Which caster configuration is preferred on a cart and why… 4 swivel casters or 2 swivel casters in the back where it is being pushed and 2 fixed/rigid casters in the front? Is there a biomechanical advantage for one design versus the other? Thanks for any guidance you can send my way. Jeannette Murphy
Sorry, had difficulty on my first try. Again, four swivel casters are best for maneuvering in tight or confined spaces. They are bad where training or tracking is required. With swivels on the rear and rigids on the front the cart becomes difficult to track when moving forward. It’s like steering a car when the turning wheels are the rear wheels. Buckminster Fuller found this out on his Dimaxion car. It caused an accident on its very first trip. Rigids on the rear and swivels on the the front the cart are more predictable in movement, also if multiple carts (2 or more) are to be pulled or pushed in tandum this configuration is best. In many instances, I’ve seen carts with all swivel casters but with a manual lock to rigidize one or two of the casters for training in a straight line.
Most people place swivels on the rear and fixed casters on the front for a cart that is pushed. This allows the worker to steer the cart with their whole body as they push with their legs. If the swivel casters are on the front (think of a grocery cart), the worker has to use their arm strength, or twisting of their torso to create a moment arm (you wanted biomechanics!) pivoting around the rear wheels that is the length of the cart, using the short lever arm of the handle. This is more of an issue with heavily loaded or hard to push carts.
Personally, I prefer all four casters to swivel, if the cart is well behaved and the surface fairly flat and level, as this cart is easier to maneuver. This is especially important for A/V carts, carts pushed through narrow doorways, or those used in tight spaces such as in a hospital operating room.
Swivel casters cost slightly more, so I think that some manufacturers use 2 swivel and 2 fixed casters to save money/reduce costs. Depending on how much you are willing to spend, you can order/specify 4 swivel casters that lock into position, and have the best of all options.
Of course, there is also the ‘diamond pattern’ option, used on some larger, industrial carts, were there is a single, larger diameter, fixed wheel located along the center of each side, and a smaller diameter, swivel caster located in the center of the front and back. This style cart actually rocks or ‘teeters’ on the side wheels, allowing the worker to tilt it onto either the front or back caster for steering, and to pivot in a very tight circle.
Whatever you choose, don’t overlook caster quality, compatibility of the wheels with the floor surface (carpet, hard surface, oil resistance, etc.), and periodic maintenance to make sure that they turn smoothly and easily (again, think of shopping carts!)
You have two great replies. Tip: the more info you give about your application, the better will be replies to your query. My two cents is a great caster company I found after an exhaustive, 8-month search (really!) for small casters — found 2 types with 14mm wheels — Tente: http://www.tente.com/
David Alan Foster
Advice on this topic is given in “Guideline for design and selection of trolleys” which is included as Guideline 6 of our “Manual Handling Resource” (WorkCover, NSW 2004): see pages 86-93 of the pdf; http://www.workcover.nsw.gov.au/Publications/OHS/ManualHandling/manual_handling_resource.htm
Ergonomist, WorkCover Authority
New South Wales, Australia
Our publication “Manual Handling Resource” contains advice on a large number of popular topics but it is a rather lengthy compendium,
so you might want to look at these these while you are scrolling through :
Thank you for the responses I have received regarding my caster question. Here are two pictures that better explain the situation. The cart in question is used to access a large hospital grade autoclave. It is pushed a short distance and there is one 90 degree turn in a somewhat resricted area that must be made before aligning the cart with the autoclave. The operator must also make several small corrections to connect the cart to two rails that allow supplies to slide into the autoclave. jam
I was interested in the Cashier Workstation Redesign Case Study you mentioned in your post, but was unable to access the website. Is it possible to acquire this information in some other way?
Carts that are either long and/or have a high amount mass much easier to control with 2 swivel casters rather than 4. Carts that are smaller, require precision placement, or have a low mass 4 swivel casters usually works. Based on your pics I would go with 2 swivel casters. Ensure you purchase larger casters.
The other option is to get casters that can be locked into palce. This will allow you to test which is most effective, 2 or 4 swivel casters.
My spies tell me that you might need a fast broadband system to open all of them. All I can suggest is that you could try clicking your way down these lists of hyperlinks to see how many of them work.
Please start at the top of each list and work your way down: it seems to be the ones nearer the bottom of the lists that are causing problems for most people.
a) Manual Handling
b) Office Jobs
Ergonomist, WorkCover Authority
New South Wales, Australia
Any recommendation concerning the use or representation of a particular brand of product in this document or any mention of them whatsoever (whether this appears in the text, illustrations, photographs or in any other form) is not to be taken to imply that WorkCover NSW approves or endorses the product or the brand.
The castor array with a resultant central steering reaction point provides the best alternative for self tracking in a straight line, and lowest steering forces when required (resolves steering / load related forces). The disadvantage with the market trolley configuration (large centre wheels / axle supporting the load rocking between castors either end) is the rocking and potential instability rollover.
Research and development (& commercial manufacture) that I have done over the past 12 years has resulted in a number of international patents on our 5 wheel steering chassis and user interface. Publications of my research are: ESA conference – Gold Coast 1998, IEA SanDiego 2000.
Many thousands of trolleys are in the field over the 12 years with Zero incidence of injury in high manual handling risk applications.
The task related design of the load space and the generic chassis are key aspects of trolley design.
B.Eng (Mechanical & Ergonomics) Grad Dip OHS Risk Mgt.
MHFESA, MRMIA, MIEAust. CPEng.
email: [email protected]
Looking at the photos of your cart/caster application, most of your responses do not apply! It appears the cart may have a docking device for alignment to move the sterilization cages into and out of the sterilizer via the cart. I don’t know how far you travel with the cart, but having all swivel casters is your best bet if it is over a short distance. You can’t change to a larger caster wheel, which makes the cart easier to move, unless you invest in modifying the cart in order to maintain a compatible docking and transfer height.
Thanks for looking at the pictures of the carts and your response. I think you were absolutely correct with your assessment of the problem. The employees only have to push the cart 20 feet, at the most. The most difficult part is making those final adjustments to “dock” the cart. The past discussion, with so many different perspectives, was enlightening! Thanks again for your assistance. Jeannette
I forgot to mention that one of our other publications also had some advice on castors for trolleys. This is
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