@e4d yeah.... it's not the total torque that changes, it's the torque per step. So simplified you got two coils and we are looking at two teeth on the rotor. Coil A is at full current so it's pulling the full torque into that position on tooth A which is a full step position. A half step will put half current on each coil so you only have half the torque pulling into the middle of the two teeth. Continue to put full current on coil B, and zero on coil A and you get full torque to move you from the mid position between Teeth A and B to the full step position of B.

Whether you microstep or not you go through full current on a coil in the full step positions so your total torque is the same over a distance, but how well you constantly and repetively hit a microstep outside that full step position decreases as you increase the number of positions between full steps. TLDR; the tiny changes in current may not actually move you that tiny amount between the teeth, but when it comes to the tooth being fully lined up it's all the same.

So I have a super annoying high pitch whine on a pair of Sunon 12v fans (MF25101V1) in a push/pull on a mosquito clone. While I'm replacing the hot-end heater I figure it should be an easy thing to either fix or identify why my fans have this high pitched induction coil whine that slowly claws at your soul. Might as well fix while things are torn down... and into the rabbit hole i dove. Threw my scope on it since I felt like it was some electrical noise was carrying through to the fan motors. Of course I did, I'm using switched mode supplies. Regular 12v rail had all kinds of electrical noise at 500Hz, 1kHz, and 100kHz.

Well, somethings causing it right? Let's start with filtering some culprits out. I try a capacitor to filter it... nothing. Ok well, a temporary voltage offset on the noise but the waveform didn't change at all? Fine...grab a toroid and do a simple choke...scream.. multiple LC filters ...and still no response...Am I a ghost now? WTF is this sorcery?!

So eventually I snip a fan out and blissful silent air flow... So it turns out that the issue was running two fans off the same cable right up to their own leads... Noise is gone soon as each fan gets it's own wires back to the terminal strip (they're wired always on).

I'm just happy the noise is gone and won't question why I've never had an issue wiring this way before. Still I thought I'd share in case someone has a whine / high pitched noise they can't get rid of, then here's one possibility.

TLDR; Parallel DC Fans sharing a power cable can cause high pitched feedback sometimes, intermittently, and in just the right way to test your sanity.

Here's the three versions I when changing my bed.g for my delta printer. They use 32 points and it generates a column that I can cut and paste into my bed.g It works for me, my calibration runs in the 0.01 mm range. Feel free to make a copy and do whatever you want with it, I'm just sharing in hopes of it being helpful to someone. Please watch the printer carefully until you're confident it's working for you, while it works for me I'm just throwing it out there to help and don't make any claims to it working flawlessly although I can't see how it'd go bad if you use values reasonable to your machine.

Variables to change are:
-bed size (the outer ring of probe points)
-Calibration Factor
-Oversize factor (only on the oversized one where I use it to dial in my arm lengths)

The first one is my default arrangement
12 points at the bed size distance (perimeter), 12 more at 2/3 the bed size distance, 7-points at 1/3 and one for the center.
https://docs.google.com/spreadsheets/d/1trfFyw2LqvRUeq3WPKtEaKaRGZOVwk4034zErVPo3jE/edit?usp=sharing

The second arrangement I get better calibration numbers from
16 points at the perimeter, 12 inside (2/3 distance), and 3 points (1/3 distance) and a center point
https://docs.google.com/spreadsheets/d/17S-CsZrUSqeNFooCKBznFLhmKTVUeivGca3umMWm86s/edit?usp=sharing

The third is what I use to test / calibrate my arm length. I calculate the oversize factor as the distance to just inside the maximum bed radius over the bed size parameter that I can test within the limits of the towers. Please be careful and watch closely if you use this one.

https://docs.google.com/spreadsheets/d/172jtcU9UQyQi1yUPvm9tagQ7Fl1T8Yxcv_s8HN2PATI/edit?usp=sharing

I will try to update if there is a major flaw, otherwise please treat it as a starting point for you play with generating your own test points.

@ignacmc

Ok, here's some pics. The first is an example of the setup. The others show thickness, the needle bearing you have options depending on the surface of the motor face, the ball bearing set while the ID being the same as the motor shaft is nice i prefer the needle bearings for contact area against the pulley.

depending on the repeatability you want, you may want to slow the feedrate which is really because of the worst part of inductive probes. Most inductive probes switch at 500hz until you you break the ~$60 retail price point for industrial sensor to get 1khz to 3 khz ( next price point is like ~$150+ and specs can get to 5khz). So the faster you're probing the larger the distance variation between trigger intervals. i use a ie5390 i grabbed off of ebay for like $30 and it operates at 1khz and i go with 60mm\min to get .003mm repeatability which is only a microstep and it levels (delta printer) to .01mm over a 300mm probe area

Long story short, all three axis stepper motor cables are shielded (EMI mesh sleeve) on my delta printer (although this could apply to any style) so I skipped doing it on the extruder. Half-assing it bit me again and it may be what got rid of the irregular surface ripple that kind of looked like a salmon skin/moire pattern that you only really see when the surface is glossy. Yeah, that really fine one that drives some of us crazier than massive ghosting does. Until this point I had no indication my electronics had any glaring issues and wrote it off thinking I had that well in hand. I just glared at the delta my mechanics blaming them as the source leaving me completely stumped for what the real cause was though. Anything that seemed a plausible mechanical source I reached out to fix hoping it would be the thing to remove those tiny artifacts even though it didn't match up with anything obvious math wise.*

I discovered this while I was playing with the new input shaping plug-in. My hotend fans are normally always on and I unplugged them while using the accelerometer to decrease the noise level on it. Then while toying with the plug-in I heard extruder noise that was almost a whine that I couldn't hear over the hotend fans. I noticed it while homing and then dead quite after homing was done made it stand out though. So I homed again and reached over to feel the motor, and it's vibrating with some oscillation when the axis motors are going. I just sat for a minute with my face in my hand and wishing I could give past-me a slap to the back of the head for stopping 3/4 of the way through on shielding the motor cables. I wanted to share my success on this in case it can help anyone else frustrated with calming the waves in the specular reflections even if it is also a facepalm moment of shame.

*- That isn't to say there aren't other things causing it in another build. I just have happened to already done my best to mitigate them in previous rabbit holes on belts, pulleys, eccentricities on anything round and rotating, arm lengths, arm joints, arm spacing, then arm rigidity, all the extruder bits, fan vibration, frame vibration, bearings (both the linear slides and stepper motor bearings), chasing this stupid pattern.

@Danal I use the same Motors on my Rostock max for years now and they've held up quite well for the abuse I did on them. I have looked for lower inductance / inertia 0.9 steppers with good torque but I haven't found one I'm confident will perform better for a decent price (I'm looking at you moons' industries...)

If you get a chance, test out my settings I scope tuned for the motors. Mine run 1500ma without getting hot and are as silent as I can expect of them.

https://forum.duet3d.com/topic/13028/my-tuned-tmc2660-settings/2

You can get the mathematical differences with one of the calculators ( i like the openscad simulator). The optimal arm spacing is dependent on your print diameter, but you also have a trade off with printable area since you'll have to move the balls further from the center of the effector. Since you can't really go further than having the joints be over lapping, that's kind of the concept to ride that optimal point at least math wise. As for how it works out in practice, not clue but there's so many little variables in the whole system that I don't see it helping that much when there's enough knowledge about the normal configuration you can easily tease out what is probably off when your troubleshooting.

Following the trinamic tmc2660 manual and spreadcycle guide I busted out my o-scope with a current probe and a helping hands on the sense resistor. The motors I tuned were Wantai 42BYGHM809 and a PG35L-048. I run a delta, and my steppers are running at 1.5 out of the specced 1.7A and they are staying significantly cooler than when I tuned by ear and they are behaving much better for me, it even got my past the .02 bed leveling barrier I was at.

Anyways, thought I'd share my efforts in case it might help someone.

Wantai 42BYGHM809
M569 P0 D2 F2 B2 Y01:09:02

PG35L-048
M569 P3 D2 F3 B3 Y03:07:02

I prefer the contactless approach and just wire in (directly with no extras has worked fine for me) A3144 digital hall effect sensors (~$1 ea.) for my endstops and slap a magnet on the moving part. You can home fast and do a slow back and return and the repeatability has been hands down better over time than contact switches I've tried.

I'll also add for me if you exclude bearing issues in motors or pulleys (I've blown the tiny bearings in idler pulleys multiple times which is why i used flanged bearings now). The next issue of high belt tension is going to be eating up the belts and teeth when your hotend or carriage eventually crashes. I think it's easy enough to tension a little more and recalibrate starting low and then go high until nothing improves.

@ignacmc i just push the carriages all the way up and tension to an equal frequency using an app. I ballpark the base tension at the idler pulley for tight but not too tight and tune from there. You have a lot more wiggle room than you'd expect, just make sure they're the same.

I've been using deltas for years (my first was a the seemecnc rostock max v2) and I've found it isn't as necessary to hit a specific tension than it is to just maintain a reasonable and equal tension on the towers. I've done all sorts of gauges and tricks for targeting a specific tension and it just hasn't mattered. That goes for pretty much all aspects of a delta though, carriage resistance, arm lengths, rod spacing, etc. The more each tower responds the same the less weird stuff you chase and are able to compensate with a setting change in software for or identify the root cause like joints.

So i couldn't recreate the issue with another cable..Frustrating when trying to show shielding fixed the issue, but I'm still confident that was what helped...mostly. Still, I had another test print showing what i have moved away from when EMF was an issue regardless of the solution ( cable pathing or shielding). I adjusted contrast so the visibility was clear even if the colors are looking a little artificial. The surface issue was apparent in any print with the outer layer lower than 60mm/s.

@ignacmc

Ok, here's some pics. The first is an example of the setup. The others show thickness, the needle bearing you have options depending on the surface of the motor face, the ball bearing set while the ID being the same as the motor shaft is nice i prefer the needle bearings for contact area against the pulley.

@ignacmc this is right, snug the pulley against the thrust bearing will limit the amount of deflection on the motor shaft. Next time you have the chance watch closely before and after tensioning motors on a delta for me the amount of force for visible deflection on the shaft is actually very little when tensioning directly against the motor (especially if you use dampers!). At the temps we are comfortable running the motors I'd wager bearing wear is in the top two motor issues after a year of use.

@bberger said in Best Choice of Motor for a Delta Printer:

Wantai 42BYGHM810

I use the Wantai 42BYGHM810 on my delta. I don't use dampers and the motors are basically silent. I have gone through 3 different sets of dampers and after chasing every other mechanical issue I could and tuning the drivers, they very much were unnecessary and only added to ghosting. Whatever your choice if you don't have a pillow block (most printers don't) then I highly recommend putting a roller bearing between the pulley and the motor case (my current preference is the needle bearings). You have to measure the space available and account for possibly adding some washers to keep your pulley centered. What this does it reduce the tension on the motor shaft, the tension on the pulley instead is applied to the thrust bearing and motor to the motor case saving your internal motor bearings. Before I started doing this my previous motors needed replacement every 2-3 years because of bearing issues on my deltas, and I feel like it helps on ghosting and tension too (that's just an added bonus so wasn't worth testing for me).

uxcell TC512 Thrust Needle Roller Bearings with Washers 5/16" Bore 3/4" OD 5/64" Width 5pcs
https://www.amazon.com/gp/product/B07VZXWSG6/

uxcell F5-10M Thrust Ball Bearings 5mm x 10mm x 4mm Chrome Steel Single Direction 4pcs
https://www.amazon.com/gp/product/B07QKKYKR8/

@clearlynotstef i used a "UMLIFE DC 6-60V 400W BLDC Three-Phase DC Brushless Motor Controller PWM Hall Motor Control Driver Board 12V 24V 48V" i got from amazon and tested a cpap motor i plan to use for my hotend cooling. It tested fine using potentiometer control (since i simply want the fan always on). The pwm control on that unit is stated to work 2.5V to 5V in case i wanted to try using it for cooling. This seems unlikely though since my berd air pump can change the print finish from glossy to flat if it goes above 50%, so i have headroom to pipe more cooling if I need to. My delta can't chase those high speeds too though... until i get to work on a 3 arm per tower mod to add the constraint/rigidity (more triangles!).

@mrehorstdmd Link below to the sleeve i used, I've used grounding strap before as well but that was much larger than necessary although cheaper. The extruder motor cable crossed a few other cables perpendicular to them so i thought interference would be low and ran up a couple feet parallel to other cables about 8 inches away from hotend wiring (fans, probe, thermistor, heater). I have twisted the stepper wire pairs before but haven't this time, i needed the length.

Still, none of the power hungry hotend components were active when I identified the issue, so i suspect the extruder wires running across the duet near the motor drivers is where it picked up noise. Ideally making a new duet enclosure and shielding that in a safe manner would reduce noise on anything else unshielded too. I don't see any indication of EMI issues elsewhere though...well besides the occasional heatbed mosfet singing. That'll have to wait till i finish with replacing the hotend fans with a cpap blower though.

If you have concerns about bare metal sleeving floating about, gutting paracord is an inexpensive way to get some nonconductive (nylon) sleeve to run the shielding. As to the specifics, i just popped out the pins of the connector on one end and ran all 4 wires in the sleeve (taped them together while sleeveing). Grounded it initially with an alligator clip between the sheath and input ground.

Electriduct 1/8" Tinned Copper Metal Braid Sleeving Flexible EMI RFI Shielding Wire Mesh (0.08" Diameter) - 25 Feet https://www.amazon.com/dp/B01BIBQBCK/ref=cm_sw_r_awdo_7CQKEEDRMG84QEZYV47S?psc=1

@oliof I plan to do this, i had fixed it right before i got started doing a bunch of gardening prints for my wife and i wasn't delaying justification for my hobby. I'll get before and after prints comparison probably saturday unless my son does the impossible and goes to bed on time tonight.

Long story short, all three axis stepper motor cables are shielded (EMI mesh sleeve) on my delta printer (although this could apply to any style) so I skipped doing it on the extruder. Half-assing it bit me again and it may be what got rid of the irregular surface ripple that kind of looked like a salmon skin/moire pattern that you only really see when the surface is glossy. Yeah, that really fine one that drives some of us crazier than massive ghosting does. Until this point I had no indication my electronics had any glaring issues and wrote it off thinking I had that well in hand. I just glared at the delta my mechanics blaming them as the source leaving me completely stumped for what the real cause was though. Anything that seemed a plausible mechanical source I reached out to fix hoping it would be the thing to remove those tiny artifacts even though it didn't match up with anything obvious math wise.*

I discovered this while I was playing with the new input shaping plug-in. My hotend fans are normally always on and I unplugged them while using the accelerometer to decrease the noise level on it. Then while toying with the plug-in I heard extruder noise that was almost a whine that I couldn't hear over the hotend fans. I noticed it while homing and then dead quite after homing was done made it stand out though. So I homed again and reached over to feel the motor, and it's vibrating with some oscillation when the axis motors are going. I just sat for a minute with my face in my hand and wishing I could give past-me a slap to the back of the head for stopping 3/4 of the way through on shielding the motor cables. I wanted to share my success on this in case it can help anyone else frustrated with calming the waves in the specular reflections even if it is also a facepalm moment of shame.

*- That isn't to say there aren't other things causing it in another build. I just have happened to already done my best to mitigate them in previous rabbit holes on belts, pulleys, eccentricities on anything round and rotating, arm lengths, arm joints, arm spacing, then arm rigidity, all the extruder bits, fan vibration, frame vibration, bearings (both the linear slides and stepper motor bearings), chasing this stupid pattern.