can't change arm_radius (aka delta radius)

Controllers Smoothie
1

IRC has been helpful but I wanted to capture this so I don’t have to repeat it multiple times!

After struggling with a hardware issue (fixed on Friday) and various issues with bad end stop switches, etc I am now back on track. But I’m running into an issue.

This is a new mini kossel build. At this point everything is wired and working. I’ve actually made a few poor prints over the past few weeks as I discovered the above mentioned issues. Yesterday the guys on IRC (thanks) helped through some endstop issues. I am now in the process of calibrating.

So using minow’s delta calibration guide - which I know inside and out since I’ve been using delta printers for almost 18 months - I’ve completed steps 1 and 2. The towers calibrated to the bed step 2 is dead on and very reproducible. However, I have non planar movement of the nozzle, at X=Y=0 it is 3.5 mm above the bed. “Not a problem” I think to myself, “an easy delta radius calibration”. arm_radius is currently 97mm set in config. Now is where things go bad…

I do not have a config-override file. I use M665 R100 to set the arm_radius to 100mm as a starting point. You add to arm_radius if the nozzle is above the bed. I then home and verify the setting with an M503 - it shows R100 and that there is no config-override file. I then send the nozzle to X=Y=Z=0 to test and it is still 3.5mm above the bed. I do this 4 times with no change. I then edit config and add R100 to it directly. Reboot the smoothie, and verify with M503. Again showing R100 and no override-config. But, sending the nozzle to X=Y=Z=0 to test and it is still 3.5mm above the bed. I then set to R50 just to test a wild situation and I still end up at 3.5 mm above the bed.

So, I grabbed the latest sources this morning and used precompiled firmware.bin. I also started with a new config file from that distribution and updated it with my settings. Restarted the smoothie, home, check config with M503 and it all is correct with R100. And again, the nozzle still ends up 3.5mm above the bed. So I create the over-ride file, and verify and test. Same thing. Reboot with override file, test, again, no change to nozzle height. I’ve set the nozzle height to values < and > than what it is to see if I could get any change and I do not.

I’m either seriously misunderstanding something or something is very odd. This is my new config file taken from the edge this morning and updated with my values: removed since I can’t post links - trust me, it looks fine!

I can change arm_radius to anything reasonable and it does not have an effect on the nozzle height. Also, when I do change arm_radius the towers are all still calibrated properly. Normally, if you tweak the arm_radius the rest of the calibration is affected - it’s an iterative process.

Any ideas? I’m at my wit’s end!

cheers,
Michael

Imported from wikidot

2

let’s try this for the config file: pastebin(dot)com/0a1RczF3

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Well, I wanted to follow up from what I just learned on the IRC. The arm_radius works differently than the equivalent delta_radius in the Marlin and Repetier firmwares. In those cases, changing delta_radius affects the height of the nozzle above X=Y=0. arm_radius in smoothieware works differently and there is no documentation that I could find to describe this difference. Changing arm_radius changes the relative height of the nozzle at the center and perimeter positions. In fact, it leaves the center unchanged and changes the height above the bed at the perimeter (for instance at each of the tower bases). I haven’t had a chance to calibrate now that I know this but it clarifies what I was seeing.

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It doesn’t actually work differently at all. Not sure why you got the results you did however if you follow the Minow method of manual calibration it would have worked perfectly…

Quote from Minow blog…

“In order to correct low-center, DELTA_RADIUS must be increased. In order to correct high-center, DELTA_RADIUS must be decreased. Adjust your firmware accordingly, re-compile and upload. Now, go back and re-adjust your tower heights using the three tower buttons, and check the center z height with the fourth button. The condition should be better…”

Note that it explicitly states you need to retest the tower bases first, then the center. If you did this then you would have seen the low/high center changing.

5

Really sorry about the confusion. You are indeed correct and I’m an idiot. I’ve been at this for a while and coupled with a bunch of other frustrating things going on, just had a complete brain fart. I even have my note book from 18 months ago where I drew pictures with arrows and annotations when I calibrated my first delta.

One good thing to report though, there was a new video posted this weekend on calibrating a kossel with smoothie ware: search “Manual Delta Calibration using M665 and M666” (I still can’t post links, probably beset given my mental state of affairs!)