Big update! I built the entire assembly using the above joint design, and sadly it seems that the thrust bearings like to 'swim' in their plastic cutouts just a little bit, which kind of defeats the whole purpose lol! There are some fixes but they push the offset link pattern even farther apart, and really it just was starting to feel unwieldy. I had an idea to try 2020 + coplanar/inline jointsby Apsu - Look what I made!
Quoteo_lampe Yeah, 2020 extrusion will make it for sure! Don't want to be nagging, but I still think carbon rods are even better and also widely available. Sure, I've considered CF rods, but I'm not sure of an easy way to mount joints to reasonably-sized rods, or cut them to the sizes I need if I can't find some that are already close. With a Delta, it's much easier because there's not nearly asby Apsu - Look what I made!
Ok, I decided to get my extra 2020 chop-sawed into appropriate lengths and try 'em with printed brackets. I just wan't getting the performance I wanted out of the printed arms no matter what I tried or how solid they were sliced/printed. Here's a short video of the idea YouTube Link Have to say... this is *by far* the strongest thing I've assembled yet, and I just tweaked the model to add evenby Apsu - Look what I made!
Quoteo_lampe Now that you've "discovered" the thrust bearing advantage, do you still need the extra beefy 608 bearings? Initially I thought, needle bearings would be useful. What do you think? There is a saying in german: There is never enough time to do things right, but then there is always time to do it again.... The 608s are way over-spec'd for the loads involved, yes, as are 8mm axles. Howby Apsu - Look what I made!
Update time After extensive thinking, modeling, simulation and empirical testing, it's clear that the un-bossed bearing mounts are insufficient to maintain rigidity once the arms get strong enough. Instead, the bearing orientation becomes the weak point, and they tilt inside the 22.2mm cutout. I worked really hard to figure out how to secure, boss, and preload the bearings without significantlyby Apsu - Look what I made!
Decided to try adding M8/608 to my previous arm design, since the lattice orientation is more correct for the needed reinforcement, and looks badass (I think ). Here's an animation showing the arm links, joint, hardware and exploded view of how the joint is assembled. YouTube Linkby Apsu - Look what I made!
Got the rest of the basic CAD done to print and assemble everything. Renderings from front and back: Effector mount is closer to correct now, though I think I'll switch the shoulder on the X (front) axis so the effector attachment is on the left instead of right (towards Y rail), helping to balance left/right extremes due to X rail positioning. I'm not sure if this approach is the "best" waby Apsu - Look what I made!
Bit of an update. I decided to investigate using M8 hardware and 608 bearings since I had some 608VVs with rubber seals on hand and a few M8 bolt/washer/locknut pieces. I came up with an arm design and bearing mounting system that actually works pretty well. Here's a cross-section view of one arm. Part of the bearing/bolt setup is visible on the left, if you're confused by what's there. Viewby Apsu - Look what I made!
Alright, got a fun update. Got everything put together minus the extra Z bracing (still waiting on extrusion delivery!). I lubed up all the joints, tightened everything down, put a little weight/indicator on the effector, and ran some gcode slow at low accel to give it the best chance of good behavior. YouTube Link Short video of 40mm/s @ 200mm/s^2 accel. There's a small hitch in the video nearby Apsu - Look what I made!
Ok, got the bracketing figured out, motors are all the same distance below the frame, active belt paths are all linear, just needed one extra idler on the Z bracket. Made some bigger and cleaner renderings to illustrate the layout. And yes, I realize I have some of the motor pinions slightly askew and the Y belt clamp spacer is shifted. Details, have to get back to work, etc ;Pby Apsu - Look what I made!
Quotemavu Very intersting! You could theoretically even go with the stepper gear wheel driving directly on a rack, thus removing belts alltogether. Yep. This can be driven any way you choose, any combination of belts, gears, water and sailboats. But belts certainly aren't Bad, there's tradeoffs, as with everything. Quote And if I understand this correctly, on every axis the force on the arm isby Apsu - Look what I made!
Small addendum, forgot I rendered a turntable of the basic CAD drawing, so here it is: YouTube Linkby Apsu - Look what I made!
WOW I printed out some arms to test their strength and rigidity, and holy *shit* are they strong! I can Maybe barely flex them against the lattice using my hands and thumbs, and only slightly flex them by clamping onto a flat surface and applying several dozen kg of force on the other end. These structures are incredibly stiff in exactly the direction I need them to be. Total weight for anby Apsu - Look what I made!
Working on several things at once, but got some more pics to share! First, the reorientation, with new arm design idea: And closeup of an arm section: Per the new orientation, it's not finalized by any means, but I *really* like this approach. Looks more elegant and "printerlike", I think. As for the arms, I discovered that most of the springiness was actually the arms themselves bendingby Apsu - Look what I made!
QuoteDavid J I wouldn't be so spiteful! No, I just meant that it would only be of any use as a 3D printer if it could move in a flat plane - if it can't then it's of academic interest only. Nice if it does work OK though. Maybe I wasn't being clear enough. What I was trying to say is that the geometry of the Tripteron design *guarantees* constrained, accurate Cartesian motion, assuming the armsby Apsu - Look what I made!
Quoteo_lampe What about your linear rails ( mgn12 I guess)? Do they show any slop or springy moves? I've replaced the balls of my rails and they run supersmooth now! ( German Wertarbeit ) They are indeed MGN12, but they don't seem to have slop or springy movement. They seem rock solid, in fact. But I do think I'll end up replacing the balls, there's slightly more noise and crunch to them than Iby Apsu - Look what I made!
QuoteDavid J The only significant disadvantage I can see so far is the space it takes on the bench with its "elbows" out. A bit like sitting next to a selfish eater at a dining table... Yep, although I believe this could be mitigated with the correct combination of arm link lengths. Maybe even curving them. Quote It would be interesting to mount a dial indicator on the central part, to see ifby Apsu - Look what I made!
Small update After looking at this video showing a different orientation of a Tripteron design, I've decided to rebuild my prototype using the same basic idea. I realized that by doing so, I can move all three motors to the bottom of the frame, and even use the exact same motor/idler brackets for all three axes! There are many benefits of this idea, such as: Lowers the center of gravity, increby Apsu - Look what I made!
It lives!! YouTube Link Very exciting As I mentioned in my reply above, there's a bit of springiness to the arm/effector system that is not present in the arms themselves, or any of the joints individually. I believe this is due to PETG brackets + belts slightly undertensioned, so I am printing out a full set of HIPLA bracket replacements. 6 hours to go, and I might think about new belt tensiby Apsu - Look what I made!
Quoteo_lampe I'm still concerned about the z-axis sagging and would like to ask, if a second z-stepper on the diagonal opposite side of the cube would make sense? From what I see, the other arms wouldn't interfere. You know the z-axis accuracy is so important for 1st. layer adhesion, I'd accept the added weight and cost for an additional set of arms,pulleys etc., just to make sure the design is oby Apsu - Look what I made!
Belts ahoy!! Running some gcode in a very handicapped configuration and "build volume" to make sure it doesn't go too far on the rails without endstops and such, lol. YouTube Link Not bad for a first draft. Now to finish printing the arms and effector in this super tough PLA; with my new joint design, I expect to be pleasantly surprised once it's all together.by Apsu - Look what I made!
Short arm (Y side) first-pass is done, and my new joint design is flawless Printed in Atomic Filament Ultra-Impact PLA, using 5x7x1mm bearing spacers, bearings flush with arm faces, outer forks have 1mm room on each side for spacers, then 35mm M5s with washers and nylock nut. Detail pics:by Apsu - Look what I made!
Making progress! Got shoulder bracket, spacer and belt clamp design nailed down and working. Waiting on remainder to print for other axes, and I also figured out how to reduce the distance between Z belt path and Z rail carriage; just add more idlers to shift the path! Woo Here's some pics PS, yes I know the Y bracket/spacer look like shit. I was iterating prototypes at way-too-fast and wby Apsu - Look what I made!
Quoteo_lampe I've used PETG to build semi-flexible but tough parts. Using CF reinforced PETG seems to be a step in the right direction, but is probably not the stiffest solution? ( and expensive too ) It's definitely not the stiffest. I just was enjoying printing everything in the CF PETG I had, and some flex is nice while figuring out joints. I intend to move to PLA immediately to increase stifby Apsu - Look what I made!
Small update, got most of the bits together for a proof of concept. Just need to model the belt clamps into the shoulders and rig belts on it. Here's where I am so far: Short video of manual manipulation Yes, the joints/arms need more rigidity. I know But I should be able to finish up usable shoulders and have it printed/assembled/moving by later tonight. I'll drop a video here when I getby Apsu - Look what I made!
In case it's helpful, here's a link to the Tripteron paper I was referencing that discusses the kinematics theory and DOF chains/some design considerations. PDF Linkby Apsu - Look what I made!
QuoteOrigamib The print volume doesn't match the arms unfortunately, so enclosing the printer is difficult. When the Z arm reaches 0,0 for X and y, it will extend outside the build volume by about half the distance of y, so a 40cm cubed build volume needs an 80cm wide and 60 cm tall frame. This is assuming the arm is nearly fully extended at the furthest point away from its base. A corexy canby Apsu - Look what I made!
Quoteo_lampe *signed* The z-axis will be the toughest part regarding accuracy. Like with deltas you might want to use 0.9° steppers. An 8bit controller would do, though. I don't think the Z will be any more difficult with accuracy, per se, but I'm currently using 20T pulleys on 1.8° steppers, which gives me 200 micron/0.2mm for full steps. 12T would give 125/0.125mm. Quote All the arms are worby Apsu - Look what I made!
Quotethe_digital_dentist Interesting mechanism! I think the most critical part of the build is going to be the hinged joints. Once you get the platform/extruder moving around I think you'll find that the L shaped frame isn't going to be nearly rigid enough- look at the size of the frame members used on the machine in the video. Yeah, it is! And yes, the joints are definitely critical. The L-frby Apsu - Look what I made!
Howdy folks Decided to make a thread to track my progress in designing and building a Tripteron 3D printer implementation. I'm pretty far already, and have most of a frame designed/printed/built, since I had pretty much all the parts already. First, a link to a video of the Tripteron example robot, built at the University lab that came up with the mechanism YouTube Link And the CAD models I haby Apsu - Look what I made!