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This article doesn't seem to actually answer the question well...

If you want to see the problem, watch carts being put in the cart storage pens and watch carts being returned from those pens to the store.

A very small percentage of the carts will end up in pens off kilter, then pushed in by the entire line of carts behind them. This bit of pressure can bend the wheel attachment. Now you say "this is only one or two carts", but in a busy store that cart can be cycles 5-10 times a day so this abuse adds up.

Then, watch the carts get returned to the front of the store. The handler pulls out a 40' long 'cart snake' that is unwieldly and heavy. You'll watch them drag the entire line sideways at points to get it in line with traveling the right direction and to line up with the return lines. Getting dragged sideways both wears flat spots in the wheels and it can bend the castors or pop the soft part of the wheel of its rim.



> Getting dragged sideways both wears flat spots in the wheels and it can bend the castors or pop the soft part of the wheel of its rim.

This may be an American problem. In the UK and many European countries, shopping carts ("trolleys") have castors on all four wheels; they will quite happily glide sideways. This makes them more maneuverable in the smaller stores, at the cost of being more difficult to control - more like the ship in Asteroids than a go-kart.


Ya a few places have these in the states, but as you say the control issues are problematic. The whole, an object in motion stays in motion tends to mean if you're pushing one of these heavy carts and try to turn it will rotate about its own axis rather than make a corner.


I have actually come to prefer the all-castoring design. It requires more skill, but less force and the acheivable performance is superior. To turn a cart with fixed wheels, you must apply torque to the push bar. As well as being too narrow to give good leverage, the cart is quite dynamically stable and so resists this torque, so you must slow down or tolerate a wide turning radius.

To turn a fully castored cart, you apply physics - all you have to do is orient the cart so that is pointed sideways, then push hard. The key is then to maintain the cart pointing 90 degrees to the direction of travel throughout the turn, so that you can oppose centripetal force merely by pushing - no torque required. When the turn is complete, simply stop pushing. The cart will at this point still be oriented sideways of course, but you can correct this easily at your leisure.


I am from Europe and we have storage pens with a roof (no idea if it's the same in the USA) and coin locks. Carts still rotate a lot over the day, but I know that blocked or off the ground wheels basically stopped being a problem once those pens with coin lock became a thing.

And yes, we don't usually have those 10m cart snakes, only if one pen overflows and workers take a huge chunk to relocate them.


The other part that affects things is the locking wheel to deter theft. All that does is make the person taking the cart drag it, flattening out that wheel.




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