I finished designing and building my first delta printer, a 2020 extrusion based on the Kossel Mini by @Johann_Rocholl . This one I printed has a 300mm diameter print area with a maximum 500mm print height.
All the printed parts except for the effector and effector accessories were (re)designed in SolidWorks - my first SW project. It uses the same fasteners as the Kossel Mini, except instead of m3 nuts, it uses m3 slide-in extrusion nuts from Misumi.
The bed is a mdf base, a silicone heater mat, and a 300mm diameter borosilicate glass plate. The mat is a 110VAC 500W heater that gets up to ABS temps in about a minute.
I also designed a zero-cross sensing PWM controllable triac solid state relay for controlling the hot-bed. It has an ATTiny45 on board listening for a PWM signal which it then uses to control a zero-cross-synced triac for perfect PWM control of mains A/C.
The design comes with three vertical motion solutions, a plate for a standard steel linear rail, a printed linear-bearing employing 5/16" delrin balls (also based of Johann’s design), and a printed PLA bushing, show in in the prototype. The bushing took a few design attempts to ensure there is no play in any direction, and to ensure that it’s adjustable in the future, if any play develops.
I’ve just finished assembling and ensuring the electronics are all in order. Now, on to calibration and a test print.
Looks great, thanks for sharing! I’d be interested to hear comparison test results of the different linear carriages… Could you imagine running all three at the same time, one on each tower?
@Joe_Mosfet , I’m not sure a PWM controlled SSR is really needed. IIRC, Marlin doesn’t actually drive the bed that quickly. I’ve been using a standard opto-isolated SSR for a long time without any issues.
Still, very interested in the board schematic/bom for that. Seems like it would be amazingly useful for other projects.
@Johann_Rocholl I actually printed a few different printed bearings, and really none of the balls flowed very smoothly. It was loud, and personally I feel the pla bushing offers smoother motion.
First, a video showing the 2020 bearing redesign:
Then a video showing the pla slides and comparison:
@ThantiK , the problem I encountered with the bang-bang control of the bed on my cartesian bot, is that it doesn’t offer a consistent temp - wavering even a few degrees caused a pattern to appear in Z of smaller objects.
Once I switched to PID on the bed (15khz), and was able to maintain a constant bed temp, that Z patterning disappeared.
@Joe_Mosfet I use PID control of the bed, but I’ve never seen a 15khz PWM from it. Just checked the Marlin firmware as well, and there’s no mention of PWM required for PID control.
PWM only gets enabled if you set #define MAX_BED_POWER to something other than 255. Which in most cases, you really don’t need.
Interesting, I’m using Repetier-firmware and it does allow me to specify the PWM frequency - I believe this frequency is used for all PWM control on the Mega, but I could be mistaken.
In any case, I believe PID control does a better job if it can PWM the heater rather than on/off it.
15kHz? I love over - engineering! The temperature is probably rock steady at that rate! My only concern (totally guessing here) but does that rate tax the Arduino’s meager CPU resources?
@SirGeekALot Well, the KoSSR has it’s own ATTiny45 which is dedicated to analog sampling and zero-cross synching, so there really is no added load on the main board. In fact, since this gets hooked up to any available PWM pin, the heater fet on the main board is available for other purposes.
Just an FYI, by PWMing the bed you are most likely generating an “powerful” high frequency radio noise signal. Not really something you should worry about (but it might disrupt your USB connection).
This is however, a concern if you go for something silly as CE or FCC certification.
@Joe_Mosfet 50hz or 60hz is low frequency, and if you turn on/off at the zero-crossing there is no problem there. However, if you do phase cutting (what most light dimmer do) then you are generating a lot of EMF.
Hi Joe, great design.
Do you have more detailed build log? I am considering building it myself - the version with rails.
What rod length have you used? 360mm?
Best regards,
Marko
I have a friend working on a proper build guide, though any Kossel Mini build guide should work, save for a few details.
My carbon fiber rod lengths were cut to 360.25mm making the axis-to-axis length (what the firmware asks for) of 394.25mm. That being said, this length is optimal to ensure proper motion (no less than 21 degrees angle from the bed) and maximize print height. If your rod lengths are slightly off, no big deal. The important thing is to make them all the same length.
The linear rails is the best option, in my book. While a little expensive (for 700mm long rails) it adds rigidity to the vertical extrusions and offers superior motion.
Please let me know if you plan on building this, as I’d be more than happy to assist in any way I can.
Yeah Johann deserves big credits. But larger designs with 15 x15 are not so stable.
So how stable is this design? I would probably build smaller version like 420x875 or 360x800, have not decided yet. But have came across 60cm rails and I am planing to use them.
Joe, do you mind sharing details of heatbed PWM schematics? I didn’t found suitable 300mm kapton heater and now I am looking into your solution (round silicon heatbed is available), since it also doesn’t need big power supply. What wattage is actually needed for heatbed - will 200W be enogh? My plug here has 230V, so cca 1A.
@Marko_Bukovec If the corners are printed in PLA, the machine is certainly stable. I worry that the softer ABS would make it less so.
600mm rails would work well with 800mm vertical extrusions.
The heatbed controller’s schematics can be found https://github.com/mosfet/kossr including the firmware for the ATTINY on board. Since you say you’re on a 230V plug, I assume that also means you’re on a 50hz AC as well - the firmware will need to be updated for this.
As for the heated bed, it was custom made by @Johnny_Tang at http://keenovo.com, I’m sure he could give you a quote needed for diameter and voltage requirements as well as desired wattage. The one I’m using is a 300mm diameter, 110VAC 500W with adhesive backing.
