To ask an engineering question please visit our forum site at Eng-Tips.



Browse our archive of questions and answers below or to access our old forum database of over 10000 questions and answers please visit the old Ask@ forum.

Centrifugal Force??
Last Post 28 May 2012 06:02 AM by RCK_PE. 3 Replies.
AddThis - Bookmarking and Sharing Button Printer Friendly
  •  
  •  
  •  
  •  
  •  
Sort:
PrevPrev NextNext
You are not authorized to post a reply.
Author Messages Not Resolved
rudyeb
New Member
New Member
Posts:2

--
02 May 2012 07:49 AM
    I have a small motor that spins at 20,000 RPM. I have attached a steel wheel that has a plastic rim and a steel tire. When I turn the motor on, there is a force that is acting against the motor that feels like it s a centrifugal force or something. What is the actual force known as?

    Secondly, how does one determine the best wheel design, OD, ID Thickness to have this force be as much as possible with this motor?
    Does a large OD with a small steel tire create greater force than a smaller OD with a larger steel tire?

    I do hope I made some sense here and appreciate any input anyone may have.
    Thank you,
    Rudy
    Steen_Casey
    New Member
    New Member
    Posts:1

    --
    05 May 2012 02:29 PM
    Centrifugal force is the outward force caused by the wheels inertia attempting to keep every part of the wheel going straight rather than curve around the center point.

    You may want to state what the sizes of the wheel and motor are along with the application to help determine what you will need. Also you could say what your credentials are to get better answers for the people on here don’t know if their talking to a mechanical technician with 10 years experience and a doctorate or a 12 year old working on a school project which greatly changes what needs to be in the answer.

    There is a multitude of forces acting against your motor, I don’t know all of them for I am not a physicist but am only going off of my experiences working with car wheels. There is friction so depending on how the wheel was attached to the motor you may need to adjust the bearing(s) and make sure nothing is rubbing. There is also rotational inertia, so if the wheel or tire is off balance even a small amount it will have tremendous effects at high speed. the placement of the weight can reduce this effect, by focusing the weight more towards the center of the wheel you will have less rotational inertia allowing the wheel to spin faster easier but if you’re working on something that requires a specific wheel size then that would give less support to the outer edges of the wheel giving you less strength. If that is the case and you need to maintain the strength of the wheel as well then you can perhaps use different materials to achieve the same strength with less weight and a better balance.

    As for your second question the wheel design would have to depend on the motor. A small motor will need a small light wheel in order to spin it, and a large motor would likely need a stronger wheel to keep from breaking it. Another factor is price for if this is a high standard project with a high budget then you can make a custom wheel of a design and material specifically for the forces your dealing with, or it could be just a side project of some sort with a low budget in which case youll want to use whats available and close enough to what you might want.

    Hope this helps until someone who actually know what they’re talking about can give you a better answer. Feel free to add to or make changes to anything I have said because I know there has to be people smarter than I on an engineering website.
    shekharsaad
    New Member
    New Member
    Posts:37

    --
    13 May 2012 07:49 AM
    at the time of starting your motor feels the force called Inertia force. centrifugal force created by rotations not by force.
    as you use larger wheel motor need larger torque to take its desired speed. Make sure torque of your motor is greater than total mass of wheel*radius of wheel(Kg-m).
    RCK_PE
    New Member
    New Member
    Posts:2

    --
    28 May 2012 06:02 AM
    Answer 1: There is also gyroscopic force which is a function of inertia and speed. This is the force that keeps bicycles, motorcycles, etc. from simply falling over while they are moving. Even a small wheel rotating at high speed will generate forces that you can feel. The classic experiment is spinning a bicycle wheel while hanging onto the axle. As you try to steer the wheel you can feel a resisting force trying to keep the wheel straight. The faster the wheel spins, the more force is required.

    Answer 2: In general, for a wheel to rotate a such a high speed, you will want to concentrate mass (presumably the steel, so
    small OD
    for the steel parts) as closely as possible to the motor shaft and minimize the overall mass of the wheel to only what is needed to do the work you need to do. Also, the strength of the materials comes into play. The farther away from the motor shaft the higher the force will be to pull it apart (a=v^2/r). Note that the force increases as the square of the velocity.
    You are not authorized to post a reply.