PAPRa Build Guide (Nov 2020 Edition)
How to build the November 2020 version of the Tetra PAPR.
IMPORTANT NOTE
Our most recent analysis has shown that this device has significant CO2 rebreathing issues. Please do not use this product as described below; we’re including these instructions to show progress towards the ultimate PAPR products.
3D Printed Parts
You will need to print, using an FDM printer, PLA resin, at 0.2mm spacing:
| Part | Quantity | STL File Location |
|---|---|---|
The fan box bottom half (holds the fan) | 1 | |
The fan box top half (holds the filter) | 1 | |
The fan box funnel that takes air from the fan into the hose | 1 | |
The fan box grill that holds the filter in place | 1 | |
The battery case to hold the battery and fan control board | 1 | |
The battery plate to protect the fan control board | 1 | |
The face mask | 1 | |
Spacers | 4 |
The files used in this build are v 1.0; later versions will require updates to this documentation. You can download all files together here: https://github.com/tetrabiodistributed/papr-print-files/releases/tag/1.0
There are also stencils for the foam cutting parts.
| Part | Quantity | STL File Location |
|---|---|---|
Filter Gasket Stencil | 1 | |
Box Gasket Stencil | 1 |
Bill Of Materials
You will need to buy these parts (prices fluctuate, so are not included here):
| Count | Description | URL | Number in Package |
|---|---|---|---|
1 | Onyehn DC Motor PWM Speed Controller3V 6V 12V 24V 35V Speed Control Switch Mini LED Dimmer 5A 90W | 2 | |
1 | UTUO Brushless Radial Blower Dual Ball Bearing High Speed 12V DC Centrifugal Fan with XH-2.5 Plug 120mm by 120mm by 32mm 4.72x4.72x1.26 inch | 1 | |
1 | 2Pack Upgraded 3.5Ah M 12 Battery for Milwaukee 12V Battery Lithium XC M 12B Batteries | 2 | |
2 | Baomain Male Spade Quick Splice Crimp Terminals 6.3mm Crimp Connector Non Insulated | 100 | |
1 | Guardian Technologies FLT4010 Genuine High-Performance Allergen Air Purifier Replacement Filter A With Activated Charcoal Layer | https://www.amazon.com/gp/product/B003AKNK4A/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 | 1 |
2 | TOTOT 30 Pack 5.5mm x 2.1mm 3 Pin Female DC Power Jack Panel Mount Screw Nut Kit DC Socket Electrical Plug | 30 | |
1 | Donner 60CM Guitar Pedal Power Cable Cord 10-Pack | 10 | |
8 | binifiMux 150pcs M4 x 0.7mm 304 Stainless Steel Hex Nuts Bright Finish | 150 | |
8 | 50 Pcs M4-0.70 x 20mm Button Head Socket Cap Bolts Screws, 18-8 Stainless Steel, Allen Hex Drive, ISO 7380, by Fullerkreg,Come in a Plastic Case | https://www.amazon.com/M4-0-7X-Available-Stainless-Machine-Fastener/dp/B081JYXLK7/ | 50 |
6" | BNTECHGO 20 Gauge Silicone wire 10 ft red and 10 ft black Flexible 20 AWG Stranded Copper Wire | 120 | |
6" | 20 awg Solid wire kit Electrical wire Cable 7 colors 23ft each spools 20 gauge UL1007 Tinned Copper Hook up wire kit breadboard wire for DIY | https://www.amazon.com/Electrical-colors-spools-UL1007-breadboard/dp/B083DNGSPV/ | 276 |
Heat shrink connector covering (optional) | |||
1 | 2mm Craft Foam | https://www.amazon.com/Foam-Sheet-X18-2mm-White-pack/dp/B004M5QGBQ | 10 |
7 | Frost King EPDM Rubber Self-Stick Weatherseal Tape, D-Section, | https://www.amazon.com/Frost-King-Self-Stick-Weatherseal-D-Section/dp/B00FQ5A5RM | 204 |
6 | Nashua Dryer Vent Installation Tape | 1080 | |
4 | MTP 1" Seat-belt Black Polyester Webbing Strap | 30 | |
4 | 1 Inch Plastic Triglides Slides | 100 | |
2 | CPAP Hoses (possible candidate-- this product is 3 feet, you may want something longer or shorter) | https://www.amazon.com/Gray-Standard-CPAP-Tubing-foot/dp/B073GBQN73 | 200 yards |
(Length depends on head size and wearing preferences) | Bathing Suit Elastic | https://www.amazon.com/Elastic-Shed-Protector-Handmade-Stretch/dp/B088DB6JQ8 |
Here is a picture of all the parts, printed and purchased, for the build:
Recommeded Tools
These tools are recommended. URLs are for tools purchased and used in the building of the prototypes:
| Description | URL |
|---|---|
Iwiss SN-48B Pin Crimping Tool | |
4-3/4 In. Bent Long Nose Pliers | https://www.harborfreight.com/4-34-in-bent-long-nose-pliers-63819.html |
Soldering iron | |
A hex screwdriver for the m4 screws | |
Flush cutter | |
X-acto knife | https://www.amazon.com/Xacto-X3201-N0-Precision-Knife/dp/B00004Z2TQ |
3D Printer (note the size of the print bed for the fan box) | |
A deburring tool | |
#0 Phillips head screwdriver | https://www.homedepot.com/p/Husky-8-in-1-Screwdriver-with-LED-Light-232360016/301959976 |
CPAP hose cleaner (for maintenance) | https://www.amazon.com/Cleaning-DreamStation-Diameter-Stainless-Cleaner/dp/B08HLQV2VK/ |
Building the Battery/Controller Box
We start by building the battery controller box. You will need these components on hand:
Battery Case ("M12 Controller Body")
Battery lid ("M12 Lid")
Crimper
Needle-nose pliers
Soldering iron/solder/soldering tools
2 red jacketed stranded wire ~2-3 inches (7-10 cm) long
2 black jacketed stranded wire ~2-3 inches (7-10 cm) long
Heat Shrink (to protect wire connections)
2 Male Spade Quick Splice Crimp Terminals
Flush Cutters
Wire stripper
Deburring tool
Philips head screwdriver
Build Steps
Prepare the wires
Cut the wires to size.
To do so, you will need to cut them down to their lengths (our build used ~3 inch/10 cm lengths). We prepared all six wires (4 stranded and 2 solid) to be basically the same dimensions: ~3 inches/~10 in length, 0.5 cm insulation stripped from both ends.
Tin the stranded wires.
Follow this guide here: https://www.thespruce.com/tinning-stranded-electrical-wires-1152893
Video describing the amount of wire to be tinned:
Photo showing tinning of the wires:
Crimp a red and black tinned wire each into the spade connectors
How to crimp:
Here’s a photo for bad crimping:
and the video explanation:
Attach remaining red and black tinned wires to the power socket
How to build the power socket with tinned wires:
Attach remaining red and black solid wires to the power socket
How to build the power socket for the fan box with solid wires:
Final prepared wiring looks like:
M12 controller circuitry
Snip a portion of the spade connector
A video describing this step:
Clean the M12 battery holder spade ports
On the inside of the printed M12 box, there are two slots where the spade connector should fit in. These slots may have some extra plastic around them due to print quality issues, so use an x-acto knife to clean those slots:
Insert the spade connectors into the M12 box
These spade connectors should be inserted with red on the left, black on the right. The snipped connector should slide in place and prevent the spade connector from coming back out again.
Tab to hold the spade connector in place:
Wire orientation:
Test the spade connectors are in place:
Install the board into the M12 box
This video captures the entire process:
Essentially, these steps are followed:
Remove the knob and nut from the control board
Install the power plug into the box
Connect the knob and spade power wires to the board (red to plus, black to minus, spades to DC in and power plug to motor control)
Place the board in the box
Screw the nut and motor control knob onto the board from the outside of the box
Check the connection by turning on the power knob and looking for the red LED on the board to light up
Close access to the circuitboard using the M12 Lid
You may need to deburr the edges of the hole:
The final board:
Congratulations, you have completed the assembly of the power box for your PAPR!
Building the Fan Box
You will need these parts for this step:
Fan box
Filter box
Completed power plug with solid wires
Dryer tape
Funnel
Weather stripping
2mm foam
Filter Box Stencil
Box Gasket Stencil
An x-acto knife
The deburring tool
Hex screw driver
HEPA Type-A Filter
Hex screws
Hex nuts
The fan box is assembled in such a way that different regions of the HEPA filter are used for the inspiratory and expiratory air pathways, and uses foam, dryer tape, and weather sealing to ensure the separation between chambers.
Install the fan, funnel, and power
Install the power socket
This socket will allow the guitar cable to connect the fan box to the power box so that the knob on the power box can control the fan. Inserting the socket is fairly straightforward, and is explained in this video:
Connect the fan to the power cable.
Insert the red wire into the side fan connector where the red cable enters the connector, and the black wire into the black side of the fan connector. You can test by plugging the guitar cable into the power socket and into the fan socket; turning the knob should power the fan.
Install the funnel and fan in the box
Place the dryer tape around the junction between the fan and the funnel, and then slide the complex into the hole into the fan box. Once the complex is snapped in place, wrap the rest of the tape around the junction between the fan and the funnel.
Test that the fan blows
Connect the guitar cable between the M12 power box and the fan box. The knob should control the fan and allow for variable blower settings, and air should not be coming out of any part of the system except one side of the funnel.
Install the foam and weather stripping
This video explains the process and explain the reasoning behind the different types of sealing:
Use the stencils to cut foam inserts
There are three foam inserts, and two have stencils in this build that are 3d printable. Cutting the foam follows the procedure outlined in this video:
After the foam is cut, punch holes for the screws in the Box Gasket foam
The purpose of this step is to allow screws to connect the fan holder box to the filter holder box and not twist the foam insert.
Place foam cut to match the foam gasket inside the filter box
As per this photo, finger fitting is fine:
Place the nuts and spacers inside the filter box
As per this photo. Drop the nut in first, and then the spacer. A mallet may be required to facilitate insertion of the spacers, depending on print quality. A hammer may damage the PLA.
Place the foam cut to match the box gasket insert around the outer lower edge of the filter box
As per this photo:
Connect the two boxes
Take the foam insert portion remaining from cutting the Box Gasket foam, and place that between the two boxes. You will need to cut out the foam to match the image below:
Place hex nuts in the outer screw wells and screw the boxes together.
Place the weather stripping on the rails of the filter box
Following this photo: https://photos.smugmug.com/photos/i-fQ7gKh2/0/X2/i-fQ7gKh2-X2.jpg
Install the filter and the top grill
The filter should fit directly into the top, but will be a tight squeeze. Place your filter with these lines down towards the fan:
Attaching to the Mask
Attaching to the mask is a matter of first deciding where the box will be worn (on the chest, as a backpack, or some other orientation). We recommend cutting the webbing such that the box can be worn comfortably with the m12 controller box threaded through the webbing. You may need someone to help you with this:
The hoses can be fit by tension by pushing into the mask and into the funnel boxes.
And now your PAPR is done!
Mix and match colors by doing various prints:
The printed box has 8 locations that are intended to thread 1-inch webbing, and the M12 controller box also has a slot for the same webbing, so that the controller can be worn on the webbing. If you use the recommended webbing, cut the lengths that you need for how you want to wear the box, being careful to use a lighter or some other open flame to melt the ends of the webbing to prevent fraying in the future. The arrangement of webbing is much more of a personal style choice, and there are plenty of configurations that someone can choose.
The mask can be held in place with elastic, a shoestring, or another form of cloth or plastic that will fit through the printed holes. We use the listed bathing suit elastic.
Care and Maintenance
This PAPR has been found to easily exceed n95 filtration both for the wearer and for those around them (in the sense that the wearer’s exhaled air is filtered). These types of devices can last for a long time, but some care and maintenance must be performed.
The filter should last for around 3 months with relatively constant use. The system will just blow less air as the filter becomes more clogged, so replace the filter if your PAPR is not pushing enough air for you.
The battery will need to be charged after several hours of use. If you’re using the PAPR for more than a few hours at a time, you may want a second battery.
Water will condense in the exhalation hose during the normal course of use. We recommend regularly cleaning out the hoses; there are several CPAP hose cleaning kits, or a bottle brush could work as well, with one candidate in the tool list above.
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Last modified April 27, 2021: add past build guide for Nov 2020 (1df2622)