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Old January 13th, 2014, 04:02 PM   #16
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Re: Where to put sandbags on C stands, boom stands, conventional stands.

It seems to me that the purpose of a sandbag is move the center of gravity of the rig (the stand itself and everything attached to the stand) closer to the point that is the average of the locations where the stand legs meet the floor. Of course this is a bit complicated since the stability of the stand relies entirely on friction and gravity and anything attached to the stand is mechanically attached. The ideal sandbag attachment would probably be one where it, too, is mechanically attached without any room for movement or shifting relative to the system in the event of unintended forces acting upon the system.

Breaking it down, though. I would think first of all that letting a sandbag rest wholly or partly on the ground might jeopardize its connection to the stand. If someone collides with the stand, it will at first act as though there is no sandbag is on it, though hopefully once it moves enough the sandbag will finally be part of the system and may stop the movement. Better, however to avoid any movement at all since that initial movement of the stand before the sandbag is engaged might be enough to change the position of the sandbag or set in motion some other forces that would keep the stand moving even once the sandbag is engaged.

It makes sense that as long as the sandbag is placed anywhere on the base where it is supported entirely by the base and not by the floor, it won't matter much to the system if it is on a leg or around the post. However, the height of the shorter legs nearly guarantees that if the sandbag is hanging on one, it will be partly supported by the floor and will not increase the mass of the system perhaps until it is too late.

I think some may put sandbags on the back legs since it may seem to bring the center of gravity away from the load, but I think that is generally outweighed by the benefits of avoiding allowing the sandbag to be supported by the floor and of increasing the weight and therefore friction of the front leg which is by far under the most stress. Of all the legs, any slippage or movement of the front leg would be the most catastrophic, and its greater length also protects better than the other legs against the sandbag sliding off. Also keep in mind that the most stable point or the point that is the average of the positions where the legs meet the floor is not the stem/post but just in front of the post on the front/long leg since it is longer than the others.

I'd say hang off the front leg is my first choice. Wrapping the sandbag around the stem allows the bag to swing or move less but I think is a bit more prone to allowing the sandbag to be kicked off though it depends on how full the sandbag is. Wrapping around the stem is probably my second choice and the place where I'd put my second sandbag if I want to hedge against my first placement :)
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