Open Wood Chair (english version)

 
Tutoriel
Creation of a low-cost electric wheelchair from wooden pallet and an arduino card.
  • Difficulty : Moyen
  • Duration : 3 jours
  • Budget : <50 euros
 

Introduction

Open Wood Chair is a customization by My Human Kit of the Open Wheel Chair project made by the american Open Wheel Chair Foundation.

The goal that we share with this foundation is to share documentation including a bill of material, plans, and instructions step by step allowing anyone to build a wooden electric wheelchair for children.
The idea is to make it accessible to anyone with a minimum of technical ressources, recycling a maximum of parts, whose maintenance and scalability are also guaranteed. It's a work in progress published under CC-BY allowing free usage, modification and distribution.

The main innovation of the Open Wood Chair project compared to the Open Wheel Chair one, is to use wooden palette (available almost everywhere on the planet) instead of PVC pipe for the chassis frame.

We could also imagiine other adaptations from local ressources available around your place like bamboo for the chassis frame, fabric made locally for the cushion covers, etc. In order to make the wheel chair compatible with a manual propulsion, we swap the driving wheels from front to rear in a way that it's always possible to make the wheel chair without the electric motors, with common big wheels.

 

The Team

In October 2016, the team from the hackathon "Fabrikarium" at Lycée Airbus, Toulouse, was composed of:
Michel & Jacqueline You,
Gérard & Bernadette Véron (afficionados MHK),
Patrice Navarri (Airbus Toulouse),
Jean-François Soucaille (Airbus Toulouse),
Dirk Thalheim (Airbus HH),
Olivier Heinry (FLOSS Manuals) for the documentation,
Philippe Pacotte (sympathisant MHK) for modelisation and 3D printing

 

Step 1: Measure of your child

The scores given in the list of materials are intended for a child of 4 years old ( height of 102 cm Source). If your child is taller, you can expand the size of few centimeters for the armrest, front and rear frame, and if needed the depth of the seat. On the contrary, you should not change the dimensions of the frame on which are fixed the wheels and motors.

 

Step 2 : Buy and group together materials and tools

Get all the materials listed in the tab "Matériel et outil". If can't get some, feel free to adapt the needs with some material around you.

 

Step 3 : Unmount the wooden palettes

There are a lot of different qualities for wooden palettes that can be used to transport many products, and some of them are toxic. Be carreful when you choose it. Pay attention to the mark, and get one tagged "NIMP15" with a logo looking like an ear of corn with the initials HT, meaning that they got a thermic treatment. At the opposite, the initials BM mean that they have been treated with bromide which is toxic and forbidden in european union since 2010.

Choose some wooden palettes recntly assembled, because it's more difficult to get out nails and stapples from dry wood.

Security :
Don't forget to wear protection equipement when unmounting the palettes : protection glasses, gloves and earplugs, security shoes. Check also that your tetanos vaccine is up to date.

Instructions :
Lay down the palette on the reverse side. With the crowbar, remove the nails from the soles: start with the middle board, it is easier to remove. Book the boards.Then put the pallet on the ground always on the back (its floor) and chase the rafters (quadrangular blocks) with the mass.Once this is done, remove the remaining staples and nails. We begin by hammering the staples on the side of the rafters and we finish extracting them with the pincers.Finally, we sanding boards to remove splinters, a step in which the wearing of the mask is highly recommended. Here you are with a stock of raw material!

 

Step 4: Debiting the pallet wood

We begin by cutting the longest boards, paying attention to the nodes, potentially brittle, or to the slits that appeared during the dismantling, especially of dry wood. You can do this with a miter saw, failing that with a hand saw in a miter box. Refer to the list of material marked "palette" for the list of boards needed.It is also helpful to break the sharp edges after the flow by quickly passing the sander at 45 °.

 

Assembly instructions

The wooden frame will be assembled in two parts: first the base, then the armrests and finally the seat with its backrest. The propulsion unit, the footrest and the cushions will be assembled at the end.

In order to guarantee the regularity of the alignment of the holes, we start by constructing two drilling templates. The first will be used to perform the prephase end plank and the second for lateral pre-drills.

 

End screwing jig

Take a fall, cut off its end properly at 90 °. Then draw a line parallel to the end at a distance corresponding to half the thickness of the pallet wood.

Example: if your pallet wood is 14mm thick, you draw a line 7mm from the end so that the screw enters the heart of the wood. You will then drill 2 holes 10 mm from each edge with a wood drill a diameter below the diameter of your screws, so that the wire can still bite the wood without breaking it.

 

Side screwing jig

Take a fall, cut off its end properly at 90 °. Then draw a line parallel to the end at a distance corresponding to the width of the pallet wood (in our case, 50mm). Then draw the diagonals. You will then drill 4 holes 15 mm from each corner with the same drill as before.

Tip:The assembly goes much faster if you organize your boards in packages according to the dimensions. You can note the dimension directly on the piece as we did here with the mechanical pencil, note that will be removed by sanding once the assembly is done.

 

Assembling the chassis base

Frame assembly

Gather the different parts needed for this step:
- 3x25mm screw
- 4x35mm screw
- 2 x 600mm
- 4 x 313mm
- 2 x 83mm
- 2 x 36mm

The use of wood glue, clamps and squares is highly recommended.

 

Adding reinforcements

We must now assemble 2 boards of 83mm within 600mm boards, at bringing future-wheel drive. We start by marking the thickness of the board, then we use the lateral screw template aligned on this mark to pre drill the first screw.

 

Armrest assembly

Gather the different parts needed for this step:

- rear pillars: 2 x 450mm
- front pillars: 2 x 530mm
- side cross members of the seat: 4 x 300mm
- 12 screws 3x25mm
- wood glue

Arrange in front of you aligning the ends of the 4 uprights. Use the side screw template to mark 2 pre-drilled holes at each end. Then mark each amount of a line at 245mm from the pre-drilled end. Repeat the pre-drilling operation.

 

Assembly of the wheels

Gather the different parts needed for this step:
- crossbar: 1 x 345mm
- 2 crazy wheels diam. 100mm
- 6 screws 4x35mm - wood glue

We begin by screwing the 345mm horizontal beam on which will be fixed the crazy wheels across the front of the chassis. The end tapping template will be used, first for the first two screws and then 90 ° on the front crossmember, where only one screw will suffice.

 

Assembly of driving wheels

Gather the different parts needed for this step:
- 2 fixing plates for geared motors
- 2 geared motors Takanawa RS-555
- 2 full wheels diameter 150mm and their hubs
- 8 pan bolts 5 x 50mm + nuts
- 8 screws m4 x 30mm countersunk head
- 4 wood screws 4 x 45mm
- 4 wood screws 2 x 25 mm
- Allen wrench

We begin by assembling the plate to the gearmotor, then the wheel to the assembly. Once done, weld the power cables. Once the two wheels are assembled, they are fixed to the wooden frame.

 

Assembly of the plate to the geared motor

If countersunk screws are used, you must first mill the 8 small diameter holes, eg with a HSS 6mm drill bit. If you use flat head screws, you can go there. Drilling to be used Place the plates facing the motor, matching the circled M4 holes in the illustration. Thread using 4 screws m4 after removing a drop of threadlocker at half thread. Repeat with the other set, paying attention to the orientation. The two assemblies are symmetrical and not identical.

 

Assembly of the wheel

Assemble the wheel on its hub, also distributing the four bolts. Do not hesitate once again to put a drop of net brake.

 

Assembly of the set

This is a crucial step for the future rolling behavior of the chair. In order for the wheelchair to move straight when it is running, the drive wheels are arranged at the rear. To prevent the idling wheels from locking up, their vertical axis must be perfectly vertical.
It's up to you to play between adjusting the bolts at the front and the height at which you screw the engine blocks at the rear. To do this, it is better to work on a perfectly horizontal workbench, just check it with a spirit level. You then place the wheelchair on the back and on its idlers at the front and find the right height by using the level bubble placed parallel to the axis of one of the crazy wheels. Check this on both sides, otherwise the chair will tend to turn. This done, you can present your engine-wheel block on the chassis by presenting the plate cutout from the front. Make a mark, then attach the plate using the 4 x 45 mm screws on the reinforced rear and the 3 x 25mm screws on the rear post of the seat. You can pass the screwdriver through the spokes of the wheel.

 

Manufacture of armrests

Manufacture of armrests

 

3d printing of the joystick case

To house the electrical contacts of the joystick of the accidental tearing or splashing of water, it is recommended to shelter it in an insulating box. We have modeled and printed a custom ABS case. You can find the source files at our Github repository.
Toutes les mesures n'étaient pas bonnes, nous avons forcé le passage du joystick dans le logement puis resoudé le plastique avec un décapeur thermique réglé au minimum.

 

Cabling the joystick

Current prototype: two tablecloths come out of the joystick.

------------------------ -------------- JOYSTICK

> A GND tablecloth (VIOLET GRAY WHITE BLACK)

wiring to the arduino: all connected to the GND arduino.

> A sheet corresponding to the joystick contacts.

Cabling to arduino:

pin:
-----------

8: BLUE
9: ORANGE
10: GREEN
11: YELLOW

---------------- SHIELD DF DC ROBOTS DC MOTOR DRIVER 15A ------------------------

pins arduino pins shield
----------------------------
4: M2_EN
5: M1_pwm
6: M2_pwm
7: M1_EN
5V 5V
GND GND

--------------------------------

 

Mounting the joystick on the armrest

 

Cable fixing on the frame

 

Installation of the box containing the electronics

The case is attached to the back of the chair.

 

Footrest

 

Dressing of the armchair

You will need a sewing machine as well as the following:
- 1 foam of 50mmX390mmX300mm (folder)
- 2 pieces of fabric 350mm X 470mm (backrest)
- 2 velcro straps aka 50 x 25mm sewing scratch (backrest)
- 1 strap of fabric of 120 x 900mm (Footrest)
- 1 strap with a buckle (seat belt)

Sew the cushion cover for the seat as well as the one for the backrest.
Then prepare the fabric band for the foot block by sewing a velcro strap to close the fastener.

 

Congratulations!

Congratulations, if you have reached this far, it is that the chair should look like the picture below :)