DrahflowApr 6, 2023

The past two days I have a brain-worm / project idea of building a 3D printer via a wall-mounted 6DOF parallel robot driven by 8 linear drives (i.e. the typical z-axis spindles) mounted in parallel on the wall.

+ That would make the robot over-determined and should avoid any singularities but add extra stiffness
+ Should be able to retract very near the wall when not in use
+ Uses mostly the same building blocks 8 times instead of different mounting methods per axis
+ Able to print in arbitrary 3D paths
- Slicers will not support this out-of-the-box
- I heard there is a thing called "inverse kinematics" and allegedly I need to understand that, OTOH I feel it should be simple to intersect the strut-length induced spheres with the linear drives and that should answer all practical questions.
- Doing this as my first ever CAD project seems a bit overambitious, speaking from the outside perspective.
- I have never built a 3D printer before
- I have never built a robot before
- I have never driven a stepper motor before

Any input/suggestions welcome.

Show threadDrahflowApr 11, 2023

Usable workspace is a lot smaller than I imagined, maybe there are better ways to put those linear drives?

In any case, shoutout to the authors of WeBots, awesome software.

Repository (much undocumented): https://gitli.stratum0.org/Drahflow/parallelprinter

Drahflow / ParallelPrinter · GitLab

GitLab Community Edition

GitLab
Show threadDrahflowMay 5, 2023
So, I ordered a Nema23 stepper, somehow imagining it to be a smidgen bigger than the "normal" steppers. Turns out it's actually 1.2kg and looks extremely eager to turn just about anything.
Show threadDrahflowJun 7, 2023
tfw I assemble the first axle for real and realize the back-wall is pretty much EUR-pallet sized (leaving just 5cm on each side to add the necessary stabilization to keep the print-bed at 90 degree angle).
Show threadDrahflowAug 4, 2023
Turns out it is a bunch harder to get a 1.2m wall stable relative to a horizontal surface, than I anticipated. But after some iterations, I can now pull with my full weight and it'll not perceptibly move.
Show threadDrahflowAug 20, 2023

After carefully tracing the 4 cable colors from the board to the stepper motor, I finally crimped a nice dupont connector. For the JST-XH socket. After having found them most incompatible, I finally crimped a nice JST-XH connector. Turns out I'm not actually that good in carefully tracing 4 colors.

BUT ANYWAY, I now have a working stepper connected and it's looks as if I knew what I was doing.

Show threadDrahflowNov 17, 2023
The endpoint laser beam is extremely finely adjustable (which is good because I need to aim at a 2x2mm sensor over ~1m) in two axes. Less fortunately however is the fact that one of the two axes is the laser diode's optical one.
Show threadDrahflow

Just because C doesn't have coroutines doesn't mean I won't use them. (And the machine can now drive to a defined home position.)

https://gitli.stratum0.org/Drahflow/parallelprinter/-/blob/main/firmware/src/homing.c?ref_type=heads#L51

firmware/src/homing.c · main · Drahflow / ParallelPrinter · GitLab

GitLab Community Edition

GitLab
Dec 7, 2023 at 11:12pmWeb
Show threadDrahflowDec 7, 2023
Also, I'm quite impressed with the light barrier's precision. A single measurement appears to discern ~2μm across the beam.
Show threadDrahflowMay 24, 2024
I have recently again been disappointed by the fact that PLA does have neither the tensile strength nor the elastic modulus of adamantium (not even at 80% infill).
Show threadDrahflowAug 12, 2024

1. Want to build a 3D printer
2. Surely it can't be that hard
3. ?????
4. Learn about Lagrange multipliers to find solutions to finite element simulations I need to identify parallel robot singularities as a substep in optimizing 3DOF joint positions.
5. ?????

[TIL. And yeah, that's ultimately the point.]

Show threadDrahflowAug 20, 2024

Progress. I now have code to compute the forces acting on each strut within a complex truss construction.

E.g. on a simple tripod, loaded at the tip with a force vector of (0, 0, 0)N and fixed at the three feet, the algorithm now gives me
14.14N along the first strut, -0.00N along the second and -NaN on the third.

Show threadDrahflowAug 21, 2024
Current yak-shaving level: Improving the 3D-engine I use to render the finite element simulation results (for debugging / cross checking the linear equation solver and finite element generation).
Show threadDrahflowAug 30, 2024
On the plus side: I have now convinced myself that the simulation is correct and can re-use the FEM code within the printer firmware to adjust for strain.
Show threadDrahflowOct 8, 2024
Issuing movement commands and specifying 10μm increments. Fuck yes.
Show threadDrahflowDec 5, 2024

The automatic calibration software needs to tie together
* stdin (me)
* /dev/ttyACM0 (hardware control board)
* /dev/video0 (USB microscope)
* a TCP/IP socket (microscope + computer vision debug video stream)
* a bidirectional pipe via adb (the program on the tablet drawing targets)
* calbration.dat (output file)
* a timer
in one massive event loop.

I like where this is going. :P

Show threadDrahflowJan 3, 2025

While trying to connect the first iteration of the calibration software to the printer, I see this line: "Intercepted from printer: No free target buffers. Send slower.uffers. Send slower."

Cackling like the madman I am at the fact that yeah, looks like something is indeed not going well with some buffers.

Show threadDrahflowJan 8, 2025

Last night, I tested the first iteration of the calibration auto-focus algorithm (to measure z).

Algorithm: "Best: (392 390 -803.2504)"
Me: Lmao, who doesn't love extra digits. But maybe I shouldn't report it up to 100nm. *moves the machine back to z=-803.240 and reruns autofocus*
Algorithm: "Best: (392 390 -803.2505)"

WAT.

Show threadDrahflowFeb 22, 2025

It seems legit 🤯

Current status:
`X/Y deltas: dx: 0.00076176, dy: -0.00046126`
`X/Y deltas: dx: -3.662e-05, dy: -0.00095162` (as in, X is off by -36nm)

Watching the auto-targeting algorithm reliably move to within 1μm of the desired position in x/y and trying to get the z moves to the same precision reliably.

Show threadDrahflowJun 17, 2025
Watch me overthink the task of holding two 15mm aluminium t-beams in place
Show threadDaniel BohrerOct 8, 2024
@drahflow wow that's nice
Show threadDaniel BohrerDec 8, 2023
@drahflow nice :) reminds me of when I hacked on FreeRTOS in my university days :)