Hack the Hollow's Wolverine Grow Cube for the ISS

We are West Hollow middle school from Long Island, NY. We are aspiring engineers that meet once a week in a club called Hack the Hollow in which we design, code, and build a number of maker projects. You can check out all the projects we work on HERE. Our main focus has been to study the future of food and environmental robotics. We have assembled and maintained an automated vertical hydroponics farm in the back of our science lab with our teacher Mr. Regini. We have also participated in the GBE program for the last two years. We know this challenge called for high school students, but we were too excited to wait two more years to introduce you to the Wolverine, named after our school mascot. This is kind of what we do!

In this project, you will find a lot of the things we love to use including Arduino, Raspberry Pi, and all the electronic goodies that go with them. We also enjoyed using Fusion 360 as a step up from TinkerCad to design the cube. This project was a perfect opportunity to cut our teeth on some new maker platforms. We were broken up into design teams that each had to focus on one aspect of the Grow Cube. We broke it down into the frame, lid and baseplate, lighting, grow walls, water, fans, and environmental sensors. We have made links in our supplies list to all of the materials we are using if you need help visualizing the parts that are discussed in the steps that follow. We hope you enjoy!

Frame:

• 1" 80/20 aluminum extrusions
• Tee nuts
• Support brackets
• Hinges
• T-channel compatible glider joints
• T-channel compatible tube and wire guides
• Magnets to hold doors closed
• 3 x magnetic reed switches

Grow Walls:

• Farm Tech low profile NFT channels
• NFT channel covers
• Corrugated plastic sheets
• Magnets to hold removable channels in place

Lid:

• Corrugated plastic sheet
• 3D printed LED grow light fixture (Fusion 360)
• Plastic standoffs and hardware for electronics

Lighting:

• Addressable neopixel strips from Adafruit (60LED/m)
• Neopixel connectors
• Neopixel clips
• 330uF, 35V decoupling capacitor
• 1K ohm resistor
• Silvered HVAC aluminum foil tape
• Buck converter

Water: (Our favorite feature):

• 2 x Nema 17 Stepper motors
• Adafruit Stepper Shield for Arduino
• 3D printed linear actuator syringe pump (Fusion 360)
• 2 x 100-300mL syringes
• Tubing with Luer lock connections and tee/elbow joints
• 2 x 300mm x 8mm T8 lead screws and nuts
• 2 x flew coupler
• 2 x pillow bearing blocks
• 4 x 300mm x 8mm linear motion rod shaft guides
• 4 x 8mm LM8UU linear bearings
• 4 x DF Robot capacitive resistance moisture sensors to monitor soil and control syringe pumps

Air Circulation:

• 2 x 5" 12V fans
• 5" fan filter covers
• 2 x TIP120 Darlington transistors and heat sinks
• 12V power supply
• Panel mount barrel jack connection adapter
• 2 x 1K ohm resistors
• 2 x flyback diodes
• 2 x 330uF, 35V electrolytic decoupling capacitors
• DHT22 temperature and humidity sensor w/ 4.7K ohm resistor

Electronics:

• Raspberry Pi 3B+ w/ Motor HAT
• 8GB SD card
• Arduino Mega
• Adafruit perma-proto breadboard
• 2 x 20x4 i2C LCDs
• 22AWG stranded connection wires
• Dupont connector kit
• Adafruit SGP30 air quality sensor w/ eCO2

Tools:

• Soldering iron
• Solder kit
• Helping hands
• Crimping and stripping tools for wires
• Screwdrivers
• Coffee (for Mr. Regini)

The frame is going to be constructed using light weight 1" 80/20 t channel aluminum extrusions. It will be held together with aluminum elbow joints and t nuts. In addition to keeping weight down, the channels will act as guide paths for our water lines and wiring.

The cube will rest on a set of rails equipped with gliding joints that will allow the cube to be extracted out from a wall to expose not only its front face, but both of its sides as well. The inspiration for this came from one of our students thinking about the spice rack in his kitchen cabinets at home.

Using simple hinges, the front and sides will have doors that can swing open when the cube is pulled out on its rails. They are held in place by magnets when closed. All 6 panels of this cube are removable as all of the faces are held in place by magnets as well. The purpose of this design choice was to grant easy access to all surfaces for seeding, plant maintenance, data collection, harvest, and cleaning/repairs.

You can see our design for the panels in the next step.

The first element we thought about was the materials to use for the walls themselves. We knew they needed to be light weight, but strong enough to support the plants. White corrugated plastic was chosen over clear acrylic even though we loved the pictures of V.E.G.G.I.E where we could see the plants inside. The reason for this decision was because most of the view would be obstructed by the plant channels, and we wanted to reflect back as much of the light from our LEDs as possible. This logic came from inspecting the unit we were sent as part of our GBE participation. As stated in the previous step, these plates are held to the aluminum frame with magnets so they can be easily removed .

Attached to these plates are three channels of low profile NFT growing rails that we use in our hydroponics lab. We like this choice because they are constructed of thin PVC with covers that easily slide off for implanting the growing pillows. All growing media will be contained within specially designed pillows that we saw are already being used on the ISS when we read THIS ARTICLE. All paneling between the rails will be coated in silvered HVAC insulation tape to promote the reflectivity of the grow lights.

Our openings are 1 3/4" and spaced apart by 6 inches on center. This allows for 9 planting sites on each of the cube's four panels yielding a total of 36 plants. We tried to keep this spacing as consistent with what we had red about Outredgeous lettuces. The channels are milled with slots to accept our moisture sensors that will be monitoring soil humidity and calling for water from the syringe pumps. Hydration will be distributed to each individual plant pillow through a medical tubing watering manifold attached to these pumps. This syringe-based watering method is something we researched as a best practice for both precision watering as well as overcoming the challenges of a zero/micro-gravity environment. Tubing will enter the base of the plant pillow to promote root growth toward the outside of the cube. We will rely on capillarity to help the water diffuse throughout the growing medium.

Finally, we wanted to find a way to make use of the base plate. We created a small lip on the bottom face the would accept a grow mat to grow micro greens. Micro greens are known to have nearly 40 times more vital nutrients than their mature counterparts. These could prove very beneficial to the diet of the astronauts. This is one article our students found about the nutritional value of micro greens.

We referenced our linear actuator syringe pumps in the previous step. This is by far our favorite part of this build. NEMA 17 stepper motors are going to drive linear actuators that will depress the plunger of two 100cc-300cc syringes on the lid of the grow cube. We designed the motor housings, plunger driver, and guide rail rig using Fusion 360 after checking out some great open source projects on Hackaday. We followed this tutorial on Adafruit's amazing website to learn how to drive the motors.

We wanted to find a way to free up the astronauts from the task of watering. The steppers are activated when the plants within the system call for their own water. 4 capacitive moisture sensors are plugged into the plant pillows in various locations throughout the grow cube. Every planting site in the system has a slot to accept these sensors milled into their grow channels. This allows for the placement of these sensors to be chosen and periodically changed by the astronauts. In addition to maximizing the efficiency by which water is distributed within the system, it will allow for the visualization of how each plant is consuming its water. Moisture thresholds can be set by the astronauts so that watering can be automated according to their needs. The syringes are attached to the main watering manifold with Luer lock connections for easy refilling. The grow panels themselves make use of a similar connection protocol to the watering manifold so they can easily be removed from the cube.

The data collected by the sensors can be read locally on a 20x4 LCD screen attached to the lid or remotely where it is collected, displayed, and graphed by the system's integration with either Cayenne or Adafruit IO IoT platforms. The Arduino sends its data to the onboard Raspberry Pi using a USB cable which then makes its way to the internet using the Pi's WiFi card. Alerts can be set on these platforms to notify the astronauts when any of our system variables have exited their preset threshold values.

The lid of our grow cube acts as the brains of the entire operation as well as provides the housings for critical growing elements. Extending downward from the underside of the lid is a 3D printed LED housing that provides light for each of the grow wall plates as well as top lighting the micro greens mat on the bottom. This was again designed in Fusion 360 and printed on our MakerBot. Each light bay holds 3 LED strips that are shielded by a concave support. This support is silvered with HVAC insulation tape to maximize its reflectivity. The wiring travels up a central hollow column to access power and data on the top of the lid. The size of this housing was chosen to have a footprint that would allow the plants growing around it to achieve a maximum height of 8 inches. This number was found to be an average height of mature Outredgeous lettuces that we grow in our vertical hydroponic gardens in our lab. They can reach as large as 12 inches tall, but we figured astronauts would be grazing on these as they grow making this a cut-and-come-again grow cube.

The neopixels we are using are individually addressable which means we can control the color spectrum that they emit. This can be used to modify the spectra of light the plants are receiving during different stages of their growth or from species to species. The shields were meant to allow for different lighting conditions on each of the walls if necessary. We understand that this is not a perfect setup and that the lights we are using are not technically grow lights, but we felt is was a nice proof of concept.

The top of the lid houses two 5 inch 12V cooling fans usually used to control the temperature of computer towers. We designed it so that one pushes air into the system while the other acts as air extraction. They are both covered with a fine mesh screen to ensure that no debris is pulled out and into the astronaut's breathing environment. The fans are shut off when any of the magnetic reed switches attached to the doors are open to prevent unintentional air contamination. The speed of the fans is controlled through PWM using the Motor HAT on the Raspberry pi. Fans can be conditionally sped up or slowed down based on either temperature or humidity values fed to the Pi by the embedded DHT22 sensor within the cube. These readings can again be viewed locally on an LCD or remotely on the same IoT dashboard as the moisture sensors.

In thinking about photosynthesis, we also wanted to account for the CO2 levels and overall air quality in the grow cube. To this end, we included a SGP30 sensor to monitor for eCO2 as well as total VOCs. These too are sent to the LCDs and IoT dashboard for visualization.

You will also see that our pair of syringe pumps are mounted along the side of the lid. Their tubing is directed down the vertical channels of the aluminum extrusion support frame.

We designed Wolverine using the knowledge we have acquired from our time growing food together. We have been automating our gardens for several years and this was such an exciting opportunity to apply this to a unique engineering task. We understand our design has humble beginnings, but we are looking forward to growing along with it.

One aspect of the build we could not complete before the deadline was image capturing. One of our students has been experimenting with the Raspberry Pi camera and OpenCV to see if we can automate the detection of plant health by way of machine learning. We at the very least wanted to be able to have a way to see the plants without having to open the doors. The thought was to include a pan-tilt mechanism that could rotate around the underside of the top panel to capture images of each grow wall and then print them to the Adafruit IO dashboard for visualizing. This could make for some really cool time-lapses of the growing crops as well. We suppose that's just part of the engineering design process. There will always be work to be done and improvements to be made. Thank you so much for the opportunity to participate!