Marlin Motion Related Configuration.h Settings for MakerFarm i3v

[printbus]

UNDERSTANDING ACCELERATION
No demonstration or conclusions in this post. For those that need it, this provides a basic explanation of acceleration. Those that are already comfortable with it can roll their eyes and go back to what they were doing.

Assume an object with a fixed linear speed. Acceleration describes how rapidly the speed is changed. If the speed is going up, acceleration is positive. If the speed is going down, the acceleration is negative, and is usually called deceleration. A high acceleration leads to a rapid change in speed. Low acceleration leads to a slower change in speed.

For our printers, the acceleration units could be stated as something like mm/sec^2, mm per squared seconds, or mm per seconds squared. In this thread, I've been consistent at describing the Marlin acceleration units as mm/sec per second, since I find that to be the best way to describe them. Speed is given in mm per second, or mm/sec. Acceleration is an amount of speed change, in mm/sec, that will occur for every second of duration. Or mm/sec per second.

EXAMPLE: An object is at rest and accelerated at 10 mm/sec per second. After one second, the object is moving 10 mm/sec. After two seconds, the object is moving 20 mm/sec. After three seconds, the object is moving 30 mm/sec. And so on.

Now consider a printer axis capable of 500 mm/sec per second acceleration and a maximum axis feed feed rate of 100 mm/sec. The axis will accelerate rapidly from a dead stop and quickly hit the maximum feed rate of 100 mm/sec. The speed stops increasing, and the axis continues moving at the 100 mm/sec limit.

The post describing the Marlin jerk settings demonstrated how a low jerk setting in one axis can dominate over higher jerk settings for other axes in a three-dimensional move. The same applies to acceleration settings. The rate at which Marlin accelerates from a point will be affected by the lowest of the acceleration settings for the axes involved in the movement.

As with the jerk settings, the farther apart the axis acceleration settings, the more this limitation can come into play. Again, without knowing enough about Marlin move planning to think otherwise, this suggests a premise that acceleration settings are best set to the same value or the at least the same ballpark.

Reiterating a point mentioned on the prior recap post, Marlin has two acceleration settings in the configuration.h file. DEFAULT_MAX_ACCELERATION has terms for specifying an acceleration for each axis. DEFAULT_ACCELERATION has a single value. Look at these as just two ways to control the acceleration, with separate gcodes. The acceleration used will be the lowest value that from the two. The MakerFarm default for DEFAULT_ACCELERATION is 500 and DEFAULT_MAX_ACCELERATION is {1000,1000,5,1000} for X,Y,Z and E. Based on the lower values between the two, the acceleration terms used will be 500, 500, 5, and 500 mm/sec per second for X, Y, Z and E respectively.