doorstep climber
Submitted by eeerie on Fri, 11/13/2009 - 16:41
Project to make public spaces more accessible for wheelchairs.
For the biggest part of my life I've been using a wheelchair to move around.
The electric wheelchair is one of the main inventions for people who are physically challenged, to be able to go wherever they want to go. Since the introduction many people who didn't leave their homes up until then found themselves able to take part in the normal things of live. Through the years the most common chair has evolved into a compact machine, capable of driving arround for about 40 kilometres at a speed of 9.5 kmph.
But unfortunately a lot of spaces haven't evolved around the use of wheelchairs. Many buildings and public parks are still used to people beeing able to climb up some small steps.
To overcome this problem I want to make an attachment to the chair that will enable it to drive over the most common obstacles, like doorsteps and pavements. To acomplish this I was thinking of placing ramps over the wheels that could be slided in front of the wheels, and retracted after use.
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Project Blog
Doorstepclimber - The problem and a solution
The problem with the cast not fitting the tire turned out to be something we had overlooked. After examining 6 tires we concluded that the tires themselves where made up out of 2 half tires glued together.
This results in the profile not being aligned the same way on different tires, and therefore we aren't able to make a "one size fits all" mall.
We had to shift focus on a fixed profile, so we decided to have a look at the wheel itself. Maybe it would be possible to modify the rim. So we went to the basement and removed the wheel of my spare wheelchair.
Now we are looking into ways of making a rim ourselves. We are considering laser-printing multiple layers of corian, cutting out of metal with a plasma cutter, or casting aluminium.
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Doorstepclimber new tracks
After our first attempt on the tracks we where faced with a new set of challenges. In order to produce the tracks we would have to make about 100 tracks, which would take ages to cast, and a lot of rubber to produce. Also we would need to find a way to connect them to each other in a secure way.
Therefore we where forced to look at alternative designs.
Alex came up with the idea of making a thinner track design with a lot more length. It would be impossible to make a track mould entirely cast at once, because you would need to make a mould with a 6 axes drill to reach all the details. Therefore we looked at ways to make tracks that could be welded or glued together.
Our new attempt would be focussed on making track parts approximately a third from the total length of the track.
Advantages for this design are:
- faster casting, because we only need to cast 3 pieces to produce an entire track
- lower cost, because we would use less material
- better locked for using welding / glueing
- less noise while driving, because of the reduced volume of material touching the ground
First thing to do was remodelling the track. I loaded a picture of the clay tracks that we made for the previous model into illustrator and copied the basic track shapes.
Then i imported these files in cinema 4d and used them to model the new track
I focussed on the middle part of the tire to make the track smaller and it wouldn't interfere with the outer parts.
Meanwhile Michiel also made a new model that was a bit closer to the actual tire.
We decided to have a try with Michiel's design first, because it would seem logical that this would be more stable and not roll of the tire that easily. So we loaded the design into the shop bot and made a very nice mall.
We did need to order a special set of cutters of 1/8"
After that we wanted to see if this would fit the tire, so we had to cast a prototype. We used a fast drying plastic for this purpose.
Strangly this cast didn't seem to fit on the tires a had on my chair, but somehow fitted perfect on the tires i had given Michiel to examine.
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Doorstep Climber - The Mould
After deciding that we were going to put tire tracks on the front wheel, we had to decide how we were going to mount them on the wheelchair.
If we were going to make it into some sort of add-on, that would be usable on normal wheelchairs, we would need to find a way to attach it without the need to completely rebuild he chair.
So the decision was made to put a track around the normal front tire, expanded to a pulley which would be attached in front of the wheel.
Making the tracks:
During the Fabacademy the subject of moulding and casting was brought up. In this lesson we would make a mould in which we could cast similar items. This would be a perfect opportunity to make track shoes, which needed to be similar.
A track shoe is a part of a tire track. These parts can be attached to each other to make a track.
First drawings:
There are a few things to keep in mind while designing the shoe.
- First, it needs to have grip on the front tire. This will be accomplished by adding a profile in the inside of the shoe that matches the profile of the front tire.
- Second, it needs grip on the surface. So a profile for maximum grip is added to the outer surface of the shoe
- Third, the track needs to stay on the tire. Therefore the shoe needs to be a little curved on the inside to match the curve of the tire.
- Fourth, the shoes need a way to connect them to each other.
Photo’s of the wheel and tire:
Photo’s of tire profile:
To make the mould we needed a 3d design of the shoe to cut out of chemical wood. The mould is formed around the cut-out. Michiel decided to model the shoe in Blender.
Photo’s Blender:
Make a positive -> use it to make a negative -> use the negative to make lots of positives
Photo’s carving the positive:
Educational moment: When you want to cut out a rough carving with a 6mm drill, and want to do a finishing carving with a 3mm, you should make sure that the drills have the same length, so they can both cut the same depth.
Unfortunately we have to do the carving again, and to make sure it goes alright we’ll be using the same drill for as well the roughing as the finishing.
Second try:
After the first attempt there had to be made a new mal. To speed up the process, an attempt was made on the bigger cutter, the BZT pf 1000c Milling Machine. This was a lot faster. We were able to do a roughing and a finishing in one day, but the result was a lot less smooth then made on the modula.
Picture mall on BZT:
So a decision was made to return to the modula. First the bottom half of the track shoe would be milled out.
The milling was done in three cycles. A rouging and finishing with a 6mm drill, followed by a finishing of the top layer with a 3mm drill.
Screenshots of the modula screens:
After milling for 2 days the first 2 stages were done, and after some re-aligning the third stage was finished within a couple of hours.
Pictures milled out positive
The modula was reset, and the milling job for the top half was activated. This part would consist of only to jobs, a roughing and a finishing both with a 6mm drill.
Meanwhile the negative of the bottom half was made by pouring a silicone rubber compound in the milled out shape. This compound was made from the materials that had to be combined.
Pictures of the materials and the mixture.
Before pouring in the mixture, the milled out shape was sprayed with a mold release spray, so the rubber would come out of the form more easily. Then the mixture for the rubber compound was poured in.
Pictures of the spray and the pouring.
Educational moment, The mixture has to be stirred very thoroughly. We could have stirred it for a bit longer, but the end result is acceptable. Also when pouring in the mixture you should somehow vibrate the part in which you are pouring the mixture to decrease the amount of air bubbles.
After 2 days the rubber had hardened out. So the bottom part of the mould was done. The modula was still milling though, so we could made the second part of the mould yet.
Pictures of the rubber mould
After this the upper part of the mould was milled out. It turned out to be a three day job for the modula and it didn't even complete the job. Halfway the finishing part it stopped. But since we realy wanted to start casting we decided to use this any how.
Pictures of the milled out top part:
This part was filled up with a silicone rubber compound to make the top half of the mould.
The last step after having the complete nould was to cast the final piece. Since we were going to use it on road, we wanted to use a rubber that was close to the one we'd like to use in the end product.
After some research we came on a rubber called: Vytaflex 60. When mixed it can be poured in to the mould, and when dried its a sturdy rubber with still some flexability.
After 2 days of drying the final result was revealed:
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doorstepclimber slide rail
Just found out that the ground clearance of the middle part of the wheelchair is about 8 cm. This will be a problem when you lift the front part of the chair to high. This will cause the bottom of the battery box to get stuck on the doorstep (or other object we are trying to climb)
Therefore I'm looking into ways to lift the box, or make it slide over the doorstep, until the back wheels hit the obstacle.
At the moment I'm looking into the possibility to attach a rail at the bottom of the box. this rail could let the box slide over the obstacle without damaging it.
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Doorstep climber caterpillar tracks
The first contraption we where thinking about seems to be a little fragile. The telescopic arm that is used to place the ramp in front of the wheel has to be able to hold the complete ramp including any electric motors that are needed to balance the ramp. Therefore I have put that idea in the icebox for so far.
The next plan is to transform the front tires into little caterpillar tire tracks looks more promising. We want to accomplish this by placing a smaller wheel in front of the front tire, and connect it with the front wheel by tire track.
The biggest advantage of this idea is that we don't need to add any motors or electronics. The power that is needed will mostly come from the front tires itself. Also should it be possible to make it an add on, so it can be attached as well as detached, making it portable. This will mean that there is no need for big changes on a basic wheelchair (with front wheel drive).
The biggest disadvantage is that the extra wheel will be taking up some space.
The first part of the construction will be a way to attach the extra wheel. by making a triangular structure it'll ensure some strength. Best would be if it could be attached to the chair on fixed positions.
At the end of the structure a wheel could be mounted.
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Doorstep climber research
Found some interesting chairs that are already in existence or in development.
4 wheel drive called iBot.
Crawler based Galileo
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Doorstep climber crawler
Second idea is to attach a crawler on to the front tire. Attaching a second small wheel in front of the front wheel, and connecting them by a crawler will make it able to lift the front of the chair on to obstacles.
pro's:
- Steady structure. After attachment it will be able to function without complex movement.
- Can use power from wheelchair itself.
- Rugged look and feel.
cons:
- Less shock absorbing then an air tire.
- Sticks out in front of the chair
- the back wheels still some way to get over the obstacles as well
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Doorstep climber Brainstorming
First idea was a ramp like structure, mounted to the side of the char. Using a robotic arm, a plateau could be lowered in front of the wheel, making a ramp on to the obstacle. After the wheelchair has passed the obstacle the arm would retract the plateau so it could be used again on a next obstacle.
pro's:
- universal plateau that allows the chair to go over bumps as well cross gaps
- can be stored above the front wheel
- adjustable angle for different heights of obstacles.
cons:
- fragile arm. When hit it could bent, leaving the device and chair unusable
- the device will increase the total width of the chair.
- complex movement of arm and ramp
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