cable-driven Arm puppets

Sydney Curry

does anyone know if they can help me out when it goes to making a Cable driven puppet arms for a child or doll-sized animatronic? I am working on a bike cable-driven chucky doll and need some help on how the arms move. Thanks!!!  

Chris Ellerby

I'm sure we can help you.  What type of challenge are you facing?

/Chris

Sydney Curry

I made a prototype to represent what the arms look like in production stage, but the arms have no way of rotating at the shoulders and the pulley in the elbow doesn't have a way to keep the cable on the pulley track. 

Chris Ellerby

I think we'll need to start with your goals.   What type of movements are you looking for?  How many cables are you planning on using?  

Do you have any photos of your prototype to help us visualize how it's currently working, so we can see what might be changed to help you get it to where you want it?

These courses may also help you:
https://www.stanwinstonschool.com/search?text=cable

/Chris

Sydney Curry

I will take some pictures, but I must say that I'm sorry, but can't take the courses since I am on a close to always on a tight budget and can't take any courses, I thought it being the best thing to get help from pros from the forum without taking courses. But I can't say for sure how many cables but I wanted to have full range of motion in each arm and bend at the shoulders and elbows, but I have had limited options as to where to turn to for help.

Sydney Curry

The first half of the arm is the top and the second is the image below. I'm sorry the pictures are in Low- Definition  

Chris Ellerby

Are you relying on gravity for the return movements?  In the second picture, it looks like a single cable controls that segment and terminates by the joint.  You can do this with a single cable, but will have less control than if you used a pull/pull configuration with 2 cables, one for each direction of movement.  (left/right, up/down, etc)  If you want to save on cables you could use a spring to help the arm return to its neutral position, so you don't rely on gravity alone, which can be an issue if the arm raises or turns and gravity can't help it back.  Though you have to fight the spring's tension when you move against it, so that can introduce more force into the system.  2 cables in a pull/pull configuration gives the best control though.

If you want to add more degrees of movement (like shoulder rotation, or shoulder forward/backward) you would just need to add more cables and more joints.  With 4 cables and a ball and socket joint, you can get some good movement for a shoulder joint.  Then for rotation, you can add another rotational joint to the bicep so the entire arm can rotate.

As you start to add more cables the challenge becomes how to control them all, so you may want to look into designing a joystick-style controller, that can handle 4 cables at its base and a handle twist to control an additional 2 cables.  That would give you control over the shoulder and upper arm rotation, so you would still need another controller for lower arm raise/lower, and any wrist/hand/finger movement you want.

/Chris
 

Sydney Curry

I have to rely on a cable to return to neutral position because the joints are somewhat stiff and were crafted from scrap pieces of sheet-metal  and I used to Bowden cable method for the arm so I can use less cable to control each arm movement. But the cable system I was going for was something along the line of something like in this screen shot I took of the Behind the scenes footage for Cult of Chucky. 

Chris Ellerby

You're on the right track.  You'll just want to add enough cables and articulation points to get your desired range of movement.

/Chris

Sydney Curry

And one other thing I wanted to know the answer to was what the black cylinder that is built in the bicep area? at first glance, I thought it looked something like a black DC motor or something. And I assume it is for arm rotation in said area?

Chris Ellerby

It's hard to tell from the picture if it's a servo or stepper motor, but it is most likely a cable-driven mechanism for rotation.

If it's a fully cable-driven puppet, as many of the Chucky puppets were, it would be a cable mech.  For example, you can see the setup below:

https://www.icollector.com/TELEMETRY-CHUCKY-ANIMATRONIC-PUPPETRY-RIG-12-AXIS-24-CABLE-FULL-RANGE-OF-ARM-MOTION_i31862161

/Chris

Sydney Curry

I am familiar with telemetry rigs myself as they were used for cable manipulation for each cable that is used in mechanical puppetry. some of the Gremlin puppets, I believe ,used the same concept from the Gremlins 2: The New Batch 

Sydney Curry

Ok, so I ran into another problem with the prototype arm .I found a way to make the arm rotate back and forth, but the problem is that the two cables are in the pulley, and the cables that are exposed from the ends of the housing to shoulder pulley arm being "twisted" against the back/forth joint that causes the rotation in the shoulder as it is being rotated , causing the movement for the up/down cables to not work right. is there any way to to fix the issue? 

Chris Ellerby

Without pictures or video, troubleshooting mechanical issues (especially on custom designs) is next to impossible. 

One concept that may help is making sure that each cable mechanism can move on its own without having to fight/interact with another mechanism.  This typically means the housings will terminate at the same segment that is being moved.  So if you have a chain of linkages, each with its own cable controls, each segment should be self-contained. 

You may need to do a lot of testing and prototyping to find out how to stack things to work for your application.

/Chris

Sydney Curry

ok then. I will take your advice into consideration. Thanks.