Envidrawer 2 - Materials and casing assembly

2 Nov 2020

Previous blogs	Description
#1 - Introduction, the plan and materials preparation	In this blog post we describe the project's main concept and some initial high-level design of it.

Next blogs	Description
#3 - Modelling, cutting, planting!	The title says it all: this part describes some modelling we did before cutting some holes in the drawer and finally planted some vegetables!
#4 - Plants, harvests, and fertilisers	First harvest, problems with plants and used fertilisers. All that went off-script for our plants in the artificial environment.
#5 - Piping and pumping - water and liquid fertiliser delivery system	Design and development of water supply system.
#6 - Mix of fixes	Final touches to water supply system and small redesigns/fixes.
#7 - Ride the lightning - Wiring diagram, pinout and components discussion	Diagram of the circuit, pinout for most components, wire choices and their connections
#8 - Pulling the strings	LED and Fan control circuit, overview of BJTs and MOSFETs with a handful of useful general information
#9 - 3D printing	Detailed description of 3D printed components, their presentation and some tips
#10 - Software, architecture and the benefits of good preparation	Big explanation of the software and its architecture
#11 - Summary	Our final post before the end of the challenge!

Summary

Choosing the materials

This is the second blog post on our Envidrawer project, focusing mainly on the design of the the drawer itself, or more precisely - its casing. If you are not familiar with our project, please do look at the previous blog post where it is summarised.

We decided to use wood as the main material for the drawer as it is one of the lightest compared to its alternatives (metal/plastic). Additionally it is the easiest to get in larger sizes and is eco-friendly . A tip for anyone who is considering building something out of wood - buy preprocessed wood. We initially wanted to buy raw, unprocessed planks and build it out of that, but the process is simply not worth the time if you don't have the required machinery (such as a planer). So we settled on using 3 types of wood - some common pine planks, an MDF board for the top of our drawer and a plywood board for the bottom of our drawer.

Here is a picture of it:

Cutting the wood

We then varnished the wood and cut it into smaller pieces to get as close to our desired dimensions as possible.

Dimensions we aimed to get:

Outside casing: 200cm x 90cm x 19cm (length x width x thickness)

Inside casing (The drawer): 180cm x 87cm x 16cm

This is assuming the wood's thickness is around 2.5cm (that is why the width of the drawer is 3cm narrower, and the height 3cm shorter.

Because the material choice was limited, we decided to decrease the length and height slightly, so the outside dimensions we settled on are: 190cm x 60cm x 17cm. And the inside dimensions: 175cm x 57cm x 15cm.

There is a 2 cm gap in height to compensate the size of the wheels.

The exact wood elements we bought:

3x 200cm x 14cm x 1.9cm - processed pine planks

1x 200cm x 12cm x 1.9cm - processed pine plank

2x 120cm x 60cm x 0.9cm - plywood boards

2x 120cm x 60cm x 0.6cm - MDF boards

Here are the dimensions of all the elements after being cut and short description where they are used:

1x MDF board 70cm x 60cm x 0.6cm - to achieve a total length of 190cm (Outside casing)
1x Pine plank 190cm x 14cm x 1.9cm - back wall of the outside casing
1x Pine plank 56cm x 14cm x 1.9cm - left wall of the outside casing (total length 57.9cm including the back wall thickness)
1x Pine plank 38cm x 14cm x 1.9cm + 1x Pine plan 18cm x 14cm x 1.9cm - right wall of the outside casing (total length 57.9cm including the back wall thickness)
1x Plywood board 55cm x 57cm x 0.9cm and 1x Plywood board 120cm x 57cm x 0.9cm - to achieve a total length of 175cm and width of approx. 57cm to compensate for the wall thickness of the outside casing (which is around 1.9cm)
1x Pine plank 175cm x 12cm x1.9cm - back wall of the drawer (inside casing)
1x Pine plank 175cm x 14cm x 1.9cm - front wall of the drawer
2x Pine plank 53cm x 14cm x 1.9cm - side walls of the drawer (total length of 56.8cm)

Final (expected) dimensions:
Outside casing: 190cm x 60cm x 14.6cm (where the height inside of the casing is 14cm)

Inside casing (The drawer): 175cm x 57cm x 14.9cm (where the height inside of the casing is 14cm to the highest walls)

Since the inside casing is higher than the outside, we aim to elevate the outside using 3D printed legs screwed to the bottom of the casing, to achieve the final height (inside of the casing) of 17cm.

This may be increased or decreased depending on the size of the wheels moving the drawer.

Assembling the drawer

With these elements prepared we begun the assembly, here is what we aimed to get: (Modelled and rendered in Fusion 360, by us )

We connected the outside and the inside frame together using 2 right angle connectors on each corner held in place by 4 16mm screws for each connector. We then secured them with a single 50mm screw at each corner.

The frames were connected to the top and bottom using 14 50mm screws spread out evenly across the perimeter of the boards and secured at weak points (board connections, corners) using 25mm screws.

Here is a corner of the inside casing (the drawer). A 50mm screw is visible linking the outside frame (on the left) and two 25mm screws securing the corner of the bottom board to the frame (on the right).

And here is the final outcome:

Summary

There are still some improvements to be made, e.g. adding a support for the top part of the drawer to keep it in a single plane (it slightly bends near the not secured end, as you can see in the picture above ^^), but it already closely resembles our 3D design.

With the casing mostly done, next on the TODO list is ensuring that the bottom part of the drawer is watertight so the plants can grow in peace .