Large Tentacle Advice
Scenario
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Hi, brand new here, making my first tentacle mechanism. Loved the tutorial with Richard Landon. My idea is for a body puppet that has a fairly large 4-way tentacle that goes vertically over the actor's head, with an eye on the end of it adding some weight. So tentacle itself will be about 3 ft long, eye will be a 10 or 12" painted acrylic dome, lightweight ripstop nylon fabric for skin.
Since this is my first time I'd love advice on materials and sizing so that its plenty strong, yet as lightweight as possible since will be carried by actor via backpack. May decide to do 2 stage for more nuanced maneuverability.
Will need to withstand wear and tear over time.
Questions:
*Is spedometer cable strong enough for such a large, upright, weighted tentacle? If not what other materials are better?
*I have read on some forum posts that you don't need to anchor each disc to the center cable, can just use spacers in between -is this true? What disadvantages come with this shortcut?
*How large diameter do vertebrae discs need to be?
*Cable sizing - how large do I need to go?
*Disc material - will delrin or nylon hold up for heavy use? Can I use acrylic or whatever is around and just glue to speedometer cable?
*Advice where to buy Delrin, Nylon, the internet is confusing!
*What pitfalls should I be aware of making a large tentacle with weight on the end?
*Any advice appreciated!
Thank you so much
Scenario
Since this is my first time I'd love advice on materials and sizing so that its plenty strong, yet as lightweight as possible since will be carried by actor via backpack. May decide to do 2 stage for more nuanced maneuverability.
Will need to withstand wear and tear over time.
Questions:
*Is spedometer cable strong enough for such a large, upright, weighted tentacle? If not what other materials are better?
*I have read on some forum posts that you don't need to anchor each disc to the center cable, can just use spacers in between -is this true? What disadvantages come with this shortcut?
*How large diameter do vertebrae discs need to be?
*Cable sizing - how large do I need to go?
*Disc material - will delrin or nylon hold up for heavy use? Can I use acrylic or whatever is around and just glue to speedometer cable?
*Advice where to buy Delrin, Nylon, the internet is confusing!
*What pitfalls should I be aware of making a large tentacle with weight on the end?
*Any advice appreciated!
Thank you so much
Scenario
Post edited by Scenario on
2
Comments
A two-stage design would be good, as the second stage can focus on moving the weight of the eye, and not the weight of the entire tentacle.
Speedometer cable should work for you.
You can use free-floating spacers, but any slop may result in having to pull the cable more to get the desired movement and reduce accuracy a bit.
The size of the discs will be determined by your unique design.
For cable size, you just need to be thick enough to handle the weight you will be moving, thicker cable is stronger, but also weighs more meaning you have to apply more force.
Delrin or Nylon would be better than acrylic, as they are less brittle. If you have any are of movement that you are worried about the cable cutting in, you can use a brass bushing, where the cable passes through. For purchasing these materials, you can look for a local plastics supplier, otherwise the internet may be your best bet.
As far as pitfalls, the most common issue I see with tentacles is caused by not understanding how much force may be required to move some tentacle designs. Leverage in your controller will be a big factor in helping get the power to freely move the tentacle through its range of motion. There's a reason many tentacle mechs are controlled by 4-foot-long levers anchored to the floor.
My advice would be to prototype small, troubleshoot the design when it's less expensive to make mistakes, and then scale up.
I hope you can share your progress on this project with us!
/Chris
thanks!
/Chris
Video:
Figured I'd post and see if anyone has thoughts why is not performing properly. Seems the speedometer cable is too flimsy, and for some reason the cable isn't returning properly when pulling lever backwards, you can see @ 30 seconds in the video that the cable bends outwards by the pulley instead of returning through housing. Holding my thumb to help direct it helped a little bit. Only 2 cables are hooked up for this draft.
Materials:
Universal speedometer cable
Dorman 10104 Universal... https://www.amazon.com/dp/B000COB422?ref=ppx_pop_mob_ap_share
Discs are aluminum cut with 2 inch hole saw and drilled by hand on drill press Pics of jig for the sake of future people researching how to for their own projects.
Flange coupling from Amazon
4Pcs 3.17mm Flange Coupling... https://www.amazon.com/dp/B08333PNZQ?ref=ppx_pop_mob_ap_share
Cable
DGOL 100 feet 1/16 inch (1.5 mm)... https://www.amazon.com/dp/B07V1STRY1?ref=ppx_pop_mob_ap_share
Housing
Farbetter Lined Bicycle Brake... https://www.amazon.com/dp/B082Y77712?ref=ppx_pop_mob_ap_share
Pulley is a clothesline pulley from home Depot, DIY aluminum frame, with cables clamped by a bent washer and screw (wouldn't trust it forever but so far it holds!)
Also, and I'm sure you've checked this thoroughly: is the cable taught (evenly)? If the housing is a fair bit larger than the cable, it gives room for the cable to move around more than it should within the housing, which will take away motion from what you want to move.
The first issue appears to be because it's not being held in place. Locking the base of the tentacle down helps direct the forces better, which is why it worked better when the first section was being held. Other than that, make sure there's no extra slack in the system.
Having a longer lever and the controls attached to a table may also help you apply more force when needed.
/Chris