does anyone know how does the central lock mechanism in articulated arm (magic arm) works?
The magic arm usually used to hold camera, with only 1 knob, it can lock all sides. How?
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Locking the ball joints: Rotating the handle also rotates two cylinders with a section cut out. (see photo)
When rotated to a locked position, each cylinder pushes on a rod in each arm, applying force to the ball joint, holding the ball joints in place by friction.
When unlocked, each rod slides into the cut out in the cylinder, releasing the force on the ball joint.
Locking the central pivot joint: Rotating the handle presses the two halves of the arm together, locking two rings of teeth together (pictured below). I am unsure of the exact mechanism to convert the rotational force from the handle into force pressing the halves together.
Images used: Spare part pdf under the downloads tab on this Manfrotto product page https://www.manfrotto.us/magic-arm-kit-143a-003-035
Product comparison image from this product listing page. I have not idea if this is a reputable website or not, I just found my image there. dx.com/p/aputure-a10-multifunctional-magic-arm-stabilizer-grip-for-camera-black-387217#.WHGSchsrLb1
I can't post more than 2 links yet, so you may need to add three "w" and a period before the third link to get it to work.