H-Bot and CoreXY Configuration

Version Support: This arm solution is supported in both Smoothieware v1 ✅ and v2 ✅

H-Bot and CoreXY are two types of motion systems that use a crossed-belt configuration to move the print head or cutting tool in the X and Y directions.

Both systems use two motors to control X and Y movement, with each motor contributing to motion in both axes. This design reduces the moving mass and allows for faster, more precise movements compared to traditional Cartesian systems.

What is H-Bot / CoreXY?

In an H-Bot or CoreXY system:

Alpha motor (Motor 1): Contributes to both X and Y movement
Beta motor (Motor 2): Contributes to both X and Y movement (in different combinations)
Gamma motor (Motor 3): Controls Z movement independently

The key difference from Cartesian is that moving in the X direction requires both X/Y motors to move, and moving in the Y direction also requires both motors to move (but in different combinations).

Mathematical Relationship

For CoreXY and HBot:

Alpha position = X + Y
Beta position = X - Y
Gamma position = Z

This means:

To move +X: Both alpha and beta move forward
To move +Y: Alpha moves forward, beta moves backward
To move diagonally: One motor moves, the other stays still

CoreXY vs H-Bot: While the math is the same and Smoothieware uses the same code for both, there are mechanical differences in belt routing. CoreXY uses a specific belt path that eliminates certain artifacts. In Smoothieware configuration, both corexy and hbot select the same implementation.

Why Use H-Bot / CoreXY?

CoreXY and H-Bot offer several advantages:

Reduced moving mass: Motors can be mounted to the stationary frame
Higher speeds: Less inertia allows faster acceleration and deceleration
Better precision: Less vibration from moving motors
Compact design: Efficient use of space in the frame
Smoother motion: Belt arrangement can provide better motion characteristics

Common Applications

3D printers - Especially speed-focused designs (Voron, Hypercube, etc.)
Laser cutters and engravers - Fast, precise X/Y movement
Small CNC routers - Where speed and precision matter
Plotters and cutters - Vinyl cutters, pen plotters

Configuration

To configure your HBot or CoreXY machine, set the arm_solution parameter in your configuration file to either corexy or hbot:

arm_solution corexy

arm_solution hbot

[general]
arm_solution = corexy

[general]
arm_solution = hbot

Both options use the same implementation in Smoothieware. Choose the name that matches your mechanical belt configuration.

Complete Configuration Example

# CoreXY arm solution
arm_solution                                 corexy

# Alpha motor (X/Y motor 1)
alpha_step_pin                               2.0
alpha_dir_pin                                0.5
alpha_en_pin                                 0.4
alpha_steps_per_mm                           80
alpha_max_rate                               24000    # mm/min - can be very high!

# Beta motor (X/Y motor 2)
beta_step_pin                                2.1
beta_dir_pin                                 0.11
beta_en_pin                                  0.10
beta_steps_per_mm                            80
beta_max_rate                                24000    # mm/min - can be very high!

# Gamma motor (Z motor - independent)
gamma_step_pin                               2.2
gamma_dir_pin                                0.20
gamma_en_pin                                 0.19
gamma_steps_per_mm                           400
gamma_max_rate                               300

# CoreXY homing (optional but recommended)
corexy_homing                                true

[general]
arm_solution = corexy
corexy_homing = true

[actuator]
alpha.step_pin = PG0
alpha.dir_pin = PG1
alpha.en_pin = PJ2
alpha.steps_per_mm = 80
alpha.max_rate = 24000
alpha.microsteps = 32
alpha.driver = tmc2660

beta.step_pin = PG2
beta.dir_pin = PG3
beta.en_pin = PJ3
beta.steps_per_mm = 80
beta.max_rate = 24000
beta.microsteps = 32
beta.driver = tmc2660

gamma.step_pin = PG4
gamma.dir_pin = PG5
gamma.en_pin = PJ4
gamma.steps_per_mm = 400
gamma.max_rate = 300
gamma.microsteps = 32
gamma.driver = tmc2660

Speed Settings

It is recommended to set the alpha_max_rate and beta_max_rate to the highest speed your steppers can achieve.

These settings refer to the actuator speed (the physical X and Y stepper motors), which on a CoreXY system can run nearly twice as fast as the requested Cartesian speed when moving in certain diagonal directions.

For example:

If you want a maximum Cartesian speed of 200mm/s (12000mm/min)
Set alpha_max_rate and beta_max_rate to at least 24000mm/min
This allows the motors to keep up when moving diagonally

Important: If your max rates are too low, diagonal movements will be slower than expected, and you may experience motion artifacts or missed steps.

Homing Configuration

If you are using endstops for homing, enable CoreXY homing mode:

corexy_homing    true

This tells Smoothieware to handle the motor coordination properly during homing operations. Without this setting, homing behavior may be unpredictable.

Getting Direction Right

Movement in the X or Y direction always involves both alpha and beta motors, which can make configuring a CoreXY solution confusing.

If you find that movement is incorrect after wiring and configuring your printer, the following solutions may help:

Problem	Possible Solution
My axes are swapped	Invert the signal of one motor by adding or removing ‘!’ from its dir_pin
One of my axes goes in the wrong direction	Swap the alpha and beta motor cables, or swap the pin assignments in config
Both axes are mirrored	Invert both alpha and beta dir_pins by adding or removing ‘!’
Diagonal movements are wrong	Check belt routing - ensure it matches CoreXY or H-Bot topology

Systematic Direction Testing

To systematically test and correct directions:

Test X movement: Command G0 X10 and verify the toolhead moves in the +X direction
- If wrong, try inverting one motor's direction pin
Test Y movement: Command G0 Y10 and verify the toolhead moves in the +Y direction
- If wrong, try swapping motor cables or inverting the other motor's direction
Test diagonal: Command G0 X10 Y10 to verify coordinated movement
Test homing: Run G28 to verify endstops work correctly

Advantages and Disadvantages

Advantages ✅

High speed: Reduced moving mass allows for very fast movements
Good acceleration: Motors mounted to frame reduce vibration
Precise: Less flex and wobble compared to moving motor gantries
Compact: Efficient use of frame space
Proven design: Used in many high-performance 3D printers

Disadvantages ❌

Complex setup: Getting directions right can be confusing initially
Belt management: Long belts require careful routing and tensioning
Motor coordination: Firmware must handle coordinated movements
Troubleshooting: Problems can be harder to diagnose than Cartesian
Limited Z performance: Z axis is still typically a moving bed

Comparison with Other Arm Solutions

Feature	CoreXY/H-Bot	Cartesian	Linear Delta
Setup complexity	Medium	Low	High
XY speed potential	Very high	Medium	Very high
Z speed potential	Low	Low	High
Moving mass	Low	High	Very low
Calibration difficulty	Medium	Easy	Hard
Build volume shape	Rectangular	Rectangular	Cylindrical
Mechanical precision needed	Medium	Medium	High

Common CoreXY Machines

Well-known CoreXY designs include:

Voron (V0, V1, V2, Trident) - High-performance 3D printers
Hypercube and Hypercube Evolution - DIY CoreXY 3D printers
BLV MGN Cube - Modular CoreXY 3D printer
RatRig V-Core - Large format CoreXY printer
Many commercial laser engravers and cutters

Troubleshooting

Problem: Motors make noise but toolhead doesn’t move

Solution: One motor may be wired backwards. Check that both motors are energized and swap one motor’s cable polarity if needed.

Problem: Toolhead moves diagonally when commanding straight lines

Solution: The motor directions are likely incorrect. Try inverting one motor’s dir_pin with ‘!’.

Problem: Movements are slower than expected in certain directions

Solution: Your alpha_max_rate and beta_max_rate may be too low. Increase them to at least 2× your desired Cartesian speed.

Problem: Layer shifts or skipped steps on diagonal moves

Solution: This usually indicates the motor speeds are too high for diagonal movements. Either:

Reduce your Cartesian max speed
Increase alpha_max_rate and beta_max_rate
Increase motor current (if motors are running too cool)

Source Code

For developers or those interested in the implementation details:

v1: HBotSolution.cpp
v2: HBotSolution.cpp