Rostock Delta Robot- Commissioning

Setting up the firmware for this printer hasn't been much more difficult than the linear style RepRaps that I've built previously. It's simply been different.

The major difference has been overcoming the limitations of the computational speed of the Arduino hardware. Using the latest  jcrocholl / Marlin firmware from GitHub, I found that the printer would stall for upwards of 5 sec. periodically throughout printing. This is because with a Delta system, there is more computation required to calculate each point in space. In order to ease the buffer load of the Arduino, I had to make some adjustments in the firmware, particularly of the Delta Segments and Acceleration values.

Under this line:               Delta Printer
I changed:                      #define BAUDRATE 250000
To:                                 #define BAUDRATE 115200

Under this line:                #define DELTA
I changed:                       #define DELTA_SEGMENTS_PER_SECOND 200
To:                                 #define DELTA_SEGMENTS_PER_SECOND 100

Under this line:                //// MOVEMENT SETTINGS
I changed:                      #define DEFAULT_MAX_ACCELERATION      {9000,9000,9000,9000}  
To:                                 #define DEFAULT_MAX_ACCELERATION      {4000,4000,4000,9000}

After making these changes, the pauses ended and the printer has been successful in making prints runs up to 6 hours long.

Another change I made was with the mechanical function of the printer. I had originally installed some bargain bi-polar stepper motors that I got on eBay. These were not supplying enough torque. During long print runs, a stepper would skip and the print would be lost.

I changed to 3 bi-polar stepper motors that I purchased from www.pololu.com. They are NEMA 17-size and have a holding torque of 3.2 kg-cm (44 oz-in).

Unknown size on left. On right is a 44oz-in NEMA 17

I also added heat sinks to the Pololu A4988 drivers and a cooling fan. Since this change, I haven't had any problems with missed steps.

 Another change I made was with the hot end. I was wired up with the E3D-v5 hot end, but I haven't had much luck with it. I swapped it out with the hot end design from RepRap Pro. This hot end has become my favorite along with the Maker Gear hot end.

The filament feed works beautifully by using a spool box from what was www.thefutureis3d.com. The site is now linked to www.indimension3.com and I don't see the item available. I'm sure one can be made easily since it's basically a box and lazy susan device. What is nice about this particular spool box is how nicely it fits on top of the Rostock frame.

Printing has been of fairly good quality. I'm still working out some issues with cooling. Even with the orbit feature of Skeinforge, I'm getting too much distortion on the fine tips of pyramids and cones.

A cooling fan will help solve these issues, but I prefer to keep the mechanical parts to a minimum.

Overall, I consider this printer to be my second best for printing large pieces. The build envelope is roughly 180mmx180mmx350mm (7" x 7" x 13-3/4").

Rostock Delta Robot- Electronics

Assembling the electronics for the Rostock Delta has been achieved with far more ease than any of the other printers I've constructed. The physical design of the printer has much to do with this.

By having all three stepper motors located in close proximity of the Arduino/RAMPS controller, the wiring is  routed more efficiently.

Placing the end stops has been the confusing part. I haven't found any clear information on the placement, and I'm still not sure if I need six or only the three I placed. I'll determine this when I setup the firmware and make the physical calibrations.

The heat bed was simple. There isn't the usual setup of screws and springs. I'm not sure how the leveling will be accomplished, but I’m sure that will also be clarified later.

 I added a 1/4" foam core barrier between the wood base and the heat plate. This should allow for insulation and also enough of an offset allowing for the attachment of a glass plate with clips.

I’m using the old extruder design from my RepRapPro Mendel. It mounts beautifully on the side and allows for perfect positioning of the Bowden cable and the filament feed.

The hot end is the E3D-v5 1.75mm filament version. I downloaded the parts for the mount at thingiverse.com (thing:80616). With a few minor modifications, I made it work. I wanted to be sure the hot end was easily removed with its cabling and Bowden tube, so any future repairs can be made with ease.

 

Up next, will be software setup and calibration.

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.