Variable Diameter Wheels

[greencactus3]

well offtopic but square wheels would keep the axle movement linear if the ground it were rolling upon was half circles... theres plenty of articles onthat all over the place if you're interested.. like square wheeled bicycles.

waaaaaaaay offtopic but with all the ways people have done and attempted multispeed robots, anyone try a variable wheel diameter? not in the transmission but like the wheel(or w/ tire) that touches the ground... it expands, and itll basically be like a higher gear. and also give more ground clearance... so little junk wont be in the way when its going fast but when it pushes, the center of gravity goes lower andmore torque is applied via smaller diameter wheels.
if you're tricky, you can probably pull that off automatically with some sort of centrifugal system.

[KenWittlief]

Originally Posted by greencactus3

waaaaaaaay offtopic but with all the ways people have done and attempted multispeed robots, anyone try a variable wheel diameter?

wow, I think you just blew my mind!

a sort of cone shaped wheel with a bit of a curve to it.

when one end is contacting the ground the 'wheel' diameter is very small, the other end large, and inbetween, infinitely variable!

all you need is pnuematics to tip the cone towards one end or the other.

[Andrew Blair]

Holy monkey! so if you could put them flatish, you'd be almost un-pushable! But I think i'd try to run them with a motor setup Ken. It'd be smoother, and more variable, unless you rig up a special exhaust valve.

[KenWittlief]

like this!

[greencactus3]

whoa. i was thinking a MUCH more complicated idea. but that is nice! hm.... if you'rw going to have variable angles on the axles, there has to be a way to incorporate that to do a multidirectional... something different from an omniwheel or a transwheel, or a rotating thing... w/e they were called. cant rememebr it right now tho.... hmmm.... darnit.. shoulda thought about it myself and blown everyone's mind at the competition lol. except i didnt have the variable andgle idea.... darn... woulda been cool for rookies to come out with a totally new concept like that and had it work tho. oh well' ill think of sumthing else

[Madison]

Originally Posted by KenWittlief

wow, I think you just blew my mind!

a sort of cone shaped wheel with a bit of a curve to it.

when one end is contacting the ground the 'wheel' diameter is very small, the other end large, and inbetween, infinitely variable!

all you need is pnuematics to tip the cone towards one end or the other.

Okay, I think I'm correct now -- wouldn't this end up being a hemisphere?

If you started with the driving shaft parallel to the ground, the wheel circumference would equal that of the hemispherical equator. As you pitch the shaft toward vertical, the effective wheel circumference approaches zero as the hemispherical pole comes into contact with the floor.

Does that make sense?

I have examined other methods of using centripetal force to engage a shifting mechanism. I would like, someday, to build such a thing to better get an appreciation for its challenges.

[greencactus3]

Originally Posted by M. Krass

Okay, I think I'm correct now -- wouldn't this end up being a hemisphere?

If you started with the driving shaft parallel to the ground, the wheel circumference would equal that of the hemispherical equator. As you pitch the shaft toward vertical, the effective wheel circumference approaches zero as the hemispherical pole comes into contact with the floor.

Does that make sense?

yup. makes sense. although i doubt anyone'll really need it to turn 90 degrees tho.. so a hemisphere will work fine but by having a "custom" curved cone shape, you can vary the surface contact patch are too. well i guess diameter and tire material play an effect into it, the skinnier it is the easier it is to turn so maybe you can have a small contact patch in "high" and a bigger contact patch in "low". and well you can make the transition between "highest" and "lowest" at different rates too. oh. you can even use different materials so high can be slipperier than low. WOW. this idea is incredible. you can have the grippiest tires possible in the "lowest".. you dont even need to be able to turn.... and have an omniwheel at the "highest" so you can manuever as fast as you want..... again. WOW... the possiblities of such a system...

Originally Posted by M. Krass

I have examined other methods of using centripetal force to engage a shifting mechanism. I would like, someday, to build such a thing to better get an appreciation for its challenges.

wanna share?

[greencactus3]

oh... sorry..... this is getting WAAAAAAAY off topic.... anyone want to move this into a new thread that would be more appropriate?

[sanddrag]

I'm liking the idea of hemispheres as wheels. You could actuate their tilt with pneumatic clyinders if only high and low were desired, or you could do it with a lead screw for much more variation. I'm just wondering what to make the hemispheres out of (and how) and what tread material to cover them with and how).

[Madison]

Originally Posted by sanddrag

I'm liking the idea of hemispheres as wheels. You could actuate their tilt with pneumatic clyinders if only high and low were desired, or you could do it with a lead screw for much more variation. I'm just wondering what to make the hemispheres out of (and how) and what tread material to cover them with and how).

What's further interesting about using hemispheres as wheels is that you can maintain constant driving power to them. You can drive all four "wheels" with a single gearbox. You do not even need to vary the power output to vary its speed.

This, to me, is far more interesting the square wheels. Who wants to file for a patent?

[KenWittlief]

you could also have one of these somewhere in your drivetrain, and have a variable speed transmission

instead of having the cone/hemisphere in contact with the ground, it drives an internal wheel that is part of the drivetrain.

[greencactus3]

Originally Posted by KenWittlief

you could also have one of these somewhere in your drivetrain, and have a variable speed transmission

instead of having the cone/hemisphere in contact with the ground, it drives an internal wheel that is part of the drivetrain.

but again, with frictiontype gearboxes, more can go wrong. i think its more worth lookinginto having the cone/himisphere as the final part rather than within somewhere.
i have a feeling something of the like has been patented tho. i have seen tilt wheel rc toys.... not sure if variable speed/torque was the point of those tho..
but if not, twould be sweet.

What's further interesting about using hemispheres as wheels is that you can maintain constant driving power to them. You can drive all four "wheels" with a single gearbox. You do not even need to vary the power output to vary its speed.

if you drive all 4 wheels with the same gearbox how can you turn? or are you saying about the angleing?
a leadscrew...hmm... or wormgear....or....

[Madison]

Originally Posted by greencactus3

if you drive all 4 wheels with the same gearbox how can you turn? or are you saying about the angleing?
a leadscrew...hmm... or wormgear....or....

By varying the diameter of the effective wheel on one side or another, you can vary the speed at which it travels a given distance. Make the wheels on the left larger than those on the right and your robot will turn right, for example.

[greencactus3]

Originally Posted by M. Krass

By varying the diameter of the effective wheel on one side or another, you can vary the speed at which it travels a given distance. Make the wheels on the left larger than those on the right and your robot will turn right, for example.

oohhhhh i see.... well thats kinda akward tho. no more skidsteer...

Originally Posted by ken

one of the benefits of a variable transmission like this: it can be in the high rpm part of the drivetrain, right on the motor for example

where the energy is hi rpm and low torque, so you would not need as much friction between the two surfaces, and the parts could be fairly small.

hmm.. true. but well for the sake of this thread, lets not talk about those cvts. lets just talk about variable diameter wheels. <nice title btw.

Dang, you just had to ruin it for us with that one little line! You are 100% correct though. I had totally forgotten about the thrust load issue. Nuts.

you mean balls?
[/quote]Like you said, it can be done, but now it doesn't seem as easy or fun anymore.[/quote]
well i saw a robot that had omniwheels on an extreme angle. people are doing it already. just not on a swivel...

and as for not changing robot height, then the center (of the sphere) of the face of the hemisphere must be within the angling axis. so dpendin on how bulky that wheel+gearbox+motor tilting assembly is, it may not be that practical.
but other than load issues for the cylinder or w/e angles the assembly, why not let the robot height vary? it might come useful. high off the ground for high speed movement so you cant get snagged on each carpet crease. and low down to push. and its kinda easy to lift the robot on a bar again if the game calls for it now too. retractable...

[Madison]

Originally Posted by greencactus3

oohhhhh i see.... well thats kinda akward tho. no more skidsteer...

Save for making a zero-radius turn, it'd be almost exactly like skid-steering. In fact, since you could keep the motor output at a full 12V throughout the turn, you'd be putting out more torque at the wheels during a turn than a traditional skid-steer arrangement would.