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Discussion Starter · #1 ·
Greetings,

For my latest prop, I want to make toddler-sized version of Sam from Trick 'r Treat. I want him to be sitting on a mini park bench, looking in his treat bag. His head will turn to the side to stare at the TOTs via a servo and controller. Using a 1" pvc skeleton along with some Spider Hill Joints for his upper body, I am trying to figure out the best way to mount the servo. I want to follow the plan below, with a static lower body. The cross for the neck will have a reducer to accommodate a length 1/2" pvc for the turning mechanism. The head will be a 8" styrofoam ball. A micro servo will fit easily inside the cross. I just have to figure out how to mount it and if it would support the weight of the head. I did consider making a "ribcage" frame. That would have made mounting the servo easier, but with all the fittings and extra pipe, it would way to big for the footie pajamas I want to use.
Any advice would be appreciated.

Here is a reference photo for the pose.
Chair Sitting Furniture Child Leisure

And the diagram of the frame via Spider Hill Prop Works
 

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I would highly suggest against a micro servo for this. Go with a standard servo and mount it somewhere below the tee.
 

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Discussion Starter · #3 ·
Thanks J. I figured a std one would be better for weight and torque issues. No sure how it would mount below the tee, though. What about mounting the servo in the head?
 

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So you are not going to build this so it could "Take-a-Punch"? Maybe it's just "ME", but spending time and $ only to have some idiot "accidentally " punch or slap or kick, something as valuable as this will end up being..... No. say it isn't so!
 

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Thanks J. I figured a std one would be better for weight and torque issues. No sure how it would mount below the tee, though. What about mounting the servo in the head?
Mounting the servo in the styrofoam head won't work if the pvc neck is fixed into the styrofoam. Make a bracket to attach the servo somewhere below the cross tee and connect linkage from the servo to the 1/2" pvc of the neck. You'll have to cut a slot in the 1" pvc to connect the linkage to the 1/2" pvc. Not sure how much slop there is with the 1/2" inside of the 1", this may or may not work.
 

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Discussion Starter · #6 ·
Gym, Luckily, that hasn't happened in 7 years of haunting. I was going to place him in an area where the TOTs wouldnt be close enough to touch him. But making him heavy duty is not a bad idea.
 

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What if the servo was fixed into the head and just the horn was glued to the neck?
The horn would have to be attached to the cross tee, not the neck. With the servo in the head and the horn on the cross, they won't be on the same plane which will be difficult to connect a workable linkage.
 

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Discussion Starter · #10 ·
J, I think you're misunderstanding what I am trying to do with is. The servo horn is the part that screws on the servo shaft that turns , right? If the 1/2" neck is fixed on the spine, and the servo is fixed in the head. If you fix the horn to the 1/2", when you activate the servo, wouldn't that turn the head?
 

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Discussion Starter · #11 ·
Dog, That is cool! Unfortunately, Being a toddler-sized prop, I'm working with very limited space.
 

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J, I think you're misunderstanding what I am trying to do with is. The servo horn is the part that screws on the servo shaft that turns , right? If the 1/2" neck is fixed on the spine, and the servo is fixed in the head. If you fix the horn to the 1/2", when you activate the servo, wouldn't that turn the head?
Typically there are 2 horns, a servo horn and a control horn with linkage connecting them. The only way this would be possible is to install the servo in the bottom of the head with the shaft facing down, in essence, the shaft would become the "neck" of your prop. Fix a round or 4-way horn to the top of the spine and insert the servo shaft into it. With a foam head, this may work but it's not gonna withstand any abuse or the servo shaft will break.
 

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Discussion Starter · #13 ·
Typically there are 2 horns, a servo horn and a control horn with linkage connecting them. The only way this would be possible is to install the servo in the bottom of the head with the shaft facing down, in essence, the shaft would become the "neck" of your prop. Fix a round or 4-way horn to the top of the spine and insert the servo shaft into it. With a foam head, this may work but it's not gonna withstand any abuse or the servo shaft will break.
Thank you J. The durability of this option, was my main concern. So do you think if I fix the neck into the head, I can directly mount the 1/2" onto the servo horn, and cut out a window in the cross to mount the servo into. BTW the cross piece has a 3/4 to 1" reducer that has just a little wobble. Or should I devise some sort of linkage with the servo mounted outside the cross?
 

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At this point it's kinda trial and error to see what works best. Try to keep the servo horn and the control horn in the same plane so the linkage lines up.
 

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Discussion Starter · #15 ·
At this point it's kinda trial and error to see what works best. Try to keep the servo horn and the control horn in the same plane so the linkage lines up.
That's the fun part. I'm going to assemble the main frame then play around with the movement. Do you think a regular servo would be ok or a HD with metal gears?
 

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I typically use HITEC HS-425BB servos for all movements in my 3-axis skulls and talking skulls. It's a very reliable standard ball bearing servo at a very reasonable cost. The only thing I use micro servos for is eye movement.
 

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Discussion Starter · #17 ·
Here's Sam's current progress. Using Spider Hill Propworks, cut guide. I assembled the frame from 1" pvc. With a little advice from Chris and Denny from the Hauntcast crew, I heated and bent the pvc spine.

Balloon Toy Hand Ball Helmet

So next is adjusting and padding the frame and ordering the servo and controller. I am still not sure how go about mounting the servo. I think it's going to be surface mounted to the cross on the chest side. Then cutting a window out of the cross to access the 1/2" pipe. Then putting a screw on the 1/2 with a linkage attaching it to the servo horn. I would welcome any more suggestions.

Here is a view of the cross from the top. about 4" of the 1/2" pvc is sitting in the spine before the curve.
Propeller Propeller Vehicle
 

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When I created the mourner prop, I had to make a decision on how to get the head to turn on her. My solution was to dremel out a square in the tee where the arms came out of. I was using old hockey net pieces so they were pretty thin. I dropped the servo into the square and secured it with some screws and then eventually zip ties. I bought a collar for the servo that connected to an aluminum arm. I glued the arm into a foam skull. I then covered the whole setup in a plastic rib cage so it looked good! Here are a few pics to help!

Machine Toolroom Metalworking
 

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Discussion Starter · #19 ·
A little more progress. The way I had the 1/2" pvc inside the 1" cross with the 3/4-1" reducer, it had too much wobble. I found 2 VW rod bushings that fit perfectly inside the 1" pvc of the spine and cross. So now the 1/2 rotates smooth. I also cut i window out of the cross. Still needs to be cleaned up, though.
I do have one question, though. To get the smoothest 90 degree rotation, what would it be best to mount the servo? Vertically or horizontally?
Auto part
 

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Discussion Starter · #20 ·
When I created the mourner prop, I had to make a decision on how to get the head to turn on her. My solution was to dremel out a square in the tee where the arms came out of. I was using old hockey net pieces so they were pretty thin. I dropped the servo into the square and secured it with some screws and then eventually zip ties. I bought a collar for the servo that connected to an aluminum arm. I glued the arm into a foam skull. I then covered the whole setup in a plastic rib cage so it looked good! Here are a few pics to help!

View attachment 284878
LPF, you wouldn't happen to have a close of the servo would you?
 
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