Force Calculation to balance arm

In summary: I am glad I could contact someone who knows more about this than me.In summary, Mr Howell calculates 676N as the required torque to hold the arm in position, while another person calculates 3833.18N as the required torque.
  • #1
gavhowe
4
0
Hello,

I am after a little help on an applicaition, I need to calculate the force require to hold a pivoted arm in a position using a pneumatic ram. Basically the arms C of G is 740mm up the arm, and the arm weights 100kg. Roughly 1000N working at an offset of 147mm. The arm is 16 degrees from vertical, with the ram at 62 degrees to the arm, so it is pulling to hold the arm in position.

I attach a diagram to give all the information

I had a friend take a look and he calculated 676N, I am not sure if this is correct. As I could not follow is method or workings. I attach them as well.

Thanks

Mr Howell
 

Attachments

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  • Applicaitonworkings001.jpg
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  • #2
The arm is rotating around the pivot at its lower end, right? The pivot at the end of ram's shaft is there just to allow the ram / arm angle to change freely.

Moments should be taken about the pivot at the base of the arm. I see a larger ram force being required than what you (and your friend) calculated.
 
  • #3
yes the arm is free to rotate around the pivot at the base of it. The ram will slightly change the angle of the arm when it moves in and out.

My calculation were, to first calculate the torque at the pivot:

100kg x 9.81 x 0.147m = 203.07 Nm

so 203.07 / .06m = 3384.5N to support at the pivot point of 215mm up the arm. If the ram was at 90degrees to the arm.

So need to calculate the angle from 90 degrees to the arm to the real position of the ram.

90 - 62 = 28 degrees.

3384.5 / (cos 28) = 3833.18N

But I am not happy that my method is correct as it is vastly different end figure then my friends.
 
  • #4
Calculating torques requires that you use the components of the forces that are perpendicular to the moment arm. So, for example, the torque about the pivot point due to gravity would use the component [itex] mg \; sin(16°)[/itex].
 
  • #5
Ok I have had another look at the problem and tried is a different way, please could some let me know if this is correct:

981N*0.74m*Sin16 = ? * 0.215m*Sin62

(981N*0.74m*Sin16) / (0.215m*Sin62)

= 1054N
 
  • #6
gavhowe said:
Ok I have had another look at the problem and tried is a different way, please could some let me know if this is correct:

981N*0.74m*Sin16 = ? * 0.215m*Sin62

(981N*0.74m*Sin16) / (0.215m*Sin62)

= 1054N

Now THAT looks good!
 
  • #7
thank you
 

Related to Force Calculation to balance arm

1. How do you calculate the force needed to balance an arm?

The force needed to balance an arm can be calculated using the equation: Force = Weight x Distance. This means that the force required to balance the arm is directly proportional to the weight of the object being held and the distance from the pivot point.

2. What is the pivot point in force calculation for balancing an arm?

The pivot point is the point at which the arm is attached to the object being held. It is the point where the arm can rotate or pivot, and it is also the point where the force is being applied.

3. How does the weight of the object being held affect the force needed to balance the arm?

The weight of the object being held directly affects the force needed to balance the arm. The heavier the object, the more force is needed to balance the arm. This is because the weight of the object creates a downward force that must be countered by an equal upward force to keep the arm in balance.

4. How does the distance from the pivot point affect the force needed to balance the arm?

The distance from the pivot point also has a direct impact on the force needed to balance the arm. The farther the object is from the pivot point, the more force is needed to balance it. This is because the longer distance creates a greater torque, or rotational force, that must be countered by the force applied to the arm.

5. Are there any other factors that can affect force calculation for balancing an arm?

Yes, there are other factors that can affect force calculation for balancing an arm. These include the length and weight of the arm itself, as well as any external forces acting on the arm, such as wind or friction. In addition, the position and movement of the arm, as well as the strength and stability of the pivot point, can also impact the force needed to balance the arm.

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