More like…
G90 ; absolute mode
G1 X5 ; go to X=5
G1 X5 ; should not move.
G91 ; relative coordinate mode
G1 X5 ; go to X=10
G1 X5 ; go to X=15
Yes, G90 put the coordinate system in absolute mode. X, Y and Z are then always based on distance from the origin.
G91 is relative mode, so coordinates are based on distance from the current (or at least last commanded) position.
Cncjs is great. Not spam.
Thanks @SupraGuy , definitely the coordinate system mode. g91 worked as I was expecting. Although I didn’t need to use the g in front of the movement. Just the x and distance.
I now have it all calibrated for x and y
Z is a bit of a different monkey. The current grbl firmware I’m using only allows for up or down not a specific angle. Which is ok, I just need to adjust the geometry of the pen arm so it doesn’t travel up too high.
I’m also using a rubber band to hold it down, but getting the right tension is tricky. too tight and it slams down. I might look into a method to add a spring instead and a way to adjust the position of the spring for more or less tension.
@jeffeb3 , I agree. Cncjs is really nice. I just went a tries it and ignored the windows defender warning.
So speaking of pen up/down control.
the grbl firmware I’m using only controls up or down, but not speed or angle.
Angle is not an issue, I have modified my geometry to work with the servo arm and angle range.
the speed is an issue.
currently I’m using a rubber band to hold the pen down. So when the servo arm go down the pen slams down. Now, with my new geometry the travel of the arm holding the pen is less, so I do need to see how that works and if it is as much of an issue.
But it would be really nice if I could control the speed of the servo arm through the range. Even better would be able to control the angle of the arm, but lets start with speed.
it does seem doable based on what I am reading here.
https://www.reddit.com/r/hobbycnc/comments/122kbjl/arduino_grbl_servo_control_precision/
this post references this grbl firmware, which I will download and compare with what I have.
I would love to figure this out, but I do lack coding knowledge and experience of all this so I could use some help. I do want to learn it though.
step 1 - what firmware changes do I need, or is the one above what I should use and change too.
step 2 - what do I need to do in post processing that controls the speed. I think this is the biggest gap I am seeing now. the articles talk about what gcodes to use (M3Sxx), but how do I get them in the final file? Manually add them in or is there an automated method in PP, or can it be done in cncjs?
FYI, this is the current grbl firmware I’m using.
So I successfully plotted the first gcode using a pen. now I need to set up the drag knife for vinyl cutting.
One thing I am noticing is that my X axis stepper (driving the belt) is getting really hot. I can only touch i for about 2 seconds. but the motor for the y axis (roller) is just fine.
any thoughts for this?
could I have the belts too tight increasing the amount of torque needed to turn it? seem odd, but just making a guess.
other thoughts?
Here is a video of the first gcode plot.
I do need to find a solution to support the servo wire. I just need to get some material for it.
Very nice and interesting pen plotter.
For the cablo to servo don’t you like the “tape measure trick” solution discussed in the forum a few years ago? Better than a cable chain?
Yeah, I like the tape measure trick and should work fine. I’m trying to think of something similar but maybe a little cleaner looking.
update for this issue.
I realized I was using a 24v power supply and my stepper motors are rated for 12v. I used a 12v supply and so far no issues getting too hot.
What current do you have it set at? What specific stepper is it? I would keep turning down the current until the stepper stays under 50C.
Ahhhhhhhh, ummmmmm 
I have no idea. and every EE and any kind of engineer out there is going to shake their head at me 
I’ll need some guidance on how to find the current and change the setting - sorry.
this is the stepper I have.
I see the old school board you are using above but no drivers. So I suspect you are using a49’s or drv8825. Those have a little tiny pot you need to adjust. Start at about .7V
yeah, I’m using the A4988s. its what I had on hand from a project I never did a few years ago.
Sooooo, if I’m going to set it at .7v I suppose I would need a method of measuring that huh?
Suggestions for a moderately priced multimeter?
is there such a thing as a good one under $20?
Is there such a thing as steps/mm being different depending on the direction the motor is moving. I shouldn’t think so, but I ran a long test (1400mm - standard cricut vinyl rolls are 5’). In one direction I’m 5mm short. On the return direction I’m 1mm short.
The only other thing and more probable is the paper slipping or stretching. Paper is not entirely the most dimensionally stable medium.
Oh yeah, any meter will work great. HF might even have them for $5. Normal stuff like voltage and low current are easy.
nope.
I have a large roller cutter like this and the feed rollers have a ton of pressure. I would increase the pressure as mush as you can after that lower the acceleration as far as you can stand.
Cool, I found one for $12 on Amazon with very hi reviews and ratings.
Good idea.bi may need to resign that part to gain more tension.
A cheap multimeter will do fine for that. The expensive ones usually have other features you likely do not need
Or a more “sticky” roller.
That’s an option too.
He’s the one behind fluidnc or a major part of it right?
I did look to see if there were any servo capable boards for fnc and there are some, but looked kinda clunky.
There was one particular board though that looked a bit more refined and mentioned to reach out to him. I might look into that for another similar project - I want to make a version of this large enough for a 20"x30" foam board and attach a needle cutter to it.
So I was watching that video more. Its really cool, how many different ways people can imagine the same thing and build it. I’ve looked at 3 different versions before I started mine and chose one as an inspiration; and I feel I changed it quite a bit. and here is yet another way.
I really like his simplicity - looks like a single linear rod and the carriage is weighted on the pen side. the the pen lift mechanism is similar to another version I saw. The roller arms pivot about the carriage linear rod and connected across by another rod and held down by springs. this too is similar to one of the three I looked at but did not pivot about the linear rod.
Man, now I’m starting to rethink mine. I won’t do it because I’m so far, but maybe in the future.
