Friday Facts 12: How to use Marlin in a Robot Arm
Building a robot arm is one thing, but what about writing the code to make it run? Some people want to learn the fine points of precision stepper motor control, forward and inverse kinematics, and then debug all that stuff. For the rest, working together gets the job done faster. For those people the Marlin 3D printer firmware is a great option. Today I’m going to show how I tweaked it to run in the Sixi 3 robot arm. Please share your experience with us so we can improve this post.
Marlin?
Marlin 3D printer firmware is the code in the brain of a very large number of printers. It is very flexible with a few changes. Most people might think of printers as having four motors – one for each direction and one for the extruder. But recent changes mean that Marlin can run up to six motors. That’s great for us, because most robot arms are 6 or less.
With Marlin installed you’ll be able to control the angle of each motor by sending gcode commands and even drive them simultaneously. With Marlin’s homing routines you could locate position, and new options coming in the near future will give real time feed back (more on that later)
What needs to be tweaked
Pour yourself a drink and settle in. This list will touch at least two files and take some time… OR you can use the sixi3 branch I maintain and adjust it for your speeds and gear ratios.
I keep trying new ways to make this list less dry. What do you think?
/Marlin/Configuration.h
| Old value | New Value |
| #define STRING_CONFIG_H_AUTHOR “(none, default config)” | #define STRING_CONFIG_H_AUTHOR “(Sixi3, Marginally Clever Robots)” |
| #define MOTHERBOARD BOARD_RAMPS_14_EFB | #define MOTHERBOARD BOARD_RUMBA |
| //#define CUSTOM_MACHINE_NAME “3D Printer” | #define CUSTOM_MACHINE_NAME “Robot Arm” |
| //#define LINEAR_AXES 3 | #define LINEAR_AXES 6 |
| #define AXIS4_NAME ‘A’ | #define AXIS4_NAME ‘U’ |
| #define AXIS5_NAME ‘B’ | #define AXIS5_NAME ‘V’ |
| #define AXIS6_NAME ‘C’ | #define AXIS6_NAME ‘W’ |
| #define EXTRUDERS 1 | define EXTRUDERS 0 |
| #define USE_XMIN_PLUG #define USE_YMIN_PLUG #define USE_ZMIN_PLUG | //#define USE_XMIN_PLUG //#define USE_YMIN_PLUG //#define USE_ZMIN_PLUG |
| //#define I_DRIVER_TYPE A4988 //#define J_DRIVER_TYPE A4988 //#define K_DRIVER_TYPE A4988 #define E0_DRIVER_TYPE A4988 | #define I_DRIVER_TYPE A4988 #define J_DRIVER_TYPE A4988 #define K_DRIVER_TYPE A4988 //#define E0_DRIVER_TYPE A4988 |
| #define DEFAULT_AXIS_STEPS_PER_UNIT { 80, 80, 400, 500 } | #define DEFAULT_AXIS_STEPS_PER_UNIT { 105, 105, 105, 105, 105, 105 } |
| #define DEFAULT_MAX_FEEDRATE { 300, 300, 5, 25 } | #define DEFAULT_MAX_FEEDRATE { 5, 5, 5, 5, 5, 5 } |
| #define DEFAULT_MAX_ACCELERATION { 3000, 3000, 100, 10000 } | #define DEFAULT_MAX_ACCELERATION { 10, 10, 10, 10, 10, 10 } |
| //#define CLASSIC_JERK | #define CLASSIC_JERK |
| //#define S_CURVE_ACCELERATION | #define S_CURVE_ACCELERATION |
| #define E_ENABLE_ON 0 // For all extruders //#define I_ENABLE_ON 0 //#define J_ENABLE_ON 0 //#define K_ENABLE_ON 0 | //#define E_ENABLE_ON 0 // For all extruders #define I_ENABLE_ON 0 #define J_ENABLE_ON 0 #define K_ENABLE_ON 0 |
| #define INVERT_Y_DIR true | #define INVERT_Y_DIR false |
| //#define INVERT_I_DIR false //#define INVERT_J_DIR false //#define INVERT_K_DIR false | #define INVERT_I_DIR false #define INVERT_J_DIR false #define INVERT_K_DIR false |
| //#define I_HOME_DIR -1 //#define J_HOME_DIR -1 //#define K_HOME_DIR -1 | #define I_HOME_DIR -1 #define J_HOME_DIR -1 #define K_HOME_DIR -1 |
| define X_BED_SIZE 200 define Y_BED_SIZE 200 | //#define X_BED_SIZE 200 //#define Y_BED_SIZE 200 |
| #define X_MIN_POS 0 #define Y_MIN_POS 0 #define Z_MIN_POS 0 #define X_MAX_POS X_BED_SIZE #define Y_MAX_POS Y_BED_SIZE | #define X_MIN_POS -360 #define Y_MIN_POS 360 #define Z_MIN_POS -360 #define X_MAX_POS 360 #define Y_MAX_POS -360 |
| //#define I_MIN_POS 0 //#define I_MAX_POS 50 //#define J_MIN_POS 0 //#define J_MAX_POS 50 //#define K_MIN_POS 0 //#define K_MAX_POS 50 | #define I_MIN_POS -360 #define I_MAX_POS 360 #define J_MIN_POS -360 #define J_MAX_POS 360 #define K_MIN_POS -360 #define K_MAX_POS 360 |
| #define HOMING_FEEDRATE_MM_M { (50*60), (50*60), (4*60) } | #define HOMING_FEEDRATE_MM_M { (4*60), (4*60), (4*60), (4*60), (4*60), (4*60) } |
| //#define EEPROM_SETTINGS | #define EEPROM_SETTINGS |
| //#define SDSUPPORT | #define SDSUPPORT |
| //#define REPRAP_DISCOUNT_SMART_CONTROLLER | #define REPRAP_DISCOUNT_SMART_CONTROLLER |
/Marlin/Configuration_adv.h
| define AXIS_RELATIVE_MODES { false, false, false, false } | #define AXIS_RELATIVE_MODES { false, false, false, false, false, false } |
| #define HOMING_BUMP_MM { 5, 5, 2 } #define HOMING_BUMP_DIVISOR { 2, 2, 4 } | #define HOMING_BUMP_MM { 5, 5, 5, 5, 5, 5 } #define HOMING_BUMP_DIVISOR { 2, 2, 2, 2, 2, 2 } |
Notes
MOTHERBOARDis your choice of brain board. Anything Mariln supports AND has 6 axies will work.DEFAULT_AXIS_STEPS_PER_UNITis the gear ratio at the given joint. For all sixi3 gearboxes the ratio is 70:1 (harmonic) * 54:20 (timing belt) * 200/360 (for 1.8 degree stepper motors at full step) = 105.- Because the gear ratio is so high the motors are not physically able to exceed the
DEFAULT_MAX_FEEDRATE. If you use faster motors or a faster brain board you may be able to improve on these numbers. EEPROM_SETTINGS,SDSUPPORT, andREPRAP_DISCOUNT_SMART_CONTROLLERare not required. I use these to tweak settings for testing, run programs from the SD card, and to have an LCD panel on my robot.- Every other change is to adjust from 3 axies to 6.
Homing and Real time feedback
There are some exciting new features coming to Marlin that should make real time feedback possible. This means we’ll know the robot position without having to guess or to home. It also means we can tell when the actual position deviates from the expected position too much that a collision has occurred and that can save a lot of trouble! The new configuration options to explore are:
REALTIME_REPORTING_COMMANDSadds some “quick commands” that get processed before anything else in the gcode buffer of the robot. Great for emergency breaking and for requesting position information (Gcode “S000”)M114_REALTIMEadds “M114 R” which reports the real-time position of the robot instead of the projected position at the end of the planned moves.I2C_POSITION_ENCODERSis a first pass at adding real time sensors. This will no doubt be expanded later to include other types and features.
