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A project log for Theta Printer

A 3D printer with 4 extruders that can move independently and simultaneously

tyler-andersonTyler Anderson 04/19/2014 at 03:430 Comments

Some people have been asking about the software side of things. Right now what we have is a modified version of the Marlin firmware. Its based on the work done to make Marlin work with Delta printers, with the math changed to do the conversion to bipolar coordinates. The firmware works in two modes:

Cartesian emulation mode

In Cartesian emulation mode, the firmware does the conversion from Cartesian to bipolar coordinates on the fly. Basically it acts like a normal printer and you can use it with standard slicing software. The only difference is that you must specify the speed in °/s instead of mm/s. This has the side effect of throwing off the estimated completion time in the host software.

Native bipolar mode

In this mode, the G-Code is given to the printer directly in bipolar coordinates. It requires special slicing software (which doesn't exist yet) but it is the only way to take advantage of the full capabilities of the printer.

You can switch between these modes using the G93 and G94 commands. G92 works as you would expect in each mode. Homing also works (G28) except it is disabled for the platter (θ₁ axis), since it is homeless.

Currently there is no support in the software for using more than one extruder. The electronics package we intend to use for driving all 10 motors has not gone into production yet. Hopefully this will happen soon, since people have started throwing buckets of money at that company. If not, I may have to make a one-off order to OSH Park and get the ball rolling.

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