Printing an upgraded primary arm
Replication
Category: Reprap Morgan
Preparing to build Morgan01
This weekend I am cleaning up the SCAD code, and making improvements to all of the parts in preparation to build Morgan01 (Morgan0’s first child…)
When you build parts over an extended time you lose track of how many parts there actually are. So far there are 23 different STL’s some of which needs a couple of pieces.
Some of the improvements include:
- Ported pipe adaptors – allowing wires to be placed inside the frame in stead of dangling down the sides.
- Calibration marks on the arms, to fine tune the arm length for the inverse kinematic transform, and make tuning much easier.
- Fixed some 45 degree rule violations all over, making it more “Reprap” 😉
- New SCARA calibration cross, that might double as an icon for Morgan.
more info, and pictures soon.
More extruder updates
My new extruder
The old one was hard to use, with the idler to the inside. I printed the Prusa version of the Eckstruder by Eckertech, http://www.thingiverse.com/thing:27322 with my herringbone gears for it http://www.thingiverse.com/thing:57510
Great improvement. I can now retract filament at 50mm/s, improving prints quite a lot in terms of ooze prevention.
Of course, a nice new extruder needs to be celebrated… with the obligatory Spool holder – mounted right below the extruder.
Peace in the home
I upgraded to a wades style extruder in order to get rid of noise and to up the extrusion speed – My mostly wooden Wades has a much too high gear ratio. The only problem – the gears it was designed with is extremely noisy, especially at the 8mm retraction I need on the Bowden to limit the ooze.
After completing tuning, this is what I made first. The difference in both noise levels and extruder operation is noticeable.
Print quality is also starting to look very good. I will publish the Slic3r settings used when I am done tweaking, in order to give future Morgan operators a smooth start.
Pushing uP too Hard
As part of a string of experiments to do with speed and quality, I wanted to see what the effect would be of pushing the number of kinematic calculations per second up a bit. Initially I did not see a lot of difference, but after pushing it to 500 I saw a difference in the accuracy of the head movement.
This was the end effect though…
The printer actually slowed down significantly to cope with the maths, and the feed rates did not translate. It also seem that some fill lines got left wayside…
To increase speed and quality together, the processing power of the electronics needs to be upped, or some form of preprocessing needs to be performed, perhaps with proprietary polar gcode that the printer can use raw. I’ll be looking into the latter some time in the future.
In the mean time the firmware gives a good balance of quality and speed, allowing brisk non-printing moves, while quality is user selectable by the printing speed.
Draft printing redefined…
Stepstuck revisited… DRV8825
In April 2012 Nophead from HydraRaptor fame, brought us the micro-current hack for the pololu 4988 stepper motor driver carrier. http://hydraraptor.blogspot.com/2012/04/stepstuck.html
Now, it is my turn…
The amazing DRV8825 driver carrier has a similar flaw, strange jumping of steps in 32th micro-stepping mode.
After doing a bit of research, it seems that we need to put the chip in FAST decay mode, by pulling the DECAY line of the chip to 5V. Luckily the DRV has exposed pins, so I carefully soldered the DECAY pin (19) to the M2 pin on the board (will be 5V when 32th uStepping is enabled.)
Movement as smooth as butter!
Calibration and tuning
Calibration of your 3d printer is sometimes even more important than building it, and being SCARA, Morgan is not very forgiving in this regard. You have to get it right in order to get something resembling the stl you fed to your favorite gcode slicer…
I don’t like working too hard though, and thus I spent even more time writing up a calibration routine that will make it child’s-play… Well, almost.
Here is the wheel I printed for a small tricycle. The orginal calbration routine zeroed the arm angles to a line drawn on the top platform. While it works well enough, it caused the wheel to be slightly oval. While this does not subtract from it use, it is not quite how it is supposed to be.
In order to fix that, I had to change the way the calibration is done in order to focus on the angle difference in stead of the actual angles. Psi is now calibrated to Theta.
I am going to make some special phantoms in order to make the calibration process a bit smoother. After playing a lot with the steps per angle, I found a way to calculate the steps. The steps combined with the scaling factors makes it possible to get a perfect circle.
And… it prints!
After a very long wait, my SCARA RepRAP is finally printing. I printed 4 calibration cubes and a piece of a tricycle wheel (in the wrong colour…)
In the video you can see the new hall-affect end stops, my “Mostly wooden Gregs’ Wades” extruder, the mounted hotbed all working together to print a tricycle wheel.
What you cannot see is the new additions to the firmware that sports:
- Quick calibration routines (in Mcodes) Calibration of the arms can be done in as little as 2min without having to calculate the relative arm positions for the arms – for any size machine…
- Axis scaling: it is not possible to easily calibrate the x and y print sizes by steps alone, and therefore the machine has internal and Mcode adjustable scaling factors to ensure your prints come out the right size
You can check my Youtube channel (quentinharley) out for some footage…
Happy times!
I have a couple of upgrades to the frame coming, focusing on the z-axis stability without having to add another motor. There might also be an upgrade to the arm configuration in the pipeline soon. I also thought about a practical way to install more than one hotend on the arm – bringing multi-head printing to SCARA.
Big Weekend!
This weekend will see the pre-flight test and some documentation before the big test… How well does it print!
This week I had limited time, but I completed the firmware for the test, including a very nice electronic calibration section that will allow you to calibrate a Morgan SCARA in around 2minutes. No hardware adjustment needed after the build…
Can’t wait!
Auto homing is functional!
Yes, I got it working this weekend. Yes, I did not have time yet to properly document it.
Real job before play…
I’ll see if I can make some time to document the changes tonight at H4H.
