marlin feature request / idea: speedometer (gcode command that returns the current speed)

I've been playing with various acceleration and jerk settings, and have been using the M220 command to set the speed factor during a print, but I'm not sure how to find out the cumulative effect of all of these interrelated settings. I was just thinking it'd be neat to be able to send a gcode to get a report of the current speed. It'd probably report the X and Y, and Z speeds separately, as that would require less calculation than coming up with a dot product (or maybe it could display the X and Y speeds display on LCD). I'm kind of surprised such a function isn't already part of gcode (maybe it is and I just haven't discovered it).

Has anyone else thought such a feature would be useful? Does it already exist? Can anyone offer a tip as to how I might go about adding it to the firmware or care to weigh in on whether or not such a function would be desirable/possible?

Thanks.

You're confused by all the options, so you want to add yet another option? Hmm.

Typically, you set speed with the F command and that's it.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

The ability to set the speed is not the end of the story --does it not interact with several other settings (some of which make calculations based on acceleration) such that it's difficult at any given point to determine at what speed the print head is moving? I just think it'd be nice to be able to get a readout. I'd learn from it.

When I watch a print, I don't know for certain which of my slic3r settings is affecting that part of the print, it's not always obvious whether it's printing a perimeter (180mm/sec), small perimeter (60mm/sec), infill (220mm/sec), top solid infill (50mm/sec), a bridge, etc. And then there's the interaction with the XY jerk setting in the firmware, which is specified in mm/s^2, and other limits. If I set my printer to print at 2000mm/sec, it's not going to go near that speed due to the XY jerk setting as well as the X, Y max speed limits in the firmware. If I had a readout, I could be able to see whether the various limits were keeping the printer from reaching the desired speed, could adjust the limits, and then watch to see how the print is affected. As it is now, I can change my speed settings but at a certain point it becomes difficult to tell by simply watching the printer whether they're having any effect or whether the various limits are coming into play.

You "readout" is the G-code sent to the controller. Printrun/Pronterface (experimental branch) allows you to watch it, if you turn on G-code debugging in the main menu.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

@ Traumflug

I think you are misunderstanding what he is looking for. He would like to know the current step rate divided by the steps per mm at any given time. Not what the gcode has been set too. For reasons such as acceleration never allowing the move to reach the set speed in the Gcode. Or the E steps per mm limiting the move speed, etc etc. Also for when you use all the great features of Marlin that allow you to adjust the print live. Like M220 (speed multiplier) M221 (flow multiplier) being able to adjust the max feed rates live, etc, etc. All of these change the speed of the print without ever adjusting the Gcode F speed.

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I will take a look at the debugging readout. Thanks for the tip.

I still think it would be very useful to be able to get a report of the actual speed of the printhead after the board has interpreted the gcode and subjected it to the speed and jerk limits. Actual speed. Much like one can set and forget the extruder temperature with M104 but it's still useful to have an M105 command to check on it even though, if everything's working properly, M104 and M116 should suffice.