How to create effective compliant mechanisms with 3D printing

compliant mechanisms are one of the most satisfying things to play with but they can also be very functional too today we explore the best tips for Designing and 3D printing your [Music] [Music] own complaint mechanisms are truly amazing but there's no reason we need to be stuck as mere observers we can design and make them ourselves in this video I'll share with you some tips for doing just that my Patron Jeff requested a guide on this late last year and it's finally here but before the tips first a definition I think most people have an implicit understanding of what a mechanism is but technically a mechanism is a device that transforms input forces and movements does something with them giving us output forces and movement here is a simple example of a mechanism we can all relate to as set of pliers on one side we have our handles that counts as the input then we have a pivot and our Jaws on the other side and thanks to the length of the handles versus the Jaws we have a mechanical advantage which means the real output is our scream when we squeeze our finger so how does a compliant mechanism differ well instead of having joints it's flexible and works through defamation this set of tweezers is a compliant mechanism that we probably already familiar with it's made from one piece and it relies on the flex of the material to close create an output based on the input of the user's hands not enough of an output to get that scream so instead let's introduce the compliant ping mechanism from the Wikipedia page again this one is all one piece and relies on deformation for movement and to create mechanical advantage now the opening is not that large and it is hard to get your finger in so it's questionable to use this on adults but for small children I guarantee you you'll get your scream so in summary where traditional mechanisms are made from multiple pieces joined together with Bolt and bearings to facilitate movement a compliant mechanism is designed to be one piece from the very beginning and rely on flexing to allow movement and achieve the intended purpose compliant mechanisms are pretty popular on YouTube because they're so satisfying to watch previously I made this video where inspired by a wooden laser cut glasses box I took to CAD and used linear patterns to create a similar formation and I released these patterns so anyone could import them as a modifier into their slicer and add bendy segments to otherwise rigid objects printed with a rigid filament but you've probably seen much more popular videos like this one from veritasium that offered a deep dive on compliant mechanisms and their applications this video from RC life on where Simon used a compliant mechanism for thrust vectoring on an RC flying wing and more recently this viral video by Mark Rober where he collaborated to create the world's smallest nerf gun using a compliant mechanism there's something these three videos and these pliers all have in common they were all designed by the compliant mechanism research lab at Brigham Young University according to these videos Larry Hal the chief Professor literally wrote the book on compliant mechanisms and in part because of this BYU CMR are famous for the compliant mechanisms and they have some great resources on their website here we can see the one piece Blaster from the microba video the pliers from the veritasium video and the two degree of Freedom space pointer from the RC lifeon video this is a fantastic resource for learning there's numerous files you can download for free print for yourself and see exactly how they work if you look hard enough you will find examples of compliant mechanisms in objects around your house but trust me it's much more satisfying to learn by making some yourself which is why it's no surprise that most of the objects we're about to explore are from BYU CMR the aim here is to examine a range of compliant mechanisms and then identify some rules for making our own we'll start off with those same pliers designed by BYU CMR if we examine them we can see they have three points of deformation which are the equivalent of hinges 1 2 and three and if you watch them carefully this is where the movement comes from as the handles are pushed and the Jaws open and close this by stable switch is designed in a very similar way when we push down on one of the levers it snaps into a held position and that's because this is an over Center mechanism which is why it doesn't like holding this position and once past the center point pushes and locks into the new stable position so how about the one piece compliant Nerf blaster this one's a little bit different and it's actually made up of two mechanisms the first of those is the trigger and that's designed to rotate when you pull your finger on it we can see there's two parts of plastic that deform for this and then we have the second mechanism which this time is linear and is activated by pulling back on the finger plunger that will then lock the plunger against the trigger and we can see in these Springs we have a lot of stored energy if we now load in a dart and then pull the trigger that stored energy is released and the dart becomes a projectile how about something completely different 3 printed origami this looks like a flower but is actually a flasher hexagon I don't know what that means and I'm sure someone will tell me in the comments what I do know is that it folds like origami to have two states and that playing with it is quite satisfying there's a video on the printables page showing you how to make all of these creases and if we shine a light from underneath we can see that much of the plastic is thick but these sections that are designed to crease are purposely kept thin at around 0.2 mm stst on printables has quite a lot of experiments with compliant designs including this spiral spring 23 this one has multiple applications and again is very satisfying to play with firstly if we rotate the center separately to the outside it acts like a torsion spring storing energy and then releasing it and this is evident whichever way we rotate it but then if we turn it on its side we can see that it also acts as a vertical linear spring as well and not only that for the F more we can rotate it from side to side giving this quite a few degrees of freedom remember that this is a rigid filament but it's designed to make the final product compliant you might remember a fractal Vice that I designed my own version of in a video previously it can articulate to conform to almost any shape but in doing so it has a lot of moving parts and complexity so instead here is a compliant mechanism version by bubs builds the aim of course is the same to make a flexure that can deform when press and therefore Contour to the shape of almost any object instead of many moving parts we instead have one made up of multiple segments within sections that are designed to flex and it does do this pretty well it's not as mesmerizing as the other fractal Vice in part because this version is a little bit stiff but more on the print settings to avoid that later and finally my own bendable pieces which you can find on printables these are again printed in a rigid filament but anywhere where the pattern is applied they become quite flx flexible to the point where they have multiple degrees of freedom these work great in torsion traditional bends a combination of the two and they'll even work with a limited capacity in compression and tension onto the rules and we start by answering the most important question and that is what is the best material for 3D printing compliant mechanisms when you find compliant mechanisms in plastic consumer products it's most likely in the form of this a living hinge as seen on the top of this jar this is another over the center mechanism that likes to snap into one position or the other and typically these will be injection molded from polypropylene plastic but PP is very uncommon in the world of 3D printing so you might think the next best bet is to use TPU a purposely flexible filament but as we can see here on this by stable switch it won't actually lock into position and therefore it won't function as intended compared to the rigid filament and that's because TPU is typically too flexible it does have memory and wants to return to its original position but it's not particularly responsive in doing so previously in this model I designed some compliant mechanism Springs to act as a suspension and they do work but they highlight another problem with TPU over time it can deform permanently here's the car with the body on and as you can see the suspension is sagged and killed all of the wheel clearance this used to roll nicely but now it's just jammed another popular filament is PLA and you might have some success with this depending on the design of the mechanism I picked this B aable switch for back-to-back testing because the middle joint needs to flex quite a bit and that makes it quite demanding and this exposes pla's weakness it can be fairly brittle and as we can see here one of the joints has snapped after not too many cycles if we examine the remaining joint we can see that it's white damaged and was probably going to break soon too I think probably the best filament choice is nylon as it has a small amount of flex without being anywhere near as floppy as TPU this switch still locks into the position that it should should yet it doesn't feel too rigid and like it's going to fail and I have run this version through many many cycles and it shows no signs of failure anytime soon but here's the thing about nylon it's one of the hardest filaments to print it needs to be kept really dry and if printed without an enclosure and sometimes when printed with one it likes to deform and peel up off the bed so with this in mind are there any close Alternatives this version is printed with the same settings but in ASA it's got a satisfying snap to the motion and so far it has survived many cycles without any damage but there is a little bit of discoloration in the Flex Points suggesting that it won't last forever so not as good as nylon better than PLA and for many people still hard to print unless you have an enclosure so here's my best compromise pet G the switch has a satisfying snap action and I've been through many cycles without the joint failing and we can see up close that there not the decoloration from permanent defamation I still don't think that it's reliable as nylon but given how much easier it is to print I think it's a fantastic compromise everything you see here apart from the blue pliers is printed in PG to great effect how about some more tips first up let it cool before bending I.E using the mechanism compliant mechanisms are so much fun to play with but don't rush in as soon as they finished printing or you may risk breaking them without breaking them consider a thin print if you've ever tried to peel it off before it had cooled down you might have noticed that once it did it would stay permanently deformed and with these prints we don't want to risk permanent deformation ruining our mechanism when in the slicer check and control your seams you'll notice in this print that by default it's trying to put the seam in the skinniest part and that happens to be the section that we need to flex and remain reliable when it bends if you don't address this probably the first time you use the mechanism it's going to snap every slicer has a way for you to manually position seams the handiest here is probably paint on seams and should paint them near but not on the skinny Junction that deforms you then need to double check that the junction has consistent extrusions on a similar note arak perimeters may be problematic we can see here that we have arak perimeters on and when we slice the model previewing by linewidth shows some variation across this Junction based on my experience in making this video this can be quite problematic without changing anything else if we switch to Classic and then reslice we can actually see that this section was too thin for the Extrusion to actually take place using a Ruck perimeters will hide this but it does make for a weaker joint in some cases this print looks okay but the first time we change the mechanism we hear a small crack and have a partial failure and now it no longer clicks into position to get around this if it's someone else's model the simplest thing you can do is to scale it up this will hopefully then give the junction enough width that you can get full width extrusions which will hopefully make for a reliable mechanism with this in mind if you're designing the mechanism yourself you want to match the Bendy sections to Extrusion width multiples your slicer should have a section with your line widths these are the widths of each Extrusion as they're laid down probably the ones we're concerned with the most are outer wall and perhaps default and in this profile they're each set to 42 mm so let's say we're designing a mechanism with a thin section that we want to bend right from the start we should go in knowing exactly how many perimeters we want across this section one perimeter means an extrusion on each side so two in total we can do a simple calculation to work out just how wide this bit should be and then we can come into the sketch and alter accordingly if I think this looks a little bit skinny and I'd like to add more perimeters The Next Step Up would be two which makes four in total so once again I can size my geometry to suit this calculated approach should save you headaches later on related to this we can tune the amount of flex with our perimeter quantity remember that Vice flexure that I printed too stiff if we look at G-Code we can see that that was printed with three perimeters all around and the thicker the plastic the stiffer it's going to be by simply lowering this to two perimeters we should be able to increase the flexibility of the mechanism and conversely by upping the amount of perimeters we can stiffen it and I did exactly this on this compliant spring with thin medium and thick from left to right the spring on the left is a lot softer and the one on the right as you would expect is stiffer one of the key principles when designing your own compliant mechanism is to add length to ensure durability and the reason I picked this bable switch as my torture test is because it doesn't follow this principle here's the initial State and we can highlight the starting angle in green and here's the secondary State again with the angle highlighted in Green Let's Start by removing the image and then enlarge the two before finally aligning them where we can measure an angle of 40° this is how much that middle joint has to flex each time we take it between the two positions and 40° isn't huge but the problem comes from the fact that that flexing takes place over only around 2 mm here's a length of old brittle PL to demonstrate this principle if we have a big curve we can bend it right back on itself 180° and we can do this all day however if we try for that same angle over a shorter length the filament will soon fail the key is to spread out the bends over a longer distance here are three mechanisms that have the same job Flex the two handles together on this first one the length of the flexing is quite short it's likely to fail on the second one we extend it and this one should last much better and on the third one we're spreading out the bending over this entire length so this one will last the longest we can see examples of this on the Blaster Trigger notice how long the bending segments are we can also see it on these flexy panels each small segment only needs to move a couple of degrees but the sum of all of this is a large range of movement but the best example is the spiral spring as each length is really long wrapping around and around the center and that makes this mechanism reliable another quick design tip fillet fend off fatigue if we come back to our last example obvious weak points are these Square edges so the easy solution for this is to just add fillets in any Corners KN points that bend this will stop the stress from concentrating in the sharp corners and finally we can multiply geometry to add strength and force that spiral spring has a surprising amount of energy that it can store and that because it doesn't just have one spiral around the outside it's actually got three each starting in the center and anchoring around the perimeter but the best example of this is the Blaster each of those sections that start straight and then have a curve when recoiled work in Harmony and the reason there's so much force built up is because there's 12 of them when designing you can multiply the same geometry to increase the force let's say we're in this piece a lot stiffer but we don't want to make the top section too thick another solution for this is to just multiply the geometry and with this configuration you're going to need a lot more force and therefore have a lot more spring thanks to the multiple archers for me 3D printing is the near perfect manufacturing technique for making compliant mechanisms firstly it's easy to iterate secondly we have a lot of control over the slicer settings and therefore the output and finally compared to something like laser cutting we can vary the thickness over the object I hope the tips in this video will help you if you plan to design or print your own I'm currently using them in my own project where I want an opening to be closed kind of kind of like a roll the door it's my hope that I can create a part that flexes to follow a curve but then can compress and act like a spring when one part is rotated more design and testing needed but you will see this in future thanks Jeff for making the video request thank you BYU CMR for all of your great designs and thank you so much for watching and until next time happy 3D printing compliant mechanisms good day it's Michael again if you like the video then please click like if you want to see more content like this in future click subscribe and make sure you click on the Bell to receive every notification if you really want to support the channel and see exclusive content become a patron visit my patreon page see you next time

Channel: Teaching Tech

Views: 39,033

Keywords: 3d printing, 3d printer, 3d print, 3d printed, compliant, mechanism, design, create, how to, guide, tutorial, filament, examination, analysis, analyse, bend, spring, torsion

Id: xV36ITRjP_4

Length: 17min 14sec (1034 seconds)

Published: Fri Jun 21 2024