Meg-Mo Floating Balance Explained - Maybe!

Discussion in 'Lawn Mowing' started by Richard Martin, Aug 15, 2003.

  1. Richard Martin

    Richard Martin LawnSite Fanatic
    Messages: 14,699

    Objects that are out of balance tend to want to be in balance. This is why an unbalanced object shakes when it is rotated. A car tire is an example. As the unbalanced tire rotates the heavy and light ends of the tire want to equalize their weight. Since the tire is a solid object the weight cannot move and the tire shakes as a result.

    Mower blades are the same way. To balance them you can either remove weight from one side of the axis or you can move weight as it relates to the axis. The Meg-Mo blades move the weight as it relates to the axis.

    To get an idea of how moving weight affects balance find yourself a yardstick. Balance the yardstick on your finger at 18 inches. The yardstick should sit perfectly level. Now if you move the yardstick either way even a quater inch the yardstick will start to lean in the direction that you moved it. Simple isn't it?

    Okay, now we know that unbalanced object shake as they attempt to balance them selves. We know that if you move weight you can either balance or unbalance an object.

    (At this point I suspect that a bunch of lights just came on)

    Now since the knives (blades) on Meg-Mo blades are able to move up and down as well as back and forth we are able to deduct (using our giant man brains) that, unless the knives are grossly out of balance, the Meg-Mo blades are able to balance them selves.

    Any questions?
  2. Doc Pete

    Doc Pete LawnSite Gold Member
    Messages: 3,469

    Yes Richard, who sold you that bill of goods? Look, moving "up and down" does nothing to balance the blade since their distance from the center of rotation doesn't change. Second, moving back and forth is called "lead and lag", which occurs all the time in a Helicopter and is a "constant", depending on where the "center of weight" is located on each blade, which again doesn't not change. If, however, these "center of weight points" could change in relation to the distance from the center of rotation, as the disc spins, then your statement is true, but they don't.
    Actually, just use your head, if moving "front to back" could change the balance, then as the blades fold back while encountering heavy grass, the system would go out of balance and shake like heck.
    Furthermore, if back/forth and up/down movement was occurring, it would have to occur twice every revolution (continually rebalance) or 120 times a second. FYI, 120 comes from assuming 3,600 rpm, which breaks down to 60 times a second and times twice a second.
    At that rate, if the pieces where really moving that amount they would wear out in no time, regardless that they'd have no bearing on balancing. Sorry, we're still at the Mumbo Jumbo stage.
  3. Doc Pete

    Doc Pete LawnSite Gold Member
    Messages: 3,469

    As I've said, balance is not a big problem.....Just keep quiet about it and don't try to give me a snow job about it...........
  4. John Gamba

    John Gamba LawnSite Fanatic
    from ct
    Messages: 10,812

    I Don't Know what Pete Said, But It sure Sounded Good.
  5. geogunn

    geogunn LawnSite Gold Member
    from TN
    Messages: 3,010

    richard--I dunno a thing about the meg-mow discussion but I thought I'd comment on the physics involved of a standard blade.

    in dynamic studies, rotational theory does not support your statment that an unbalanced rotating object will try to balance itself.

    in the ratio of centrifugal vs. centripital forces, at least in theory, an object rotating about an axis will demonstrate a force in the ratio 4 to 1 in favor of the extended limb of rotation.

    so actually, an out of balance rotating object will want to be even more out of balance as rotational forces increase.

  6. Richard Martin

    Richard Martin LawnSite Fanatic
    Messages: 14,699 wrote:

    If, however, these "center of weight points" could change in relation to the distance from the center of rotation, as the disc spins, then your statement is true, but they don't.

    Ah ha. But the center of weight point does change as the knives swivel on the bolts. When the knives are all of the way out then the entire diameter of the blade from tip to tip is 20.5 inches. But when the knives are all of the way in then the diameter is greatly reduced by about 8 inches.

    Also the up and down motion of the knives does contribute to balancing. Lets use an auto tire to prove this.

    If up and down were not necessary to balance a blade then why are wheel weights placed on one side or the other of a tire rim to balance it? Using your explanation one would assume that the weights could be placed on one side of the rim and achieve balance but we know that is not true.

    geogunn wrote:

    so actually, an out of balance rotating object will want to be even more out of balance as rotational forces increase.

    I have no doubt that you are more learned in this area than I am. But again I am going to use the auto tire analogy to disprove this.

    Say you're driving down the road at 35 mph and you notice that your tire is out of balance a slight bit. There is a slight shake in the steering wheel. Using your theory as the speed increases then the balance should get worse and worse until the vehicle becomes undrivable. But we know that it doesn't. We all drive cars and see this happen. Sometimes the vibration disappears. I know that harmonics definately play a part in the disappearence of the vibration. Where did the vibration go? Why didn't it get worse? Did harmonics act on the tire assembly to balance it out?

    Don't get me wrong. I'm not trying to be a smart guy here and no one sold me a bill of goods. I'm just trying to get a handle on the floating balance. My Giant Man Brain is working overtime. :D
  7. Doc Pete

    Doc Pete LawnSite Gold Member
    Messages: 3,469

    So?????.......Stop right there. Once the blades spin up, they fully extend, period. The force on each blade to extend is in the "hundreds of pounds" of force. Answer this... What in God's name do you think would keep each blade from fully extending??? Balance??? Really, think about it.
    Who is feeding you this misinformation???? Use your head. You're a smart guy. What does the "weight" of each blade have to do with how far they extend??? Really??? Come on. I hope I'm sounding like the days of old ;)
    Please, I don't mind balancing things, but don't feed me a sales gimmick, it only lowers the standard of the product.
  8. Doc Pete

    Doc Pete LawnSite Gold Member
    Messages: 3,469

    Furthermore, if the blades "COULD" actually be made to move in by some sort of lever linkage attached to the other blades, Here's what would occur. This would cause the weight of the blade to be dispersed "behind" the imaginery line draw though the blade bolt hole, through the center attaching bolt and through the blade opposite to the other blade. This in turn would put the complete disc out of balance because the "balance center" would not be off center of the point of disc attachment.
    Here's a picture. The blue line shows the balance center of the two opposite blades balanced going through the center bolt hole. Now, moving the one blade back moves the center line of balance between the two blades and puts in off center of the center bolt causing vibration. This condition can happen with any combination of blades. Please, also understand the blades cannot possibly move forward, or ahead of the centerline of balance to "somehow" counteract a force. Likewise, both opposite blades cannot possibly decide to move backward automatically to balance the system.

  9. Cut This!

    Cut This! LawnSite Member
    Messages: 48

    You guys are spending WAY too much time on this.

    If you're not seeing or feeling a vibration in your mower deck, do you really think any minor in-balance that may or may not exist will cause a problem?

    Maybe it's time to argue about something else.

    You're basically beating up the balance theory of a sponsor who has given any unsatisfied LS person a 30 day money back guarantee. (Actually, I'm not even sure anymore if it's his theory or one of ours).

    So either take him up on his offer or don't buy the Meg-Mo blade: but in the end, arguing this point is... well... pointless.:dizzy:
  10. Spindles, who needs them? After all, they are highly overrated. LOL

    The concern here is expensive spindle life. If the blades are bad out of balance, many people wouldn’t even notice right off. Some would assume it’s normal for these new blades and run the mower anyway, hoping the problem will just go away (which eventually it will, hehe). But the time it takes to prematurely wear out the bearings is directly proportional to the amount of mass, the angular velocity, and the number of cycles (revolutions).

    Not feeling vibrations doesn’t mean anything. If the blades are “slightly” out of balance, it would take much longer than 30 days to wear out the spindles, but it would be too soon. It would probably take a lot longer than 30 days to wear out the spindles if they blades are very much out of balance.

    Some people don’t care. I guess they figure on replacing spindles, and other vibration sensitive components like they do worn out tires. If that’s someone’s point of view, fine. But like Switchless was saying, just don’t try to give us some half-cooked idea about how these Meg-Mo blades magically balance themselves.

    Meg-Mo blades look like a good product. But frankly, it’s just that kind of “salesmanship” (or lack thereof) that keeps me from trying these blades myself. Simpleton claims like: “the blades don’t nick;” “they don’t need sharpening;” “these blades balance themselves;” etc. etc. remind me of: “Congratulations! You’ve just won ONE MILLION dollars (payable in $33,333 installments over 30 years).” Which comes out to be around $60 a day. Don’t hold me back. LOL

    I’m not going to judge someone for their lack of communication skills. But if I had a business to run, and was serious about it, I’d either learn how to CLEARLY use the English language to answer potential customer’s questions directly, or hire someone who could. I find many of the replies posted by the Meg-Mo rep to be difficult to read, much less understand.

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