Z motor acting strange at start of print

[Farr0wn3d]

I was helping a guy convert his V4 machine to e3d v6, to be clear its a brand new machine and has the updated z motor and lead screw. so I got all the hardware on the head switched over and did the pid autotune procedure, and proceeded to calibrate it with several calibration prints, which went fine. when I went to leave we set it to print a filament drive body and for whatever reason, during the first few commands of the start script, right at the command when it would go from moving off the bed to lowering the nozzle to 0.4 the z motor would make a sound like its ran into something (that squawk noise I'm sure everyones heard) and wouldnt actually raise the bed to the 0.4 position (I thoroughly checked to make sure its not running into anything, and I can enter the start script manually in the communication window and it works fine). it happened over and over and I couldn't figure out why. what I ended up doing to bandaid the problem was to move the "move to 0.4" command from before the purge to after it, and that made everything okay for whatever reason....

The only thing that comes to mind is that when I did the autotune and updated the values in the firmware (which was the black z motor firmware from the wiki page), that maybe theres a glitch in the firmware that rears it head at that moment? any ideas?

[jsc]

A guess: the Z move is being commanded without an explicit speed, and thus takes effect at the last seen speed, which is too fast. Try putting in an explicit speed at the problem move.

[Farr0wn3d]

Thanks for your reply JSC,

I was curious why it seemed that when I moved the "z to 0.4" command from before the nozzle purge to after it, that the bed raise speed seemed very slow compared to normal, I wonder if it was taking the speed from the nozzle purge command in this case?

I'll keep that in mind

[3dPrintingMD]

Have him start with a clean V4 profile, that will fix it.

[Farr0wn3d]

can you explain your reasoning?

[3dPrintingMD]

All I can say is that if I was to try to use a v3 profile on a v4 machine, i would get the same noise you referenced.

Deleted all profiles, started with a new v4 profile, never an issue again. (I don't remember the exact reasoning).

[Pekish79]

i had the same problem was a wrong acceleration/speed in the code i inserted the wrong number

[Farr0wn3d]

I was actually using the same profile that I use on my machine with my v6. I uploaded all my personal profiles when I did the work.

[Pekish79]

depend from the firmware if ur machine has an older one maybe a command is changed in the recent firmware the most noticeable is:

Marlin notes: After Mar11-2015, the M204 options have changed in Marlin:
P = Printing moves
R = Retract only (no X, Y, Z) moves
T = Travel (non printing) moves

The command "M204 P800 T3000 R9000" set the acceleration for printing movements to 800mm/s^2, for travels to 3000mm/s^2 and for retracts to 9000mm/s^2.
M204 Repetier
M204 X[Kp] Y[Ki] Z[Kd] -
Set PID parameter. Values are 100*real value.

Before S normal moves T filament only moves and T was used to speed up acceleration in retraction often people switch from the 3000 defaul to 9000


so if in ur machine you use M204 T9000 and copy that in a new machine with the new firmare that will make the travel accelleration 9000 not the retraction
this is why mine was doing that weird noise just exactly in the same position u mention.

[Farr0wn3d]

I think you have it exactly right! I recall being annoyed that the carriage seemed to be whipping around in its travel movements before the print began. This makes much more sense now. Thank you very much Pekish79