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Endstops

End-stops are small interrupters that you put at the end of each of your axes. When you boot your machine up, Smoothie has no way of knowing the position of each axis. When it starts a print, Smoothie moves the axis until it touches that interrupter, and when it is hit, it declares that that is position 0 for that axis. And does so for all axes.

This allows Smoothie to then precisely know where everything is relative to that initial position. It is quite convenient as it saves you the hassle of actually moving the machine into that position when you want to start a print. Automation is great.

However, end-stops are not necessary, you could do without them. They are just so convenient that most machines use them.

End-stops can also be used as Limit Switches which prevent the machine from attempting to move beyond the physical limits of the axis (by pausing/stopping movement when triggered), see the Endstops page for details about configuring Smoothie to use End Stops as limit switches.

NOTE Smoothie does not allow you to use a zprobe as an endstop. An endstops must be dedicated to being an endstop and cannot be used as a zprobe and vice versa.

smoothieboard-endstops.png

Endstop Wiring

This will concentrate on the most common type of end-stops : the mechanical ones. Other types exist like optical or hall-o sensors, see the dedicated appendixes for those.

TODO : Do those appendixes

Fancy Smancy

There are plenty of fun and futuristic endstop types around : optical, laser, magnetic, force-sensitive, infrared, inductive, etc…

However, please note that the general feedback from the community, is that most of those are either less precise, less repeatable, or much more difficult to get to "work right", compared to the classical "mechanical" endstop.

The mechanical endstop is actually likely the most precise, repeatable and easy to get to work option you have at your disposal. Just because these other options exist and have been explored by the community, does not mean they are better.

You might happen have a good reason to use a fancy endstop, but if you don't, it's likely a good idea to stick with a mechanical one.

Mechanical end-stops are simple interrupters : when not pressed, they do not let the current pass, when pressed, they let the current pass. By connecting a digital input pin on the Smoothieboard to the interrupter, and connecting the other side of the interrupter to Ground, the Smoothieboard can read whether or not it is connected to Ground, and therefore whether or not the end-stop is pressed.

Most mechanical end-stops have 3 connection points, to which you have to attach your wires :

  • C : Common
  • NO : Normally Open, meaning it is not connected to C when the interrupter is not pressed, and connected to C when the interrupter is pressed.
  • NC : Normally Closed, meaning it is connected to C when the interrupter is not pressed, and connected not to C when the interrupter is pressed.
endstop-basic.svg

Wiring a basic NC endstop

You want to connect the Signal ( green in the schematic ) and Ground ( blue in the schematic ) pins for the end-stop on the Smoothieboard, to the C and NC connection points on the end-stop.

For each endstop, we connect C to Signal and NC to Ground because this means the digital input pin ( endstop connector ) will be connected to Ground in it's normal state and cut from Ground when the button is pressed. This approach is less prone to noise than the reverse. See here for more information.
Another positive effect of this approach is, that if a wire breaks for some reason you get the same signal as if the endstop is pressed. That makes sure that even with a damaged wire you are not able to overrun the endstop.

Order is not important as polarity is not important here.

Make absolutely sure that you do not connect VCC ( red ) and GND ( blue ) to a mechanical (microswitch) endstop! Depending on your wiring that may fries your smoothieboard instantly or when the switch gets pressed. There is a wiring where this not happens and you switch the signal between VCC and GND, but if you're not careful enough you damage your board.

You want to connect your X end-stop to the X min pins, Y end-stop to the Y min pins, and Z end-stop to the Z min pins.

Testing

The default configuration most probably already has everything you need : the pins are already correct and the default speeds are reasonable.

Once they are wired, you can test your end-stops.

To do this, reset your Smoothieboard, then connect to it using host software like Pronterface or the web interface.

Now connect to your Smoothieboard over the serial interface. Power your machine on by plugging the PSU into the wall.

Now in Pronterface, home one axis by clicking the small "home" icon for that axis. Begin with X, then Y, then Z.

If your axis moves until it hits the end-stop, then stops when it hits it, moves a small distance back, then goes a bit slower back to the end-stop and stops, that end-stop is working fine.

On the other hand, if the axis moves a small distance in the wrong direction, then stops, you have a problem : your Smoothieboard always reads the end-stop as being pressed. So when you ask it to move until the end-stop is hit, it reads it immediately as pressed and stops there.

Another problem can be that the axis moves and never stops, even after the end-stop is physically hit. This means your Smoothieboard actually never reads the end-stop as being pressed.

There is a command that allows you to debug this kind of situation : in Pronterface, enter the "M119" G-code.

Smoothie will answer with the status of each endstop like this :

X min:1 Y min:0 Z min:0

This means : X endstop is pressed, Y and Z endstops are not pressed.

Use a combination of this command, and manually pressing end-stop, to determine what is going on.

If an end-stop is read as always pressed, or never pressed, even when you press or release it, then you probably have a wiring problem, check everything.

If an endstop is read as pressed when it is not, and not pressed when it is, then your end-stop is inverted.

You can fix that situation by inverting the digital input pin in your configuration file. For example if your X min endstop pin is inverted, change :

alpha_min_endstop                            1.28^

To :

alpha_min_endstop                            1.28^!

Here is the exact mapping of pin names to inputs on the Smoothieboard :

Endstop X MIN X MAX Y MIN Y MAX Z MIN Z MAX
Config value alpha_min alpha_max beta_min beta_max gamma_min gamma_max
Pin name 1.24 1.25 1.26 1.27 1.28 1.29

More information can be found here. http://smoothieware.org/endstops

Configuration

The config settings for Endstops are as follows :

Option Example value Explanation
endstops_enable true The endstop module is enabled if this is set to true. All of it's parameters are ignored otherwise.
corexy_homing false Set to true if this machine uses a corexy or a h-bot arm solution
delta_homing false Set to true if this machine uses a linear_delta arm solution
rdelta_homing false Set to true if this machine uses a rotary_delta arm solution
scara_homing false Set to true if this machine uses a scara arm solution
alpha_min_endstop 1.24^ Alpha ( X axis or alpha tower ) minimum limit endstop. Set to nc if not installed on your machine.
alpha_max_endstop 1.25^ Alpha ( X axis or alpha tower ) maximum limit endstop. Set to nc if not installed on your machine.
alpha_homing_direction home_to_min In which direction to home. If set to home_to_min, homing ( using the G28 G-code ) will move until it hits the minimum endstop and then set the current position to alpha_min. If set to home_to_max, homing will move until it hits the maximum endstop, and then set the current position to alpha_max
alpha_min 0 This gets loaded after homing when alpha_homing_direction is set to home_to_min and the minimum endstop is hit.
alpha_max 200 This gets loaded after homing when alpha_homing_direction is set to home_to_max and the maximum endstop is hit.
alpha_max_travel 500 This determines how far the X axis can travel looking for the endstop before it gives up
beta_min_endstop 1.26^ Beta ( Y axis or beta tower ) minimum limit endstop. Set to nc if not installed on your machine.
beta_max_endstop 1.27^ Beta ( Y axis or beta tower ) maximum limit endstop. Set to nc if not installed on your machine.
beta_homing_direction home_to_min In which direction to home. If set to home_to_min, homing ( using the G28 G-code ) will move until it hits the minimum endstop and then set the current position to beta_min. If set to home_to_max, homing will move until it hits the maximum endstop, and then set the current position to beta_max
beta_min 0 This gets loaded after homing when beta_homing_direction is set to home_to_min and the minimum endstop is hit.
beta_max 200 This gets loaded after homing when beta_homing_direction is set to home_to_max and the maximum endstop is hit.
beta_max_travel 500 This determines how far the Y axis can travel looking for the endstop before it gives up
gamma_min_endstop 1.28^ Gamma ( Z axis or gamma tower ) minimum limit endstop. Set to nc if not installed on your machine.
gamma_max_endstop 1.29^ Gamma ( Z axis or gamma tower ) maximum limit endstop. Set to nc if not installed on your machine.
gamma_homing_direction home_to_min In which direction to home. If set to home_to_min, homing ( using the G28 G-code ) will move until it hits the minimum endstop and then set the current position to gamma_min. If set to home_to_max, homing will move until it hits the maximum endstop, and then set the current position to gamma_max
gamma_min 0 This gets loaded after homing when gamma_homing_direction is set to home_to_min and the minimum endstop is hit.
gamma_max 200 This gets loaded after homing when gamma_homing_direction is set to home_to_max and the maximum endstop is hit.
gamma_max_travel 500 This determines how far the Z axis can travel looking for the endstop before it gives up
homing_order XYZ Optional order in which axis will home, default is they all home at the same time, if this is set it will force each axis to home one at a time in the specified order. For example XZY means : X axis followed by Z, then Y last. NOTE This MUST be 3 characters containing only X,Y,Z or it will be ignored
alpha_limit_enable false If set to true, the machine will stop if one of the alpha ( X axis or alpha tower ) endstops are hit
beta_limit_enable false If set to true, the machine will stop if one of the beta ( Y axis or beta tower ) endstops are hit
gamma_limit_enable false If set to true, the machine will stop if one of the gamma ( Z axis or gamma tower ) endstops are hit
alpha_fast_homing_rate_mm_s 50 Speed, in millimetres/second, at which to home for the alpha actuator ( X axis or alpha tower )
beta_fast_homing_rate_mm_s 50 Speed, in millimetres/second, at which to home for the beta actuator ( Y axis or beta tower )
gamma_fast_homing_rate_mm_s 4 Speed, in millimetres/second, at which to home for the gamma actuator ( Z axis or gamma tower )
alpha_homing_retract_mm 5 Distance to retract the alpha actuator ( X axis or alpha tower ) once the endstop is first hit, before re-homing at a slower speed.
beta_homing_retract_mm 5 Distance to retract the beta actuator ( Y axis or beta tower ) once the endstop is first hit, before re-homing at a slower speed.
gamma_homing_retract_mm 1 Distance to retract the alpha actuator ( Z axis or gamma tower ) once the endstop is first hit, before re-homing at a slower speed.
alpha_slow_homing_rate_mm_s 25 Speed, in millimetres/second, at which to re-home for the alpha actuator ( X axis or alpha tower ) once the endstop is hit once.
beta_slow_homing_rate_mm_s 25 Speed, in millimetres/second, at which to re-home for the beta actuator ( Y axis or beta tower ) once the endstop is hit once.
gamma_slow_homing_rate_mm_s 2 Speed, in millimetres/second, at which to re-home for the gamma actuator ( Z axis or gamma tower ) once the endstop is hit once.
endstop_debounce_count 100 Debounce each limit switch (not homing endstops) over this number of values. Set to 100 if your endstops are too noisy and give false readings. Used for limit switches only
endstop_debounce_ms 1 Debounce each homing endstop for this number of miliseconds. Set to 1 if your endstops are too noisy and give false readings. Used for homing only
alpha_trim -0.1 DELTA ONLY Software trim for alpha ( X axis or alpha tower ) stepper endstop (in millimetres ). When the endstop is hit, the axis will move this distance towards the endstop (negative values move endstop away from the endstop )
beta_trim -0.1 DELTA ONLY Software trim for beta ( Y axis or beta tower ) stepper endstop (in millimetres ). When the endstop is hit, the axis will move this distance towards the endstop (negative values move endstop away from the endstop )
gamma_trim -0.1 DELTA ONLY Software trim for gamma ( Z axis or gamma tower ) stepper endstop (in millimetres ). When the endstop is hit, the axis will move this distance towards the endstop (negative values move endstop away from the endstop )
move_to_origin_after_home false If set to true, once homing is complete, the machine will move to it's origin point

Reading

You can use the M119 command to show the status of the configured endstops.

M119 answers this way : 

min_x:0 min_y:0 min_z:0 max_x:0 max_y:0 max_z:0
ok

If an endstop is not connected the pin should be set to «nc», and it's value will not be reported.

This is in particular useful when setting up your machine : you can issue the M119 command with your endstops unpressed, check that the values are 0 ( which would be correct ), and issue the command again with your endstops pressed, check that the values are all 1 ( which is correct for pressed endstops ).

If an endstop always reports 0, it probably means that it is not wired correctly.

If an endstop's values are inverted, it probably means you wired the pin as NO when it is NC, or the opposite.

You can reverse a pin in the configuration file by adding or removing a «!» character after the pin number ( see Pin Configuration ).

For example if the beta min endstop is inverted in your diagnostics, change :

beta_min_endstop   1.26^

to :

beta_min_endstop   1.26^!

Inverted

If, when homing, your endstop moves a few millimeters, and stops, it most probably means it's inverted ( it thinks it's already hitting the endstop, and moves back from it ). Just invert it in config and see if that helps.

Homing

You use the G28 command to home your machine.

For example : 

G28 Z0

will home the Z axis.

And :

G28

will home all axes which have endstops enabled (all three by default).

CNC mode/GRBL mode

The firmware-cnc.bin is in CNC mode and by default uses grbl compatibility mode in this mode G28 does not home, it goes to a predefined park position (defined with G28.1). To home in CNC/GRBL mode you issue $H, (or G28.2).

Notes

Currently only min or max endstops can be used for homing.
Do not set endstops for axes that shall not be homed.

Note for Deltas using M666 to set soft trim

When you home a delta that has non zero trim values, you will find that X and Y are not 0 after homing. This is normal.
If you want X0 Y0 after homing yo can set `move_to_origin_after_home true` in the config, this will move the effector to 0,0 after it homes and sets the trim. However note this may crash into your endstops, so make sure you enable limit switches, as this will force the carriages off the endstops after homing but before moving to 0,0.

Limit switches

Endstops may be configured to act as limit switches, during normal operations if any enabled limit switch is triggered the system will halt and all operations will stop, it will send a !! command to the host to stop it sending any more data (a recent dev octoprint and recent Pronterface support this).
A reset will be required to continue, or sending M999, make sure you move away from the endstop though before trying to move.

To enable enstops as limit switches the following config options can be used, they are disabled by default.

alpha_limit_enable                          true            # set to true to enable X min and max limit switches
beta_limit_enable                           true            # set to true to enable Y min and max limit switches
gamma_limit_enable                          true            # set to true to enable Z min and max limit switches

When one axis is enabled both min and max endstops will be enabled as limit switches, setting an endstop pin to nc will disable it.

Retract

After homing the axis is usually left triggering the endstop, this would prevent that axis from moving, so when limit switches are enabled after homing the axis will back off the endstop by the *.homing_retract_mm amount.

The downside is if you home to 0 and at 0 the endstop is triggered going to 0,0 will cause a limit switch to fire. The workaround is to set homing offset to -5 or enough to back off the endstop so when you go to 0,0 it does not trigger the endstop.

That way you can home, and safely go to 0 without triggering a limit switch event. An alternativve is to set min/max X/Y to -5 rather than 0.

Azteeg X5

On an Azteeg X5 mini with only 3 endstop connectors you can still connect two microswitches in series set to normally closed to ground and connected to the relevant input, this will allow for min and max limit switches to still work.

Usage example with home offsets

Here is a common sequence that you may do to set bed height, this need not be repeated unless the bed changes.

; Home
G28
; move to 5mm above bed
G0 Z5
;  then manually jog down until nozzle is on bed or just traps a sheet of thin paper
; sets the Z homing offset based on current position
M306 Z0
G28
G0 Z0
; check nozzle still captures thin sheet of paper
M500
; saves the results in EEPROM equivalent

External ressources

General video about mechanical endstops