peristaltor (![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png)
peristaltor) wrote2013-05-03 06:45 pm
peristaltor) wrote2013-05-03 06:45 pm
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It Was A Good Idea, I Guess
You know you had a good idea when someone beats you to it.
Years ago, I saw in empathetic agony a guy trying to get his wheelchair up a curb cut-out that was just a bit too steep for his arms to handle. I saw the problem; he didn't have enough leverage. I started doodling.
Keep in mind that I was at the time very interested in electric-assisted bicycles, going so far as to help sell them in town. When you are a hammer, all manner of problems look nail-y. I figured that a regular wheelchair suffered from two things in hilly environs;
The last one, I figured, could help with the first. You see, one of the biggest engineering challenges with electric-assisted bikes is deciding when to engage the electric torque. Most bikes are just fine without assist; it's only when they hit hills that the riders need assistance. (And if you've ever been to Seattle, you know why that might be a bit of a concern.) Some designs put a simple switch near the rider. Give it a nudge or a click and the motor engages. I had one of the earliest, a ZAP dual-motor design. I could choose from two speeds only, but in practice used only one (I'm big). It was simple and cheap . . . so cheap, in fact, that it was worth every penny. Why? It engaged the bike by simply rubbing on the back tire. Just a bit of wet on that tire and it was spinning freely, doing nothing useful.
In my defense, that design was one of the only ones available when I bought it. In just a few years, several would come out that would bury that Neanderthal. The best used some kind of regulator to give the rider only the power he/she needed, and a linkage to the bike that did not drag when the motor wasn't being used. The best would gauge the torque by sensing how hard the rider was peddling; the greater the tension on the pedal or chain, the more torque provided. This did two things well. It saved limited battery life, and worked to help the rider rather than carry the rider. This gave the rider more range and ability without becoming a motorized transport.
And this brings us back to the poor fellow confined to the wheelchair.
I've pushed maybe a hundred wheelchairs (boats are not the best environments for the those with mobility challenges). I've seen the gamut. One thing I started to notice is that chairs, like bikes before, were either powered or not. No in-between. This makes sense, given that the batteries that powered the bikes were unavailable until very recently. You do not want a typical car battery powering a vehicle that might tip over. The newer gel-cell lead-acid batteries didn't spill, and could even be mounted sideways. I did start to see some of the fancier powered chairs with gel-cells, but they were, again, strictly power chairs. The occupant could not assist the propulsion, since the powered chairs used small, out-of-reach wheels.
What's the problem with the powered chairs? Well, nothing . . . much. For one thing, the occupant cannot assist the chair. This means that the range is exactly what the batteries and motors deliver, and nothing more. For most applications, that's no big deal. After all, they were designed to help assistance in areas where power for charging is readily available.
For me, though, one of the benefits of electric-assist bikes was the fact that people who could not ride before now could. Elderly, injured, or just out-of-shape riders flocked to the store to once again enjoy the activity their conditions denied them. And most importantly, they got some exercise. For people struggling to get any, getting some was a boon, often one that after a time with the assist bikes, allowed them to ride standard bikes.
Ask anyone confined to a wheelchair how easy getting exercise might be. I saw people wither away after their upgrade to powered chairs simply because they didn't have the strength to exercise their arms. They went from having pretty strong arms to having pretty weak ones simply by dint of not being able to move them enough.
So, I reasoned, why not an electric-assist wheelchair?
I toyed on paper with all kinds of designs, mimicking the motor-wheel interfaces I'd worked with on the electric-assist bikes. One significant problem; people engaging the wheels with their hands don't have the luxury of flicking a switch with their fingers. The interface would have to be built in to the same mechanism that let them push the wheels. After some doodling, I reasoned one could attach a lever to the outer hub of each wheel with a one-way ratcheting coaster attachment, albeit a special one. After all, wheelchairs occasionally need to go backwards (unlike bikes). Try to back a bike with your leg near the pedal and you'll see the problem in a hurry. The coaster will have to reverse, probably using a simple switch. Not a problem, but it meant that I couldn't use simple off-the-shelf bike coasters.
To get the switches needed, I imagined two ski poles, each attached to the hub of the chair's wheels. The handle area would have a brake and thumb switch for the power. At the hub, I designed a torque interface similar to a torque wrench; the harder you push, the greater the motor power delivered. A simple electronic interface would allow the motor to run after torque fell, since once the rider pushed the bar all the way down, he/she would need to bring it back. If the motor didn't sustain and decay after torque was lost, this would be an exercise only in frustration.
The lever would also help without the motor. I imagined this would give that poor guy on the curb cut-out enough oomph to overcome the barrier, even without the motor. And the design would allow the battery and drive motors to be small, adding less than 25 pounds to the un-modified chair. Compare that to the fifty pounds just of batteries most power chairs carry, not to mention the beefed-up frame design and high-drag fat wheels necessary to carry batteries, motors, and occupant. Oh, and in my design the batteries would be removable, meaning the chair could still be collapsed for transport in standard vehicles.
I thought it was a good design. So good, in fact, that I recognized it here.
Let's see if LJ is still fucking with TED video embeds.
Really, you need to see this video. I'll wait while you leave LJ and their silly no-frame decision (which I still really, really hate).
They made some changes to my design, of course. I never got a prototype built. If I had, I, too, would have seen that my levers on the outside of the wheels would have made the chair wider and fucked up access to tight spaces. I had a thought of including gearing, but I was opting for hub gears that would have motor interfaces; their chain gears make more sense, and gives me an idea of how better to sense torque for the motor assist. The chains also allow them to put the pivot for the poles farther forward, allowing the user to better lean into the push. I also like the single wheel in the front with the extension. That gives more stability at speed (as you saw in the vid). I never got past the extra on-demand hill-climbing to consider that my design would allow for extra speeds. Duh.
I think brakes would still be a good addition. They could be mounted on bike-styled handle grips that slide up the poles, making it relatively easy to reach the fingers around and slow momentum without having to release the poles and grab for the wheels. I notice that the video doesn't show these on anything but flat terrain. Bumpy, yes; but no hills. Revealing. Imagine trying to negotiate a roly-poly dirt track of a neighborhood. Grab poles and push! Release poles and grab wheels! Grab poles again! It's like the keyboard/mouse transition that drives me nuts, having to move the hand from one to the other all the damned time, only on the chair this transition speed would be essential. And what about the coaster brake problem with reverse? They also didn't show chairs backing. These additions would increase costs, of course; but my chair was designed for the US. Added costs are the reason for health care! Those Jags the medical supply people drive don't pay for themselves!
Well, I'm bummed that I didn't get a prototype built and learn these lessons on my own. I'm fairly unskilled as a tinkerer, and would have had to learn how to build bicycles just to make something that wouldn't kill on the first go-round. I should be thankful that my pencil pushing never killed anyone. That's reassuring. I am glad that someone built, tested, and improved my notion. I'd also be jazzed to see an electric-assist version someday, even if I don't get a chance to build it.
If you read this and decide to build it, drop me a note. I abhor patents, so go to town.
(In fact, the fact that I'm writing this means if you build it, you can't patent it. Prior art trumps the process of securing protection. This LJ entry is enough to nullify the idea that the idea had never been considered. I guess I'm a bastard who cares more for people's mobility and exercise than I do for the American Way of becoming a rentier society. Ah, well.)
Years ago, I saw in empathetic agony a guy trying to get his wheelchair up a curb cut-out that was just a bit too steep for his arms to handle. I saw the problem; he didn't have enough leverage. I started doodling.
Keep in mind that I was at the time very interested in electric-assisted bicycles, going so far as to help sell them in town. When you are a hammer, all manner of problems look nail-y. I figured that a regular wheelchair suffered from two things in hilly environs;
- A lack of climbing power when the chair needed it; and
- A lack of leverage.
The last one, I figured, could help with the first. You see, one of the biggest engineering challenges with electric-assisted bikes is deciding when to engage the electric torque. Most bikes are just fine without assist; it's only when they hit hills that the riders need assistance. (And if you've ever been to Seattle, you know why that might be a bit of a concern.) Some designs put a simple switch near the rider. Give it a nudge or a click and the motor engages. I had one of the earliest, a ZAP dual-motor design. I could choose from two speeds only, but in practice used only one (I'm big). It was simple and cheap . . . so cheap, in fact, that it was worth every penny. Why? It engaged the bike by simply rubbing on the back tire. Just a bit of wet on that tire and it was spinning freely, doing nothing useful.
In my defense, that design was one of the only ones available when I bought it. In just a few years, several would come out that would bury that Neanderthal. The best used some kind of regulator to give the rider only the power he/she needed, and a linkage to the bike that did not drag when the motor wasn't being used. The best would gauge the torque by sensing how hard the rider was peddling; the greater the tension on the pedal or chain, the more torque provided. This did two things well. It saved limited battery life, and worked to help the rider rather than carry the rider. This gave the rider more range and ability without becoming a motorized transport.
And this brings us back to the poor fellow confined to the wheelchair.
I've pushed maybe a hundred wheelchairs (boats are not the best environments for the those with mobility challenges). I've seen the gamut. One thing I started to notice is that chairs, like bikes before, were either powered or not. No in-between. This makes sense, given that the batteries that powered the bikes were unavailable until very recently. You do not want a typical car battery powering a vehicle that might tip over. The newer gel-cell lead-acid batteries didn't spill, and could even be mounted sideways. I did start to see some of the fancier powered chairs with gel-cells, but they were, again, strictly power chairs. The occupant could not assist the propulsion, since the powered chairs used small, out-of-reach wheels.What's the problem with the powered chairs? Well, nothing . . . much. For one thing, the occupant cannot assist the chair. This means that the range is exactly what the batteries and motors deliver, and nothing more. For most applications, that's no big deal. After all, they were designed to help assistance in areas where power for charging is readily available.For me, though, one of the benefits of electric-assist bikes was the fact that people who could not ride before now could. Elderly, injured, or just out-of-shape riders flocked to the store to once again enjoy the activity their conditions denied them. And most importantly, they got some exercise. For people struggling to get any, getting some was a boon, often one that after a time with the assist bikes, allowed them to ride standard bikes.
Ask anyone confined to a wheelchair how easy getting exercise might be. I saw people wither away after their upgrade to powered chairs simply because they didn't have the strength to exercise their arms. They went from having pretty strong arms to having pretty weak ones simply by dint of not being able to move them enough.
So, I reasoned, why not an electric-assist wheelchair?
I toyed on paper with all kinds of designs, mimicking the motor-wheel interfaces I'd worked with on the electric-assist bikes. One significant problem; people engaging the wheels with their hands don't have the luxury of flicking a switch with their fingers. The interface would have to be built in to the same mechanism that let them push the wheels. After some doodling, I reasoned one could attach a lever to the outer hub of each wheel with a one-way ratcheting coaster attachment, albeit a special one. After all, wheelchairs occasionally need to go backwards (unlike bikes). Try to back a bike with your leg near the pedal and you'll see the problem in a hurry. The coaster will have to reverse, probably using a simple switch. Not a problem, but it meant that I couldn't use simple off-the-shelf bike coasters.
To get the switches needed, I imagined two ski poles, each attached to the hub of the chair's wheels. The handle area would have a brake and thumb switch for the power. At the hub, I designed a torque interface similar to a torque wrench; the harder you push, the greater the motor power delivered. A simple electronic interface would allow the motor to run after torque fell, since once the rider pushed the bar all the way down, he/she would need to bring it back. If the motor didn't sustain and decay after torque was lost, this would be an exercise only in frustration.
The lever would also help without the motor. I imagined this would give that poor guy on the curb cut-out enough oomph to overcome the barrier, even without the motor. And the design would allow the battery and drive motors to be small, adding less than 25 pounds to the un-modified chair. Compare that to the fifty pounds just of batteries most power chairs carry, not to mention the beefed-up frame design and high-drag fat wheels necessary to carry batteries, motors, and occupant. Oh, and in my design the batteries would be removable, meaning the chair could still be collapsed for transport in standard vehicles.
I thought it was a good design. So good, in fact, that I recognized it here.
Let's see if LJ is still fucking with TED video embeds.
Really, you need to see this video. I'll wait while you leave LJ and their silly no-frame decision (which I still really, really hate).
They made some changes to my design, of course. I never got a prototype built. If I had, I, too, would have seen that my levers on the outside of the wheels would have made the chair wider and fucked up access to tight spaces. I had a thought of including gearing, but I was opting for hub gears that would have motor interfaces; their chain gears make more sense, and gives me an idea of how better to sense torque for the motor assist. The chains also allow them to put the pivot for the poles farther forward, allowing the user to better lean into the push. I also like the single wheel in the front with the extension. That gives more stability at speed (as you saw in the vid). I never got past the extra on-demand hill-climbing to consider that my design would allow for extra speeds. Duh.
I think brakes would still be a good addition. They could be mounted on bike-styled handle grips that slide up the poles, making it relatively easy to reach the fingers around and slow momentum without having to release the poles and grab for the wheels. I notice that the video doesn't show these on anything but flat terrain. Bumpy, yes; but no hills. Revealing. Imagine trying to negotiate a roly-poly dirt track of a neighborhood. Grab poles and push! Release poles and grab wheels! Grab poles again! It's like the keyboard/mouse transition that drives me nuts, having to move the hand from one to the other all the damned time, only on the chair this transition speed would be essential. And what about the coaster brake problem with reverse? They also didn't show chairs backing. These additions would increase costs, of course; but my chair was designed for the US. Added costs are the reason for health care! Those Jags the medical supply people drive don't pay for themselves!
Well, I'm bummed that I didn't get a prototype built and learn these lessons on my own. I'm fairly unskilled as a tinkerer, and would have had to learn how to build bicycles just to make something that wouldn't kill on the first go-round. I should be thankful that my pencil pushing never killed anyone. That's reassuring. I am glad that someone built, tested, and improved my notion. I'd also be jazzed to see an electric-assist version someday, even if I don't get a chance to build it.
If you read this and decide to build it, drop me a note. I abhor patents, so go to town.
(In fact, the fact that I'm writing this means if you build it, you can't patent it. Prior art trumps the process of securing protection. This LJ entry is enough to nullify the idea that the idea had never been considered. I guess I'm a bastard who cares more for people's mobility and exercise than I do for the American Way of becoming a rentier society. Ah, well.)