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Why is "touch zero" much faster than any other feed rate?

Software Ground Control
#1

I’m using ground control, and it seems to me that the Z axis moves much faster when touching zero for calibration. Basically, it seems like the motor is free running.
But when you send a “G0” code to bring the bit up, it seems like it’s much slower.
Anybody know why that might be?
how do I get my Z retracts to go “up” as fast as touch zero goes down?
Frankly, it even sounds different. when I’m touching zero, it’s clearly running full out.
when I retract to safe height, it’s almost like it’s trying to hit a specific rate and correcting along the way; much more “buzz/whine” sound for retract than for touch zero, which just a running motor sound.

Also, somewhere in the commands or the status that is displayed in the lower right, it says that the Z-feed rate is 1 or 2mm/min. I know it’s going way faster than that.

thanks!

M

#2

Basically I think you nailed it :grin: The motor can’t track a position at 100% speed, because if it fell behind even a little bit it would never be able to catch up.

That being said there maybe something going on with your z-axis feedrate which could be limiting the speed. I think that there is a setting for that.

#3

okay…so puzzle me this…
why would it run “fast” and not track position as well…during the calibration step?
it seems like running with very high position accuracy would be needed during calibration.

Maybe I should clarify, it runs at full speed on the way Down to touch the plate, and runs slower when retracting after touching.

-M

#4

You can run as fast as possible if you’re trying to hit a wall. Once you hit that wall, though, you want to slowly take steps back so that you know exactly how many steps away you are. You really didn’t care how many steps it took to get to the wall just that you got there. You also tend to walk slower if you want to get one step away from the wall and not hit it.

The Maslow is doing the same thing. It can move as fast as possible until it gets that electrical signal. It didn’t need to count the encoder steps along that path. But, once zero was found, it needs to count the number of steps it is taking and does it slower to make sure that it doesn’t miss a step.

1 Like
#5

that makes sense.

#6

What Z mechanism do you have? There have been several on maslows, ranging from separate screw actuated router carriers that tend to be relatively speedy, to motors attached directly to the router’s own adjuster (on the original Ridgid routers) that tend to lose races with thick molasses.

#7

I have the maker made version that drives the Rigid router base’s own adjuster screw.

However, what I’m wondering about is why during certain operation it is very fast and others not so.
So…comparing it’s own performance to itself during different operations.

don’t get me wrong…upgrading to a C-beam style Z axis is on my upgrade list, but I’m not there yet.
First a better chain slack system…still running the bungee cords almost a year into it…

-M

#8

in the gcode there is a feed rate setting that tells it how fast to move.

and in the maslow settings there is a max feed rate that the machine will try to
go.

David Lang

1 Like
#9

What is the feedrate coded into the “touch zero” funtion for Z-axis? (ground control) is it the same as the max feedrate?
The status box in the lower right seems to indicate 1mm/min, but I know it’s going much much faster while it’s going down to touch zero. it’s the fastest i’ve ever seen my z-axis motor move.