Dual Gantry Configuration

This page describes how to set up configuration for a Dual gantry setup. The example given is a Shapeoko with a Dual Y gantry.

Overview

A dual gantry setup uses 2 motors to drive a single axis. Commonly the dual gantry is the Y axis, but not always. The 4 motors on TinyG can be used to support a dual Y gantry like so:

Motor	Axis
Motor1	X Axis
Motor2	Y1 Axis
Motor3	Y2 Axis
Motor4	Z Axis

The Y2 axis has reverse polarity from Y1 as the 2 motors are facing each other and therefore need to turn in the opposite direction from each other.

Note that the 'A' axis is not used. Only the 4 motors and the X, Y and Z axes.

Settings

Here are some example settings for a Shapeoko dual Y gantry setup. You will probably need to experiment to get exact settings for your machine, but this is a good starting point. The maximum velocities and feed rates are set intentionally low and can probably be set higher with tuning.

Motor 1 (X Axis)

Setting	Description	Notes
$1ma=0	Map to X axis	0=X axis, 1=Y axis, 2=Z axis
$1sa=1.8	Step angle in degrees	Set 1.8 for 200 step / revolution motors, 0.9 for 400 step / revolution
$1tr=36.54	Travel per rev in mm	This value should be calibrated to your setup
$1mi=8	Microsteps to 8	Experiment with 4x microstepping for more power
$1po=0	Polarity normal	Set polarity so X travels to the right for positive values (G0 X10)
$1pm=0	Power management mode	0=axis remains powered when idle

Motor 2 (Y1 Axis)

Setting	Description	Notes
$2ma=1	Map to Y axis
$2sa=1.8	Step angle in degrees
$2tr=36.54	Travel per rev in mm	This value should be calibrated to your setup
$2mi=8	Microsteps to 8	Try 4x for more power
$2po=0	Polarity normal	Set polarity so Y travels to the rear of the machine for positive values (G0 Y10)
$2pm=0	Power management mode	0=axis remains powered when idle

Motor 3 (Y2 Axis)

Setting	Description	Notes
$3ma=1	Map to Y axis	Same as Motor 2
$3sa=1.8	Step angle in degrees
$3tr=36.54	Travel per rev in mm	MUST BE THE SAME AS MOTOR 2
$3mi=8	Microsteps to 8	Should be the same as motor 2
$3po=1	Polarity reversed	MUST BE OPPOSITE MOTOR 2
$3pm=0	Power management mode	Should be the same as motor 2

Motor 4 (Z Axis)

Setting	Description	Notes
$4ma=2	Map to Z axis
$4sa=1.8	Step angle in degrees
$4tr=1.25	Travel per rev in mm	The stock Shapeoko Z screw is 1.25 mm / rev
$4mi=4	Microsteps to 4
$4po=0	Polarity normal	Set polarity so Z travels up for positive values (G0 Z10)
$4pm=1	Power management mode	1=axis shuts off when idle. Can also use $4pm=0

X Axis

Setting	Description	Notes
$xam=1	Axis mode normal
$xvm=10000	Velocity maximum	Max velocity for axis, aka "traverse rate" or "seek"
$xfr=10000	Feed rate maximum	Maximum feed rate for that axis. Limits F words to this value
$xtm=220	Travel maximum 220mm	Used by homing to know when to give up
$xjm=5000000000	Jerk maximum	That's 5 billion
$xjh=10000000000	Jerk homing	That's 10 billion - jerk used during homing operations
$xjd=0.01	Junction deviation	For cornering control
$xsn=1	Minimum switch mode	1=homing-only
$xsx=0	Maximum switch mode	0=disabled
$xsv=3000	Search velocity	Homing speed during search phase (drive to switch)
$xlv=100	Latch velocity	Homing speed during latch phase (drive off switch)
$xzb=3	Zero backoff	offset from switch for zero in absolute coordinate system

Y Axis

Y axis commands will drive both Y motors.

Setting	Description	Notes
$yam=1	Axis mode normal
$yvm=10000	Velocity maximum
$yfr=10000	Feed rate maximum
$ytm=220	Travel maximum 220mm
$yjm=5000000000	Jerk maximum	That's 5 billion
$yjh=10000000000	Jerk homing	That's 10 billion - jerk used during homing operations
$yjd=0.01	Junction deviation	For cornering control
$ysn=1	Minimum switch mode	1=homing-only
$ysx=0	Maximum switch mode	0=disabled
$ysv=3000	Search velocity	Homing speed during search phase (drive to switch)
$ylv=100	Latch velocity	Homing speed during latch phase (drive off switch)
$yzb=3	Zero backoff	offset from switch for zero in absolute coordinate system

Z Axis

Setting	Description	Notes
$zam=1	Axis mode normal
$zvm=600	Velocity maximum
$zfr=600	Feed rate maximum
$ztm=100	Travel maximum 220mm
$zjm=50000000	Jerk maximum	That's 50 million
$zjh=100000000	Jerk homing	That's 100 million - jerk used during homing operations
$zjd=0.01	Junction deviation	For cornering control
$zsn=0	Minimum switch mode	0=disabled
$zsx=1	Maximum switch mode	1=homing-only
$zsv=600	Search velocity	Homing speed during search phase (drive to switch)
$zlv=100	Latch velocity	Homing speed during latch phase (drive off switch)
$zzb=3	Zero backoff	offset from switch for zero in absolute coordinate system

Additional Settings

Setting	Description	Notes
$ja=2000000	Junction acceleration mode normal	max centripetal acceleration around corners