Best posts made by oliverracing

So I asked a few months ago about what this kinematics would be classed as and David helpfully pointed out it was just a polar but moving the arm and not the bed.

As I've been forced to take 3 weeks holiday by work due to the current Pandemic, so I thought I'd give it a go making one! Reusing all the hardware off my old printer, I have put this together...

31*32cm build area but in theory with a bigger bed and enclosure could print a 50cm radius semicircle with very little changes to the mechanics.

It's surprisingly stiff and has a ~30:1 ratio on the swingarm stepper so hopefully enough torque and resolution. If this works out I'll replace the 2020 of the swingarm with 20mm carbon tube so reduce the inertia and get some aluminium plate laser cut to replace the existing mechanism as that is the main source of flex.

Now I've just taken a backup of my old settings and just about to dive into the firmware setup, I'll report back with how it goes!

Ouch, but yeah your review seems to echo everything else I've read about them. I very nearly bought in on the original Kickstarter and kicked myself I didn't but looking black seemed to have dodged a bullet!

So for anyone reading this - please if you are using a Tevo Tarantula (or an extruder from one), check the bowden tube isn't pulling back into the extruder gear on retractions!

Yep, almost 100% sure this is the issue that started this whole mess! Then swapping in a stepper motor with different wiring at the plug caused me to blow the driver! Ahhh. Lesson learned (£170 lesson sadly - new TMC2660 chips and eventually a new board). On my setup it's impossible to see into the drive gear so I couldn't tell this was happening and when extruding the mangled bowden tube then pushed back to where it was meant to be but almost completely closed stopping it extruding properly! No idea how I got away with it working for a few years as it seems a flawed design!

So it appears m669 with axis coefficient is the way forward.. along with an upgrade to 2.05/6

It prints! (video)

Very happy to have got it going and the ease of changing stuff from DWC2 really helped. I have had to do a bit of a tweak in Cura to get the correct build area but nothing silly, just blanking off the unprintable area.

I've ordered a lighter swingarm (65g vs 265g) which should reduced the inertia of the beam which seems to be a bigger issue than the inertia of the hotend as the arm swings much faster when nearer the pivot. I will also get a smaller stepper for the hotend as currently using a fairly heavy duty one that's overkill with the 3:1 ratio.

I am going to hold off on the metalic pivot pieces as reckon I can get a big improvement with a better designed version of what I'm already using with some cross bracing. Will update with progress!

@Phaedrux Yeah, I'd did chuck a Bowden setup on it to see if that improved anything but there wasn't a massive improvement near the pivot as the MOI of the swingarm/beam seems the be a much greater issue than that of the hotend assembly, due the swingarm moving much quicker when the hotend is nearer the pivot. (Bad ringing near pivot) The precision/torque issue is then more apparent at longer reaches due to the arm deviating by as much as ~0.5mm when getting caught on a existing printed track, the Bowden did help slightly with this but not enough to keep with it at the moment. The hope is 3x more torque, double the resolution, improved stiffness and lighter beam will help massively.

I also print flexible filaments fairly often and a 600mm Bowden (that's fairly curved at points) really doesn't work well with the softer filaments in my experience.

I have considered the zesty nimble (or making something like it as like the challenge) or maybe a igus linear square drive along the swingarm powering the direct drive extruder but reckon that could be as heavy as a pancake stepper.

@Nemesis1782 Yeah, there are a few benefits over other formats apart from the need for fewer parts and coolness but for me those were two of the biggest driving factors.

Other pluses to this design were that I have a fairly limited space for this printer to live (60cm60cm50cm) but will hopefully be moving in a couple of years to somewhere I can give it more space, so this would with only a small change to the mechanics (increase the sweep of the arm) and firmware be able to print a 55cm radius 2/3 circle assuming I can make a bed that big, going for a nicely ratioed rectangular area of 64x38cm which is pretty impressive for a printer so compact.

As a very rough indication of useable area of the printer I am using the filled orange square at the moment but the current unchanged mechanics can reach the grey area (if no wall in the way) It would be a small change to the mechanics to be able to add the tan area (only needing a new pivot piece) which would in theory allow the non filled green area. Doing this would leave the bed without an edge on the y=0 axis that would require either a bit more slicer trickery or the ability to move the axis (x,y,z) relative to the polar coordinates. Either that or a plugin to modify the gcode after slicing?

Brother currently asleep from a nightshift so can't really do a test video (it resonates through his wall), but the new swingarm (1/2 the weight, 3x as stiff + adjustable to allow squaring up) and NEMA23 powering it is a massive improvement and seems to match where I had my old cartesian in terms of speed and quality. Not yet tuned speed and accelerations as suspect ringing could be pretty bad it high jerk and acceleration values but only one way to find out!

Got a quick video whilst doing a semi test print on the V2 of the printer. Carbon swingarm, NEMA23 and lighter hotend all come together to work really well - youtube link (using up some terrible old filament to make a spool drawer set, colour change via a pause and swap filament)

Printing with a 1mm nozzle/ 0.5mm layer so approaching max flow rate of the volcano at ~50mm/s in that video and reaches vmax pretty quickly which is nice as only way to get quicker from there is a supervolcano! In the purpose of testing I am going to try upping the acceleration to the point where the ringing becomes noticeable but other than that I'm very happy and now gonna get on with other projects.