Panel versus Mold Construction for Longer Camera Crane Arm

[SimonWakley]

I am looking at replacing an existing aluminium camera crane arm (see photo) with carbon fibre box sections. Creating and using molds seems expensive and hard to get the high tolerances required. Cutting panels and edge bonding them and glueing/riveting to aluminium end pieces that would allow them to be connected to the crane end to end and would be significantly cheaper. Can I get similiar gain in stiffness and weight reduction using this method? Is there a study or any information about these opposing constuction methods. Beauty is not the major concern: cost effective lightness and stiffness is.

Thanks,

Simon

Short arm cranes shown at

http://www.cameracontrol.com

 

[MikeHalloran]

Edge bonding precured panels is more difficult than you have imagined it. Carbon fibre RP is not magical, but it's still priced as if it were.

Conjecturally, the simplest, cheapest (but not cheap) thing you could do now to save weight is vacuum- chuck the panels you've got and pocket mill them to thin the 'webs'.... assuming they're currently overdesigned and primitive, which is not apparent from the photos.

You need to hire an aerospace structures engineer to answer your questions, or to help you rephrase them in a way that makes it possible to answer them with some precision.



Mike Halloran
Pembroke Pines, FL, USA

 

[FEMdude]

The lightest solution would be to make a conical thin-walled tube out of aluminum or carbon, and overpressuring the inside (like missiles or coke-tins).
I'd probably go for flat carbon panels, bolted and bonded to extruded aluminum end pieces.
Flat panels are relatively easy to manufacture even with the highest modulus fibers.

 

[rstupplebeen]

I would assume that your design needs to carry a load and deflect less than some distance. From here it can be approximated by a simple hand calculation to get in the right ballpark for cross section and material properties. I would look at standard pultruded sections such as box beams or I beams. Hope this helps.

Rob Stupplebeen

 

[cpinz]

1)You can think the arm like as box beam with two vertical webs and two horizontal caps ( as box beams of wings)
In this way you don't need curved mold, as in a conical geometry, and it will be easy to layup sandwich panels that will be later jointed by adhesive or bolt.

For stiff and cheap solution try glass fiber for outer and inner skins of panels, and unidirectional carbon as reinforcement if the loads applied give excessive displacement. If displacemnt is not high, maybe only glass could work,
For extremely stiff structure you can use only carbon in fabric and unidirectional tape (solution more expensive) but be aware of contacts with any part of aluminium ( fittings, plates...)to prevent galvanic currents and corrosion

2) You can create two open C sections and join them frontally to form a rectangular close section ( as F1 monocoques or airplane fusolages)


3)For core of panel use pvc or in alternative honeycomb if you want to keep the weight as low as possible

bye
Cpinz

 

[MikeHalloran]

I'm guessing that extreme stiffness is a primary design goal, so as to avoid exciting any natural responses in the structure, which would be reflected in the camera image. At least that would explain the current geometry.

But, if it's not satisfactory, that could possible come from localized deflection where the loads are applied, or from odd distortion of the tube involving wrinkling of the walls and shear of mechanical joints.

[ It's not clear from the photos: Does the big tubing separate or collapse for shipment? How are the sections held together? I can conjecture ways to separate and telescope the structure for shipment, such that it would require far fewer than 15 big crates. I assume there's some reason why that wasn't done already, or was done and then un-done. ]

I.e., exactly what problem are you trying to fix?



Mike Halloran
Pembroke Pines, FL, USA

 

[PanelGuy]

I have a friend who has done work like this. The main objective was to reduce the weight whist using the stiffness of the Carbon to reduce the vibration. His Carbon booms extended 40 feet at least and allowed a filmaker to run it through a near perfect 40'hemisphere without tipping over the quarter balanced on edge on the camera mount. That is why you want the carbon.

He is a composite guy and did some funky stuff. I am guessing you are not His boom was used in a shot on the Wedding Crashers where you start with the birdseye wedding view and come down and travel down across the lawn into the tent etc...seamless and beautiful.

cpinz has got the simplest concept of the equations. Determine a Carbon plate that has the properties of the aluminum and go from there. I recommend using a composite or aluminum extrusion to bond (rivet minimally) the panels on the corners. If done right, with no rivets, you could probably go to the inside edge and use it as a bearing rail.

There are a ton of options for adhesives, call your local guy that you trust and he can hook you up. Also whoever you buy the panels from should be savvy enough to work you through alot of this.

Let me know if you need help, sounds fun.

 

[SimonWakley]

Hi,

Thanks to everyone who posted a response - it's a great help as I have 0 experience in this field. (I will attempt to answer some of the questions that people have posed)

The arm that is shown in the picture is a single welded fabrication from 5mm ali sheet. I am looking cut the nose off and insert 1-3 5' box sections between the arm on the base and the nose section (which may have to be re-fabricated in composite to reduce weight) This way I can have a 8' arm or a 13' arm or a 18' arm or a 23' arm. Telescoping is a later possibility, but beyond my current engineering plans.

The arm needs to be light and stiff so that it is easy to transport and the camera does not shake (much) when the arm decelerates and I do not need huge counter weights which then require more power etc to accelerate along the track. The larger rig on my website is 1600 lbs so it is lighter than many would think.

So - My current plan would be to cut out 4 panels with a 45 degree bevel and corner bond the panels into a box section and maybe overlay some carbon on the inside and outside seams for extra strength/beauty. Once this is done, I could bond some ali sections onto the open ends to allow me to bolt the box sections together. I would use pre cured honeycomb panels of appropriate strength.

There seems to be some back and forth about the galvanic action of aluminium as well as the differences in thermal expansion. I could limit the thermal expansion effect by using several smaller sections rather than an entire square frame on the ends, but if I use the right epoxy and the rig does not live outside (though it does on occasion get wet) I should not run into trouble with corrosion?

Is there a book/manual on doing this or is this forum the best source of info in this area?

Of course for accuracy I would have to fabricate an entire jig to get the aluminium inserts to all line up, but I could not see a way to make this whole thing and THEN bag and bake it so precured panels seems the best.

Photo is of the existing design with all ali construction (I have a single piece protype of this arm)

Thanks,

Simon

PS PanelGuy I saw that shot and thought it was a steadicam operator on an Akela crane? Not so? Simon at my website

 

[rodneybennet]

Hi Simon,

For other polymer or composite material suggestion you may also want to take a look at:

http://www.composite-agency.com/materials-forum.htm

Their experts give advice on material selection and service/shelf life of polymer and composite materials (their global/baseline assessments are for free)

Cheers,

 

[sreid]

Just a comment for thought. Is it possible that a truss made by welding aluminum tubes might meet the stiffness/weight requirements?

 

[MikeHalloran]

As could a box beam made of <1mm sheet aluminum, with a mess of rivets.



Mike Halloran
Pembroke Pines, FL, USA