This Expanding Mechanism is Crazy Clever

this is mechanism 224 an expanding pulley design depicted in the book 507 mechanical movements originally published over 150 years ago many of the mechanisms found in here date back to the first industrial revolution an age of steam engines and rudimentary methods of power transmission and automation many months ago one of my patreon supporters suggested i take a look at the expanding pulley design and try to recreate it in cad and in this video i'll show you how i reverse engineered this forgotten mechanism and then used it to create this fully 3d printed lockbox let's get started [Music] i must admit out of all the mechanical movements in this book it's one of the more daunting designs to look at and initially i didn't quite understand how it even worked to quote the description two to four represents an expanding pulley on turning pinion d to the right or left a similar motion is imparted to the wheel c which by means of curved slots cut therein thrusts the studs fastened to the arms or the pulley outwards or inwards thus augmenting or diminishing the size of the pulley simple right well actually kind of is to start let's remove the pinion from the equation as it seems to be only used to lock the position and we'll also remove all but one arm of the pulley this arm is constrained by a track that constrains it to a linear motion in one axis only and it only interacts with the central disc with this pin sitting in this slot the pulley arm is forced to follow the slot and bam it moves outwards or inwards depending on the direction of rotation what we have here is a basic cam and roller cam and roller mechanisms are fantastic at converting rotary motion into linear actuation and even today in a world of computerized solutions to mechanical problems they're still used in tons of applications like your car unless it's a koenigsegg in this design though the slot in the central disk is the cam and the pin in the pulley arm is the cam follower now unlike most other cams you'd find there is no continuous movement here it has very discreet start and end points but the principle is the same what i find really neat about this approach is you can greatly affect the behavior of the mechanism with only very subtle geometric changes for example changes to the arc size and its angle affect the force required to actuate the arm as well as how far the discs needs to rotate to do so you could even program complex motion using some kind of organic path i have this sewing machine which uses cams to do this but i digress maybe i'll cover that on a future video so when you patent this cam and follow a movement around the central axis you end up with this and i've 3d printed it the movement is honestly far smoother than i imagined it would be but i can already see some glaring issues it's supposed to be an expanding pulley right but i can't see it being a very good one for a start there's huge gaps unless the pulley is at its smaller size and as the pulley changes size the arcs become no longer concentric i tried to achieve a happy medium by making the pulley segments concentric at the halfway point but even with such a small range of movement i can imagine it's almost like trying to drive with a hexagonal wheel combine these design concerns with the sheer complexity of what would normally be an incredibly robust simple object and i suspect this design didn't see very much use but i would love to be wrong if you know of any actual examples of this expanding pulley design in the real world please comment below so there's no question that this mechanism is gorgeous in operation but it's kind of bad at what it was designed for so i started trying to think of alternate uses originally i thought perhaps some kind of expanding wheel for a robot design to navigate over varying terrain sizes but the gaps between the spokes as well as that concentricity issue would make it a terrible choice and that's overlooking the challenges of coupling motors to the expanding mechanism and driving it reliably and blah blah blah no i feel that this mechanism is better suited to some kind of puzzle in 2018 i designed and printed a range of impossible dovetail puzzles these classic machinist projects look like they're locked in place by dovetails at impossible angles but instead they employ a trick in which the two sides slide apart revealing the illusion and what's really quite neat is that the illusion also works with a hexagon as demonstrated here once again it really does look like the parts aren't possibly locked together but they're not so i had an idea what if we combine this with this and well it took a long time but the result was well worth it this is my expanding mechanism lock box version one this design uses 3d printing for the mechanical components and laser cutting to form the sides and top of the box and a ton of fasteners to hold it all together i've taken a cue from the original mechanism 224 diagram and returned to driving the center wheel with a pinion gear which lets me keep the mechanism locked behind this nice clear top cover but keeps it nice and visible which is important because the mechanism movement truly is beautiful as the disc rotates the gold dovetail shape bolts retracts simultaneously and then the whole mechanism can be lifted free allowing access inside now you might be thinking hey that seems like how the door to a bank vault would operate and initially i thought so too but it turns out the locking mechanisms for volts are far more complex employing all manner of gears and complex linkages i think there's perhaps two main reasons that this and follower approach isn't used first i imagine you'd need immense force to operate the numerous bolts and this mechanism doesn't allow much scope for gear reductions or force multiplication but secondly and i think this is most critical this design doesn't really lock opened or closed in fact it can easily be back driven and the original designer tried to mitigate this with a crappy pull to lock the pinion gear but i think with some carefully considered design tweaks we can make this lockbox a little bit more lock and a little less just box and i think it also looks way too much like one of those awful spinning ash trays from the 50s blah version 2 is entirely 3d printed i've removed the need for any kind of fasteners whatsoever it prints cleanly with no supports and i'm really happy with how it turned out in this design there are now shallow cutouts in the slot which prevent the mechanism from being easily back driven by simply pushing on the bolts now you really do have to turn the gear with the pinion gear key and i ran with the hexagonal theme and designed the container to resemble some kind of alien artifact patterning variations of the makey's muse logo around the sides and creating this complex top cover which displays a mechanism while securely holding everything in place i think as is this design could be a super fun addition to a treasure hunt or gift this christmas but there's still one niggling detail i wanted to resolve you can still open it without the key by rotating the disc by hand sure it goes against the spirit of design but for hardcore puzzle enthusiasts i think that's just not good enough this third this is one of the most complex 3d printed models i've ever created it doesn't look visually different to the other one but the disc shield turning not until you find the key that is like all good things in life the solution was magnets and this magnetic latch is one of my favorite designs of the year because it's completely hidden away yet operates with such a satisfying sound it does mean the model now requires one m3 screw and two neodymium magnets but we can't 3d print magnets yet well at least i can't by the way all of these were printed on my two creality ender 3s in a range of pla filaments shocked i know i used prusa slicer and i'm i'm blown away by the quality i can now achieve off these incredibly affordable 3d printers so you could definitely print stuff like this at home on your low-end 3d printer anyway that look can be defeated by inverting the box but i figured that's an easy rule to put into place for a puzzle and if you really wanted to you could put a small bit of metal to attract the magnet from the rear and that would be enough to hold the latch in place when it's inverted but that's just a bit too far even for me if you're interested in a deep dive on this design and tips to make your 3d prints more successful i've got a video here outlining some of my favorite more advanced modeling techniques and it's definitely worth checking out i had an absolute blast exploring the possibilities of this obscure expanding pulley mechanism over the past few months and i hope you found this video interesting if you want to print one yourself you can find links to in the video description along with a full assembly guide and i'll be sharing the step models on my patreon as well i put a ton of work into making it printable on low-cost 3d printers that need for support material but do keep in mind the main body of the block box is a good 24 hours of printing so print the test pieces first to ensure your machine is capable of holding the tolerances and clearances required if you did enjoy this video then maybe consider subscribing because here on makers music is my aim to empower your creativity through technology and i'm forcing you again very shortly catch later guys bye

Channel: Maker's Muse

Views: 1,143,829

Rating: 4.9214001 out of 5

Keywords: 3d, printing

Id: LU77kPf25Yg

Length: 9min 6sec (546 seconds)

Published: Sun Nov 15 2020