Need help in re-designing rotating joint 1

[dkmulford]

Hello everyone. I am a civil engineer by education, however, I have a side business that manfactures amateur and professional camera mounts.

My professional camera mount, called the Pro-Mount, is used by professional videographers to videotape from within trees (i.e., whitetail deer and bear hunts for the Outdoor Channel, Sportsman Channel, ESPN Outdoors, etc.).

My Pro-Mount is able to level vertically and horizontally. I am trying to redesign the "shoulder joint" which provides the horizontal leveling. Please see the pictures below.

Currently, the shoulder joint is two 3 inch diameter plates. The front plate has two slots with two 3/8" hex bolts passing through the slots and into keenserts located in the back plate. There is a stainless steel 1/2" diameter shaft extending through the center of both plates.

My problem is that when the arms are fully extended 90 degrees to the tree (and in line with the rotation of the shoulder joint), the joint can slip. Obviously slipping is dependent upon the force applied to the two bolts and the load applied to the end of the arm. Altough the TV type cameras weigh about 30 to 40 pounds, I would like the arm to be able to handle about 80 lbs without slipping. Additionally, I would like to incorporate a handle in place of the allen bolts so the user doesn't have to carry an allen wrench. Doing this reduces the amount of force the user can place on the bolts.

Is there a book out there that might help us design this joint to maximize the clamping effort?

By the way, we can't increase the diameter of the two plates and the two materials must be aluminum. Additionally, the joint must provide enough rotation to allow leveling (say minimum of 15 degree each direction).

Thanks for your help,
Darren

 

[automatic2]

If you consider that the holding force is pressure over area, you'll naturally tend to increase pressure, or the area. If you want to keep the circular area small, then rather than contact the face, contact the circumference. Lengthen your shafting to increase area. Use a clutch shoe type mechanism to grip the OD, and play with leverage to increase shoe pressure. Could be done in place of the worm gear concept.

 

[unclesyd]

Here is another design coupling that I believe would work with a few modifications.

http://cf.victaulic.com/products/results.cfm?nowild=yes&style=Style 78&keyword=

 

[notnats]

A clamp I have used is based on a cotter with a cylindrical recess machined into it. A boss, in your case 3" od x say 1-1/2" bore supports a 1-1/2" shaft which will carry the camera arms. The cotter can be Ø1/2" and is similar to the cotter that used to be used on bicycle cranks but has a recess with a 3/4" radius machined into it instead of a tapered flat. The boss is cross drilled for the cotter at 3/4" from its axis and spot faced to allow a clamping nut to load the cotter and clamp the shaft.

This has been a messy description, but if you are interested email me at

jeffstanton@optusnet.com.au

and I will send you a sketch

I don't know what machining facilities you have available, but a simple way to machine the cotter is to tighten a bolt into the boss then bore both the boss and bolt together. Cut off the bolt head to finish the cotter.

Easy to make and clamps very tight, I first saw it on a spot welder being used to clamp the electrodes into the arms.

Jeff

 

[twinie]

Eliminating the rotating joint altogether seems like an attractive option.

Is it possible to enlarge the spikes on the mounting base and provide a spirit level (as suggested before) and simply instruct the user to attach the base to the tree in a level fashion while strapping it into place? By enlarging and possibly sharpening the spikes the tightening process would be less likely to cause the base to shift off level. Also by providing a smooth surface for the attachment strap to slide thru by possibly filletiing the slots may also help to keep the base positioned while tightening.

It seems like this would reduce the complexity and weight.

If you were intent on providing fine adjustment your rotating joint could be modified with two jack screws. One on each respective disk - pushing on a stop on the opposite respective disk. Although this would not allow a lot of rotational adjustment it would provide enough to compensate for initial missalignment of the mounting plate and would certianly be capable of handling the torque. Helicoil inserts in the aluminum would also help with longeivity of the joint.

If you are interested in the equal and opposite acting jack screws e-mail me with some dimensions and I will be happy to model something up quick for you.

 

[puckdady]

Hi. You probably already solved the problem, but I'll throw this out there anyway. You should leave the shoulder joint as is.
In my opinion leveling should be done closest to the point where the level surface is required.The camera mounting plate.
Provide some sort of adjustment to the mounting plate attatchment. Maybe a simple ball joint with
the adjustment mechanism under the plate so that the camera can be easily held while the fine leveling adjustments are being made.

 

[notnats]

The problem with that, Puckdady is that each time the arms are rotated about their pivots, the camera will nead re-levelling. Also, if the arm pivots are not vertical, the arms will tend to swing under their own weight and need improved locking at the pivots.

Jeff