Homework - Cyril Wichers
Chris Ellerby
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Homework for live workshop student Cyril Wichers
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Chris Ellerby
Admin
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As I want this to be not only functional, but also a bit of a demo-piece, and because I felt like doing a bit of machining, I took a slightly different approach to the design.
I added a base, which is made from a solid piece of aluminium.
For the "spine" I used a piece of brass rod I found in my materials bin. I milled a couple of flat spots on the front and back to mount the rod ends (as an extra bonus, they're also not able to rotate anymore). The spine is recessed in the base and is held in place with a bolt that screws in from the bottom.
The axle is made out of silver steel. I turned down both ends to fit the rod ends, so I don't need collars to keep it in it's place. It's less flexible, but it looks better (at least, that's what I think)
Facing a piece of aluminium for the base...
I mounted the servo brackets to a piece of aluminium flat bar. Then milled a flat spot on the back of the silver steel axle and attached it with a couple of button head screws.
On further inspection, it turned out that there was a piece of pipe in the neck of my mannequin head (probably for attaching it to the body). I machined a piece of aluminium to fit inside, leaving a flange, so the head would rest on it (I glued the adapter inside the head using epoxy when the mechanism was finished). I also drilled a hole for a center pin.
Then I machined the top plate. It has a pin on the top and on the bottom. One is used as a center pin to locate the adapter, the other is used to attach the top plate to the universal joint. I drilled two holes at 90 degrees and machined a couple of brass pins to fit inside them. These are used to attach the rod ends and provide enough clearance for them to rotate. Finally, I drilled and tapped three holes for the screws that attach the adapter to the top plate.
I made the links out of 5mm silver steel rod, which I turned down to 3mm at the ends. I cut an M3 thread on them to attach the rod ends.
Nice snug fit between the adapter and the top plate:
Head fitted.
I used a similar way of mounting this one as I did for mounting the first two servos. I fixed the servo bracket to a piece of flat bar, milled a flat spot on the "spine" and drilled and tapped a couple of screw holes.
Then I machined a flange, which I attached to the silver steel rod using a set screw. I shortened two rod ends by aproximately 5mm and attached them to eachother using a small piece of allthread, to form a really short link between the servo and the flange.
I mixed the servos for the "nodding" motion, so I can control them with one stick. When I move it up or down (pitch), the servo's move in the same direction. I also mixed in the roll, so when I move the stick to the side, the servos move opposite to eachother, which produces the "curious puppy"- look.
The third servo is attached to the other stick (rudder), to control the turning-motion.
Unfortunately, there's some play in the rod ends and the universal joint, that's why it's a bit wobbly.
Here's a pic of my shop:
As to the neck mechanism; I sourced some better quality rod ends, which eliminated some of the play/wobblyness. What's left looks to be caused by play in the servos themselves, probably because they're cheap Chinese ones. These are great for prototyping, but not so much for heavy duty use (as in: balancing a 2 lbs glassfibre mannequin head) For now they'll have to do, since a set of Hitec servos will set me back almost 150 Euros.