Belted Kinematics (draft)

A 3D printer needs three axes of motion. Driving all three axes can be done in several different ways.

Bedslinger Cartesian

The simplest motion system, bedslinging moves the toolhead in X and Z, and the bed in Y.

This makes the two fast axes move completely independently. The X linear guide moves only slowly in Z, and the Y linear guides are completely stationary. This reduces friction when accelerating diagonally.

All belt runs are as short as possible for each axis with a minimum of idlers for low friction.

All XYZ motors are either stationary or slow-moving.

The motion itself is simple but the print itself moves and puts higher loads on the Y linear guide system. Additionally, the bed should be built as lightly as possible without losing rigidity.

Box Cartesian (Serial X-Y)

Box Cartesian kinematics moves the X rail, together with the X motor(s), in the Y direction.

This allows the print to move slowly or not at all (depending on Z kinematics).

All belt runs are as short as possible for each axis, with a minimum of idlers for low friction.

The X motors move quickly in Y, making wiring an important consideration as well as their effect on the center of mass.

The X rail gets loaded during Y acceleration, increasing friction.

CoreXY

CoreXY has two stationary motors with two P shaped belt paths combined to move both the toolhead in X and the X rail in Y. One motor changes X+Y and the other changes X-Y.

This allows the print to move slowly or not at all (depending on Z kinematics).

Belt runs are long in CoreXY, and differing tension between the two belts tries to rack the X axis out of square.

CoreXY has a lot of idlers on the belt path, causing higher friction particularly with higher belt tensions.

All motors are stationary or slow-moving.

HBot

HBot has two (or four) stationary motors with one H-shaped belt path that moves both the toolhead in X and the X rail in Y. One motor changes X+Y and the other changes X-Y.

This allows the print to move slowly or not at all (depending on Z kinematics).

The belt run is long in HBot, and any X acceleration causes belt tension that tries to rack the X axis out of square.

HBot has a lot of idlers on the belt path, causing higher friction particularly with higher belt tensions.

All motors are stationary or slow-moving.

MarkForged

MarkForged kinematic has dedicated short Y drive belts moving the X axis, and a T-shaped X belt path moving along one side and the X axis. Moving the Y axis motor(s) alone will move the toolhead diagonally, but moving the X motor will move the toolhead only in X.

This allows the print to move slowly or not at all (depending on Z kinematics).

The Y belts, which carry a heavier load, are short belt paths. The X belt is longer but the toolhead is comparatively light.

The X axis has a lot of idlers on the belt path, causing higher friction particularly with higher belt tensions.

All motors are stationary or slow-moving.

Cross Gantry