Firmware Question Taz 4

General Software
#1

I have a quick question regarding the default firmware for the Taz 4.

I noticed that on the Q3 firmware the default firmware has the following lines of code:

#define HOMING_FEEDRATE {50*60, 50*60, 8*60, 0}  // set the homing speeds (mm/min)

// default settings

#define DEFAULT_AXIS_STEPS_PER_UNIT   {100.5,100.5,1600,866}  // default steps per unit for TAZ {X,Y,Z,E} 
#define DEFAULT_E1_STEPS_PER_UNIT     800                    // default steps per unit for second extruder (800)
#define DEFAULT_MAX_FEEDRATE          {800, 800, 8, 50}      // (mm/sec)
#define DEFAULT_MAX_ACCELERATION      {9000,9000,100,10000}  // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for skeinforge 40+, for older versions raise them a lot.

My questions are:

HOMING_FEEDRATE
I have seen some users lower the Z homing_feedrate values from what is indicated. For example i’ve seen 480 & 380 from some…
Does this help prevent the printer from missing steps while performing Z homing? I have noticed that occasionally the Z Axis will stall but only while homing. All other print moves seem to function normally.

DEFAULT_AXIS_STEPS_PER_UNIT
For this the defaults of {100.5,100.5,1600,866} do not match the values printed on my acceptance record (Specifically the Z value. I understand the variance for the E value. The acceptance record uses a value of 400 for Z vice the indicated 1600. When 400 is placed there the Z axis does not move correct distances. For example when commanding it to move 100mm it only moves ~20ish? what value plays a factor for this offset? With 1600 written to firmware it appears to move correct distances to the best of my measurement capabilities, but why?

DEFAULT_MAX_ACCELERATION
Lastly what is considered an accelerated start movement? this value seems consistent across multiple users but I do not fully understand what it means.

#2

Slowing down the Z axis homing rate can help ensure smooth movement.

We increased the microstepping amount and thus had to increase the steps per unit to compensate in a later version of the firmware.

#3

Lastly what is considered an accelerated start movement? this value seems consistent across multiple users but I do not fully understand what it means.

I can only assume that it is the absolute maximum amount of acceleration that could occur. I’m assuming that it is in mm/s^2 but it could be in mm/min^2 but that seems slow. These don’t really matter too much to the average user. what you should be concerned with are–as you mentioned–extruder steps and the acceleration that is set a couple of lines further down. The default value is 500.