Hi,
In recent weeks, I have been repairing "electric wheelchair" and similar devices for a local non-profit. There appears to be a lot of variation among these designs. And, within a design, there are innumerable customizations that apply based on the needs of the user (a "one size fits all" solution is impractical to addressing the needs of this divers population).
Among other things, the "performance" characteristics of a particular "chair" (?) can be "programmed". I suspect this governs things like top speed, acceleration, control sensitivity, etc. (though I haven't yet explored the details of this "programming")
For example, in a home environment, one typically wants slower speed operation and tighter control/maneuverability. OTOH, cruising down a sidewalk you would prefer a higher speed (as you would tend to have larger distances to cover!). And, of course, the physical capabilities of the user also factor into play (e.g. someone using a mouthstick would have different "control abilities" than someone using a joystick, etc.)
[AFAICT, there is no way for the *user* to alter this programming. I.e., no button to select "sidewalk mode" vs. "living room mode". So,the programming must have to be a compromise]I was test-driving one chair, recently and had an experience reminiscent of "Mr Toad's Wild Ride" (ending in a high-speed crash into a door!). Apparently, the chair in question is designed to be *fast* -- running at about 7 MPH (most people walk at a 3MPH rate). The design of the controls makes driving this a real challenge in an indoor environment!
Often, the charity discards these chairs as (practically) irreparable. Batteries usually need to be replaced (~$200). Or, the charger is damaged. Or, cosmetic issues. Or, the controls are too "customized" (e.g., the original owner's particular disabilities are too unique to find a similar user).
And, folks who "need" these often can get them (ahem) "for free" from their insurance policies, government agencies, etc. So, why bother with "something used"?
I am tempted to "rescue" the drive train (mechanism + electronics) from one of these "racing" (i.e., those that move at ~6-7MPH) wheelchairs to make a toy vehicle.
My first thought was something like a Segway. But, that's pretty boring. And, the idea of standing while riding is not appealing. Especially having to stand *still*!
My second thought was electric unicycle. However, I suspect the wheelchair mechanisms are too large for that *and* the speed much too high! (I've wanted to learn how to ride a *real* unicycle for years... but fear my body is too old to survive the consequences of the "learning process" :> Even moreso if that process was undertaken on a *powered* unicycle!)
The third thought was electric skateboard (one or two wheeled). But, that brings me back to standing, etc. I also wonder if local ordinances are written to prevent *any* "powered skateboard" use (after the uproar over those 50-100cc "buzz boards")
Conventional electric bicycles are also boring -- too "common" to buy an add-on kit that converts a regular bike to a "powered bike".
So, the idea that I am playing with is two *very* large dia wheels (e.g., maybe 48") with a chair hanging below their axis (i.e., the seated driver's head is below the top of the wheels). Note the absence of a third (or fourth) wheel to steady the device!
Then, use a Segway-style control mechanism that attempts to keep the drivers seat "level" by powering the wheels accordingly. E.g., this seems to be a variant of the Inverted Pendulum problem. Finally, a "control stick" that basically just shifts the center of mass around relative to that seat (I am thinking of simply mounting the considerable battery weight on the bottom of that stick so that pushing the stick forward moves the batteries back/seat forward thereby causing the controller to power the wheels forward as it tries to re-level the seat. Etc.
Something similar would apply for left/right control.
Also, I figure I would have to rethink the wheelchair mechanisms as scaling the wheel dia up by a factor of 4 (the existing wheels are ~1 ft dia yielding that 7MPH!) would dramatically impact power requirements (and speed!).
What issues might I encounter in the control system design that I should be wary of? Ive seen enough videos of contraptions like this "going wrong" (e.g., one wheel motorcycles) and have no big desire to add my own to that notorious collection! :>
Alternatively, any better, "interesting" applications for these sorts of motors/mechanisms? They're too big/powerful for "small loads" (e.g., imagine making an RC car with them: "Riderless", you could probably gear it to run at 50MPH!). They just seem too cool to casually discard!
Thx,