Moment calculation help needed

[JMLH]

For years we have been using this old method to measure torsion spring torque with constant rod and strap loaded weight (see the file attached: picture 1.pdf). We add the weight until the rod turns to target position.

We need to make a new machine to measure the torque in order to make it faster to use. There will be hydraulic cylinder + force sensor to turn the rod and measure the force. In order to be able to calculate comparable result, we need to understand the physics of the old method.


If the rod angle is horizontal (center on the picture), let's say 0°, the case is pretty simple; T = 0,1 m * 9,80665 m/s^2 * 1000 kg = 980,665 Nm.

The reason I wanted to ask your help, are the left and right cases on the picture, where the rod angle is ±15°. The strap loop is placed on top of the rod end and the strap loop is about 1 meter long (not pictured here), and the strap is basically non-elastic. I need help to determine if my distances on these cases are right or not; d(1) = 0,115 m and d(2) = 0,08662 meters. Or are they all 0,1 meters? What is your opinion on this?

 

[goutam_freelance]

What is the type of connection between strap and rod? It seems the rod is angularly deflecting the specimen at the left joint of rod.

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[HTURKAK]

The moment/torque developing is not an opinion but fact..

M= T= r X F if you want to calculate the moment with scalar multiplication , r is the vertical distance from force direction to center. and r = d*COS A and for ±15° r=0.1* cos 15=0.0966

M= T= r X F = 0.0966* 9,80665 m/s^2 * 1000 kg = 947 Nm.

You can calculate also with vectoral product ...

P.S. = The assumption is , the strap hanging the weight is either flexible , or hinge connected to the rod and weight block.

 

[JMLH]

The strap is about 1 meter long loop, just placed on top of the rod.

Da*n, I writed it wrong. CORRECTION: Actually we have used to measure only the vertical force, just the way it's pictured on the 3 examples. It's been enough to determine if the tolerance is acceptable or not. The new method allows us to measure the torque, or actually calculate the torque based on the force sensor and linear sensor data.

But I also want to calculate the old data as in torque in order to be able to compare the results of springs tested with new and old method.

The question here is what is the distance between rod hinge point and center of force on the rod, on every three situations.

Maybe I need to test if the strap is flexible or non-flexible. One method would be to measure the same spring with old and new method and that way find out how the strap acts. Considering the strap is that long, I'd quess it stretches a little on that distance, so we can assume the position of force with respect to rod ON TOP OF THE ROD is a constant (=the strap / rod acts like a hinge).


Another question; is the force applied to rod on the centerline of the rod OR on top of the rod like the mark X on the file attached: picture 2.pdf? Rod thickness is 20 mm and the strap is considered 0,00 mm thick on the picture. If the later one is correct, it affects the distance when calculating the torque.

Is it correct way to calculate the torque like it's pictured on file: "picture 2.pdf" using 94 mm as a distance?

 

[3DDave]

Imagine if the angle was vertical - then the horizontal distance is zero so the torque is zero.

The more general formula is Torque = Force * distance between axis and location of force * sin(angle between F and d)

So if F is at right angles to d, then the sine is 1. This factor is always 1 or less.

 

[Strong]

You just need to add a digital/analog inclinometer to measure the slope angle. An angle correction would only apply when the torque arm is not horizontal. That's two measurements force and angle. Another method would be to use a torque sensor, such as a strain gage bridge on a cylindrical adapter that holds the rod under test.

Walt

 

[JMLH]

I already found an angle meter laying around wtah I can use. That sure helps.