Mounting a Sprocket to a flanged /plastic wheel a bad idea ?

[amberwolf]

You could mount it on there the same way wheelchair handrails are done to their wheels, by using spacers on the bolts that secure it, to hold it out away from the wheel for the chain.

I recommend that you put the bolts as far outward in the wheel as you can, so there is less torque on them and their moutning points on the wheel.

I also recommend you bolt a spacer on the hub-hole of the sprocket so that it fits as tightly as possible around the hub of the wheel. Will help give more support to the assembly.

 

[amberwolf]

You just need whatever spacer type/size will bring the sprocket out far enough from the wheel itself to allow the chain to run on it without touching the wheel. That will be determined by:
--where on the wheel you put the mounting holes (as far outward in it's radius as possible) because the wheel's thickness appears to vary
--the distance from the surface it's being bolted to, to the inside edge of the sprocket
--the thickness of chain vs distance you want to allow between it and the wheel
--space you have between the wheel and the fork legs (or frame) holding it.

Realistically, it's probably easier to build an assembly that bolts to the fork/frame and friction drives the wheel, with the friction drive probably driven by belt or chain from the motor. (or use the motor can or shaft as the friction roller).

 

[amberwolf]

You can freewheel with any drive, in theory. The freewheel operates in the "same" direction as the drive, so that if the wheel is rolling faster than the motor/roller, it doesnt' spin the motor/roller, but if the motor/roller spins faster than the wheel, it does drive the wheel.

That's the same way the freewheel in a bicycle rear wheel works, etc.

That ebay wheel looks just like the stuff that McDesign has for sale cheap on ES.

 

[amberwolf]

Then it sounds like you need a different kind of "throttle" control. What you probably want is for the motor to not freewheel, but instead for the controller to detect you pushing against it (by voltage generated by it's forced rotation) and then engage the motor to match that speed, until you stop pushing.

I dont know how to do this, but it should be possible.

Essentially it is turning the kneewalker into a "bionic leg with wheels" for you.

There is a wheelchair that does this with it's in-wheel assist motors, which have the batteries in the wheel itself. I've forgotten the name but can go look at one of the batteries I happen to have from such a chair. It detects the push on the wheels and simply boosts the push so that it remains at the same speed the rider is attempting, but reduces the torque the rider has to put into turning the wheels.

 

[bigmoose]

OK, I did exactly this for our team in the FIRST robotics competition about 12 years ago.
See those 5 pie piece shaped sectors in the wheel? I machined aluminum inserts that exactly
fit within each pie section out of 1/16 aluminum. One piece on each side of the wheel. I put
a bolt through the center of each pie section that captured the sprocket. When we upped the
drive power I used some devcon metal filled epoxy also in the sandwich. Some of these wheels
are still being used by the high school team, now 12 years later. We never broke a drive based
on this concept.

 

[bigmoose]

I grit blasted the aluminum pieces and used the devcon to fill the void between the two pie plates
that sandwiched the plastic spoke pieces. The devcon does not need to bond to the plastic. The
devcon is not necessary for lower power. You can just space the aluminum pie plates with a washer.

I looked for a picture of the finished wheels, to no avail. I think I have some extra machined aluminum
pie plates in the lab if you need a picture of them.

 

[amberwolf]

There is a wheelchair that does this with it's in-wheel assist motors, which have the batteries in the wheel itself. I've forgotten the name but can go look at one of the batteries I happen to have from such a chair. It detects the push on the wheels and simply boosts the push so that it remains at the same speed the rider is attempting, but reduces the torque the rider has to put into turning the wheels.

Did you have any luck ?

[curious]
che

No, I am still doign the city-ordered cleanup of my place. It will be at least two weeks before that is done, and then however many weeks after that before I can re-arrange things so I actually have access to them, once I figure out which of the many piles of boxes I stuck them in. I have no time to sort things out while doing this, so stuff is just being put wherever it fits, adn there is a lot of it.

Best bet right now if you need the info is to google around for that type of wheelchair, cuz I really don't know when I can do it.