Thread: Moving Arm Mechanism for 3 Axis skeleton?

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Does anyone have any ideas on how to control the arms on a 3-axis skull/skeleton? I would imagine some kind of pneumatic/hydraulic control would need to be used but haven't really seen any tutorials.

Thanks.

I have done this for a few years now.

The first incarnation looked something like this:
http://www.youtube.com/watch?v=2vfa_KcCHr8

I built a bit more sturdy versions a year or two later:
http://www.youtube.com/watch?v=yo4DG99Ugkc


These are the ones I use in my Quartet videos. One such video is here:
http://www.youtube.com/watch?v=Np3leCt161o

I am happy to answer any questions if you have them.

Originally Posted by HalloweenBob

I have done this for a few years now.

The first incarnation looked something like this:
http://www.youtube.com/watch?v=2vfa_KcCHr8

I built a bit more sturdy versions a year or two later:
http://www.youtube.com/watch?v=yo4DG99Ugkc


These are the ones I use in my Quartet videos. One such video is here:
http://www.youtube.com/watch?v=Np3leCt161o

I am happy to answer any questions if you have them.

Animating the arms of some of my skeletons is on my to do list for this year. I've been looking at some pneumatic options but like this much better. Do you have any close up pictures of the mounting brackets and how they are attached to the skeleton? Are you using Bucky skeletons?

Here is my version of an animated arm

Well HB, looks like ya left yourself wide open for another Tutorial / detailed info on your skelly arm movement / set up......inquiring abnormal minds like mine would also love to know....LoL Love that set up, looks very smooth & realistic movements ( if a living skeleton could move it's arms..LoL ) !

I would also like to build a few moving arms skelly's to go with my 3AS's for this next year. Seems like once you've crossed the 3AS line,.....there's no going back on costs.....LoL
Now to sell my soul, again...(cough,cough) for newest version of VSA's 5 Pro....... ( wish I had bought Brookshires console before #5 release came out, can't use MonkeyBasic's Helmsman without it & stuck buying VSA 5 just to be able to.....wish I could still buy / obtain console 4.0 version......sigh,....oh well it's just money growing on tree's..... )

I did a simplified arm movement (only up and down) for my skeletons this year. Some photos are in my album. http://www.halloweenforum.com/member...eton-band.html

Here is a vid of the testing of it.
http://www.youtube.com/watch?v=ryTgstWLOv0

Originally Posted by HalloweenBob

I have done this for a few years now.

The first incarnation looked something like this:
http://www.youtube.com/watch?v=2vfa_KcCHr8

I built a bit more sturdy versions a year or two later:
http://www.youtube.com/watch?v=yo4DG99Ugkc


These are the ones I use in my Quartet videos. One such video is here:
http://www.youtube.com/watch?v=Np3leCt161o

I am happy to answer any questions if you have them.

Bob, I'm looking to use some of my Christmas money for materials for this project.
What servos are you using for each of the joints?
Do you have any pictures of the aluminum brackets themselves that you use?
How do you attach the shoulder joint to the Bucky? That seems to me to be the most critical part.
Thanks for any help you can provide. This will be a fun project!

OK, here is what I have, although I have made some minor adjustments since I took these pictures.

This is the right arm. All of the parts are the same for Right and Left except for the clamp that holds it to the skeleton.

The hollow arm bones come from "Barney" Skeletons. You can find them all over the web and on ebay. They are super lightweight and the same scale
as the Bucky skeleton, so they look good, and they are hollow which also helps hide wires.

OK, let's get started.

First, I prepared the lower arm, by cutting out a slot for the servo. You can see the slot and how it fits on in pictures 4,6,7 and 8.

Picture 4
http://halloweenbobshaunt.com/Arms/04.jpg

Picture 6
http://halloweenbobshaunt.com/Arms/06.jpg

Picture 7
http://halloweenbobshaunt.com/Arms/07.jpg

Picture 8
http://halloweenbobshaunt.com/Arms/08.jpg

These all show the elbow servo. In this prototype, I use cheap Chinese knockoff servos (MG995 - Tower-Pro knockoffs) They worked but were noisy and had a poor failure rate. they have been replaced with Hitec HS-985MGs Also, I added a piece here. It is basically a thin aluminum rectangle just a little larger than the dimensions of the servo. I cut a mounting hole out of it and set the servo in it before attaching it to the aluminum attachment with the rod. This takes the stress off the two small holes in the plastic tabs of the servo. I found that fast motion could snap those tabs off and this bracket which holds the servo transfers that stress to all 4 holes and the entire body of the servo so nothing breaks off. I will try to get a picture of that piece soon and add it in this thread.

Then, using PVC cement, I glued the wrist joint of the barney in place so that it could not move. No picture on that.
Picture 01 shows the lower arm connector that is attached to the MG995 servo. It shows the set screw to keep the rod at the right angle...
I'll get to that later....and you see the rod that slides down inside the plastic lower arm. You can see the two 6-32 screws that hols the
bracket to the servo.

http://halloweenbobshaunt.com/Arms/01.jpg

Picture 02 shows a wider shot of the same thing.

Picture 2
http://halloweenbobshaunt.com/Arms/02.jpg

Picture 03 shows the rod from a different angle. It shows the 6-32 tapped hole in the rod. That is where the plastic arm get's screwed in
just to hold it in place. See the screw that holds in the Plastic arm in Picture 05. In Picture 08 you can see how the screw aligns with
the hole tapped into the rod.

Picture 3
http://halloweenbobshaunt.com/Arms/03.jpg

Picture 5
http://halloweenbobshaunt.com/Arms/05.jpg

Picture 8
http://halloweenbobshaunt.com/Arms/08.jpg

Picture 09 shows the same servo with the arm attached from the other side.
Picture 9
http://halloweenbobshaunt.com/Arms/09.jpg

Picture 10 shows the main clamp (right hand clamp) Being held up to the shoulder blade. This is from the back side. You can see the cutout
that is there to avoid hitting the bump in the shoulder blade at the back. The left hand bracket would have the cutout on the opposite side. The twist servo bracket would also be screwed in at a different angle. Holes are drilled all the way through the shoulder blade so that they line up with the screw holes on either side of the main bracket. Then the screws are inserted clamping the clamp on like a vice. The large holes further in on the shoulder blade were from a different project.

Picture 10
http://halloweenbobshaunt.com/Arms/10.jpg

Pictures 11 - 14 show the areas I file down slightly to give square edges and allow the clamp to hold position better. The last two pictures
show the area I need to file down a little to make room for the twist servo.
Picture 11
http://halloweenbobshaunt.com/Arms/11.jpg

Picture 12
http://halloweenbobshaunt.com/Arms/12.jpg

Picture 13
http://halloweenbobshaunt.com/Arms/13.jpg

Picture 14
http://halloweenbobshaunt.com/Arms/14.jpg


You can see the rest in the video. The Shoulder servo in this case is a Hitec HS-805MG. It is a large 1/4 size servo and should only be used if you have a way to hide it because it will show. The skeletons I use these on have clothing hiding those parts so they don't show. You do need the extra torque and I have also added an assist spring to this design as it was needed once I put the clothes on the arm and there was more resistance.

On one skeleton where I didn't cover as much of the arms, I used more expensive higher torque servos that were smaller. (Hitec HS-7980TH) These are the same size as the standard servos but have even more torque than the HS805MG!

For the twist servo, I used a Hitec HS-645MG, although you could probably get away with a lesser torque servo here, I recommend metal gears to to the weight that this servo supports from it's arm.

That should do it.

Bob,

How have those MG995 servos worked out for you? I bought a small batch to try them out and I think that they seem to work really well. The one thing that I did was I opened each one up and hot glued the 3 wires to the circuit board. I've read that this is the weak point for these servos. I do like how much torque these servos have. Also, do you use these servos inside your skulls or do you prefer a different servo with less torque?

Great work on these skeletons!! Can you figure out how to make them walk?

Bob, those are great and answer a lot of questions. And quick too!
However, I'm still not sure of the different brackets that make up the shoulder joint. It looks like you're using a combination of 1/16 and 1/8 inch aluminum for those. I assume you had to custom make the elbow joints?
Steve