Castor Wheel Contact Patch

[LeRepeteur]

Hello again all!

Simple question I'm assuming, but I can't seem to get the information I'm looking for via the web so I thought I'd try here. Working on a project where I need to find the contact patch of castor wheels on a Mr. Big Tool Box. There are 8 castor wheels that are 7" x 2" in size. Overall, the max weight allowed for each castor is 1-ton, while the total weight of the toolbox is 1198 pounds. Just need to know the area each wheel is contacting the floor so I can accurately represent it.

If someone could point me in the right direction that would be great. Everything I have found so far is making me use tire pressure so anything would help.

Cheers,
LR

 

[SwinnyGG]

You won't be able to get an exact value. You need to estimate. How conservative you estimate depends heavily on what exactly you're trying to accomplish - which you haven't told us.

 

[IRstuff]

Your best option is to actually measure the contact patch:

> cover the bottom of the wheel with something that will transfer to the floor below, one option might be double-sided tape on the ground and contrasting dust on the wheel. Jack the toolbox up, slide in the tape, release the toolbox, make firm contact, jack the toolbox up, remove the tape and measure the area. If your substrate for the tape has a measurement scale, you can then take a picture and use any number of imaging processing tools to measure the area of the patch.

> people have driven tires over a transparent window and directly photographed the contact patch through the window. But this requires pretty strong windows, so not necessarily applicable for a student project

TTFN (ta ta for now)
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[3DDave]

That patch will also change with the roughness and irregularities of the floor. If the floor isn't concrete or steel, the elasticity of the floor may also be a large factor - consider the contact patch with dirt.

 

[LeRepeteur]

Thank you 3DDave and IRstuff. I don't have the toolboxes in front of me due to it being a customer request. We are seeing if multiple toolboxes on castors would break through our floor we currently have in a standard version of a trailer we are designing. Wanted to make sure I incorporated the correct distribution of weight on the floor with the toolbox castors.

I am going to assume/estimate like SwinnyGG replied with and see where she lands. I'll probably run another test with a singular contact point for the castors instead of the contact patch so i can see the difference.

Cheers and thanks for all the help

LR

 

[BridgeSmith]

Unless your floor is perfectly flat, for design, you should assume the weight is distributed to only 2 casters, so a 600 lb point load.