Variable Diameter Wheels

[KenWittlief]

Originally Posted by Andrew Blair

This is really what a toriodal CVT is. Just with one wheel.



http://auto.howstuffworks.com/cvt6.htm

oh MAN! they stole our idea! darn time travellers! :^)

[CJO]

In 2005 we had a long talk about "Dude, think about how cool a CVT would be", and then we had a longer talk about "Dude, think about how cool a 300 lb robot would be"

[Andrew Blair]

Originally Posted by KenWittlief

oh MAN! they stole our idea! darn time travellers! :^)

Ken, this is me > smiling.

[Veselin Kolev]

Easiest way to make your hemispherical wheels tilt is to have the motor and wheel all tilt together. 10 lb tilting assembly, with the weight of the robot on it. Sorry, but I'll pass.

But actually... it can be done. If you think about it, as the hemi-wheel tilts, it does not change the height of the robot. All you need is strong bearings on the tilting axis, and thrust bearings on the hemi-wheel. All it takes is the will to do it, and soon enough you'll see that it isnt that hard. You know, I bet you swerve drive is harder to do.

And as for me, I would control it with pneumatics. 4 cylinders, all at the same height, digitally set. When they reach the correct height, use a double and single solenoid to lock the cylinder where it is. fun fun. I will bow to the team that pulls it off.

[Andrew Blair]

I can't say i'll bow, but I will spend every spare minute ogling their drivetrain!

[sanddrag]

Originally Posted by Veselin Kolev

thrust bearings on the hemi-wheel.

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.

Like you said, it can be done, but now it doesn't seem as easy or fun anymore.

[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.

[greencactus3]

Originally Posted by M. Krass

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.

true. and you worded that very nicely.. i was only imagining zero radius turns and one side put. one side on turns. i guess depending on how much angle you can turn... like if you can turn the hemispheres a full 180 then you have a conventional skidsteerable robot.
but i just noticed... even if you do use only one motor for the entire drive, youd need 2 motors(or cylinders) to move the angle of each side independently. while if you do a rightside motor, left side motor, you can do the angling with a single motor or cylinder.

[Cuog]

For tilting the wheels it could be done quite easily:

have two sets of motors like an average robot this year, then have it drive a shaft that goes to the wheels, make a u-joint and an extending shaft that allows the angles of rotation you need,

the wheels would be on a folding down assembly that would pivot with the u-joint and extend the shaft as it needs, also i would use pneumatic pistons to raise and lower it setting the pressure desired for a certain height and the robot will push the pistons back in, so if you get hit in the front your front wheels begin getting more torque and the rear more speed to allow you to level yourself out becuase of these conflicting drives and then you lift the pistons up all the way and BOOM high torque

Gonna try it,
Cuog

[greencactus3]

Originally Posted by Cuog

For tilting the wheels it could be done quite easily:

have two sets of motors like an average robot this year, then have it drive a shaft that goes to the wheels, make a u-joint and an extending shaft that allows the angles of rotation you need,

the wheels would be on a folding down assembly that would pivot with the u-joint and extend the shaft as it needs, also i would use pneumatic pistons to raise and lower it setting the pressure desired for a certain height and the robot will push the pistons back in, so if you get hit in the front your front wheels begin getting more torque and the rear more speed to allow you to level yourself out becuase of these conflicting drives and then you lift the pistons up all the way and BOOM high torque

Gonna try it,
Cuog

waaait! i dont understand! where does the ubolt go? im so confused with your description... can you draw a picture for me?

[KenWittlief]

why use a Ubolt (universal joint) on each side? each set of wheels (left and right) can have one motor, and the motor tips with the wheel assembly as a unit.

Im wondering, would you want the high torque on the outside of the wheels or the inside? when you are leaning on the outside edges of the wheels your bot is more stable, which would be ideal in a shoving match, having more power to steer under heavy resistance

but having the outside edges down at high speed would also be good, if you are going to make high speed turns, to keep your bot from tipping

I could go either way on this one, depending on the game itself.

[Cuog]

yeah im bad at explaining, if the person on my computer leaves soon i can finish inventoring it, otherwise it may have to be hand drawn and scanned oh well

heres try II:

each wheel is mounted on a bearing setup that rotates on the base, the wheel has a shaft that runs into it, the shaft goes up to the pivot point and has a u-joint at that spot, the u-joint connects to a telescoping rod inside the robot which is then connected to the motor however you like.

[greencactus3]

Originally Posted by KenWittlief

why use a Ubolt (universal joint) on each side? each set of wheels (left and right) can have one motor, and the motor tips with the wheel assembly as a unit.

Im wondering, would you want the high torque on the outside of the wheels or the inside? when you are leaning on the outside edges of the wheels your bot is more stable, which would be ideal in a shoving match, having more power to steer under heavy resistance

but having the outside edges down at high speed would also be good, if you are going to make high speed turns, to keep your bot from tipping

I could go either way on this one, depending on the game itself.

im with ken on this. no need for a universal. a "conventional motor>gearbox>wheels" can all rotate. no problems there..

hmm. well it does depend on traction and speed but a high speed robot will be faster at zero radius turning (as in angular acceleration) if the track width is smaller. but also harder to control that way. if you do the high speed on inside, high torque on the outside, and have all four wheels on a sort of parallel 4 bar link, and at "neutral", the robot is on about the "center" of the cone, you lean all 4 wheel to the left and the robot turns left in a gentle swoop. so itll kinda handle like a motorcycle. kinda...
but thats offtopic. sorry.
um. personally i think i would go with torquey on the inside. faster to turn with even massive "low gear" and more stability at high speeds.

[KenWittlief]

another application for these cone shaped wheels would be railroads and subways.

as you enter a train station the tracks would be wider, the train would slow down and have more torque (stopping and starting power) (no need to tip the wheels)

then out in the great far-betweens the tracks would be placed closer together, and the train would take off like a bat out of you-know-where