It’s been about 5 years since I ran this fun little machine but since I’ll be showing some middle school students how to use a Prusa i3 recently donated so I thought I’d show the Mini Kossel too. It has all the working exposed and easy to see.
Just love watching a delta type 3DP do its thing.
You don’t see many Deltas anymore since the need for speed has taken over.
The “need for speed” was THE reason for the delta since 3 motors moving simultaneously summed for the motion and the effector was very light weight with just the hotend on it. Cartesian machines started off with the hotend on the extruder so there was lots of weight getting moved around and the Y axis was a big moving mass too.
Along came Cartesian machines with bowdens(like the deltas) and that helped some but it was the creation of the CoreXY and Hbot designs which brought speed to the Cartesian format 3DPs.
The long bowden makes retraction tuning a pain and so there tends to be some stringing. But light weight extruders were designed and now many deltas have the extruder on the hotend/effector.
Another problem with the delta’s were the arms and those Traxxis joints. I solved that by finding out freezing the metal inserts, boiling the plastic for 15s and snapping the plastic onto the metal insert a certain way resulted in squeaking tight joints. I tried to spread that information but it didn’t get around much and effort was put into magnetic ball setups.
And then there was the fact that the 8bit AVR wasn’t capable of doing the delta kinetics corrections so line segments needed to be somewhat long or else the AVR would stall and cause blobbing in the prints. Hence the reason I went to LinuxCNC on the BBB when Charles Steinkuehler wrote the PRU code for the BBB to do the hard work of the realtime motion control. The PRUs on the BBB are 200MHz processors which operate independent of the BBB’s ARM CPU(ya, just one). But they have access to shared memory which makes comms between software parts work well.
Things like Klipper and Remora do something similar but with hardware offboard of the main kinematics controller.
But boy, the delta motion is just soothing to watch. It’s like a choreographed dance.
Yes it’s very mesmerizing!
FWIW, I built this Mini Kossel back in 2014 as a low cost 3D printer. You can still see the attempts at 3D printing slides/carriage mounts which used nylon screws to keep tight. The cost of parts were under $200 but used a Sanguino for the controller instead of the BBB/CRAMPS controller.
It’s a shame the other 3D printer and laser cutter vendors didn’t pick up on the carriage roller wheels I used. Two thirds of the width ride flat on the rails and only the center section interfaces with the slot. Very little slipping friction/wear. Unlike the V-rollers used on all of the budget 3D printers and diode laser cutters.
I love my big K280 Delta… Which is a Kossel design too, but scaled up. Watching it is totally mesmerising, it can be very, very fast when it needs to be. But has needed a lot of love to get reliable.
I use it for art and smaller parts but if I need dimensional accuracy I reach for my Cartesian machine because calibrating a relatively flimsy delta is tricky, and needs to be done regularly as the machine and environment (especially temperature) change.
The Duet3d controller and IR height sensor it uses to auto calibrate do a pretty good job, but print anything over 150mm and you can probably measure the error by eye using a hand ruler. Right angles often turn out slightly crooked, things can fail to fit properly.
It’s due to the machine itself, I could fanny around adding bracing and rigidity, work on thermal expansion, bed warping, height sensors etc… Then print test shapes and do corrections; repeatedly… However I decided some time ago that life is too short for that 
And anyway, it it does very well as it is:
My ‘big’ Mini Kossel was also a problem but it was my first 3D printer build so I learned a ton from dealing with the issues. I was also strapping it into the passenger seat of my truck and taking it all over town showing it off since way too many hadn’t seen a delta and way too many had 3D printers they couldn’t get working. And mine is made of 1515 extrusion! For the big one I ended up using linear bar bearings bolted to the 1515 so that stiffened things up alot. I then modified the upper mounts and that made a big difference.
But I also keep my effector very light and I use a small PEEK fan and for part cooling I use one squirrel cage fan much like how you see on my standard Mini Kossel. I’ve printed a few things over 100mm tall but then again I’m only running it at around 150mm/Sec and travel speed around 200mm/s so not crazy fast.
I see you have springs on your arms to take up slack in the traxxas joints. I was stunned when I made my first Mini Kossel that there were not instructions on how to assemble the joints so there wasn’t slop in them. It’s really easy to assemble them without slop by freezing the metal parts for a few hours, getting water boiling, place a hard insulator on a flat surface and
1-put a metal part down standing on one end
2-put a plastic part in the boiling water for ~15sec
3-pull the plastic part from the water with wooden tongs
4-locate the recessed side which has a slight recess and bevelled hole
5-place on the cold metal part and press it on quickly using a send plastic part
when it comes to room temp it will be a tight fiting assembly.
And there have been some crazy structures put on weak Mini Kossel frames over the years. But I think 2040 extrusions are the way to go today.
@dougl , This reminds me I need to do a ‘Show and Tell’ for my Sunflower (my Kossel), like you I found it the perfect learning experience. The K280 was quite a good hardware kit and it deserves some discussion. For instance the rod arms were pre-assembled with the joints pre-fitted, all straight, and all the same length too. I checked! The supplied controller, extruder and electronics in general are, however, best forgotten.