instructables

DIY Compact 3D Printed Animatronic Eye Mechanism

by Ikkalebob

My previous instructable was an attempt to make an eye mechanism that was as accessible as possible to asmany people as possible, but in this project I wanted to design something that was more of a middle-groundbetween accessibility and quality. This design features some more speciality parts such as servo ball-links andpushrods but it's still quite easy to build. It uses a mechanism design which is commonly used in professional eyemechanisms, but it circumvents any machining by using parts that are designed for 3D printing. Compared to myprevious design, it is much more compact, robust, and a little lighter.

Another feature of this design is that it's designed to use snap-in eyes which can be replaced, and used with other3d printed components to cast a highly realistic dome over the painted eye. This process is quite involved so Ihave another instructable on how to make the eyes, but if you'd prefer to use simple 3d printed eyes you can dothat too.

The requirements aren't too high, but I'd recommend that you be fairly comfortable with 3D printing beforeattempting this project - you will need a printer that can reliably print at 0.15mm - 0.2mm layer height, and it'll needto be calibrated well enough to print small parts to be quite strong, which also entails using decent-quality filament.If you're using something like an ultimaker or makerbot you should have no trouble at all, but for folks like me usingcheaper 3D printers you may need to go through a bit of trial and error to get your print settings perfect. If you'relooking for something easier, have a look at my previous instructable.

Also, making the eyes was a tricky process and not necessarily needed to make this project, so check my otherinstructable for how to make the eyes.

Supplies:

Screws: https://amzn.to/32PAPo7 (this kit should cover you)Around 40*M2 x 6mm screws6* 10mm M2 screws6* MG90s servo screws (these come with the servos: https://amzn.to/33VfIlF)

https://www.youtube.com/embed/ihXxbQefl1c

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Hobby Components4* M2 Servo Ball-links: https://amzn.to/2Kq8fDK

4* M2 x 25mm Pushrod Connectors: https://amzn.to/32XQXEt (keep in mind this is just2mm threaded bar - you could always cut down a 25mm bolt or some plain threadedrod)

ElectronicsArduino Uno: https://amzn.to/2XoMolo (or anything that can accept three analoguesignals, one digital and communicate through SDA/SCL ports)Adafruit PCA9685 16-Channel Servo Driver: https://amzn.to/2NQeNNT

5V Power Supply, around 4A is more than enough. Here is mine(http://tiny.cc/is4cdz)

A female DC power jack to match your power supply, to be soldered to theservo driver board

2-axis Joystick: https://amzn.to/2NR4JnYPotentiometer (optional): https://amzn.to/2r0nADSPush-to-make switch (Some joysticks have this built in, but its easier to control whenits seperate: https://amzn.to/32Wnvyh)

10k Resistor: https://amzn.to/374seRUJumper cables: https://amzn.to/2NToCuw6* MG90s servos: https://amzn.to/2NToBqs

Also, a pin vice hand drill might be useful for adjusting hole sizes: https://amzn.to/2CLsCqG

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https://www.instructables.com/ORIG/FQK/NKQR/K0YBKRYP/FQKNKQRK0YBKRYP.zip…Download

Step 1: Printing

Most parts print fine without needing supports, and 0.2mm layer height or less is ideal. Lower is likely to be betterdepending on how good your printer is, there will be an ideal layer height for maximum strength – mine is 0.2mmbut it's not a bad idea to experiment with yours to find where it is.

It might also be a good idea to tweak your extrusion width to try and get a nice solid infill, this is particularlyimportant on the eyelids as there is a point where the print transfers from being primarily vertical to horizontal andthis can result in poor extrusion. My settings for the eyelids using Slic3r Prusa Edition were:

Extrustion multiplier: 1.1x (in filament settings)Default extrustion width: 160%Height: 0.18mmPerimeters: 3

100% infill was not necessary for any components but many will end up fully infilled due to the small size. I dorecommend using several perimeters/shells to ensure that parts with holes have enough strength - this cansometimes result in warping though so don't go to high with it. My tip is to get a nice fat cooling fan!

I used PLA for everything other than the eyes, but I think ABS would have been a better choice due to the lowfriction it tends to have, and the flexibility that would have lended itself well to the snap-fit parts. PLA has theadvantage of holding screws very securely though (not to mention that it's way easier to print), so maybe don't gettoo hung up on material choice.

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Step 2: Post-Processing

Many parts may need adjustments to run smoothly,the eyelids in particular are likely to need quite a bit ofsanding because the tolerance between the eyes andthe lids are fairly tight (which makes it look morerealistic). the tolerances I've used in this design forstationary parts is around 0.2mm, and for movingparts it's up to 0.6mm, obviously different printers willhave different abilities so unfortunately there may bea little post processing required.

I'd recommend sanding anything that's obviously outof shape as soon as its printed, but some problems

may only become apparent once you start putting themodel together. Just keep a small file or craft knifehandy to adjust bits as you go. Its also best to drill outholes that act as pivots to ensure they're the perfectsize, so refer to the graphics to figure out what to drill.

If you encounter any big problems with mis-alignmentyou can always use a heat gun to make the PLAmore malleable and re-adjust it, but I can't imagineyou'd need to.

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Step 3: Assembly

With everything printed, you can begin putting the model together. It may be useful to refer to the video for thisstage. Also there's all the reference pics in one folder in my download, including an .stl of the complete model youcan look at.

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1. Start by attaching the pushrods to the eye links. Screw in very carefully to avoid de-laminatingthe links, if this happens you may need to drill the hole to be larger or make your 3D print stronger(increase temperature, decrease layer height etc). Attach a ball-link to the other end of the pushrod,and try to ensure all four pushrods are the same length. Attach servo horns to the ball-links - two ofwhich should attach at the fourth hole from the centre, and the other two which attach to the secondhole from the centre - in both cases the bolt head should be on the side that has the raised sectionon the eye links, and the servo horn should be underneath the ball-link.

2. Using the M2 x 6mm screws, assemble the inner eye mechanism. Its critical to get everything inthe right orientation, so check the graphics and/or the video to make sure you have it right. Firstattach one pushrod to the large pivot with the bolt head on the side of the eye connector with theraised section, along with the eye centre holder. Then attach a pushrod to the small pivot with thebolt head on the flat of the eye connector.

3. Flex the eye adaptor to accept the large and small pivots. Ensure everything is able to movesmoothly, and sand/cut anything that isn't. Check everything is oriented correctly, then repeat step 2to make the other eye mechanism - but keep in mind this will be a mirror image of the first.

4. Plug in the servos to the left and right bases using M2 x 6mm screws - the wires should comeout towards the back of the mechanism - i.e., the opposite side to where the raised part is. Then usean M2 x 10mm screw to attach the eye mechanism to each base - check above to ensure they goon the right way. It's a good idea to use some glue between the eye holder and the left/right basetoo to ensure it doesn't rotate.

5. Attach the four eyelid holders with 3 M2 x 6mm screws each. Note that the sloped part shouldface the outside (but both should face the same direction each side of the overall mechanism, checkabove to be clear on this point). Also screw in an M2 x 10mm screw to each eyelid holder such thatthey face inwards towards each other. These don't go in all the way - it may be helpful to wait untillthe eyelids are in place to work out exactly how far in they should go.

6. Load the sub-base with two MG90s servos facing each other, held in with M2 x 6mm screws. Linkthe two bases by attaching this sub-base to the left and right bases using four M2 x 6mm screws,and also attach the front strip which uses six M2 x 6mm screws.

7. Work out which eyelid is which with reference to above and link the two pairs with the eyelidactuator arms. Attach a servo horn to each of the eyelid arms on the second hole from the centreusing an M2 x 10mm screw.

8. Plug in the eyes first, then slide in the bottom eyelid assembly, flexing the eyelid holders to getthe lids into the pivots. Then attach the top eyelid assembly. Don't worry about linking up any of theservo horns yet.

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Step 4: Electronics and Final Assembly

By referring to the graphic, upload the code to thearduino and wire everything up. Check the Adafruitguide if you need help setting up the servo driverboard. All servos should now be powered and in theirneutral position, so use this opportunity to link up allthe servo arms to the servos with the eyes facingstraight forward in a neutral position. You can justplug them in, then disconnect the power to screwthem in properly. I'd recommend testing the motionwith your joystick at this stage to make sure there areno issues. If the eyes are facing slightly differentdirections, you can unscrew the ball-links andtighten/loosen them on the pushrods to adjust thedirection of the eyes.

For the eyelids, its best if you set the servos to be inthe blinking position so you can line them all up in the

centre. Do this by either holding down the blink switchor creating a short over it. The eyelid servo horns arein an awkward position to accept a screw, but itshould be possible to flex the assembly enough to geta screwdriver in.

Your model should be complete! If you want to seehow to make the realistic eyes, check my previousinstructable. I'm also planning on releasing aninstructable soon to show you how to make acontroller, so check back if you're interested!

If you're interested in following my progress on thevarious robotics and animatronics projects I have onthe go, consider checking out my Patreon page to geta look behind the scenes.

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