Hand Drive

Phase Two

We are taking the hand drive to a new level for independent studies. We are completely redesigning it. We realized with our last model that we couldn’t move backwards, and that was a problem.

We are now remaking the hand drive without the free wheel mechanism. The free wheel was what was preventing the wheelchair from going backwards. We are making our own ratchet mechanism, which is very similar to the free wheel, but it allows us to go backwards. Instead of having one ratchet like the free wheel, it has two ratchets each on a different plane. Depending which ratchet is engaged, it allows the wheelchair to go either forward or backwards. The two ratchets are connected by cables which allows the user to disengage one ratchet and engage the other through one swift and easy motion. Our first model is almost done!

How it Works

Once we made our wooden prototypes it was time to start making 3D models. We started the modeling process with a clean slate. We made a new spider attachment that will fit more snug to the wheel, so hopefully it won’t pop off as easily. The gears for the ratchet are also on the spider attachment. We made the gears with a plate in between them so that the ratchets won’t slip out of place. Through testing the gears, we learned we don’t want the gear to curve as much, but want it to be more of a right angle. It really takes a minimal amount of distance for the gears to cover, for them to be functional.

The lever piece houses the ratchet and the cabling. The lever is on the outer side of the ratchet. The lever piece consists of a disk with holes placed for the ratchet pieces to fit into. It also has pulleys for the cables, and a hole through the center where it screws into the spider piece. The level isn’t as complex of a piece compared to the spider, but it has to line up and fit perfectly with the spider, which is a frustrating little challenge for us to have.

Frustrating

Once we really started to chug along with our model, disaster struck. Fusion, the program we had been using for modeling, had decided it didn’t like our model anymore and therefore it wouldn’t work. We ended up having to remodel the entire project in different files. We lost a day and a half of work time in this process.

Progress

Once we remade the models in different files, and got the project back to the point it was before, we started moving forward again. One of our design challenges was figuring out the springs in the design. The springs push the ratchets into the gear, and are essential to the design. In our initial wooden prototypes we used coil springs. The unfortunate part about those springs is that they are too bulky. We want our project to be as slim and sleek as possible, so we started looking into other options.

We ended up creating a spring from a piece of steel. It is a thin strip of steel that wants to stay straight. We found that if we use it in our design a little bent, it will want to stay straight- thus acting as a spring to get straight. We modeled and printed a prototype with this design. We found that the steel spring was pretty hefty, and too much spring. We are going to see if we can get more flexible steel to tone it down a little bit.

Once we realized the steel spring was too hefty, we started to come up with an alternative. We made a design with the regular coil springs as a back up in case the steel doesn’t work. I am personally routing for the steel springs, because it is a much more elegant design.

Cables

Once we had figured out the basic ratchet mechanism, we had to figure out how to make it work with cables. Only one of the ratchet pegs can be down at a time, and depending on which ratchet is down determines whether the user is wheeling forward or backwards. The cables are used to easily switch which ratchet is down, thus changing the direction of the wheelchair.

The tricky part is figuring out how to use one cable to cause one ratchet to go down and one ratchet to go up. We were originally thinking the ratchets would each want to go a separate way naturally, because of the springs. When the cable was pulled, it would push one ratchet down and pull the other up. This wasn’t the most elegant solution, because the cables were getting tangled with the gear when the ratchets spun.

Our new solution is to have the ratchet pegs be different. One ratchet peg attaches to the top of the cable and another ratchet peg attaches to the bottom. This way when the cable is pulled, it pulls one down by its back, and one up by its toes. We haven’t tested this solution yet, but it is looking good.

Bikes

Throughout the project, we are finding more and more similarities to a bike. All of the cabling for our project is bike cabling, and we are going to use a bike break for the handles. It is interesting to compare a wheelchair to a bike and see the similarities.

Hacking the Wheelchair

Starting off

We are beginning a studio making wheelchair accessories. We started off this studio by learning Autodesk Fusion, the software we will be using for this project. Fusion is a 3D modeling software that allows you to edit dimensions and sizes on models you make. We spent the first few days making objects in the software as exercises. I made a phone case.

Once we were done learning the software, we brainstormed as a studio group on what improvements a wheelchair needs and how we can hack it. We want to accessorize the wheelchair as apposed to redesign it. We broke up into groups and started to brainstorm more in-depth.

Our group decided on making the wheelchair faster. We live in a busy fast paced world that the wheelchair hasn’t necessarily kept up with. We want to use a ratchet mechanism, which would allow the user to wheel faster in the chair in a rowing motion as opposed to a wheeling motion, a similar motion to the arms on an elliptical machine. We are mainly focusing on the ratchet mechanism moving the wheelchair forward but hopefully if we have time we can work on brakes as well.

Attachments

We started off the day with a lot of bike parts. We wanted to get the parts from the bike wheels to see if we could use them for our project. We took the wheels apart and explored, and found that we already had some mechanisms from parts that we could recycle instead of creating our own. We started making attachments that would make the parts usable for our particular situation. The tricky thing is that because of the parts that we have, the wheels can only turn one way so we have to use a slightly different system for each wheelchair wheel. The left and right wheels are flipped mechanically. We spent the day designing separate parts for each. We should be able to test them out on Tuesday once they have all printed out. Fingers crossed that it will work!

More Parts

Today we continued the process of making parts and testing them out. We put the main part of the right side together today, and it’s looking like it’s going to work well. We are just waiting to finish the design and print one more part to finish it off. Hopefully it will work and we can start on the left wheel tomorrow.

We have put the breaks part of our project on hold, and are just focusing on the speed right now. We are chugging along!

Design Change

Throughout the studio we have kept the project pretty simple design change-wise. We have pretty much kept the same design the entire way through, but today we made a design change.

After testing our previous spider attachment design we realized that we needed to beef it up because it was breaking when we applied force on it. We also realized that the way we were connecting the 8020 bar to the mechanism wasn’t helping our design. It was giving it too much torque, and adding stress to the entire mechanism. We took out the need for a right angle with the 8020 bars and redesigned the connector to accommodate the changes. We are printing out the final pieces tonight and tomorrow!

Whoops!

Today we had a realization. After we put one of the sides together we realized that we had made two of the same sides, but in different ways. We made two of the right side, although this was unplanned and would be considered a mistake, it turned out to be a good thing. We had come up with two completely different ways to do the same thing and through doing this we found that one way was much better.

Once we had wrapped our mind around making the left side of the system, it actually wasn’t that difficult. We had all the hard parts made, and just had to edit them a little to be able to use them for the left side. They are printing out over the weekend, and hopefully they will fit right into place on Monday. We are cutting it close!