Calculating torque required to turn a stationary wheel ?

[FAlonso]

Hello all,

I wanted experienced people here to suggest me where can I find calculations for determination of torque to turn a stationary wheel ?

I am working on a machine which has a table supported by four legs and all legs can rotate aat 90 degree allowing wheels to change their orientation for movement in either x or y direction. The machine will turn its wheels into required direction before moving, which of course means the wheels would be required to turn while stationary. The turning mechanism is a worm reducer mechanism. Each leg has a gear installed on its girth which is driven by a worm. I want to calculate how much torque should this assembly provide per leg to turn it across 90 degree.

Some hints or reference material are welcome

Regards

 

[huntoon]

Hi,

I think you need to find more than torque. You need to find tractive effort required to overcome slewing and travel resistance.

Can you draw a picture of your setup to help us better understand the system?

 

[FAlonso]

Thanks for your reply huntoon.

I have the solidworks model. Just gimme some time to put some added details onto it and post it.

One thing I would like to make clear is that while steering, the cart remains stationary. It travels after the wheels have been steered to the desired direction.

 

[huntoon]

One thing I would like to make clear is that while steering, the cart remains stationary. It travels after the wheels have been steered to the desired direction.

Another parameter we need to account for is the weight of your setup. You resistance to motion will be the weight of your machine * coefficient of friction. So we need to know the surface you are operating on and the material of you wheels.

For slewing resistance, I am not entirely sure how to apply it to this setup, but we need to know the distance between the legs of your machine. The wider apart the legs, the easier it should be to turn. Think of a funny car versus an f1 car. the f1 has a wider stance (relative to it's length) which helps the turnability. Or, a limo versus a honda civic.


Adding these two values together, slewing and travel resistance, should give us the required tractive effort (in Newtons / lbf).

Torque will be then determined the gearing setup.

but we need as much info as possible tog get started.

 

[FAlonso]

OK I talked to one of my teachers and he said the main thing to be considered is the area of contact patch of the tire since it's a rubber tire on concrete floor and the rubber will surely deform under heavy load.

 

[FAlonso]

Here's the concept with some details not drawn in current model as it's a bit old and has been updated later on:

The gears you see on the girth of support legs would be driven by worm, thus resulting in the support leg being rotated.

The tires have a rubber installed on them and the entire thing will move on concrete surface. I will get the value of friction for a rubber tire on concrete surface probably from Handbook of physical quantities, apart from that I need to consider the contact patch for which I can get a rough approximation. Few hints for starting up would be helpful

Regards

 

[huntoon]

Cool design, man.

I don't know about hard rubber tires but for pneumatic rubber tires on concrete it's:
Roll resistance ratio is 0.01 (good) - 0.02 (poor)
Mean vehicle adhesion ratio: 1.0 (good) - 0.6 (poor)

 

[huntoon]

Here's where I'd start:

Tractive Force = total machine mass * g * adhesion ratio

Torque = (Tractive Force * radius )/ (# wheels)

Torque = mg* adhesion ratio * r/ 4

 

[FAlonso]

Thanks a lot sir, your help definitely means a lot to me and I am starting off from this. Of course as I discover more parameters to be taken into account, will improve

Thanks again ! Best Wishes

 

[huntoon]

My pleasure to help FAlonso. Please make sure not to take my comments as gospel though. I am offering my best guess based on what I understand in these posts. Your best bet is to fully dissect the problem and if you do come to a solution please post it here.
Thanks.