"Flow Rate Settings (float)"

Summary:

what is Flow Rate Settings (float) = 4.47 mean?

"Flow Rate Settings (float)"

conceivecreate 01 Aug 2012 02:54

Reading through Dave Durant blog
(http://davedurant.wordpress.com/2010/11/06/configuring-skeinforge-making-a-new-profile/) on adjusting Skeinforge 33, I noticed he talked about “Flow Rate” with a value of 255 under tab “SPEED”. I am using Skeinforge 35, but I have a parameter “Flow Rate Settings (float)” under tab “SPEED” which was defaulted at 4.47. Additionally, under the explanation on Flow Rate Settings (float), it says “Extrusion rate - defines how fast the extruder will push the filament trough. RapMan use this parameter to define RPM of the extruder motor. The extruder motor RPM is flow rate / 10 so if your flow rate is 150.0 that will set the extruder stepper to run at 15 RPM”

Can someone explain what does Flow Rate Settings (float) = 4.47 mean?
does this mean that my extruder is running at 4.47/10 = 0.447 rpm?

Re: "Flow Rate Settings (float)"

Jetguy 01 Aug 2012 19:07

Old extruders such as the MK3,4, and MK5 used a DC gear motor and PWM controls 0-255 with 255 being the motors max which resulted in about 2.98rpm at the actual shaft driving the filament. With a 0.5mm nozzle, this results in a required feed rate (the rate the platform moves relative to the nozzle, or in other bots, vice versa)of around 32mm/s. Basically, think of it as laying a bead of caulk and in order for the bead to stay round and not stretch, the flow rate (how fast it comes out of the nozzle) and feedrate (how fast the nozzle moves relative to the surface) must match exactly.
The DC motors were prone to failure often taking the PWM H-Bridge chip out with it. This continued into the first batches of T-O-Ms which is what I have. The community came up with several extruder firmware hacks converting PWM values into step pulses to drive a stepper driver and motor to replace the DC motor. Makerbot then released the first official stepper extruder upgrade as the MK6 and due to the now offically supported stepper formwat, the new firmware uses the same M command, but the value is seen as RPM and the firmware knows how many steps to send the stepper driver to make a full rotation.
Thus you are seeing the old way where we always used the value of 255 (AKA MAX RPM, AKA 2.98RPM) To adjust the flowrate/feedrate ratio, we adjusted feedrate since flowrate was fixed.

Thus this part :

RapMan use this parameter to define RPM of the extruder motor. The extruder motor RPM is flow rate / 10 so if your flow rate is 150.0 that will set the extruder stepper to run at 15 RPM”

Completely ignore as that only indicates Rapman (a completely different extruder than anything you've seen) used a 10:1 ratio internally. The 150 is the percentage between 255 and 0. It has little meaning because the other problem with PWM is that no two motors would run the same speed at PWM less than 255 and even in the same print job, it might vary. DC motors were not good and thus the entire shift to steppers.

All you need to know now is that 4.47 is 4.47 RPM.

Last edited on 01 Aug 2012 19:16 by Jetguy Show more

Re: "Flow Rate Settings (float)"

Jetguy 01 Aug 2012 19:41

For example, in reading that page-it's historical and has some gotchas:
The only nozzle size at that time was 0.5mm, we now have 0.4 and 0.3mm
The motor was PWM so 255 PWM is the same as 2.98RPM in modern stepper extruders

Thus, this chart only applies for a 0.5mm nozzle and 2.98 flowrate
3mm filament!!!! not 1.75 (AKA MK7, MK8)
Layer Height Width/Thickness Feed Rate Flow Rate
0.25 1.8 49.50 255
0.25 1.6 60.00 255
0.28 1.8 44.00 255
0.28 1.6 49.75 255
0.28 1.4 54.25 255
0.28 1.2 61.50 255
0.32 1.6 34.25 255
0.32 1.4 42.25 255
0.32 1.2 51.75 255
0.32 1.0 60.50 255
0.35 1.4 34.25 255
0.35 1.0 46.25 255

Know that this is very old info and most of these calculations are handled by print-o-matic.
This is the newer info and probably better guide to be using:
http://makerblock.com/profilemaker/

Last edited on 01 Aug 2012 19:43 by Jetguy Show more