The limited strength of the joint seems pretty advantageous for this application - it means that when any of the various software, hardware, or electronics failures occur that could result in the actuators fighting each other or the kinematic constraints of the mechanism, the outcome will be magnets letting go instead of the robot destroying itself.
@jwkooi
Жыл бұрын
If the magnetic coupling isn't strong enough, you could add an extra magnet to the pin that screws into the metal ball
@harrisonlow
Жыл бұрын
That's a really good idea! Hadn't thought of that before, but I'll definitely keep it in mind. Cheers!
@Suthriel
Жыл бұрын
@@harrisonlow And if that is still not strong enough, you can add some strings of fishing line around those joints, that ties both parts together, and defines the maximum range, that those parts could separate. Lust like the tendons on our joints, that keep the bones together.
@harrisonlow
Жыл бұрын
@@Suthriel That's a really good idea! Cheers 😊
@GeorgeGeorgalis
Жыл бұрын
Kuel, 😎if you put some machine polish in the ball socket and drive the ball with a drill until it contacts the magnet, you may end up with 1)best x,y fit in the socket 2)best z mag strength 3)best z ball support 4)best x,y precision. That ball won't be getting any closer to the mag, just be sure to get all the polish out, and lube with carbon powder or something.
@adammcaleer
Жыл бұрын
Cool video! Really interesting to see you walk through your design process and show the progression on each iteration of joint.
@harrisonlow
Жыл бұрын
Hey everyone, I hope you enjoyed this video on upgrading Jugglebot's Stewart platform joints! I'd love to know your thoughts on the new design and its benefits. Also, if you have any suggestions for future improvements or topics you'd like to see covered on the channel, please let me know in the comments below! 🤖🔧
@myxfit
Жыл бұрын
me, watching the first part of the video: "I wonder if something like PTFE sheet might help reduce friction and avoid wear on the magnet". you, a few minutes later: "I've bought some PTFE sheet". 👍
@TheBenenene10
Жыл бұрын
Nice! If it doesnt slide well enough dry lubricants might be an option. I'm thinking graphite and the like
@MK-lk7nc
Жыл бұрын
Man, I keep finding your videos and they're so similar to things I've worked on here (different, but similar). I went on quite a ball-joint (and, separately, magnets) kick for a while. Great stuff, love the design. One thing I'd suggest, regarding friction of the printed cup - print that part in nylon. Nylon is exceptionally smooth, and also very very strong. If you're able to print in HDPE, that'd be even better, but man that is tricky stuff to print with. Another thing that came to mind, not sure this would really be necessary but you might want to make mental note of it for later if it comes up: switchable magnets are a thing and they're pretty cool. Basically, by either wedging a piece of metal between some magnets, or not having that metal there, you can completely enable/disable a magnet. This is all done without active power. This video "How to build a switchable magnet" by Andrew Klein explains it well along with some designs. So a modified version could perhaps be used in your cup assembly, if you want a way to use overly strong magnets but still be able to easily disassemble it later. Toggle the magnet into off position, falls apart. Toggle it back to on position, probably far stronger than you'd ever need it. But as you say, you may already be at that 'stronger than you need it' level. Anyways, best of luck. Really enjoying these videos.
@MK-lk7nc
Жыл бұрын
oh and one other thing i found quite helpful for 3d printed ball joints is to take the cup part and polish it in a drill press for a moment by taking one steel ball on a post and chucking it in the drill, the high speed friction does a reasonably good job of polishing the cup. Helps smooth out the motion quite a bit. Vapor bath could possibly accomplish similar results.
@harrisonlow
Жыл бұрын
@@MK-lk7nc wow super helpful ideas! Thanks heaps! I love the idea of disengagable joints. Polishing is a great idea. Cheers!
@MK-lk7nc
Жыл бұрын
@@harrisonlow Hey no problem. Regarding polishing, I found it quite helpful to sprinkle in a little "Comet" abrasive cleaner, then drill. Gives it just enough sanding action.
@HansCNelson
Жыл бұрын
I did something very similar a few years back for a delta bot I was working on. Never did get the full machine working, but the joints seemed to work great!
@HansCNelson
Жыл бұрын
The quality of this video is absolutely horrific, but in the off chance that some of the ideas are useful, here's what I was working on in 2015: kzitem.info/news/bejne/p5-Xt5doi5mSZoI
@harrisonlow
Жыл бұрын
Just checked this out. Cool idea! Also the ball joints I referred to in my comment are not the ones from this video - these ended up being _far_ too weak...
@fast-yi9js
Жыл бұрын
provided the sheet doesnt dampen the magnetic force too much you shoould definetly holepunch a few pieces of it, the coating on most commerical magnets is designed to resist corrosion, not friction based wear.
@TheMadManPlace
Жыл бұрын
The max retaining force would be achieved if the magnet had a concave surface grind just a few thousandths larger radius as the ball. But even then, very fast reversal of direction could possibly cause the ball to lift out of the socket = crash. But so far so good...
@madhavlodha3081
Жыл бұрын
These videos are awesome. I'm trying to look for a project to start of my own. I've been a blank slate for a while and when I say this series I'm like damn that's such a sick idea. Let me know if you have any other ideas or projects in mind 😂😂.
@harrisonlow
Жыл бұрын
Nice! I've got a few ideas for future videos on the "about" tab on my channel. I usually think about things that would make my life better/easier or would just be cool in general. Good luck!
@isstuff
Жыл бұрын
I think you will want more strength. There are magnets that are cylinders with counter sunk holes in them. So you can secure them with a screw (gently, they like to shatter) but that counter sunk hole makes the ball have closer contact with the magnet. So if you don’t have enough strength, get a bigger magnet with a countersunk hole in the centre so it can hug the ball. Or a ring magnet?
@harrisonlow
Жыл бұрын
Yep, you're absolutely right. These joints ended up being nowhere near strong enough, so I've swapped them out for KD625 magnetic ball joints. I had to do a bit of adaptation to get them to move smoothly, but they're super strong. I like the idea of using countersunk magnets! I'll have to pick some up sometime to give that a go. Cheers 😊
@tHaH4x0r
Жыл бұрын
So essentially your joint is the ball sliding inside the 3d printed cup, with the magnetism just providing a preload to your ball joint. This is very similar to existing ball joint designs often found in delta robots. A cup (usually coated with PTFE) with a ball preloaded (generally by a spring between two legs). You might be able to just buy such a PTFE coated socket + ball off the shelve... Regarding the question about joint 'strength'. Important to recognize is that stiffness of your mechanism is likely not dominated by the stiffness of the rods, but by the stiffness of your bearings. Because the bearings are preloaded, the stiffness can be found as the contact between the ball and the 3D printed part, and hence the 3D printed part is likely a huge bottleneck in the design. The joints themselves present a similar stiffness in both tension and compression, with the exception in tension if the force exceeds the preload force (leading to the magnet detaching). So again, if you make the cup somehow more stiff, it would lead to a higher stiffness joint in general and improve also hysteresis, which is my following point: What would additionally concern me, is the large and unpredictable amount of friction from the ball sliding against the 3D part. This can (of course) cause a lot of wear at best, but the large friction combined with limited stiffness can cause hysteresis, which will limit the accuracy of your mechanism. Additionally, if the static friction is large enough, it can (combined with the stiffness) create stick-slip type problems which are particularly difficult to deal with in your application. As for the shape of a ball and cup joint, this is a whole science in itself. As you can imagine, getting the exact curvature the same between ball and cup is nearly impossible, so that can lead to undefined points of contact and lots of variation. Some suggestion I saw in another comment was to have the magnet directly contact the ball. I would highly advise against this, as the plating on magnets is quite brittle and I think it would wear out pretty quickly.
@harrisonlow
Жыл бұрын
Very interesting thoughts! Thanks for sharing them 😊 To address some things you mentioned: - I've since changed these joints to use a more standard approach: KD725 Magnetic Ball Joints. These are *far* stronger than what I show in this video, and after a bit of trial and error with PTFE sheets + printed spacers, they slide really smoothly with almost no stiction. - Viewing these joints in the frame of a pre-loaded ball and socket is fascinating! I'm wondering if it'd be possible to do away with the magnets and just have a piece of string or a super strong spring holding the ball and socket together. Do you know of any examples of this that I could check out? Cheers!
@tHaH4x0r
Жыл бұрын
@@harrisonlow That makes a lot of sense! I think it might be difficult to replace it with a piece of string, as you do need some compliance to be tolerant to misalignment and movements. A strong spring is definitely doable though. However, the preload force does not need to be very large! It will not make the joint more stiff. As long as the preload enforces contact between the ball and socket, the stiffness is determined by the lowest stiffness of these two. Essentially the preload only needs to be able to resist the largest acceleration forces without losing contact. If it is just slightly higher than that, it is fine. Should be fairly easy to get some ballpark values for the required preload (if you know platform acceleration, and assume that to produce the force onto one ball joint). As for an example of the spring preload on ball joints, I had a look around and the following show a couple of clear examples: ABB FlexPicker IRB 365 Festo EXPT OMRON X-delta series Kuka KR Delta Cama Triaflex Delta FLSun Super Racer/V400 (this one might be a possible source)
@nolol9907
Жыл бұрын
If you have problems with it not being smooth enough, you can add little steel roller balls that'll limit the points of contact
@joergengeerds360
Жыл бұрын
I would suggest to allow the steel balls to make full contact with the magnet, and use that as your main bearing surface, and use the concentric plastic part only to constrain the slipping motion of the ball. i would probably use a ball end mill to bring the spherical cutout of the 3d print to a tiny and smooth clearance.
@harrisonlow
Жыл бұрын
Yeah (spoiler!) once I put the robot together, the magnets weren't nearly strong enough to hold it together 😬 I've bought some legit magnetic joints with 20kg pull force and they should be arriving early next week. 🤞
@mattiasfagerlund
Жыл бұрын
You might gain strength by having three smaller magnets in a cup configuration - though as you speculate you probably won't need it.
@1800Supreme
Жыл бұрын
Use ruby bearings for the ball cups.
@germimonte
Жыл бұрын
I'd recommend some sort of lubricant, like silicon oil or graphite rather than trying to add more stuff between the ball and the magnet
@stefanguiton
Жыл бұрын
Excellent
@wolpumba4099
Жыл бұрын
I wonder how a joint based on a flexure would look like.
@harrisonlow
Жыл бұрын
I do love a good flexure joint, though I haven't looked too hard for one for this job. AFAIK it's difficult to make flexures with a large range of motion, so I'm not sure how easy it would be to make one for this joint. I want jugglebot to be able to move really far 😁
@heatherlow9848
Жыл бұрын
What, no cats!?
@harrisonlow
Жыл бұрын
Alby wanted into the room, but didn't care for cuddles this time 🙄
@Erbmon
Жыл бұрын
I mean the robot is cool but the calculus is way off 117 parts is not nuts, nuts is clearly 18. :D
@chaosordeal294
Жыл бұрын
3x fewer!! So before when it was the same number of parts of itself and it had zero fewer parts, now it has three times that many fewer parts!! So that's . . . zero. Hey, maybe using the phrase "three times fewer" when you mean "one-third as many" is dumb.
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