[Grbl_Esp32 Issue#392] 2 noob questions: axis deceleration different from acceleration – running custom G-code?

#1 – bdring 于 2020-05-04

You cannot control the acceleration on the fly from gcode. Any time the machine is idle, you can change the $120 settings.

Grbl_ESP32 only supports standard gcodes. You could hack in your own, but we do not want non standard gcode. The LinuxCNC project is a good source for standard gcode. We are not interested in supporting RepRap gcode.

#2 – iacopo 于 2020-05-04

Thanks for your reply, I see the point in avoiding non standard gcode, I gave a look at the linuxCNC project already and I see theres a set of user defined M-code: M100-M199, how would one program a function to be executed when such a command is entered?
I guess that would be pretty common on CNC machines if someone adds a custom tool for instance.

#3 – bdring 于 2020-05-04

You would have to add them to the firmware. It is not very common to add arrays of lights to CNC machines.

GrblESP32 has a few commands that branch off to user control. For example tool changing. GrblESP32 does not know how to control your tool changer, but if a user supplied a function to do that, Grbl_ESP32 will optionally pass the tool change information to your function and wait until the function completes.

I suppose that could be done with M100-M199. with that said it is probably a 5-6 hour project for someone very familiar with Grbl to do it right. New modal groups would need to be added, etc.

I can add that to the roadmap, but I don’t think any of the primary developers are going to see that as a priority.

#4 – iacopo 于 2020-05-04

I wasn’t expecting you or other devs to do this for me, I will try to tackle it, I’ve spent a couple of hours reading the code and it’s very well commented so I’ll give it a try

> On 4 May 2020, at 17:41, bdring wrote:
>
>
> You would have to add them to the firmware. It is not very common to add arrays of lights to CNC machines.
>
> GrblESP32 has a few commands that branch off to user control. For example tool changing. GrblESP32 does not know how to control your tool changer, but if a user supplied a function to do that, Grbl_ESP32 will optionally pass the tool change information to your function and wait until the function completes.
>
> I suppose that could be done with M100-M199. with that said it is probably a 5-6 hour project for someone very familiar with Grbl to do it right. New modal groups would need to be added, etc.
>
> I can add that to the roadmap, but I don’t think any of the primary developers are going to see that as a priority.
>
> —
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#5 – misan 于 2020-05-05

@iacopo you might want to have a look at Marlin firmware. It has a few of the things you are asking:
1) you can change acceleration values on the fly (only to affect to future moves), but by design, the same value is used for acceleration and deceleration https://marlinfw.org/docs/gcode/M201.html
however, if you split a single movement into a sequence of small moves, each one at a different speed, you can create the illusion of a given acceleration (or deceleration), as motion planning does not need to stop in between moves.
2) you can set values to output pins using g-code https://marlinfw.org/docs/gcode/M042.html
3) you can control RGB lights (WS8212 strips) from g-code too https://marlinfw.org/docs/gcode/M150.html

But, by the sound of it, custom code might be what you need so you have all the flexibility you want, some input to synch with the outer world, and then code that just gives one or more steppers the pulses with the right timing.

#6 – iacopo 于 2020-05-05

@misan Thank you very much for your reply, it seems like you pointed me in the right direction with Marlin firmware.
I’ll try customizing Marlin to my needs.
I gave up with custom coding from scratch because I found out grbl drives stepper motors way more smoothly than the conventional stepper libraries found for arduino.

By the way, adding a $120= line in the gcode works with grbl, so I managed to change the acceleration parameter on the fly emulating a similar effect to the M201 command

#7 – terjeio 于 2020-05-05

@iacopo If you want to use 32-bit processors, such as ESP-32, then my port/rewrite of grbl has the option to use plugin code to extend the M-code range supported – here is a template that can be used as a starting point. Parsing, modal group handling and synchronization (if required) is taken care of in the core so the code required can be quite simple.

Also be aware that changing settings with $-commands will trigger a flash erase/rewrite of the settings area. My port buffers the settings area and by default delays writing until grbl is in a idle state which may help reducing flash wear. Adding a M-code to switch writing to flash on/off is also easy to implement as the write call is passed over a function pointer.