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Zero turn radius without using swivel casters

  1. Oct 11, 2014 #1
    I'm not sure if this question fits here, but I've had trouble finding a good simple physics forum, so I signed up here :)

    I'm trying to think if the below wheel (image below) could allow for my push mower to have a zero or near zero turn radius. The edges of the wheel contour up (from the ground upwards), which should bend the blades of grass over and allow the wheel to glide over them (theoretically). The contact point of the wheel is in the middle due to the contoured edges. I would like to use this wheel instead of a swivel caster as it would still allow the mower to track straight much better than using a swivel caster. Also it would bolt right on with no extensive mods that the swivel caster would require.

    Am I thinking right? If there is any risk of tearing the grass (scalping) I will abandon this idea. These are called anti-scalp wheels however.

    I appreciate your feedback.

    zwrL9mg.jpg
     
  2. jcsd
  3. Oct 11, 2014 #2

    Baluncore

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    Welcome to PF.
    It would help if you could identify the make and model of your mower.
    Can you post us a web link that shows the caster geometry?
     
  4. Oct 11, 2014 #3
    Thank you, here is my mower: (standard 20" cut) A5JExit.jpg

    Also I said I don't want to use casters in my original post. The wheel in my first post would bolt right up to the stock axles. My question is, would this style of wheel (contoured edges) simulate zero turning due to the smooth plastic and shape. I don't want it to drag and pull the grass like the stock mower wheels.
     
  5. Oct 11, 2014 #4

    Baluncore

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    That mower is designed to be turned by pressing down on the handle to reduce the load on the front wheels, then rotating the mower about some point on the axis of the rear axle.
    I would consider replacing only the front wheels with the spherical wheels you have identified.
     
  6. Oct 11, 2014 #5
    I know that. I thought my question was pretty clear. I'm wanting to avoid pushing down on the handle bar and simply rotate the mower instead, hence my post. What I'm more insterested in is the mechanics behind this to see if this is a solid idea. Also, it was my intention of only doing the front wheels that way..

    Thank you :)
     
  7. Oct 11, 2014 #6

    Baluncore

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    I cannot see how you can possibly get the “Zero turn radius” mentioned in your title by only replacing the front wheels. The two fixed rear wheels set the centre of rotation to be on their common axis and not under the centre of the mower.
     
  8. Oct 11, 2014 #7
    Same principle as these mowers: (which is classified as zero turn by the way) Two fixed rear wheels that can move independently from each other (like a push mower) and two front wheels that can either swivel (like the below picture) or a spherical wheel like I proposed which would use sliding friction to recreate the 'zero turn'
    http://www.popularmechanics.com/cm/popularmechanics/images/Zs/zero-turn-mowers-04-0513-lgn.jpg [Broken]
     
    Last edited by a moderator: May 7, 2017
  9. Oct 12, 2014 #8

    Baluncore

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    Well, that shows a spherical wheel being used to set the level of the "mower deck", independent of the ride on frame's casters.
    Can you not just copy that?
     
  10. Oct 12, 2014 #9

    jack action

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    I understand that you think the wheel will «float» on the grass while moving sideways because of the round shape. That may be the case, I couldn't tell. It's probably safe to assume that it will do less damage than a «right angle» wheel. But two comments I want to say to help you in your reflexion.

    First, the wheel is called «anti-scalp» because its purpose is to allow the deck of mower (as shown in the picture you posted in post #7) to pivot over a hill or bump to help avoid scalping. The wheel should be slightly lower than the deck so that when the deck approaches the hill the wheel makes contact with the hill first. The wheel then lifts the deck up and over the hill. The scalping it prevents is done by the deck, not the wheel.

    Second, if what you propose was effective - as simple as you presented it - then why aren't the mower fitted with these wheels in the first place? The companies that build them are generally not that incompetent.

    But enough with the complaints, here is an idea you might like: Omni wheels.

    http://www.aliexpress.com/store/product/100mm-Double-Plastic-Omni-Wheel-basic-W049/512426_572721516.html [Broken], it works similar to this:


    You might even look at the possibility of ball transfer unit.
     
    Last edited by a moderator: May 7, 2017
  11. Oct 12, 2014 #10
    I tried 8" omni wheels last week and they failed miserably in grass due to the rollers being too small, so I'll be returning them. That is why I proposed the spherical (anti-scalp) shaped wheel. Using casters is a last resort as I want to take up less space and a 6-7" caster would require a large envelope for it to work in, thereby reducing the ability to mow up close to objects.
     
    Last edited by a moderator: May 7, 2017
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