Best posts made by michaelr123

@JoergS5

Hello!

More changes and another update. I played around with a few more harmonic drive designs, and found they all had more backlash at the end effector than what I wanted. I had better luck with gear drives, and I also have found an appreciation for the back-drivability. So I scrapped the old design, developed a 45:1 gear drive design and rebuilt it one more time. I now think I have something workable at this point!

https://youtube.com/shorts/Yw_aW_2YJ5A

As you can see in the video, the system runs very smooth.

this is still running with just manual move codes, but now that I've got an XY motion system I'm going to start rebuilding the electronics to start working on calibration! List of things to knock out:

• Get endstops and other electrical bits cabled and installed
• Calibrate XY motion system
• Finish Z axis
• install extruder system and get a toolboard working
• get the build plate setup
• print something!

I figured I'd blog my progress converting my voron 2.4 from a duet 2 system to a duet3. Along with electronics,

• I'll be going plaid with 4x nema 14 motors following aTinyShellScript's Mod: https://docs.atinyshellscript.com/v2.4/awd/#changes-needed
• Archetype - breakneck mod to a CPAP cooler for really fast printing: https://github.com/Armchair-Engineering/Archetype/tree/Experimental
• Tool board to reduce clutter - I'll design a bracket to mount the 1LC board to the breakneck board
• Rapido UHF with CHT nozzles to start pushing past 50mm^3/s

Parts are printed, everything has arrived in the mail, so now it's time to actually get started!

First thing I did was play with CAN and get that going:

Super simple. 24v to everything with the correct polarity along with the CAN cable and it all worked flawlessly. Everything's updated to the latest firmware and ready to go!

Next step:

• Covert to AWD
• Install Archetype tool head
• Rewire tool head along CPAP hose
• remove duet 2 board and install duet 3 6HC+3HC on bottom of voron.

@Phaedrux

I'm an idiot, I was using temp_1 instead of temp_0 in my config. disregard, works great now.

@JoergS5

all good points on more complicated motion systems. That's the kind of thing you don't figure out until you're actually working with it

The nice thing with this design is that I can adjust the arm lengths a bit to dial in the arm lengths to be as close as I can get them with a tape measure.

I'll post a picture of my design tonight, but I'm really happy with how it's turned out so far. It's based on a 75t HTD 3m belt. Zero back lash as far as I can tell so far. I ended up using 5mm bearings inside just riding on bolts to start, but I'm really happy with the results so far. The stationary gear is just free-floating without being fixed to a piece of 80/20 yet. I may add a built in bearing using 5mm ball bearings to connect the output side to the input. This might not be necesary once it's connected via pillow blocks and aluminum extrusion.

I found this guy who printed a harmonic drive that used a printed bearing raceway that looks really solid. He's printing the flexspline with a .25mm nozzle and dialing in his settings for PETG. I'm curious to try it. He's using it for very slow speed and low torque applications as drives for astronomy.
https://www.printables.com/de/model/309144-791-harmonicdrive-for-keen-one-eq/comments

I threw together a design for a 35:1 harmonic drive that uses a standard harmonic design with an elliptical driver using ball bearings. getting the size and shape of the ellipse took a few iterations, but again wasn't too hard to sort out.

Once you pack grease into the ball bearings and the gear teeth the design runs a bit smoother and much quieter. I printed this one from ABS with a .25mm nozzle and it turned out great. It's a lot smaller diameter than the design with a belt in it. I made the cup on the flex spline taller to help improve flexibility. I need to design in the pulley to the elliptical driver. This one is just a solid round section so I could play with it.

I might just install each design, one on each arm and play around with them to see how they perform. I'm also finding that packing the bearings is going a bit better now that I've done it a few times. Its a bit more tedious, but might actually be faster than installing all the hardware that goes into the belt design. I like the simplicity of the fully printed flex spline a lot.

quick question, is the print time in DWC 3.4.6 the actual print time or the simulated time posted by the slicer?

Thanks!

See thread --- Warning: Lost connection to Duet if you've got any ideas on how to get my printer to make it past the first layer.

@oliof

Here's what I came up with:

I have a have a 5 bar system mocked up using large ID bearings with aluminum tubes for shafts, and then then these aluminum clamps that go between the pipe and the bearings. The 32mm pipe and 32mm OD bearings pair really nicely. The joints are super stiff, zero friction, and it was pretty cheap to put this together. It'll be way more rigid than anything I could design and print. Here's a picture of the arm overlaying the working area taped out on the floor:

So far I'm really happy with how this clamp/ tube system for building aluminum frames is working out. I cut the 6ft of pipe I got into 4 pieces, so the sticks are 18" long each, which gives me a 21.25" arm length. Right now they're symmetric, but they certainly don't have to be.

I drew out the working area by just moving the arm around (faster than trying to figure out Geogebra or buying a matlab license). the Green / yellow region is what you get from having the two arm origin points being at (0,0). The red/blue region is what you get by moving them 6" apart in the X axis (12" total spread). Green being without an arm passing the X-axis for config X0, and yellow allowing a

From what I can see, I get a 42"x18" working rectangular area, and a 24"x24" working square area from the X0 orientation as I'm calling it, and I lose quite a bit of working space if I start spreading out the 1st arm center points. I'm sure there's a stability gain and probably a resolution improvement with some more optimal angles, but I really wanted to be able to print a 24" square and also be able to print a 36" thinner piece. Any ideas or recommendations?

I made a macro to speed things up. This is script I wrote:

M204 P10000 T10000 ; set acceleration
M593 P"EI3" S.025 F38 ; input shaping test 3/7/2022 change this as needed
G1 X-100 G4 S2 M956 P0 S1000 A0 G4 P10 G1 X100 F20000 ;movement code along X axis, collect data from accelerometer

One thing to remember as you're playing with accelerations, I think you need to update the M201 code in your config file to allow for an acceleration this high.

@jackantubis

I haven't even posted any pictures of my machine to this thread!

its a 400x800 print space system built around the biggest sheet of glass I could get at lowes

It's been a pet project for years now as I slowly redesign and spend money improving it. I think the gantry system is is ok shape, the electronics are now top notch with the Duet 3 the Z-axis definitely needs to be redone at some point. I reused an old v-rail setup I had on a leadscrew printer that I built a long time ago. The point of this system is to be able to print 30" or so parts for fiber glass molds, furniture, and just big parts in general out of mostly PETG and PLA, nothing crazy on the materials front, yet...

Link of it running a dual part cooling fan setup to really crank up the speed on small parts!
https://imgur.com/a/YCJaCZ9

I ordered some flexible, shielded cable from zyltech, so I'm going to move everything to that style cable inside the drag chain. I'm not a huge fan of how I'm handling the traveling YY motors. I know the right way to do it is to use drag chains on both sides, but it seems a little unnecessary at this point.

I'm excited to work on input shaping and pressure advance with this system. I think pressure advance will especially help out the super volcano nozzle. Getting the seems to form properly with a 1mm nozzle is really tough with just making it extrude extra material.

My next dream is a scara arm that travels up a rail mounted to the wall with a 2' working area to build really tall parts. I think I want to get this machine nailed down before moving on to the next one though!

@o_lampe

yep you've got it. It's a split ring design where one half matches the tooth count of the belt and the other half is +2 teeth. So for a 75t 3m HTD belt it's 75t on one half and 77t on the other. the input is the elliptical part (what @JoergS5 and I are going back and forth about bearings vs. full ellipse). The tolerance needs to be fairly tight to get zero backlash, but also needs to allow for the belt to "stretch" a tooth so the 77t side can precess +2 teeth forward. I just drew it up and it worked well on my first attempt so I guess it's not too tough to dial in?

Either of the two halves can be the output or fixed (that might be incorrect technically, but just from playing with it seems like that's true). Also remember for the belted design they're not involute gear teeth, but HTD pulley teeth.

I think I made a break through!!

I tried grounding a bunch more things:

• I drove screws through the belt on both sides on threaded into the 20x40 extrusion

• made a connector for the back of the X axis stepper shaft

*I pulled the wires out of the drag chain

None of this worked, What did work, or is working so far, was to tie a wire from ground to the screw post I put into the X-axis aluminum extrusion through the belt. It might not be anything to do with the stepper motors or belts, what I think it could be is this screw that mounts my extruder to the plastic plate scraping along the aluminum extrusion, or maybe some other source. I can see where the anodized coating is worn away long the X-axis. I'm not sure if a metal screw scraping along, or very nearly scraping along each other would cause static to build up, but this would mitigate that.

After making this change I ran the test Gcode I've been using for over an hour and it completed successfully. Adding in the hemera extruder was part of my most recent changes, and the mounting method I came up with could have created the static issue I was seeing. If I would have used a button head screw maybe I could have avoided all of this!!

I'll run some test prints tomorrow and report back!

I've been debating whether or not to comment on this thread for weeks as I'm hesitant to blame PA for the print artifacts I've been seeing, but after a lot of testing it seems to be the culprit. It's possibly I'm still getting through some acceleration/jerk tuning stuff or I still need to play with belt tension and/or IS. However, since going from 3.3 to 3.4 on my voron 2.4 build with a Duet wifi 2, I have been seeing odd bulging behaviors on roundish perimeters, or with embossed text. I can post some pictures later of some examples. I sometimes see sections that are supposed to be straight end up with a gentle concave curve.

Again, it could be that I'm just new to tuning Core XY systems, or my external stepper driver setup not being super robust, or something else entirely, but it feels like I've spent a lot of time working out print artifacts on this machine to get close to what I'd consider a perfect FDM part.

@phaedrux

I ran through wiring and discovered one had worn through the shielding near the connection point through the case. I patched this up and replaced the fuse, good as new!

@JoergS5

This is a great resource! thank you for sharing. looking over these patents really quickly I think I've seen some of this in a research paper in a mechanical engineering journal: https://journals.sagepub.com/doi/full/10.1177/1687814019850656

I noticed with the 0.8m teeth you need a lot of motion for the strain wave to have enough displacement to move over to the next tooth. It looks like these patents and design paper have some equations on how much of an ellipse you need for a give tooth size and arrangement. I wonder how much of this would be captured in a plastic gear? It looks like I've got a well defined sketch for these squared off teeth to draw something and try it!

One reason I went with the size (tooth and diameter) was to have a more reasonable sized drive and a gear ratio that wasn't quite so high. I imagine tooth width and diameter again determines holding torque. I also imagine a higher tooth count will run smoother, my current design is only 74 - 72t.

For your other question, the new design uses pillow blocks for the 20mm steel shaft. So now I'm coupling and directly turning that rather than trying to couple to the arm component directly. I haven't posted a picture of the most current design!

@jay_s_uk

Update on this, it seems like anytime you change config code that affects the endstops or the drive mapping you get this weird behavior when you just run the config file. If you completely reset the board or power cycle it everything behaves just fine.

Long story short you can run 4x Z motors split across a can connection, but you need to fully power cycle between config updates.

Update pictures:

1. AWD installed, 4 motors are all wired up and turning the right way.
2. Belts installed, archetype -breakneck tool installed. Toolboard mounted, and ready to go!

Can bus has been really easy to setup and I'm loving the simplicity in the wiring out to the tool head. I also made a decision to go for sensorless homing to completely remove the wiring harnesses from the xy axis.

Things left to do:

1. Tighten and sync AWD motors.
2. Finish wiring toolhead.
3. Install CPAP fan, wire, program it.
4. Print out frame parts for the CPAP fan because. I forgot to print those out.
5. Put everything back together and sort out firmware and macros for duet 3!!