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My 3 axis skull...in progress

589533 Views 2217 Replies 203 Participants Last post by  HalloweenBob
I have a couple of pictures of my prototype. I will take a bunch of new pictures as I make the other three skulls, but this should give you an idea of what I am doing.

I am making a singing quartet based on (That means idea stolen from) Mike C's Graveyard Quartet. Ever since I saw his video I couldn't get it out of my head.

A neighbor of mine with a machine shop has helped me with the prototype, machining some of the parts I needed, and helping with the design.

I have been using the prototype to do some programming to make sure it all works with Brookshire's VSA software. So far, so good. I will post detailed pics of every step as I start making more skulls, but for now, here's a couple of basic shots with labels on them.

The Jaw servo was not mounted yet in this pic. It is in now. You can see the mounting screws and the linkage wire in the pic. The servo mounts standing up on end. I will add pictures of that later. The eyelid servo is mounted under the plexi-glass. That one is not hooked up yet, but when it is, it will be attached to one of the eyeballs...I am using wooden balls for eyes. It will move it up and down, not side to side. The purpose is to make it appear that it is blinking. I have large fake eyelases that will be attached to the eyeballs. When the eye is moved down, it appears to be closing as the top eyelid moves down with it. In the pic below, you can see the slot cut in the eye socket where the armature will go to move the eyeball. Don't worry, I will post pictures of that as well. I am using a 3/16 rod end as the gimbal which allows movement in all directions. When I build the next one, I will have clear shots of that as well.

Feel free to ask questions, and I will answer as best I can. I now have it hooked up to VSA and it is working very well. I am using the lightweight Pirate Skull and so I do not need springs, elastics or counterweights.
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I just tried lowering the rotate servo (put it on standoffs so it hangs lower than the plate, that makes it just as bad as having the rotate cam all the way at the top of the rod.

I just don't see why I'm effected and everyone else isn't.
Just a thought but do you still have the plexi-glass template? If the cutout for the rotation is off even a little that could be your problem also. Even a 1/4" difference could make the difference. I'm so sorry your having this trouble and just wish I knew how to help you.
I see something that might help after viewing your videos. Try attaching the linkages to a hole closer to the center on the servo arm. The further out to the outside you go, the more turning takes place in addition to the straight out "pushing" you want to tilt or nod. By moving the linkage closer to the center, you get less of an arc motion. You may find that the linkages become a bit more lined up (90 degrees) as well, although yours are pretty good.

I would also try adjusting the height on your center rod of the rotate armature (move it up a bit if you have clearence). I see this has been discussed a bit already, but it shouldn't interfere with other motion. I know mine does not. Lowering the rotate servo is a viable option, but shouldn't be necessary.

It is also important that all linkage arms be as close to parallel to the plexi plate as possible.

Mine are still at a bit of an angle, but not as much as what I see on yours. That may be causing some trouble.

All in all it does seem to be working pretty well.

I should have shot video of that phase of my setup. Those videos are very helpful.
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I just noticed something else from your video. I don't know how much difference this will make, but my "Tilt" servo faces the other way from how you have yours mounted.

Both the tilt and rotate servo are mounted facing the same direction with the servo arm pointing towards the back of the skull.

The square hole in the plexi was put where it was with that placement in mind. It may help to also turn that servo (the tilt servo) around.
I just noticed something else from your video. I don't know how much difference this will make, but my "Tilt" servo faces the other way from how you have yours mounted.

Both the tilt and rotate servo are mounted facing the same direction with the servo arm pointing towards the back of the skull.

The square hole in the plexi was put where it was with that placement in mind. It may help to also turn that servo (the tilt servo) around.
I originally mounted everything the way you had them, but I noticed that the rod was rather close to the nod servo and flipped everything to try and get the spacing more like yours.

I'm feeling a little under the weather but I hope to be able to cut another plate from your template today or tomorrow and try again.

I really appreciate everyone's help and I'm sorry to have hijacked your thread. I started another thread and only double posted it here to see if I could get your input as well.
Have you tried running it without the rotate servo? If it performs properly without it, then you know that's the culprit. try it with one servo removed at a time, if that doesn't work. It really looks like your rotate servo linkage is WAY too low down the rod.
I was having the same problem with my rotation binding with the nod. I adjusted the 90 deg alignment a little, but what really helped me was to bring the connecting rod on a more even plane and out of the way of the nod. Looking at you pictures it seems that you have quite an angle on your rotation rod and that might be causing it to bind. Just a thought cause I know how frustrating it can get.

Yes, I have removed the rotation linkage and everything tilts perfectly. If you look at the design of the mechanism itself, the rotate and tilt servos are directly opposite of each other, only the rotation one is moved a hair towards the back of the skull so that it lines up with the rotation cam attached to the rod. The skull tilt motion works by shortening the distance between the center of the servo and the top of the rod, because the rotate servo is energized and holding it's position, the distance between the center of that servo and the rod does not change. Because the rotate servo is connected to a point that is not lined up perfectly with the tilt servo linkage, the plate rotates as it maintains the distance from the cam to the center of the rotation servo.

Eureka! As I'm writing this, I think I know what my problem might be! The problem may be the distance between the gimbal and either the connection point for on the top of the support rod, or the gimbal to the plate. If the distance is too long, the arc that the top of the rod sweeps through the skull on will be larger than if that distance was shortened up. A shorter sweep would mean less change in distance between the rotate cam and the center of the rotation servo which in turn means that when I tilt, the amount of unintentional rotation would be very minimal. When I created the metal bracket and through my initial setup, I figured a longer throw would be better, allowing me finer control by using more of the servos range of motion.

In an ideal world, the rotate servo would act on the gimbal itself minimizing the amount of movements from other motions it would have to deal with. I thought I had approximated what everyone else was doing, maybe the gimbal is too far down.


I actually had a similar problem early on, the screw for the rotate linkage was rubbing against the nod linkage and when enough pressure was applied it would slip off to one side or the other. As it's adjusted now nothing rubs or touches through the motions except at the very far limits of the motions well after my the skull has rotated while tilting (the rubbing is easier to fix than my current issue).

As far as the angle of the rotation linkage: I intentionally moved the rotation cam further down the rod hoping that the extra angle in there would make it less susceptible to the rotation problem. I've actually moved that thing up and down a whole bunch, bringing it right to the top, and all the way down to the bottom. I also tried pushing the rotation servo further down to keep it on the same plane as the rotation cam, by making little stand offs. Based upon my current theory above I think I was on the right track, just didn't get far enough down.

I'm actually kind of hopeful that this will minimize the problem!!! It's the first thing that makes any kind of sense. If anyone still has their skull apart and cares to measure everything up (distances between all the linkages and connecting poitns) I'd appreciate it.

I just wish I had time to work on it tonight :(.
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What made you decide to use the HS-425BB vs the HS-311 or the HS-322HD.
Basically the recommendation of others. I did look at the torque specs on that servo and they seemed to be within what I needed.

They are working fine for me, so that is good. There are probably many other servos that would also work, but I didn't have the money to experiment, so I went with a servo that I knew others were using for similar applications that worked.

I said I would post again as soon as I got these guys all dressed up.

Well, I have started the body-making.

The girl lead singer is a full bucky in a dress. She will also be wearing a wig.

I made a wooden stand that holds her up from the bolt that extends down in her pelvis. It is actually one long solid rod that goes the entire distance of the spine and holds everything together. I cut off the tailbone, and rested the end of that rod in a hole I made in the frame, and then bolted it down tight with oversized washers and nuts.

Here she is standing there:

Here is the frame I made to hold her up:

To attach the skull that I made, I cut off the bolt at the top. Slid a coupler over it, and tapped a couple holes in it to hold it tight. Now all I have to do is screw her head on right.

I left some of the vertibrae attached in front to hide the metal couplings.

For the guys, it was a different story. I had to make an entire body frame for each one. They will be fully dressed in a complete tuxedo. (I bought 3 of them) so nothing will show except for their heads and hands.

Here's how I started:

here's what it looked like from the back:

Then I started padding it out a bit. First I added shoulder pads:

You can also see where I added Chicken wire to build out the chest.

Continued in next post....
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Next, I added padding to the Chest:

A couple of arms (Made from pool noodles, held together with those nylon tie-wraps. I'm not sure of the real name for them)

Then the hands....

Almost done now. I just had to get them dressed. I put the tuxes on them the same way I would put them on a real person except that I used a staple gun to hold things in place.

There he is!

So far, I have made 2 out of the 3 Background Singer bodies. I am purposely making them different heights because all people are not the same height. I wanted a little variety and it adds to each one's personality.

Here's the group so far with one background singer missing. (They will be displayed outdoors)

More as I get things finished up.
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Looks great!!! Kinda ironic that they'll be singing about a headless horseman...
WOW, this is turning out first rate so far!!! it's at the top of my "props i want to see finished most" list!
Where did you get your skull from. I am using a bucky skull...just wish I had something with a little less weight.
Excellent work! Can't wait to see the finished video!
This is one of the places you can get the skull:


It is a plastic model from Lindberg.

If you look back through this thread, it is referenced with links a couple of different times.

My last body is built, and I am almost ready to attach the heads. Perhaps this weekend. When I do, I will post more pictures and more video.
new vid

just thought I would post some of my work. the video is not all that great . the head mec isnt like the one here. its a simple one Ill be saleing soon. nothing like the work bob put into his.
I hope you enjoy Ill have to post the pictures here soon ok
later guys

YouTube - my animatronic
I have been following this conversation in awe but, apart from wondering if Bob's neighbor is interested in adopting me, didn't really have anything to add.

Last night, while working on a shopping list for my current project, getting my grandfather's metal lathe back into good working order, I saw that Enco (http://www.use-enco.com) had ball joints and thought, "Hey, since I'm thinking about doing one of those skeleton's some day, I ought to throw one or two of those onto my order." This morning while putting my list together (and thinking about how much money I really want to drop today) I noticed Enco's price is about half of McMaster Carr's. Not sure how shipping will stack up, but though I'd share that little bit of information.
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