Vertical Mouth Cable Mechanism

sneedling

I am attempting to create a simple cable-operated mechanism for a rod puppet with a vertically oriented mouth. I am very bad at anything engineering-related, so I've been struggling. I attempted to have a loop of fishing line fed through vinyl tubing secured with a hook that would "close" when pulled downward, but after trying latex tubing and cutting various-sized wedges to create a weaker hinge, I had no success. I tried another approach with two pieces of tubing glued to the lips of a latex test skin, and it was only slightly more successful but provided very little movement. I found this mechanism online and emailed the creator but have yet to receive a response: https://www.instagram.com/p/BozhEi3nclw/?igsh=YnhnOW45M3R3dm1x but this seems to be the best approach I would need.

So far, the puppet's armature is made with brass tubing with eyelets for joints and secured with epoxy. The "head" is a piece of brass tubing that will be operated by a rod secured around my thumb, like this design by Hobey Ford: https://www.instagram.com/reel/Cuf6zm7Nish/?utm_source=ig_web_copy_link&igsh=MzRlODBiNWFlZA==

This is probably very easy but like I said, I am very illiterate when it comes to anything with moving parts, my brain is far more inclined to aesthetics than functionality so I need it to be explained to me like I'm five. I have a video with a test skin demonstrating my desired outcome but I don't think I can attach video files in the OP. 

sneedling

I cant share the video of the casted test skin but here is a WIP pic of the sculpture before I finished and molded it to give an idea of what I'm trying to accomplish: 

sneedling

Update: I've been trying to make a similar mechanism out of steel wire like this eyelid mech, but I can't get them to align, and it seems the mouth is too small for something practical with this design. 

;
credit: https://www.eldergeeksman.com/blog/2015/2/3/ithorian-eye-mechanics

Chris Ellerby

Is the skin latex or foam latex? Regular latex can be stiff and may require a lot of force to move depending on its thickness.  It's hard to tell from the photo, but it also looks like any movement of the mouth may pull on the face if the mouth does not have enough material to close on its own.

A cable-operated mechanism does seem to be a good option here.  Part 2 of this course has a section that focuses on making a mouth mech that may work for your application:
https://www.stanwinstonschool.com/tutorials/how-to-make-a-foam-puppet-part-2

/Chris

sneedling

@Chris Ellerby The test cast I did is regular latex but the final skin will be a silicone with an equivalent softness to Platsil Gel 10. I'll check out that course and see, thank you.

sneedling

I would need it to return to an open position. Could I make a little hinge out of ultrasuede or a similar matierial, or would it not be strong enough? 

Chris Ellerby

If you need it to return on its own you may need to add a spring, elastic, etc. to the mechanism.

A fabric or ultrasuede hinge should be fine.  It just depends on the range of movement and your tolerances.   Fabric hinges can move around more, so it depends on how rigid you need your hinge to be.

/Chris

Darrell Green

I wish I knew what the material is but my brain says "sticky hands". Remember those really stretchy toys that had the hand on the end of the really stretchy cord? They were always in candy machines and sold at novelty shops. If the material were available for molding.... and if I knew what it really was.

Chris Ellerby

From what I can find, the "sticky hand" toys were made out of hydrogenated polyterpene resin.  Some modern versions are made out of a low-durometer silicone with an additive to make them more tacky.

/Chris

sneedling

I used a piece of craft leather as the hinge and made two crisscrossing "tendons" like the eye mech I posted earlier, and they seem to function. I am finishing the entire puppet armature, but hopefully, the silicone will cooperate; I'll update. 

Chris Ellerby

Awesome, glad to hear you are making progress!  Looking forward to seeing your results!

/Chris

Alexander H

I may be too late now to offer some helpful advice for your project, but I recently did something similar to Adam's eyelids. I needed twelve total eyelids to close at once. Using a trigger, a nylon cable was pulled, which pulled up the top eylid on the reverse side of the pivot point which forced the eyelid closed, and some springs pulled it back into place. There are two gears inside of the eyeball that make the bottom eyelid mirror the top. I'm currently remaking this system however as it isn't the most elegant, or reliable, in how I had designed it.

The reason I had the cables going to only the top eyelids, and not the bottom, were 1) I had to be cautious of how much room was in the space in the head, and 2) with this design, I already had six cables I tuned on the handle to make them close at once (as best as I could). Doing more cables for the bottom would mean an additional six to find space for and tune.



This video of the prototype might show it a bit better, but I'm happy to post images of close ups/3D models if you need me to elaborate further!

https://drive.google.com/file/d/1sqDjheTPWd6JrwlsCwB3GAgJp24k-EVN/view?usp=sharing

sneedling

Okay so I’ve been at a loss these past few days, I made a working mechanism but I can not get it to move the puppet’s mouth at all. I remade it bigger, replaced it with two big panels of ABS, added cables to pull the bottom, and I can’t get any translation of movement despite it working without being adhered to the skin. I cut as much access material as I could form the cast, but it made no difference. I’m using fishing line as my cables but I don’t think it should make that much of difference, but I’m pulling on it as hard as I can and it won’t move. Here was my first version, it closed better than my new version but none can seem to get the required force, and the silicone I’m using is TC-5110.

sneedling

@Chris Ellerby would you recommend using a different type of "cable" and/or attaching the cables directly to the skin, I just can't understand why I can't get any movement out of the silicone. 

Sean Dalton

sneedling, The Stan Winston School has a course How To Make A Monster Puppet - Rods & Cables by David Monzingo. Chapter 15. The Jaw Mechanism should help you build your puppet. 
Regards, Sean 

sneedling

@Sean I own the DVD, I made a functioning mechanism its just that I can't get it to move with the skin.

Chris Ellerby

You can use bicycle brake cable for movements that require more force, or model airplane control cable, which is similar to bicycle brake cable but smaller.

I would also look at how you have your cable and mechanism designed, and what type of leverage that mechanism creates.   Depending on where you attach the cable and the angles you are pulling you can lose or gain a lot of force.

How are you pulling the cable, and are you using much leverage there?

/Chris

sneedling

@Chris Ellerby I am just pulling it manually to test, but I made a trigger out of ABS that's mounted on a wooden right. I have brass tubes that guide the strings horizontally, crisscrossing to pull the opposite "jaw" and eventually downward through the vinyl tube that will feed to the trigger. 

sneedling

I finally got it to work, but only one "jaw" at a time, and it still requires a huge amount of force. My old fishing line was 8 lb strength, which eventually kept snapping, and I changed it to 17 lb strength.  The puppet's neck could turn, so I fused it, and it only helped a little. I cut so much material from the back of the skin that its translucent in some spot and the mechanism still cant move. I just don't understand 

Darrell Green

Just a check point item but make sure you do not have too many sharp bends in you cable channels or any that are severely bent. The total friction over the entire line can create many extra pounds of drag that needs to be overcome. It is why knots do what they do, bind completely. Graphite powder is sometimes used to free up the resistance inside a cable channel. It can make a huge mess so be very sparing on its use. I am wishing you success. I really want to see this in action.

sneedling

@Darrell Green I'm using fishing line, the mechanisms work but as soon as I attach it to the skin it wont budge. I kept cutting off silicone and have basically mangled my casts face and it still is too rigid for 17 lb fishing line. I'm about to give up

Chris Ellerby

Are you using monofilament fishing line?  Those are often designed to have some stretch, which will dissipate some of the force you apply.   The braided lines are often a bit better.

/Chris

Darrell Green

sneedling said:

@Darrell Green I'm using fishing line, the mechanisms work but as soon as I attach it to the skin it wont budge. I kept cutting off silicone and have basically mangled my casts face and it still is too rigid for 17 lb fishing line. I'm about to give up

Can you load a photo of the other side of this area?


I am not seeing the mounted hinge pivot section. The leverage used in the other designs in this thread have a mounted fulcrum point and the leverage comes from the rod portion that is past the fulcrum. I would expect to see a pivot on both mouth parts that then extends into the body of the cast, behind the center brass and have the line connected back there.  They currently look like they are attached in the front instead. This may cause it to not follow the same path after attaching it to the skin, making it bind up or attempt to compress the cast instead of a hinging action. I will try to point to this leverage and pivot on one of the others:



This design has quite a length of rod past the pivot. This gives it a lot of strength but the more important part is the mounted/pinned fulcrum hinge which forces it to always follow the intended path. Without that it would be free to just move sideways. I think that with a view of the other side (inverse) of your picture, we could see what is needed. 

sneedling

Sorry for the late rey, but I got it to work. I scrapped the old mechanism entirely and made something based on grabber tools with spring steel. I was trying to pull the jaws horizontally, but this design the force is pulled directly backward. I also switched from monofilament line to braided, though I'm not sure how much that helped. 

Darrell Green

sneedling said:

Sorry for the late rey, but I got it to work. I scrapped the old mechanism entirely and made something based on grabber tools with spring steel. I was trying to pull the jaws horizontally, but this design the force is pulled directly backward. I also switched from monofilament line to braided, though I'm not sure how much that helped. 

Woooot!!! Excellent news! 

The mono to woven jump drastically drops the amount of travel needed on the hand side of the mechanism because now there is less overall stretch. I think that it was not a single issue but one led to the other. The horizontal pull depended on freedom of movement so it worked when not attached but bound up when attached. Pulling it in a forced path gives far more leverage so it wouldn't then need so much tensile strength but I am a big believer in stronger is better so stick with the woven. Since all of it is hidden it won't matter. Often the idea of mono is it is so easy to hide from the camera but has no need for that benefit when completely hidden so might as well have it stronger. I imagine this stronger version will allow faster closing action without the fear of snapping or stretching the line when performing in a scene. Like the old logic behind why you break your shoe laces when in a hurry. 

Great news though, still following along to see this bad boy in action.