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# Understanding Torque

## Understanding Torque

(OP)
I am working on ordering some gearboxes but I am confused on how to select the right one.

I work for a small fab shop and we are making a trailer for a foundation contractor. On this trailer will be two reels that are 20inches in diameter when empty and 60 inches when full. These two reels will be used to roll up plastic matting that will be used to drive equipment over to protect the customers lawns. The plastic matting weighs 400lbs and 300feet long. The contractor plans to unroll the matting by hand, engage the gearbox and then roll up both mats at the same time with one gearbox, so the gearbox will be mounted between the two reels.
I am at a loss to calculate the torque, maybe I am overthinking it or greatly underthinking it. Typically thinking torque I think weight * radius, which would be 400lbs * 30in=12000in-lbs. But wouldn't I have to calculate the torque needed to lift the mat from the ground up to the roll? Lets say from the ground to center of the reel is 48" * 1.33lbs(400lbs/300feet gives me 1.33lbs per foot)= 64in-lbs needed.
Then what about the torque needed to pull the mat off of the ground? I am thinking that figure would be rather high after having a vehicle driving over it, further pressing it into the ground increasing the friction.
I contacted two gear companies a few weeks ago for help but so far no replies.

Any type of guidance would be greatly appreciated. Thanks to all who reply.

### RE: Understanding Torque

A coating of mud on the mat alone, or combined with effects of mud on both the mat and the ground, will greatly affect torque requirements because of 1) cohesive forces, 2) added weight on mat, and 3) possible eccentric load on rolled mat. Plus, final roll diameter may be really big with just a little extra mud. Has the contractor already tried the mat on hand-rolled spools with good results?

What kind of safeguards are going to be implemented to make sure no one gets hung-up in the mat while it rolls up?

### RE: Understanding Torque

The sliding resistance from dragging 300+ sq ft of matting weighing 400 lbs over a grass covered surface would seem to be quite significant. When it comes to factors like friction that can vary significantly, it is usually best to do some testing.

### RE: Understanding Torque

(OP)
Thank you dvd and Tbuelna for the replies. Perhaps this is why the gearing companies have yet to reply since there are too many unknowns.

### RE: Understanding Torque

p.s. is the tensile strength of the mat sufficient to spool-in 300 feet of muddy, sticky mat?

### RE: Understanding Torque

Since drive-overs may cause the mat to become embedded in expensive lawns, you might eventually need to supply a roller, as wide as the mat, to be rolled away from the trailer under the deployed mat, so as to lift the mat locally out of whatever witness marks it makes.

Mike Halloran
Pembroke Pines, FL, USA

### RE: Understanding Torque

There would not be much friction resistance if the mat is rolled up as the trailer and truck move over it pulling up the mat as it moves along. It would be a mess to try to reel in 300-ft of mat by dragging it over the very grass that is to be protected! Perhaps the OP can specify how the mat is to be retrieved.

Walt

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