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Friction of spheres & cylinders

  1. Nov 15, 2006 #1
    Hi,

    I am doing a project involving spherical wheels. I need some help with regards to the role played by friction on motion of spheres and cylinders (normal car wheels) on roads. Will friction act forward or backwards ?? Which type of wheel would be more advantageous ??? Would appreciate any help or inputs to make me move ahead. Thanks
     
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  3. Nov 15, 2006 #2

    brewnog

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    It's meaningless to ask whether friction on a wheel acts forwards or backwards. It will act in the direction which opposes movement.
     
  4. Nov 15, 2006 #3

    Danger

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    And which type of wheel would be more advantageous depends entirely upon the application. The only reason that I can imagine to use a spherical one would be in a case such as the 'ball-bots' where rotation in all directions is needed. It would have almost no traction due to the minimal contact area with the road.
     
  5. Nov 15, 2006 #4

    FredGarvin

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    Advantageous in what respect? It's difficult to provide feedback if you don't tell us what you are trying to accomplish.
     
  6. Nov 16, 2006 #5
    Basically i am making a project based on a solid spherical wheel. I am required to show how this wheel is better than a normal cylindrical wheel in aspects such as friction. Couold i please get some help on this topic, to show that the solid sphere is more beneficial than the circular wheel (based on friction). Thanks.
     
  7. Nov 16, 2006 #6

    Mech_Engineer

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    I can't really think of any reasons the solid spherical wheel would be beneficial over the standard circular wheel for conventional applications, but I can think of a lot of reasons why it wouldn't be. Here's a couple:

    1) More rolling mass given the same rolling diameter.

    2) Solid sphere will supply no give.

    3) Mounting it with an axle through it would make it essentially a standard wheel with a bunch of unnecessary weight.

    4) Rolling resistance would only be decreased on VERY smooth surfaces, but on irregular surfaces it would be more difficult to roll.

    ...
     
  8. Nov 16, 2006 #7
    wouldn't a sphere have just as much lateral friction as friction in the direction of travel. limiting a sphere to only level ground. any uneviness or slop would make the wheel turn downhill, or if the slope was too great you would slide downhill just as much as you would traverse. (i think).

    if at speed the extra mass of the sphere will cause more gyroscopic effects. making control more difficult.
     
  9. Nov 16, 2006 #8
    assume the mass and the radius of both the wheels(sphere and cylider) to be the same.(density of the sphere being low)..hence for the same torque applied on both the wheels , the angular acceleration of the sphere would be greater.would this be a right statement. as moment of inertia of a sphere is less than that of cylinder.

    also we are considering the sphere to have an outer coating similar to that of a normal wheel.hence by reducing the pressure, one can attain more than just point contact with the ground.

    i wanted to know, how friction would effect the rolling of a sphere?
     
  10. Nov 16, 2006 #9

    russ_watters

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    Since rolling resistance is mostly a property of the materials in the road and tire, I don't think t would be relevant here. Ie, a ball bearing on a smooth steel surface has near zero rolling resistance, but then so does a metal cylinder.

    It would also hep to know what type of application we're talking about - a car? A ball bearing?
     
  11. Nov 16, 2006 #10

    russ_watters

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    Yes. But whether that is beneficial or not is another issue. As someone pointed out earlier, your contact points aren't the same, so your sphere is essentially a cylindrical wheel with a lot of extra, useless material on the sides. Why not just use a narrower wheel?
    Softening a tire is what causes rolling resistance. So the net effect will be that you'll add rolling resistance if you want to soften the tire enough to have the same contact area.
     
  12. Nov 16, 2006 #11
    we are using concept of spherical wheels in vehicles for our project. there is no axil running through the wheel. it works with rollers holding the sphere in place. we would like to know if this wheel will have more or less friction when it is put on the road. will more or less friction be adventageous?

    would softening the tyres add to the rolling resistance or help to provide more grip when a vehicle is taking sharp turns?
     
  13. Nov 16, 2006 #12

    Danger

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    I don't mean this as an insult, so please don't take it as such. Once you've investigated the incredible amount of calculation and experimentation involved in the design of both tires and suspension geometry, I think you'll realize that the concept of spherical wheels is pretty much a waste of time. I know that I would certainly never ride in a vehicle that was equipped with them.
     
  14. Nov 17, 2006 #13

    Danger

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    Another point here, which I let go by a couple of times...
    If you are indeed using the same sort of drive/control/suspension system as the ball-bots (like a computer mouse ball), then softening the wheels will cause all sorts of control problems. As soon as they're no longer rigid, they're no longer spherical.
     
  15. Nov 17, 2006 #14

    brewnog

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    Sudhu. How would your spherical tyres actually work? As Danger points out, you won't really be able to control them, but how do they support whatever is inside them? And as for friction, think of your contact patches; a sphere has a tiny contact area compared with a cylinder.

    Some severe 'thinking through' is needed here mate.

    Softer tyres increase friction and rolling resistance, but how would you soften a spherical tyre?
     
  16. Nov 17, 2006 #15

    russ_watters

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    Mouse-ball style. Ok. For certain applications there are obvious advantages to that, but we still don't really know what you are trying to do.
    From what you describe, most likely more (rolling resistance, anyway).
    That depends on your application.
    Both. Read your car's manual where it talks about tire pressure.
     
  17. Dec 21, 2006 #16

    Shu

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    Have you managed to create a system to control a sphere wheel or is this a concept design?
     
  18. Dec 28, 2006 #17
    Hi ther, Iam also a person in the virtue of producing a conceptual design in the spherical wheel, the best way to design the car is to look at the audi rsq car. it comes in the movie i-robot and it is a conceptual design of the spherical wheel car, the car has 4 spherical wheels and exactly follows the method of mouse ball rollers for producing motion in the spheres. (ie, one in the x-axis, one in the y-axis, and one in the z-axis on each and every wheel) that becomes 12 output speeds, and each roller has to rotate at diff speed to attain the direction of motion and speed on the balls, so we r going to use 2 gear, 2 motors, connected to a single micro-processor which controls every direction of motion, steering is impossible as far as my knowlegde could search and even it is available the cost is high enough to go off the roof, so the steering for our car is goin to be button system over direction and manual control over accerleration and braking as in normal cars.

    The advantages of this concept is 1.Very less power is required to drive the vehicle as contact surface of the balls are minimal and very less force is required to rotate a sphere, 2. Evenly loaded with weight can rotate in all direction remaining inline with the vertical axis of the carried weight and speed of motion, 3. Offers most easy change of direction since it doesnt need to re-align to the movement direction, 4. The anti-over turn funtion of spherical wheels is most advantageous since it doesnt have the stopage of the motion perpendicular to the direction of motion as in the cylindrical wheels, therfore the vehicles can be tall and narrow neglecting the ground clearance and centre of gravity, 5.Sphere wheels can work oblique till 15 degrees 6.Due to its shape,the sphere cdan surmout obstacles from any position,both front and lateral, instead of the traditional wheels which cannot the latral obstacles. 7. Spherical wheels can easily move because each wheel cahnges its directoin independently of the other ones. 8.Very less friction over wheel and road so greater speeds with less power. Disadvantages: 1. Control over slopes is difficult, 2. Irregular sphere can cause problems which can happen due to the irregular contact surface over the roads when in motion. 3. Less friction therefore very diffucult when braking (ABS) 4. When travelling in one direction only one rollers of the three in use, for ex. travelling in forward motion uses only the x-axis rollers, but all the other rollers are also in contact, this reduces the friction between the rollers and the balls which is the essence of frictional drive in this concept and the shape of the ball becomes irreglar easily, this is my concept and iam dying to suceed so any of u brainstroms out there read this reply, give us some thoughts.......l
     
  19. Dec 28, 2006 #18

    Danger

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    Consider the source. And, by the way, the movie had absolutely no resemblance to the original book by Enio Binder entitled "Adam Link: Robot". The new version of the Twilight Zone did it properly.

    Does the term 'spin-out' ring a bell? Any racer will tell you that while a smoke-show might wow the crowd a bit, it will lose you the race. You want maximum friction between the tires and the road to actually go somewhere.
     
  20. Dec 28, 2006 #19
    Yo Man! if u dont understand the concept i dont blame u its pretty tough to understand..... but since u dont i will tell u once more that THERE IS FRICTION between the sphere and the Road, only minimal and that is enough to keep the sphere rotating, and for the spin out, it only occurs when the sphere is deformed or out of shape, i know that it wont happen in this high standarad experiment if u do it with precision, if u cant then dont blame me!
     
  21. Dec 28, 2006 #20

    russ_watters

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    Easy, spwheel. As we discussed earlier in the thread, there is a really good reason why car tires are the shape they are. Yes, a smaller contact area means less rolling resistance, but if that were such a good thing, our cars would all already have bicycle tires.
     
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