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started designing a new mostly-plastic reprap SCARA with fishing line motion transmission and unorthodox winch for Z

Posted by realthor 
Yep, it´s great that there are at least "some" more people working on the SCARA stuff...
Perhaps we can ask him also how to implement arc movements (g2/g3)...?
I don't understand much but in the code there seems to be defined G2/G3:
#ifndef SCARA //disable arc support
    case 2: // G2  - CW ARC
      if(Stopped == false) {
    case 3: // G3  - CCW ARC
      if(Stopped == false) {

Also the effector position might be defined by these lines (no comments though about what they mean):
#define EndPointMountOffset 18
#define EndPointMountAngle 50

RepRap Lander concept on Concept Forge
RepRap Lander concept on RepRap Forums
My Things, mostly experimental stuff
For your bearing press in
your running shaft

You should use a real M8 bolt
where shaft is 8mm

then the bearing will be as straight as possible

M8 threaded rods are NOT supposed to be running spindles.

confused smiley
He everyone.

I just finished first version of SCARA based 3d printer (Actually 5 bar mechanics)

My is [youtu.be]
My Scara repository.

The mechanics discussed here seems good.

My current problems is a z wobbling.

Your may ask me about the code. Espacially if you need code support (i am programmer).
Hi Pavlo,

well, indeed, we already watched your video several times the last hours+ ! ;-)

Thank you so much for contributing your great work and for your offer to help on code! I think there might be some questions... ;-)

Kind regards
Hi Pavlo, thanks for dropping by and welcome to reprap forums.

Oh questions will come, I am no programmer, just learned CAD, now starting with openscad but coding is so intimidating at this moment.

Thank you for offering to help, I need some mentoring with all this reprap scara thing I've dived so naively into and I offer to bring the beers smiling smiley.


RepRap Lander concept on Concept Forge
RepRap Lander concept on RepRap Forums
My Things, mostly experimental stuff
You should use a real M8 bolt where shaft is 8mm

@cozmicray: Unfortunately I wasn't able to find my specific lengths of bolts (with the 8mm un-threaded body) in the hardware stores around my location. I'll keep looking though.

I will be away from the prototype for about two months so all I can do now is resolve some of the conceptual issues that I have.

Regarding the code, currently I am able to jog the motors with Quentin's Marlin fork but, as you could see from my design, I want to be able to use two hotends and Pavlo's approach seemed a good match. I will be able to re-use the code almost unmodified (as kindly confirmed by Pavlo) but there is one aspect that is inherently different for Lander from the Morgan-style printer: I have to restrict the movement to only one side to emulate Morgan (please see picture below):

The way I see it is that I have to prevent the Forearm to go to a negative angle with the Humerus at all times, thus avoiding the singularity. If I understand correctly the Forearm angle is always calculated relative to the Humerus, so one side means never allowing the Forearm to a <0deg with the Humerus. So for the homing position I think my best bet is with forearm collinear with Humerus, to one of the sides of the bot.

I am not sure how is that supposed to be done in software/endstop setup though.

PS: regarding the maximum angle both Humerus and Forearm can rotate as to avoid them colliding with the drum or with the motors mounts I would think that that can be specified in software. So basically I only need to have two endstops and have the other movements/rotations/angles specified somewhere in the configuration*.h files.

Edited 2 time(s). Last edit at 08/03/2015 09:57AM by realthor.

RepRap Lander concept on Concept Forge
RepRap Lander concept on RepRap Forums
My Things, mostly experimental stuff
sub arc-second accuracy, angstrom tolerance
with hardware store nuts and bolts


Find a Fastenal



Web The nutty co.


confused smiley
I write some code to visualize working areas 2 Arms
Just modify parameters and press RUN, to see arms reachability.

Also today i found a bug with Original Marlin Scara implementation.
Fixes here

NOTE: My firmware supports 2 configurations:
1) with #define FIVE_BAR - 5 bar SCARA with extra mount

2) Without #define FIVE_BAR - fixed bug in math for classic SCARA (2 arms).

Edited 1 time(s). Last edit at 08/03/2015 04:05PM by PavloG.
First moves of the scara bot:


I have just uploaded this video without any editing because I was so surprised seing it move. I didn't expect much but it turned out great for a prototype heavily patched due to design/calculation errors (the cardboard covers the grooves that were wrongly calculated, the tensioning of the spectra didn't work as intended, the threaded rod spindles for the drums have too much play due to smaller diameter than the 608 bearings, the bearings themselves aren't perfectly straight due to bad cold-pressing technique -actually I didn't even know how am I supposed to insert bearings in their 3d printed holes - and sooo many more smiling smiley.

I will have to make some measurments and do some testing before I will rebuild it with better materials and re-design the flawed areas.

Going to sleep for now, ciao.

Edited 1 time(s). Last edit at 10/17/2015 07:26PM by realthor.

RepRap Lander concept on Concept Forge
RepRap Lander concept on RepRap Forums
My Things, mostly experimental stuff
Very Cool !!

That´s the way of the game ....build it --> fix errors --> build it again --> ...
and you already know where to tackle things.

Will be a nice machine!
That is awesome!

I press bearings in by placing them on a hot plate and then pressing the part down on top of it.

If you don't like the play on the threaded rod, add something to shim it. Teflon tape is good if it is already close.

Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
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