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Old Feb 8th 2019, 07:40 AM   #1
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Force Equations on a Tripod Stand

I have been trying to solve a question about a load on a tripod stand. There is vertical load stacked on a tripod stand with a center of mass at a certain distance away from the center hub of the tripod. There is a horizontal force applied at a certain height and the height is known.

Need to calculate the radius of the tripod leg circle so that the tripod does not topple. Sliding is not to be considered in the calculation.

Have tried writing out the force and moment equations and there seems to be something missing as they won't balance. Please let me know if I am missing something.

Please find attached the considered equations and system in the image link.
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Old Feb 8th 2019, 12:40 PM   #2
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sorry, not seeing the attached equation

However it sounds like a centre of mass and torque problem and the only way I can think of the tripod flipping over is if it rotates pivoting on two of its legs. Is this a fair description of the problem?
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Old Feb 8th 2019, 12:53 PM   #3
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Force Equations on a Tripod Stand

Yes it is. I have reattached the image. Should give a clearer picture of the problem.

Two legs of the tripod on the left and the toppling to be considered about these legs. So I was thinking that the moments should balance out.
Attached Thumbnails
Force Equations on a Tripod Stand-unnamed.jpg  

Last edited by samiers92; Feb 8th 2019 at 12:56 PM.
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Old Feb 8th 2019, 09:09 PM   #4
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So the weight of the tripod itself is considered to be negligible and only the weight at the top matters? If that is the case then I would think you only need to find the amount of torque required to overcome gravity on the other side. I was a bit confused about what R_f stands for on your diagram. The weight of the block on the top of the tripod?
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Old Feb 11th 2019, 05:55 AM   #5
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R_f stands for reaction force. Not really sure if I should consider them.

And yes the weight of the tripod can be assumed negligible. Just the wieght above that and the horizontal force. Sliding is not an issue as the tripod is fastened to the ground.
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Old Feb 12th 2019, 02:17 AM   #6
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You might want to consider two cases: one where one of the tripod legs is immediately behind the force being applied and one where the force is between two tripod legs (i.e. along the bisector of the 120 degree angle).
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Old Feb 12th 2019, 06:22 AM   #7
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I understand that there will be the 2 cases , but this is the worst case scenario, so this is the one that needs to be considered.

Can you help with the force and moment equations?
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