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I need design a trolley with four casters, the four casters are installed on the four corners of a 460mmX405mm metal plane. And the load will be a cubic 380mmX225mmX350mm (Height is 350mm), weight about 150Kg, site at the center of the metal plane.

The dimensions of the casters is as below:

enter image description here

You see the support point of the caster and the wheel are not on a vertical line, so I'm afraid when all four wheels in the same direction, the trolley will not be stable. So I go here for some suggestions(or some formulas are better), if the trolley can works stable? Or I must change my design, such as enlarge the metal plane?

diverger
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  • Good! Welcome here in the review queues. :-) – peterh May 18 '17 at 07:05
  • Are you refering to static stability or some dynamic one? – joojaa May 18 '17 at 07:31
  • In your drawing: we cannot find the exact distance between the centre of the wheel and any of the 'support point' otherwise taking ~35mm center to center, I can immediately say that the system is statically stable, even if the load is on the border and on small side. dynamically will be your problem: but also for this you have to provide more info. – Jonathan May 18 '17 at 08:06
  • Yes, the center of the wheel and the support point of the wheel is about 35mm. – diverger May 18 '17 at 11:01
  • Crossposted from https://physics.stackexchange.com/q/333922/2451 – Qmechanic May 18 '17 at 15:46

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Consider using two of the trailing ones you show at one end and find two similar that are fixed ie not trailing at the other end. This will give stability and manouverabilty as well.

Solar Mike
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  • It's not feasible to use two fixed ones. If stick to using four such non-fixed ones, how large the metal plane should be at least? I think there must some physics behind this. – diverger May 18 '17 at 07:15
  • Look at some supermarket shopping trolleys or the trolleys / carts used for taking mail around large offices. – Solar Mike May 18 '17 at 08:18
  • @SolarMike : Plates with four trailing wheel are also quite commonly used: it gives more manoeuvrability on small spaces (like the plates to lean under the cars, or what the movers use to transport heavy loads) but is hard to lead from the side (need to lead from the middle) – Jonathan May 18 '17 at 12:57
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    @Jonathan, yes spent a long time on those crawling boards - and I exceed the OP's weight limit :) – Solar Mike May 18 '17 at 14:34
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As long as the worst case (all wheels pointing to the center) is still stable then you have no issue.

To look at the footprint first create it as if you didn't use castors. Then for cornet with a castor move the line so it's tangential to the inside of the circle the contact point makes when swiveling. Note that this may mean that the apparent contact point is outside that circle. For a rectangular base you can subtract twice the radius of the swivel's offset on each side.

Then you can use that footprint for your stability calculations.

ratchet freak
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