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Discussion Starter · #3 ·
I'm building a new wheelchair prop. I'm putting notes, links, and pics here:


I'm still a little disappointed that J-Man wouldn't disassemble his prop to show us the guts ;)
 

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Discussion Starter · #5 ·
The new 4-bar wheelchair prop build is coming along. While waiting for weld nuts to be delivered I shored up the old wheelchair prop. Amazing what the brain can do with little Texas heat and Mexican beer.


749798
 

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Discussion Starter · #7 ·
This is the kind of cool prop that motivates me to finally buy a welder.
Get a welder! Something about being able to stick 2 pieces of metal together makes me happy BUT most anything that can be welded can be bolted. No welding used above. Since I didn't know what I wanted I sat down with a stack of metal, nuts, and screws like a giant erector set.

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Get a welder! Something about being able to stick 2 pieces of metal together makes me happy BUT most anything that can be welded can be bolted. No welding used above. Since I didn't know what I wanted I sat down with a stack of metal, nuts, and screws like a giant erector set.
I won't let my spouse see this or she might not believe that I "need" a welder. :)
 

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Discussion Starter · #9 ·
Not quite J-man's version, ....... I'm trying to build something similar for this year....
Wow. I didn't know you had made any progress until I found your post in the "what-prop-project-did-you-work-on-today" discussion. If you get a chance could you post the dimensions of your mechanism, cylinder, and cylinder throw?
You have the motion I'm looking for in my new wheelchair prop. I'm still struggling setting the lengths of the bars in the simulation software. J-MAN warned it wasn't very user friendly.

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750236
 

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Wow. I didn't know you had made any progress until I found your post in the "what-prop-project-did-you-work-on-today" discussion. If you get a chance could you post the dimensions of your mechanism, cylinder, and cylinder throw?
You have the motion I'm looking for in my new wheelchair prop. I'm still struggling setting the lengths of the bars in the simulation software. J-MAN warned it wasn't very user friendly.

View attachment 750235
For sure. I'll break out the CAD model after work and see how it compares to the as-built mech. Like J-man said, there was a lot of fine tuning that went into getting it to work that wasn't obvious from the simple CAD drawing. The main challenge was to not allow the 4-bar to lock up at the top and bottom of travel. The top was easy because my coffin doesn't allow it to travel all the way up (an error that thankfully had a benefit). At the bottom I have a piece of dowel taped to the back of one of the beams to keep it from getting into a locked state.
 

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Here are the pivot center-to-center dimensions (+/-1/4" since some of them were hard to get to with the coffin in place). The important ones are 9.25" and 7.75" for the verts and 27" and 26" for the horizontal members. Note that these are not the dimension of the actual aluminum extrusion bits since the hinges I used necessitated inconsistent offsets from the beams. Some additional photos below. My cylinder is out the back and that definitely wouldn't work for the wheel chair if the person pushing it wants to have children at any point. :)

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Discussion Starter · #13 ·
Thanks so much for your time. I hope I didn't steal too much of it. You sent me exactly what I needed but I got distracted by where your cylinder is mounted. I bet I end up with a garage full of prototypes :(

750363
 

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Discussion Starter · #15 ·
I might move to the "Ever have a simple project go bad and really [expletive deleted] you off?" discussion. I've spent a lot of hours in the the Texas heat and no matter how much beer I drink, I can't get the 4-bar mechanism to provide the sitting to standing action I wanted so my mind thinks the next step is to make it more complicated. Right now I'm thinking the new wheelchair prop will feature a pile of scrap metal left from my prototypes sitting in the chair.


Road surface Asphalt Wood Automotive tire Floor


Rectangle Slope Line Font Parallel


Font Parallel Office supplies Circle Logo
 

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Man. I really thought the beers would have helped with this puzzle. For what it's worth, I've only done one scissor mech and the problem I has was lateral stiffness. I had to aim the mechanism so that it pointed down (so it wasn't fighting gravity) or it would lean horribly to the sides. This was a pretty long mechanism though so you might not have that issue (or can do a better job keeping tolerances tight so there's less play).
 

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Discussion Starter · #17 ·
Wheelchair 1 with the larger air cylinder looked like an old man trying to stand up. I couldn't push enough air through my solenoids with 1/8" ports to make it go fast. After Halloween I reverted back to the smaller bore cylinder with drawer glides to prevent the shaft from bending.

 
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