Smoothie reads G-code instructions and converts those into movement, typically by turning motors.
While that might sound pretty trivial to do, the laws of physics actually make this a bit more challenging than one might expect.
This page explains how to configure the different motion control parameters you can tune in Smoothie.
Or “the increase of speed”. You experience it every day.
When you ask Smoothie to move a certain distance at a certain speed, it starts at a speed of 0 (not moving).
If it goes instantly to the requested speed, in most cases, that won’t work: A motor cannot go from a speed of 0 to several rotations per second instantly.
It needs to accelerate to that speed.
Similarly, the axis which is controlled itself has a given weight that needs to be moved.
The faster you accelerate, the more force is required to accelerate the mass to the target speed.
This means that for any given machine, you must tune your acceleration.
And that acceleration’s value is a function of the torque of your motors and the weight of whatever needs to move.
You set the acceleration value by modifying the acceleration value in your configuration file:
acceleration 3000 # Acceleration in mm/second/second.
[motion control]
default_acceleration = 3000.0 # Acceleration in mm/second/second
The units are millimeters per second per second, which means how many “millimeters per second” worth of speed is added every second.
3000 is a pretty common value for a 3D printer or laser cutter since they have very little mass to move.
200 is a common value for CNC mills or routers since they have much more mass to move and have to apply forces to their tool.
There is no mathematical/easy way of determining a perfect value: you are going to need to try values and find the one that works best for you.
If you feel like your machine is too slow, you increase acceleration.
If your machine starts losing steps, losing its position, or shakes too much, you reduce acceleration.
Note that you do not need to reset your Smoothieboard to try new values.
You can start a “job”, and while the job is executing, try new values using the
For example,
gamma.acceleration value.
Smoothie accelerates when it starts a move and decelerates when it stops the move.
But what about if you move forward, then need to move somewhat to the right?
Do you really want to decelerate to a speed of zero before moving to the right?
That’d be a huge waste of time.
Junction deviation determines how much to slow down, proportional to how much the direction changes.
It doesn’t really have a unit, it’s just an arbitrary ratio.
The smaller junction deviation is, the more we slow down on direction changes.
The larger it is, the less we slow down on direction changes.
This generally means you can configure how much the machine “shakes” when moving: The less the machine slows down when changing direction, the more force is transferred to the structure of the machine, and the more the machine will shake.
But the more sturdy the machine it is, the higher junction deviation it will be able to handle without shaking.
Like acceleration, this is a value you will have to “play with” to find the right value for you.
You change it by changing the junction_deviation value in config.
junction_deviation 0.05 # Similar to the old "max_jerk", in millimeters
[planner]
xy_junction_deviation = 0.05 # Similar to the old "max_jerk", in millimeters
0.05 is a typical value for a 3D printer.
If your printer is very sturdy, you could use 0.1.
0.005 is a typical value for a CNC mill or router, though for some machine you might need to go to smaller values like 0.001.
You can learn more about Junction Deviation in this forum post.
Where speeds are concerned, Smoothie makes the distinction between two very important things: axes and actuators.
An actuator and an axis are two different things.
An actuator is the thing that the motor causes to move directly.
The axes are pretty much the coordinate system for the “tool”, and the system the Gcode uses.
On a cartesian machine, they are the same thing (X is alpha, Y is beta, etc. See Greek_alphabet).
But on a linear delta machine, for example, they are different.
On a linear delta, the actuator is the linear axis that moves along a tower, while the axis (or effector) is the thing at the end of the arms that moves the tool.
In Smoothie, you can set maximum speeds for both of those systems separately.
Setting a maximum speed ensures that Smoothie will never go higher than that speed for that axis or actuator.
This is useful if the machine would “skip” steps or have other problems if too high a speed was required, which is the case in most machines.
To set the maximum speed for an axis, edit the max_speed configuration option for that axis:
x_axis_max_speed 30000 # mm/min
The units for the speed limit are millimeters per minute.
To limit the speed for an actuator, set the max_rate for that actuator:
alpha_max_rate 30000.0 # mm/min
[actuator]
x.max_speed = 30000 # mm/min - axis max speed
alpha.max_rate = 30000.0 # mm/min - actuator max rate
The units for the speed limit are millimeters per minute.
You can adjust the Z while it is printing by using the WCS offsets.
For instance, to raise the head 0.1mm:
A better and easier way is in the very latest edge build.
It can be canceled with
If you want to do baby steps from the panel menus, you can easily do this using the custom_menu (see panel) feature of panels:
custom_menu.babystepup.enable true #
custom_menu.babystepup.name Baby step up #
custom_menu.babystepup.command G43.2 Z0.05 #
custom_menu.babystepdown.enable true #
custom_menu.babystepdown.name Baby step down #
custom_menu.babystepdown.command G43.2 Z-0.05 #
Here are all the options related to motion control:
| V1 Setting | V2 Setting | Description |
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Default rate for Overridden by the first |
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Arcs are cut into segments (lines) — this setting is the maximum error allowed for the line segments that divide an arc. Controls arc segmentation quality versus performance, using adaptive segment sizing. |
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Lines can be cut into segments — generally not useful with cartesian-coordinate robots — this setting sets the maximum length of any given segment; segments longer than this are cut into several shorter ones. When set to Essential for delta robots to maintain accuracy. |
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Instead of cutting lines into segments based on distance, cuts them based on time: segments are sized so that Smoothie executes about Mostly useful with When set to a non-zero value, overrides |
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Defines how many blocks (line segments) are stored in RAM for look-ahead acceleration calculation. Do not change this unless you know exactly what you are doing. Increasing the queue size uses more RAM and can cause Smoothie to run out of memory, depending on your configuration and how much the rest of your modules already use. Larger values allow better speed optimization through corners but consume more memory. |
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Acceleration, in millimetres/second/second — the rate at which the machine accelerates and decelerates during moves. Higher values make the machine faster and shakier; lower values make it slower and sturdier. Generally proportional to the weight of the tool being moved. Can be overridden using |
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Specific acceleration for Z axis movements. When set to a valid number, overrides the default When set to The Z axis often benefits from lower acceleration than XY, to prevent layer artifacts. |
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Acceleration in millimetres/second/second for the alpha actuator (X axis on cartesian). Do not set on deltas. When set to a valid number, overrides the global default |
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Acceleration in millimetres/second/second for the beta actuator (Y axis on cartesian). Do not set on deltas. When set to a valid number, overrides the global default |
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Acceleration in millimetres/second/second for the gamma actuator (Z axis on cartesian). Do not set on deltas. When set to a valid number, overrides the global default |
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Similar to the old "max_jerk", in millimeters — defines how much the machine slows down when decelerating, proportional to the vector angle of the change in direction. See here and here. Lower values mean being more careful; higher values mean being faster with more jerk. Replaces traditional "jerk" settings with a more mathematically sound approach. |
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Junction deviation for Z only moves.
Do not set this value if you use a delta arm solution. |
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Sets the minimum planner speed, in millimetres/sec — the lowest speed the planner will ever set a move to. Not generally useful. Prevents extremely slow movements that could cause stepper stalls or uneven extrusion in 3D printing. When set to |
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Duration of step pulses to the stepper motor drivers, in microseconds. The actual step pulse is generally 2µs above this value (so Setting this over about 8µs will cause severe issues with step generation. Some stepper drivers require a minimum pulse width to reliably register steps — check your driver datasheet for its "Step Pulse Width" specification and set at least 2× that minimum for reliability. Use |
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Base frequency for stepping — higher values give smoother movement. Do not modify unless you know exactly what you are doing; This is the fundamental rate at which the step generation interrupt runs — all step generation is derived from it through integer division. The maximum step rate per motor equals Higher frequencies increase interrupt load and may affect response time for other operations. |