A square wheel

[nicbordeaux]

Maybe a kind forum member can answer this one : if one has a round Wheel, and a square, both perfectly center drilled, and with an "OB weight" placed at an identical distance from the center, what will the differences be in stress or action upon the bracket or else to which the Wheel axle is attached.

Both have identical mass. Which would imply, I suppose, something horribly complex in terms of density, size and other thingies.

Both are "balanced" , but the distribution of mass is different.

ps : I wouldn't know a quadratic moment if I stepped on one, so if you could avoid quadratics you'd be doing me a favour ;-)

[ME]

As far as I know:
If you don't care about quadratics then I don't think there's hardly an issue because an equal weight is balanced on the same axle...

A circle is more compact compared to a square (hence a balloon is spherical)
This means the Moment of Inertia (MoI) of the square is bigger (When I used the quadratics correctly: 4.7% bigger) and act as like it had a little bit more mass, thus any torque on the wheel results in a little bit less acceleration, and any momentum acting on a square wheel results in a little bit less angular velocity.
Because of the larger MoI it will also resist slowing-down a bit more; but because a square is less aerodynamic that could be the biggest issue and make you want to use a circular one.

Hope that helped.

[nicbordeaux]

Yes, thank you, that did help. Looks like what is needed is a circle for initial acceration to Vmax, then flaps on the circle deploy outwards to make it a square, then the flaps retract to make it a circle on the upstroke :-)

Which is a waste of time, it's like having weights sliding about on or in a Wheel and expecting no loss due to action/reaction "contradictory forces".

Discounting aero aspects, the biggest advantage of a square is that it is easier to make perfectly balanced and centered than a circle.

Thanks again.

[ME]

Lol, you could call it a "Fly-square".

If you happen to have a working mechanism you may choose any shape you like (not our main concern)
If you don't have a working mechanism you also may choose any shape you like (try them all if you like)
If you market your working mechanism, it will probably be put inside some box anyway (eventually no one wil know or care)

Perhaps you could make it more aerodynamic with some cardboard if you really want to squeeze out some more, but by the time you actually need such 'addition' you rather want your design to be CNC-ready...

Some other considerations for circular stuff:
- Simply a "clearance" issue and a lower Center of Gravity of the whole system;
- Safety issues (with those flying corners);
- Belt brake (belt pickup) at the rim;
- ...

[nicbordeaux]

The main thing you need in case you ever mistakenly discover perpetual motion is a 12 bore, because that'll stop most things which show signs of getting out of control.

[Charinthara]

My opinion, as well as comment on.