My coreXY design is progressing to the build stage

I designed it this way to put the bed supports as close to the bearing blocks as possible.

I'll avoid printing very heavy objects on the unsupported edge of the bed. Adding more springs or using stronger springs is pretty easy.

If the print gets heavy enough to worry about the bed tilting, I probably have to worry about it flexing, too.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

There are several unknowns with the belt driven Z axis including the precision and stability of the motion. Will it wobble or walk up the guide rails as it moves?

I came up with a way to visually test it. I am printing a clamp to mount a laser pointer on the shaft of the worm drive. The laser/worm drive will be set on the bed and connected to the X axis of the controller. The Z axis will be directly driven by its motor and connected to the controller as seen in the previously posted video. As the bed moves up or down, the worm drive will rotate the laser through 10 or 20 degrees (whatever fits in the camera's field of view). The laser will hit the wall about 6-7 m away from the printer. If the bed motion is perfect, I expect a stair-step line to be traced by the laser on the distant wall, though the steps will probably be too small to see. If the bed wobbles it will cause vertical noise in the pattern on the wall. I'll capture the pattern by pointing a camera at the wall and propping the shutter open through a full cycle of the bed going up or down and the laser sweeping across its angular range.



I will run two tests, one with the laser aligned with the X axis (at the center of its sweep), and the other with the laser aligned with the Y axis (at the center of its sweep). That will provide a visual indication of non ideal motion in the pitch and roll of the bed as it moves up or down.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Here it is, ready for testing. Tomorrow...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

You might want to read the thread on CoreXZ. It uses belt drive for X and Z, but the belt is run over additional pulleys compared to CoreXY so as to give a 3:1 reduction in the Z direction.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks, I'll take a look at it.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I don't understand the scanning of the laser in the XY plane?

Angular actions are shown by laser dot far away on wall,
Linear action is just transported farther away.

Using a lens on laser that creates a line my be useful
to show angle of the line during motion,

a beam splitter may also show more.

A way to convert the linear motions to angular effects would make laser more useful.

Mirror on bed or wall with laser drive keeping spot in one place,
movement of laser is measure of errors?

A retroreflector (device or surface that reflects light back to its source with a minimum of scattering)
could really do a lot--and be usefull on your quest for sub-arcsecond accuracy?

[www.ebay.com]

I'm looking for angular effects. If the bed wobbles/tilts around the X axis (roll) as it moves up and down, the angular displacement will create a vertical displacement of the laser dot. If the bed walks up the guide rails instead of moving smoothly, the walking will cause angular displacement around the Y axis, and it will be translated to vertical displacement of the laser dot on the wall.

The laser isn't going to be spinning rapidly. It will move through a 10-20 degree arc during movement of the bed from 0 to 700 mm in Z. It should trace a stair-stepped line at some angle on the wall, with the steps corresponding to the microstepping of the X (rotating the laser) and Z axis drivers, and probably too small to see. So it should look like a line. Angular errors in the bed plate will add vertical noise to the line.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Suggestion:
Rear projection
Hang a piece of graph paper up and video laser dot from back side

??Even another use for a storm window piece of glass to hold up paper??
??Print up ( inkjet paper) expected route and compare to laser dot travel??

[incompetech.com]


?? Will dot size obliterate errors ??

Wouldn't be easier, and more precise to place an accelerometer on the bed?
Something like a Adafruit ADXL326 3AXIS ACCEL BREAKOUT BRD, lists for under $20.

I looked through the coreXZ stuff. The compound pulley schemes are interesting but without cascading them to get higher reduction ratios, it won't solve the bed-drop problem. I think that like gears, the more pulleys and belt/cord segments there are between the motor and the load, the more potential there is for backlash due to unequal tension in the belt/cord segments. Justified or not, I'm already concerned about the simple pulley and belt arrangement I have.

A combo of counterweights and compound pulleys might do the job, and for a lower cost than using a worm gear drive, but a Rino is simple and all but guaranteed to do the whole job. I'm building one printer for my own (or makerspace) use, not trying to go into mass production, so simplifying operation and high reliability are high priorities with cost a distant second (or third or fourth).

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

DC clutch/break on the Z motor, or any toothed pulley for that matter, may be an alternative.
Though if properly counter-balanced, the detent torque of the Z stepper may well be enough. Absolutely, belt ratios will help.
Most designers don't consider "what-if". Very proactive of you.

I looked at EM brakes, but brakes with sufficient holding torque cost about $50 and require the motor shaft to be grooved which means it's best to buy one with the motor attached. That increases the price to about the same as the Rino that also comes with a motor attached. I looked into the centrifugal brakes used on seat belts in cars, but didn't want to devote the time to trying to design and fabricate something like that and then debug it. I have a couple other ideas for very simple brakes that lock into the belt teeth and use the mass of the bed to apply braking pressure.

The main drawback to the Rino is that all adjustments to bed zero position and leveling will have to be done with the motor moving the bed- there won't be any way to move it by hand. It's the same sort of thing that people with multimotor Z axis drives have to put up with. In my other printer, SoM, if I want to lift or lower the X axis all I have to do is disable the motors and pull on the belt that links the two screws. That makes leveling and setting the zero position very quick and easy (though leveling is very rare and zeroing is infrequent). If the belt lifter works out well, I won't have to tweak the leveling at all after initial setup, and setting the zero position will be infrequent.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
cozmicray
Suggestion:
Rear projection
Hang a piece of graph paper up and video laser dot from back side

??Even another use for a storm window piece of glass to hold up paper??
??Print up ( inkjet paper) expected route and compare to laser dot travel??

[incompetech.com]


?? Will dot size obliterate errors ??

I'm looking for very small angular errors (tilting of the bed on the rails/bearings). By projecting the laser far away, the small angle translates into a much larger linear displacement. By measuring the displacement and knowing the distance from the bed I can calculate the error angle and linear displacement at the edge of the bed plate, where it counts. Rear projection might work if I have something to project on. I definitely have walls...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

The "Rino", it's a worm drive? For the Z, that makes total sense.

[www.ondrivesus.com]

[www.ebay.com]

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Coming soon- images from laser scans of bed lift. I have been plagued by a series of minor inconveniences, one after another. The laptop battery goes dead, the laser battery goes dead, camera battery goes dead, etc.

I had to reconfigure the controller board for Cartesian operation, then connect the scanner motor to the X driver and the Z axis motor to Y driver. Now I can move the bed and the scanner simultaneously by sending a g1 x1.5 y400 f 1000 command. The laser is shining on a wall that is 7 m away from the printer, and the motion looks very smooth to my eye, but we'll see what the camera records. So far I've only looked at roll around the X axis, but I'll set it up to look at pitch as well to detect "walking" up the guide rails.

I have found that at some speeds, some resonances occur and the weight of the scanner is a little too much for the motor and the bed drops. That won't be a problem in the final configuration because the 30:1 worm drive will be lifting the Z axis.

I am expecting the steel core HTD3 belt and 8 mm bore GT2 pulleys to arrive in the mail today. Woohoo!

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
prot0typ1cal
Wouldn't be easier, and more precise to place an accelerometer on the bed?
Something like a Adafruit ADXL326 3AXIS ACCEL BREAKOUT BRD, lists for under $20.

It's interesting, but requires a lot more screwing around, and I don't know how to translate the output to something meaningful here. I have the 30:1 drive to use for the scanner, and the camera, and I can easily translate the results from the camera to tilt numbers in the bed. It looks like a fun part to play with, though...

I have one of these that I use for initial set-up of the orthogonality of the axes: [goo.gl] I have placed it on the bed and watched as it moves and it looks very good- I don't see any angular variation beyond the noise in the device's output (it isn't very stable in the last digit).

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
I have one of these that I use for initial set-up of the orthogonality of the axes: [goo.gl] I have placed it on the bed and watched as it moves and it looks very good- I don't see any angular variation beyond the noise in the device's output (it isn't very stable in the last digit).

Nice, was going to suggest an inclinometer like that, think they use accelerometers with a digital output, haven't seen any with an SPC port to track data.

From your belt set-up, looks like drift will most likely be across the X (belt to belt), that is, rotation around the Y (pitch). The GT3 steel belts will help, suggest they're tensioned when the enclosure is at temp, or use a spring/pulley tensioner.

With the laser painted 7 meters away, you'll see 1.2mm variance with every .01 degrees that the inclinometer reads. Which translates to about .05mm over a 300mm bed. Bet you already knew that :p
Thing is, seems only effective at tracking variance in yaw, as the visually seeing drift in the Z would guess to be difficult.
Ideally, a spot directly overhead would work best for tracking pitch and roll.

Thanks for posting this build blog, very cool.

Edited 2 time(s). Last edit at 01/28/2017 02:39PM by prot0typ1cal.

Quote
prot0typ1cal
Thing is, seems only effective at tracking variance in yaw, as the visually seeing drift in the Z would guess to be difficult.
Ideally, a spot directly overhead would work best for tracking pitch and roll.

Thanks for posting this build blog, very cool.

Now that's a good idea! I have a room with a ceiling that is about 18' above the floor. All I have to do is figure out how to get an object that I can use for scale measurement up there. Hmmmm....

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

How about using a small quadcopter with some double-sided tape and the object mounted to it? Crash it into the ceiling, and you have your reference object.

I think I have an extendable pole that I can use to put a piece of cardboard of specific dimensions up there.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Distance from bed (at the bottom of the Z axis) to the ceiling is 4.95 m. A 1 degree tilt of the bed will result in an 86 mm shift in the position of the laser spot on the ceiling. That 1 degree tilt will result in 2.6 mm displacement of the edge of the bed- completely unacceptable. 0.01 degrees is probably acceptable because it results in a 0,026 mm displacement at the edge of the bed. That 0.01 degree tilt will result in 0.86 mm displacement on the ceiling. Hmmm, that's going to be hard to see/measure, even with my 200 mm lens on the camera- it is certainly smaller than the laser spot diameter. Hmmmmm.

Maybe a mirror to reflect the spot to the wall at a greater distance... Maybe I should work the other way. If I can get a 0.01 degree tilt to displace the beam 10 mm, I should be able to read that pretty easily. The wall would have to be 57 m away, or the optical path has to be that long. Hmmm...

Maybe this isn't going to work.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

What about taping a photoresistor to the wall exactly where the laser spot hits? Then you could measure even small deviations in magnitude of the light shining on it, though I doubt you could get exact angle deviations. Might still be enough to tell you if there is tilt though.

Arduino
IMU
Arduino IDE
Processing IDE
5 wires
USB cable

3D visualization of this motion sensor.

8 - 12 place numbers output also available.

[create.arduino.cc]


???? when you find out that the system has a 20 arcsecond / 40 micron error --- what will you do???

???? will you do same measurements on leadscrew drive ????

The steel core HTD3 belt will be arriving today and I may be able to start test printing this weekend (though without a bed heater), so I'm starting to lose enthusiasm for this whole measurement idea.

Edited 1 time(s). Last edit at 01/30/2017 01:58PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

The HTD3 belt arrived and the 20 tooth 8 mm bore GT2 pulleys arrived today. Since the glass core GT2 belt is already on the machine, I mounted the Rino with a GT2 pulley and ran some tests.

1) Maximum speed with this set-up appears to be 10 mm/sec. If I try to run faster the motor stalls. The Rino multiplies the motor torque by 30x, so I can increase the pulley size if I want to use GT2 belt and easily increase the maximum speed. Since the motor generates enough torque to lift the bed by itself with a 20 tooth pulley, I don't think speed is going to be an issue at all. If I want to run up to 30 mm/sec all I have to do is use a 60 tooth pulley.

I have some 10 mm wide steel core GT2 belt on its way from China, but may go with the HTD3 anyway. Print tests are in order... The HTD3 belt appears to be very high quality, unlike the cheesy glass core GT2 belt that's on there now. I have a few different HTD3 pulleys, including a 32 tooth pulley (and a couple larger ones) that will get the speed of the Z axis up to about 24 mm/sec.

2) I accidentally ran the bed down to the bottom of the Z axis and of course, with all that torque, the Rino kept turning. The way the belt is routed and with the Z axis cross bar clamped to it at two places, caused one half of the belt to become very loose and the other to become very tight. That's bad. The only way to relieve that differential tension is to loosen the pulley on the Rino and let it turn to an equilibrium point. I doubt the belt would survive that sort of abuse for long. I'll be using the max endstop on the Z axis to prevent this sort of thing in the future. Adding the Zmax switch will be even easier than the z=0 switch was.

3) As expected/intended, there is no bed drop when I cut power or reset the controller.

4) It runs pretty quietly.

Video:

[vimeo.com]
[vimeo.com]
[vimeo.com]
[vimeo.com]

Edited 5 time(s). Last edit at 01/30/2017 11:07PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

DD,
Are you using shoulder bolts or machine screws to attach the idler pulleys on your z axis? I would like to do something similar on the corexy I'm designing. Do you have any recommendations ?

Well I'm glad the rino works good because I just ordered one the other day!

I used shoulder screws, but I used them incorrectly. I just screwed them into the aluminum plate with the shoulder contacting the surface of the aluminum plate. The correct way to use them is to bore the plate a few mm at the shoulder diameter so the shoulder sits in the hole. We'll see if my shortcut holds up well over time. I'm not too worried about it or I would have done it differently. The threaded part of the screw is M6, so pretty large diameter for a relatively light load in this application.

I added washers as spacers between the bearings and the plate.

Edited 1 time(s). Last edit at 01/31/2017 02:38PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Proper belt installation method is as follows:

1) clamp one end of the belt in the lower half of the clamp on the right side of the Z axis.
2) run the belt around all the pulleys- leave the motor pulley loose on the drive shaft.
3) pull the belt tight at the upper half of the right side belt clamp and screw the clamp down.
4) move the bed up and down a few times to even up the tension at all the belt segments.
5) screw the clamp down on the left side of the Z axis.
6) move the bed up and down a few times again
7) tighten the grub screws on the pulley on the drive shaft.

Make sure you use a Zmax endstop switch and enable it in the controller. You don't want the Rino trying to move the bed past the end of the Z axis. That will be very hard on the belt (as I have witnessed)! Also, set Zmax to a realistic value in the controller configuration.

Edited 5 time(s). Last edit at 01/31/2017 08:43AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]