can drop eggs from drones for fun and science.
Step 1: Safety
We worked closely with the school and the project team to be clear about safety procedures. Neither Nick nor myself would have accepted the job without the following safety understanding and acceptance.
- Nick is the experienced drone pilot. He is the only one that will be piloting the drone and has final say in any safety mater. If he doesn't feel comfortable with any aspect of the event he can delay or cancel the event.
- The drone will fly within all relevant, current FAA regulations. For example, the drone would stay below 400ft and would fly in a responsible manner. (This was also a nonprofit event.)
- The drone would not fly over any person. The drone Nick proposed using has many safety features enabled but we all agreed that an "uncontrolled decent" of the drone for any reason or unintended release of cargo above someones head would not be a good thing.
- No one is allowed to approach the drone while it's powered on unless given direct permission by Nick. This gives Nick the ability to make sure the propellers were off and safe while anyone was nearby.
Additional notification for this Instructable: The instructions given here are for a fun and safe learning event. Please be smart when flying drones. Please be smart if dropping any object from any drone. We were very careful to fly safely and drop safely. Don't load anything hazardous on your drone. Don't fly a loaded drone over anything you don't want to drop the payload on. Don't drop any payload on any un-expecting target. Nobody here is responsible for how you fly or operate your drone. DON'T BE STUPID!
Step 2: Materials
- Eggs: Preferably "Large" eggs to save weight and size. (vs. "Extra Large Eggs". There is a difference)
- Drone: Nick offered his 3DR Iris+ rig. Plenty of spare batteries and published payload weight limit specs.
- Servo Motor: If you can find it use a sale/winch type servo. We couldn't get one in time and used a continuous rotation servo instead.
- Miscellaneous Hardware: Various 4mm and 6mm nuts and bolts, 6mm threaded rod, lock tight, solid core wire, and zip ties.
Tools and Equipment
A decent 3D printer and garage level workshop. Garage level means screw drivers, wrenches, a hot glue gun, a hack saw, digital multimeter, and a soldering iron. If you don't have a 3D printer a good Makerspace is wonderful! Dallas Makerspace has great resources!
Step 3: The Claw
After talking through several ideas we decided to cover the base requirements as soon as possible. With that in mind we came up with a simple servo mechanism that would be quick to build. It would operate similar to a claw mechanism. The plan was to tie it to the drone arm with zip ties or something similar.
Knowing that we were using the Iris+ model drone and after a little wondering through Thingiverse we found glenchung's Iris+ Range Finder Mount model. glenchung's range finder ingeniously snapped onto the drone arm without any hardware or modifications. After a few little modifications in Sketchup we had added a microservo and a catch plate. The printed parts were pretty snug so we never even added screws to the servos. Just a little solid core wire to the servo arm and into the hole in the catch plate. The radio transmitter was programmed to control the open and close positions. The settings were determined by trial and error.
With one Claw printed and installed we arranged for a test flight and proof-of-concept with FWA. It was successful and tons of fun! The test used fake eggs for easy modifications but actual eggs could be used with a short length of electrical tape that made a loop on top of the egg. The tape held just fine for short flights. With a successful test we printed three more Claws. One for each arm.
Claw Files can be found on Thingiverse: http://www.thingiverse.com/thing:855304
(Thanks to glenchung for the source files found here: http://www.thingiverse.com/thing:745817)
Step 4: Exceeding Requirements With the Rotary Dropper
The Claw met out project goals according to the 3rd grade project team with time to spare. What did we do with our spare time? Why, make it bigger and better of course!
One egg per claw and four claws meant we needed four servo motors, four outputs from the receiver and four switches on the transmitter. Nick and I both thought we could do better. More could be done with one continuous motion servo, one output from the receiver and one input from the transmitter. We developed the Rotary Dropper. (The "Revolver Dropper" just didn't seem to fit the school setting)
The concept was to use five or six egg containers mounted on a frame with a rotating bottom. The bottom would have one cut out just big enough to drop an egg. The initial servo position would be halfway between two containers thus not allowing either egg to drop. This required a servo with a range close to 360(deg) but those are hard to find. We settled for a continuous motion servo that Nick would move slowly until an egg fell and then stop. (We learned about Winch/Sail Servo motors after it was too late.)
The frame design called for two separate 3D printed brackets bolted together with space between them for a heavily modified servo arm to spin. The top bracket held the servo motor and paper cups for egg containers. The bottom bracket was mounted to the top bracket with M4 bolts. There were 3, M4 nuts placed between the brackets as spacers. The servo arm was modified from hugokernel's Parametric Servo Arms using Sketchup to be more like a servo plate it a cut out and 3D printed.
The cup and frame contraption was mounted to the underside of the Iris+ using the camera gimbal mounting threads and modifying Firdinand128's 3DR IRIS mount. The bracket from Firdinand was rearranged to accept 3, M6 threaded rods that attached to the top bracket of the revolving dropper.
Files and a Dremel were used liberally to fine tune the 3D printed parts so that everything lined up and spun freely. There was also plenty of Loctite used to keep the hardware from shaking loose.
(Thanks to Firdinand128 for the 3DR IRIS mounting bracket for DYS 3 axis Gimbel: http://www.thingiverse.com/thing:367015 and to hogokernel for the Parametric Servo Arms: http://www.thingiverse.com/thing:28566)
Step 5: Make It More Fun With Beacon Lights and a Big Red Button
To step up the fun even more we came up with "The Big Red Button and Beacon Light". I used an Arduino to monitor the status of a grossly over sized red button. When pressed the button would send a PPM signal to Nick's RC transmitter over a 3mm headphone jack. (PPM is similar to PWM but encodes multiple servo "channels" in one signal". Nick set up his Transmitter to treat the PPM signal as a "Buddy Box" or a "Trainer" signal and to repeat the signal to the Drone. The Arduino PPM signal was calibrated to move the continuous servo motor slowly for just long enough to drop a single egg. Out of fear of an overly eager Egg Dropper I added an Drop Enable switch so that the Big Red Button would only spin the motor once after the enable switch was activated.
I'll upload more pictures and circuiting later.
I've uploaded my Arduino code to this Instructable but check out these great resources for more information:
- About PPM http://www.endurance-rc.com/ppmtut.php
- If you have a Teensy handy this is awesome: https://www.pjrc.com/teensy/td_libs_PulsePosition.html
Step 6: Results!
The event was a success and a tone of fun but there is always room for improvement. Here are some thoughts on how we plan to do better next year:
- Start dropping eggs from a lower height first. We were distracted with how much fun we were having to lower the drone to 5' or 10' above the ground to guarantee a strike.
- Make sure to coordinate specifications. The drop rig was designed around a sample set of eggs. Those happened to be "Large" eggs. That didn't get communicated as well as it should have to the school and they supplied us with the more common "Extra Large" eggs. Out of six attempted egg drops per flight three to four eggs would get stuck in the mechanism and fail to drop.
- We weren't sure that the Big Red Button would work so we kept that as our project. Now that we have research and documentation behind the concept it could be a good teaching opportunity to have a set of students design and build the button themselves.
This was a lot of fun for us and I hope the school enjoyed it as much as Nick and I did!