Rostock Delta Robot- Mechanics

Building the Rostock Delta is important for me for a number of reasons:

• First, the simplicity of the design. Eventually, if all goes well, I’ll need to build larger machines. This design may prove to be the easiest route to take.

• Second,  I plan to experiment with faster printing speeds and faster printing speeds with larger nozzle sizes. The Rostock boasts a positioning speed of 800 mm/s in all three directions. 

• Third, the manner in which the electronics and stepper motors are shielded from the printer mechanics seem optimal for creating a temperature controlled chamber.

• Fourth, the bed remains stationary. This will be very important when I’m prepared to set up a system for clay extrusion. I’m certain that with the typical RepRap printer the motion of a build platform while extruding clay (especially large models) would become problematic. The Delta design will eliminate this situation.

Overall, the mechanical construction of the Rostock Delta has been the easiest of all the printers I have built. One of the major factors for this ease has been the wood support components. I downloaded dxf files of the wood members (thing:34570) and simplified the design by eliminating the intricate “crown shape” cuts which allow fastening by screw and nut. I then had a local sign shop CNC router the pieces out of MDO. This obviously provided me with perfect angles and drilled holes for the placement of plastic parts I printed on my Mendel Prusa (thing:17175).

I couldn’t find specific assembly instructions for this printer, except for the Bill of Materials list (referenced by the RepRap Rostock Wiki). I think, with some previous knowledge of a RepRap build, it’s easy to figure out.

I made a choice early on to upgrade the printed arms with bearing arms and set screws that I purchased on eBay.

 This was a very good move on my part. The fluid mobility of the joints are superb.

I also equipped the stepper motors with 40 tooth GT2 plastic pulleys rather than the 8 and 20 tooth aluminum pulleys that I’m using on my other printers. This may or not be better. The original specs for the Rostock called for the 40 tooth pulley. I've later discovered since purchasing the GT2's, that they'll  have less torque and a lower resolution than smaller pulleys. On the upswing, the GT2 belts and pulleys are designed for linear motion and this will eliminate the backlash which my T2.5 and T5 pulleys are prone to exhibit.

Overall, a very sturdy design. I’m looking forward to getting it moving.

The E3D-v5 HotEnd and bowden cable system

The E3D-v5 HotEnd from e3d-online.com is a new hotend that I’m interested in trying. It has an all metal construction (without the use of PEEK) which gives it the advantage of operating at higher temperatures.

This is important since the nylon and polycarbonate filament that’s become available requires much higher extruding temperatures.

The hotend is sold as a kit which consists of a handful of parts that are very easy to assemble. There are two design features I’d like to point out.

First, the hotend utilizes a robust ceramic resistor that's held in place by a small allen screw.

Second, the thermistor has a very nice cavity to plug into and then wrap around and through the block which provides a good anchor.

I purchased this hotend with the additional bowden cable accessory. I could have devised a bowden system from scratch, but this hotend has a coupler which screws nicely into the end. It's a nice system, but I still had to  fabricate a part to clamp it to the x carriage.

Using OpenSCAD, I redesigned the bowden mount available on https://github.com/MakerGear/MakerGear-Prusa-Mendel and designed a mount clamp on SketchUp.

The OpenSCAD file was also modified so that the bowden cable coupler could be used with the  MakerGear Brutsruder. This also required adding a M8 nut.

The bowden system is quite adaptable. By using 2 M8 nuts on each end of the couplers, I'm able to attach a MakerGear hotend and use it on my Mendel Prusa.

Printrbot Commissioning

I've completed my Printrbot's mechanical and electronic systems and now I need to tweak the programming and software for operational control of the printer. This requires a little more work with a Sanguinololu board than what's required with an Arduino based controller.

In order to load the firmware on the Sanguinololu, I had to first install a Virtual Com Port USB driver from http://www.ftdichip.com/Drivers/VCP.htm. I then plugged my Sanguinololu into a USB port and directed the Detected New Hardware prompt to the CDM driver folder. Once a port was established, my Sanguino was recognized by Windows.

Next, I needed to download a pre 1.0 version of Arduino software. I'm using 0023 and it can be found here http://arduino.cc/en/Main/Software. The Arduino program needs to be set up with some new files and a modified avrdude.conf file. I downloaded Sanguino1284p-master.zip from here https://github.com/jmgiacalone/sanguino1284p. I added the contents to the hardware folder of arduino-0023. Allow Windows to merge the tools folder and overwrite the avrdude.conf file. Now the Arduino software will recognize the Sanguino.

Next, I needed an updated version of Marlin firmware. I downloaded Marlin-Marlin_v1 from here https://github.com/ErikZalm/Marlin.

Next I needed to edit the Marlin firmware with the Arduino software. I opened the Configuration.h file and first changed the electronics board setup from the default:
#define MOTHERBOARD 33
to:
#define MOTHERBOARD 62

Next I had to get my mechanical settings corrected specifically for my Printrbot.
Under:
 // Endstop Settings
I changed the default values “true” to "false" in these 3 lines:
const bool X_ENDSTOPS_INVERTING = false;
const bool y_ENDSTOPS_INVERTING = false;
const bool Z_ENDSTOPS_INVERTING = false;
Under:
// Disable axis when it’s not being used.
I changed the default values "true" to "false" in the first 2 lines:
#define DISABLE_X false
#define DISABLE_Y false
I also changed the build volume to Printrbot size:
#define X_MAX_Length 100
#define Y_MAX_Length 100
#define Z_MAX_Length 80

Next, in order for the new fan circuit to be operative, a change needed to be made in the pins.h tab.
Under:
 *Sanguinololu pin assignment
I changed the default value -1 to:
#define FAN_PIN   4

Of course, the usual changes need to be made to the movement settings in the firmware during calibration. Finally, the edited Marlin firmware can be uploaded to the Sanguinololu.

I'm using Printrun as a host. There’s a few things to do here as well. Under Options from the Settings menu, I changed the build_ dimensions to 100x100x80. I then selected the correct port for my USB connection and set the baudrate to match my firmware.

For my first test runs, I used PLA filament and Slic3r. Slic3r has better fan control options and since this is my first printer equipped with a fan, I’d like to test the system more throughly. I used the 5mm cube steps pyramid calibration test (thing:56003) for my first run.

The fan cooling system certainly works very well for areas which are usually more difficult to print without the additional cooling.


Next, I ran some bridging tests. I made a 25x25mm open cube.

There is the slightest hint of one drooping strand on the print and several others that were printed.



Last, I ran a bridging test using the bridge torture test (thing:12925). This model requires a span of 50mm to be printed from 2 posts.

With some tweaking of the slicer options, A successful print was made.