@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.

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.

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!

@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?

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.

@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!

@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.

@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!

@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!

@JoergS5

All great points. First I need to develop a clamp that fixes the output to the shaft. From there I can figure out where the flex is coming from. I can take another crack or two at improving this aspect of the machine, but I may just need to get it actually up and running to see where I'm at. I may also need to humble myself a bit and scale down the arm depending on how testing goes. I think this is the best iteration from a stiffness and resolution standpoint.

I could switch from ABS to PLA on the ring gear to have a stiffer material there to your point. I'll also shrink the height of the flex spline as I don't think it's necesary to have so much length there with plastic. I also would like to mount the ring gear directly to the 80/20 extrusion while also further increasing the diameter. I'll need to reconfigure the motor mount a bit, but all those changes should help. Maybe I'll try making a huge harmonic drive just to see how it performs under the sort of torque. 200t at a .8M gear tooth or something like that.

Another idea I had was to just print the spline without the cup at the bottom. Then I could use a steel hose clamp to fix the the flex spline tightly to a set block that can grab onto the 20mm shaft. I'll draw up a picture here to explain, but it would also help reduce the amount of printing that requires a .25mm nozzle to help speed up prototyping.

@JoergS5

A few more updates, I installed the original all printed flex spline as well as my updated design that uses a 0.6M tooth at 118t. It seems a lot smoother and higher precision which is heading in the right direction. The next thing I need to solve is connecting the flex spline to the 20mm steel rod. 6mm sets screws threaded into the plastic are not cutting it.

Here's a quick video showing how much flex I'm getting before the screws slip on the shaft:

https://youtube.com/shorts/vS0aS8M9vDY?feature=share

This magnifies quite a bit once it gets all the way out to the end effector with the second arm set attached. I think I need to sort out this flex before I can expect any sort of reasonable print quality. At the moment, if the arm bumps into the model being printed at all it's just going to get knocked out of the way.

I'm working on better way to secure the flex spline to the rod which I think will help some. Otherwise a couple of other ideas I had:

• Large diameter / larger tooth profile flex spline system without raising the gear ratio any higher.
• Stiffen the ring gear part, there does seem to be some flex in this part as it is.
• add a second driver to the arm to double the gearing contact the rod sees.
• shorten the arms a bit. Maybe I need to take a small step back on this first crack at a scara arm.

@JoergS5

+1 for matlab too! I was convinced I was going to go to my corporate job after college and convince them to give up excel for matlab, I now use excel for everything lol.

although, I can get a student license again for only $100 through my MBA program...

@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!

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.

@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.

@o_lampe

Check out split ring planetary gears: https://www.youtube.com/watch?v=4gkbb2CBzQI&ab_channel=LeviJanssen

When I was fresh out of engineering school I was obsessed with this design however, they never ran well and were complicated to design. There isn't much info on them and there are very gear ratios that line up properly (something about everything being multiples of each other).

So far I'm a lot happier with the real-world performance from flex-splines. @JoergS5 - I agree with you you on having an elliptical driver rather than just a few sets of bearings. The HTD belt design I came up with works great as is, but I'm sure it would run better with an elliptical driver. I printed that 79:1 driver in PETG and was fairly impressed. It may need a slightly larger elliptical drive as the flex spline doesn't mesh tight enough to the ring gear as is. One other thing I don't like about this design is how tough it is to install the ball bearings and it's loud. The belt design is completely silent.

I'm going to play around with a fully printed flex spline design this weekend with a lower gear ratio as 79:1 plus a belt reduction is overkill. I'm trying to eliminate the HTD belt if possible as the they're pricey and you can't get them in many sizes both for tooth count and width.

@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

@droftarts

Awesome, thank you very much!

@droftarts

Thank you much!

one last clarification, I have a v1.2 board, so soldering the jumper on the back of the board replaces the need for a physical 120ohm resistor for the white and yellow wires (the two right most wires from the JST_ZH connector), correct? at that point do most people just pull he pins out of the connector or chop the wires very short? I won't be using a tool distribution board for this machine.