Riley Porter and Alden Hart of Synthetos has just announced their Grbl-shield, an Arduino shield purpose built for working with Grbl! Ours is in the mail, and we can’t wait to try it out. (Featured in the blogs of Make and Adafruit)

• Plug and play compatible with grbl 0.6
• Three stepper motors supporting X, Y and Z axes
• 8x microstepping
• 2.5 amps per winding (bipolar steppers)
• 12v-30v motor voltage supported
• Independent current control per axis
• Motor connectors plug compatible with RepRap and Makerbot electronics
• Uses TI DRV8811 stepper drivers

Stefan and Addie or Nortd Labs are creating an open source laser cutter. Looking for a suitable firmware they happened across Grbl and dared to try out the ultra-beta acceleration branch which turned out nicely for them:

Initially we wanted to write our own firmware from scratch for an ARM Cortex M3. Then we started playing with some open source AVR firmwares. Man, these 8-bit hackers have done some impressive work. […] In the end we only got grbl to perform smoothly (after updating to the super cutting edge code of Feb 3).

We appreciate their enthusiasm and look forward to assist them in adapting Grbl for laser cutting as much as we look forward to being able to build our own open source laser cutter from their plans.

(Also, if you’d like one, consider pitching in via the paypal links at the bottom of this page)

*) Grbl is our free, open source, high performance CNC controller written in optimized C that will run on a straight Arduino. More

Attempting to discover the best algorithm for determining optimal speed reduction in order to pass a corner at maximum speed but within a set jerk limit.

Red: The jerk-limit, Yellow: The actual jerk, Transparent blue: The sum of incoming and outgoing feed rate. The intersection between the red and yellow is the set of candidate cornering factors, the optimum one is the one where the speed is the highest, i.e. where the blue transparent layer is at its tallest.

The final optimizing algorithm must run on the AVR328 in a matter of milliseconds.

We are experimenting with real time controls for the milling operation and came up with this unit cobbled together from dumpster spoils and the Big Dome Push Button. Now we can tweak the feed rate in real time using the sliding pot, see if we suffer buffer underruns because of poor serial comms and we have two buttons for pause and emergency stop. There is an experimental branch up on github if you want to experiment with real time feed rate tweaking: Control. (Warning: The pins had to be remapped. Be sure to check config.h for the updated pin out.)

In related news: We finally have gotten through most of the code for a look ahead optimizing acceleration manager for Grbl. It is completely untested yet, but if you are so inclined you can have a look at the code in this experimental branch. The details will be explained in a proper blog post later.