Posts made by 691175002

If your goal is simply to prevent static buildup then I would use copper tape to connect the stepper frame to the printer frame. Even an ultra-high impedance connection can bleed a static charge just fine, so you don't need to do anything heavy duty.

To be honest if you crank down the screws hard enough (or use a biting washer on one of the holes for each mate) you will be grounded. The connection doesn't need to be great - they put 1meg resistors in anti-static wristbands. http://www.circuitnet.com/experts/87211.html

If you want a low impedance ground connection then you can slip a ring terminal under one of the mounting screws and run it to either the frame or the grounding bus depending on how concerned about ground loops you are. Note that grounding your steppers like this will make you look absolutely insane to most people.

Larger CNC machines respect acceleration during homing moves, but homing typically involves moving past the home switch (sometimes by a considerable margin) then backing up to the nearest encoder index.

In larger CNC machines switches can never be crushed by over-travel, they activate and allow the axis to pass. Axis travel is typically limited by rubber bumpers. Here's a small linear stage with a representative arrangement:

As the machine gets heavier you need to think of endstops as more of a notification that something is wrong than an actual travel stop. Any fault should de-energize the axis drives, after which inertia will take over and allow the machine to coast (or smash) to a stop as physics dictates.

Homing is expected to overshoot the homing switch (which is not necessarily the limit switch). There is a very detailed overview of how homing and limit switches can be placed and configured starting page 88 here: https://www.parkermotion.com/manuals/Digiplan/ViX-IH_UG_7-03.pdf

That being said, this kind of setup is far more complicated than you want in a hobby 3d printer and rigid z-probes pretty much necessitate an immediate stop.

You should be looking at acceleration as well as speed. A drawback of screws in a 3d printer is that the screw is attached directly to the motor shaft and therefore needs to be spun up without any mechanical advantage.

Every gram of screw might have the same inertia as 5-10 grams of extruder weight. The exact ratio will vary dramatically but is a function of screw diameter and lead.

I don't use any leveling system at all, I shimmed the bed into alignment by individually adjusting stainless steel spacers with sandpaper, and it has never moved since.

This system is the heaviest (and maybe also the most expensive), but if you find yourself constantly adjusting and probing the bed you have to wonder if other alignments are shifting as well.

@mattling9 said in Need Help with Stepper Motor Data (Completely Off Topic):

Can a NEMA 17 with a 10:1 Gearbox REALLY output more torque than a NEMA 23 with a 3:1 Gearbox if the output speed of the gearbox is fixed at 60RPM???

High speed motors have much greater power density than low speed motors, so your results aren't particularly surprising. When building model airplanes we often have to decide between a heavy direct-drive motor and a lighter geared motor.

For model airplanes the heavy direct drive motor typically wins after considering the weight, cost, efficiency, and complexity of a gearbox. But in your situation both motors would require a gearbox so its not surprising that the Nema17 wins. Just make sure the 10:1 gearbox survive the planned load.

This seems to have almost all of the problems of 5-axis slicing. It works when the entire part is a single feature, but for anything more complicated the nozzle will collide with the part.

For example you cannot have a wavy surface adjoined to a flat one.

Think I have see a gcode for arcs. When it's used?

G-Code for arcs are mostly a historical artifact from the days when G-Code programs might be handwritten and controllers only had a few kB of memory.

Modern CAMs will have an option to use circular movements where possible, but the truth is that modern toolpaths just cannot be expressed with arcs. Even if you are cutting prismatic shapes a constant engagement toolpath will be a mix of helixes, spirals, and trochoids, not arcs:

On a modern controller there really isn't any advantage to arcs - memory is plentiful and you have 300+ segment lookahead. When your g-code is going to be 99.99% line segments anyways, why bother using arcs at all?

The Titan has some difficult bearing alignments and sliding fits, and the idler is cantilevered off the stepper shaft. If anything is out of place it will start to skip.

As well, if you apply too much force to the bearings during assembly it will indent the raceways and grind itself to pieces. Its best to locktight that screw and stop tightening as soon as it makes contact with the lid.

The Titan is a very light and compact design when it works, but they got a little too clever.

Your first post mentioned that your components were printed in Extrudr's GreenTec PRO for heat resistance. Was it necessary to replace them with PC?

There isn't really a debate once you leave hobbyist circles. Every professional guideline is crimp-only, primarily because crimps are faster than soldering and are less skill-dependent.

It is fairly hard to mess up a ratcheted crimp (assuming you are using the correct tools) whereas a beginner soldering crimps is going to be a disaster. If you put too little solder it might not penetrate, but if you put too much or apply too much heat the solder will wick onto the contact surface and/or up the stranded wire. If this happens, it possible that the crimp will fail without warning in the future.

If I don't have the appropriate ratcheting crimp tool I'll go at it with pliars and solder, but I will inspect every joint very carefully before using it. Non-ratcheting crimping tools are garbage in my experience, and I've used some expensive ones.

@arnix said in Suggestion for servo motor --> big delta robot:

Hi. We have completed our simulation and it looks like we will need at least 12-15Nm per motor to gain top speed ( 1 pickup per sec ).

Is that before or after the gearbox? Remember that a 10:1 gearbox will multiply motor torque by ten times.

If you build a 5:1 belt reducer you only need 2-3Nm from the servo.

I'm not sure if I'm misunderstanding something here, but I was under the impression that G1 coordinated moves will always respect the configured acceleration and velocity limits regardless of their orientation.

Physical kinematic limits should only affect motion when the commanded movement is not physically possible, which should never occur outside of deliberate testing.

As mentioned, Cartesian and CoreXY printers can produce faster movement when multiple motors are driven at the same time, but this should be completely irrelevant when slicing or printing models.

(The sole exception would be a G0 uncoordinated move, but I'm not sure if any 3d printer firmwares actually perform uncoordinated movement.)

Harmonic reducers are perfect for this application but cost 4-5 figures an axis. Even second hand reducers off ebay cost $500-1,000 per axis.

To correctly size your servos you should determine the torque and speed that is required, then select the cheapest model that can meet those specifications.

You would basically start with arm length and estimated load then calculate that as a torque back through the gearbox to the motor.

You could try putting this motor into this calculator with 5:1 belt reduction and see what happens. I'm not familiar with the kinematics you are using, but I assume that if one arm can support 70-100% of the expected load then a robot with three arms will do fine.

I recommend picking low speed servos with high torque so that you can get away with the simplest gearbox possible. Faster servos have much higher power density but might require an accurate 10:1 or 20:1 gearbox which is much harder to build or acquire.

The cl steppers recommended by jrjones88 would be suitable for this application, but if they are out of your price range you can try to 3d print a belt reducer.

Use a metal pinion with <=18 teeth along with a massive 3d printed pulley in the 140-180 tooth range. Minimize belt stretch by keeping the unsupported belt length as short as possible using rollers on the back of the belt: https://i.imgur.com/nz2bYp5.jpg

I think steppers can probably work for this application, although you could try https://www.teknic.com/products/clearpath-brushless-dc-servo-motors/clearpath-sd/sdsk-models/ maybe.

Also make sure you are correctly setting acceleration for the motors, it looks a little high on the videos you posted.

Its not clear to me that the stepper motors are the weak link here. You say it lacks stability and precision, but where are those flaws coming from? Are the arms flexing? Do the pivots have play? Is there backlash in the gearbox? The only flaw that can be directly attributed to the stepper motors is slowness.

Rotary positioning applications are extremely expensive because errors are amplified by the arm length. The quality of a rotary axis is 100% dependent on the gearbox quality, and rigid zero-backlash reducers are expensive.

You can look at scara 3d printer designs for examples, but their arm lengths are much shorter than your example video. Unless you can spend 2,000-5,000 per axis (on harmonic or planetary reducers) you will probably have to DIY some kind of high ratio belt reducer.

https://www.google.com/search?q=belt+driven+rotary+table&tbm=isch

If the servo drive has optocouplers you probably need a 5-24 volt signal that can source or sink >2ma.

I've been happy with stainless spacers and fasteners. Stainless steel has roughly 1/4th of the thermal conductivity of aluminum.

You can get ceramic spacers but their length tolerance is very loose and I was worried that they would bend the bed out of shape. If you are willing to lap ceramic spacers to the same length it could be an improvement. I would probably always use stainless fasteners, but nylon plus ceramic might be rigid enough.

I also purchased an insulated heater from Keenovo and shaped the bed to reduce heat transfer:

https://3.bp.blogspot.com/-poROqujsf94/WUwYduv0EdI/AAAAAAAAAs8/gf7Jlbo-WqkkpyWk5ZE2VSTRKviMmldEQCLcBGAs/s1600/DSC_0461.jpg

https://1.bp.blogspot.com/-Oco74A6x2Mo/WUwZ7yRKUrI/AAAAAAAAAtY/ArmLUXB9usIQNNDVcYz8yKzkRp6w4ALMQCLcBGAs/s1600/DSC_0462.jpg

@deckingman said in Would This Require Custom Kinematics?:

@691175002 As the designer and builder of the printer you linked to, may I ask what is it exactly that you hope to achieve?

I'm hoping to build a multimaterial printer (~4 filaments) with a wide print area. Something along the lines of 30"x10". This is probably too large for a static bowden system, but if the extruders follow in the long axis the bowden tubes can be very short.

I'd like it if the rectangular build area let me get away with moving the extruders on only a single axis, since that is much simpler than duplicating the full XY gantry.

This project is still in the early stages, but given that the axes are mechanically separate it seemed worth investigating the possibility of using different accelerations. It might make the printer quieter, if nothing else.

Thanks dc42, one last question: How hard would it be to omit a motors acceleration and velocity limits from the trajectory planner, while still obeying the limits in the generated pulse train?

Just in case that question doesn't make sense:

If I define custom linear kinematics, both the extruders and hotend will move in lockstep. But I don't actually want them to stay aligned - the extruders are much heavier and the bowden tubes will accommodate misalignment. It is better if the extruders lag behind the hotend.

However if I configure the extruder axis to a lower acceleration within duet, the whole system will obey the that limit (I think?). So to properly desynchronize the axes, the extruder axis pulse train must be smoothed outside of the Duet, probably using a programmable servo drive - expensive and complicated.

If possible, I would like to omit the programmable servo drive and configure a lower acceleration limit within Duet without handicapping the overall system. Would it be possible to add some kind of flag which "this axis does not need to constrain overall motion" flag to the firmware, or would it be too convoluted?

This would also have applications for printers such as: https://somei3deas.wordpress.com/my-corexy-printer-build/5-colour-upgrade/

Thanks, do you have any documentation on the generalized cartesian kinematics or is it still too new?

Also, would it be possible to home the extruder and corresponding CoreXY axis simultaneously? The extruder carriage must stay within a few inches of the gantry or it will pull on the bowden connection.

(In practice there will be a mechanical stop so a desync will fault the servos.)