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2x2-x2 - The Disruptor (12 lbs/5.5 kg)
@AnnaSarol
It's Time for Some Disruption!
I named this wheelchair the Disruptor because it is high time that the Legacy Wheelchair Industry gets disrupted!
There needs to be a new way of thinking. The wheelchair industry is based on the Proprietary Profiteering Model which involves using propriety designs and manufactured parts to force wheelchair users to come to them. Wheelchairs are purposely designed and made difficult and expensive to repair in order to encourage complete wheelchair replacement at exorbitant purchase prices.
Disrupting this situation requires promoting the Universal Open-Source Model. Where wheelchairs are designed to be made and repaired from parts that are universally available using open-source designs and manufacturing methods. This is the best way to break the hold the Legacy Wheelchair Industry has on the wheelchair market and more importantly on the lives of wheelchair users.
The central realization of the Universal Open-Source Model is that if you can build a wheelchair, then you can also repair it. A wheelchair that can be easily repaired doesn't need to be super robust. For example, the weakest part of a bicycle is the inner tube. Since it is so simple and relatively inexpensive to repair a flat, most inner tubes are not made more robust. The culture of bicycling is to fix flats and replace tires as needed. Bicycles are manufactured with the assumption that bicyclists can accomplish this task. The same assumption can be applied to DIY wheelchairs. What DIYers need is a recipe (design plan) that they can use to make a meal (wheelchair) using readily available and inexpensive ingredients (materials) rather than go being forced to eat at an over-priced restaurant that justifies its high prices by having a limited menu of exotic foods.
Rectangular Camber Tube
It took me eight designs before I realized I could make a Rectangular Camber Tube (RCT) out of two pieces of wood and two sections of punched zinc square tubing by creating a box. Securing the rear wheel axles is the most critical aspect of making a wheelchair. Rather than making the frame first then securing the wheels, the RCT is made first and then the frame it built around it. The RCT provides much needed structural integrity. Securing the font casters to the frame is done by using the same punched zinc tubing (but this is done last to properly level the wheelchair.
Once you have a method to secure the wheels, you can build the frame in various ways as you desire. There is NOT just one way to complete the frame, many methods will work. But it is important to put together the frame in manner that makes it easy to replace the parts as needed. I designed the Disruptor so that every part could be removed and replaced using universally available materials.
Universal Repairability
Old Fashion Box Construction
Similar to my earlier designs, the Disruptor uses "box" geometry to create structural strength. The Lower Chassis reinforces the foot support frame. It also provides a place to mount the wheel-locks. Many modern designs do not have a Lower Chassis and use an "open" or cantilever design. As a result, many use larger metal tubing which increases the weight and only allows for high mount wheel-locks (or use expensive high strength titanium/carbon fibre). Despite these drawbacks, the open frame has become a standard because it looks "modern". My designs use old fashioned "closed" frames because they are stronger and enable the use of inexpensive materials such as wood and PVC.
Quad Wheelchair or Trike
Except for the front caster(s), a quad wheelchair is essentially the same setup as a trike wheelchair. Therefore, you can use the majority of the Disruptor design to make either or both. A quad is better indoors and in smooth urban environments. A trike is better outdoors and on rough pavement or in nature environments.
The Disputer design features a foot support frame to provide foot and leg stability and protection. This frame also provides two strong hand holds for transfers. Many conventional trike designs lack both these important features.
Substitute Materials as Needed
The least robust part of the design is the 1/4" plywood used for the seatpan and backrest. Using thicker plywood will make it more robust. Using PVC sheets will make it more weather proof. In fact, instead of using 1"x4" pine you could use a different type of wood, or PVC boards for the RCT and foot support fame. Round PVC tubes could replace the 2"x2" cedar boards for making a trike. The choice is yours.
Wheelchair Essentials
The Legacy Wheelchair Industry (LWI) controls the manufacturing of wheelchairs by controlling access to essential wheelchair components such as rear wheels, quick release axles, axle receivers, wheel-locks, and front caster assemblies. Ever wonder why standard wheelchair wheels are different sizes than bicycle wheels? Does that make any sense?
Fortunately, the LWI cannot control what if manufactured in China, India or other exporting countries. That means it is possible to purchase wheelchair essentials at a fraction of the cost. The LWI avoid this price competition by using their proprietary designs that are not compatible with universal components such as front casters. Note that rear wheels are universal assuming that the axle, axle receiver and wheel are at compatible. Hence, many of the LWI for "high end wheelchairs" use brand name 3rd party wheel manufacturers like Spinergy as their primary wheel source. Essentially, they sell you the frame and you buy the wheels separately (and they make a commission on the sale of the wheels - the more expensive the better).
Following the Universal Repairability concept, you can use universal wheelchair parts from China as I have done. I purchased the rear wheels into photos above used for $15 per wheel from a nonprofit that didn't want them. The 4"x1.5" gold/black casters are from China ($30 per caster assembly. The wheel-locks were $18 apiece. You can also use industrial stem casters. With a slight modification, you can use industrial plate casters. Once again. It is up to you.
Disrupter Specifications
Main Frame made from 2"x4"x8' Cedar board
(2) Backrest Support - 2"x2"x18"
(2) Upper Chassis - 2"x2"x22" with 1/4" taper on end
(2) Lower Chassis -2"x2"x23.5" with parallel 1/4" tapers on both ends
(1) Cross Brace - 2"x2"x10"
Panels made from 1/4"x2'x4' plywood sheet
(2) Seat Pan - 1/4"x13"x13"
1) Backrest Panel - 13"x13"
2"x2"x4" hard foam block
Made from 1"x4"x 6' Pine board
Leg frame
(2) Leg Support - 1"x4"x15"
(1) Footplate - 1"x4"x10"
Rectangular Camber Tube
(2) Camber Tube Support 1"x4"x15"
(2) Camber Tube Axle Bracket - punched zinc sq tube - 1"x1"x3" with middle two holes enlarged to 1/2" diameter to match quick release axle.
(4) 5/16 x 3.5" hex head bolt & Nylock nut
(4) 5/16x5" hex head bolt & Nylock nut
(16) washers
Caster Assembly Backet - (2) 1"x1"x3" punched zinc sq tube with middle two holes enlarged to fit stem caster axle.
Caster Assembly Spacer - (2) 1"x1"x3" punched zinc sq tube.
Wood Screws
(15) Long wood screws 3"
(30) Short wood screws 3/4"
(15) Medium wood screws 1.5"
Notes
These are the measurements that fit me. I am 5' 8" and 140 lbs.
My rear axle position is 4.5" from the front of the Backrest Support.
I am a T(4-5) paraplegic, but I like a relatively low backrest.
The seat panel suspension foam is cut into (6) 2"x2"x 1/2" rectangles. Thicker foam will raise the seat height. Thinner foam will lower it. You can also increase or decrease the seat dump by use of the foam blocks.
The backrest cushion is made from a cut up exercise mat and Gorilla tape.
Substitute as needed.