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By ianm
#196523
Hi, I am very new to the forums, and a new hobbyist as well.

I am attempting to create a Halloween animatronic wherein a skull (very lightweight styrofoam) raises 2-3 feet off a pedestal. There will be a semi-sheer material over the skull, so anything used in the lifting of the skull will be hidden by the material. The pedestal is hollow, so it can house any needed infrastructure to raise the head.

I originally thought of using a rack and pinion gear to raise the skull, but after some research thought that perhaps a worm gear (screw) would be a more appropriate approach to raising the skull. I.e., skull is attached to end of worm gear, motor moves worm gear up (probably through conduit), hence moving skull up.

In looking around at various online hobby sources, I dont see anyone that carries "long" worm gears (screws). Which makes me think that perhaps there in another, better way to accomplish this task, as there doesnt seem to be a market for long worm gears (or not that I can find anyway). I cannot use a pulley system, so the skull really needs to rise from below.

Hoping for input, thoughts, good ideas? Any input is greatly appreciated!

Tx.

-Ian
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By exeng
#196538
This is just off the top of my head but doesn't Home Depot and/or a neighborhood Ace Hardware carry threaded rod in 3ft lengths? I would look for a 1/4 20 threaded rod at one of these stores. Then somehow embed a corresponding 1/4 20 nut in conduit or PVC and hold the conduit or PVC upper end at it's highest point way fully retracted.

I assume that you have already figured out the drive motor and attachment and control part.
By lyndon
#196545
What exeng said is a good, inexpensive solution.

Your problem may be that you are searching for the wrong thing: a worm screw and a worm gear are not the same thing. The gear is a small round item, not a linear screw and the screws tend to be fairly short. The main advantage of a worm and gear system is very large mechanical advantage.

You may be thinking of a leadscrew/leadnut combination, which is essentially what exeng suggested. One issue you may run into is that off the shelf 1/4-20 thread and nut from a hardware store will have higher friction and more reduction than you need. Shouldn't be a big deal, though.
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By DanV
#196551
McMaster Carr has acme threaded rods for not too much money.
https://www.mcmaster.com/#threaded-rods/=19v8jx3
A 1/2"-10 x 3 feet long is about $6.12 and a matching nut $2.60 (in ASTM A108 grade 2 steel - you're not making anything that requires high-strength steel).
They also have fast lead screws with multiple starts but the nuts start to get pricey - like $26 or more.
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By exeng
#196552
A 1/2"-10 3 feet long is about $6.12 and a matching nut $2.60
Wow that is a great find. Everytime I looked for Acme rods the price was too prohibitive for what I wanted to do.

With respect to the application discussed here, precision is not a concern so the acme threaded rod my be overkill, but hey, for that price why not.

Yes some 1/4 20 rods may have more friction than desired but if you try the nut and rod in the store you can fine one that turns freely. Also, spinning the nut up and down multiple time helps to loosen the things so that there is no binding. I would use an elongated nut which would be easier to secure in the Skull conduit.