RepRap: Blog

Accelerating RepRap from Adrian Bowyer on Vimeo.

The experimental four-dimensional GCode interpreter is now five-dimensional. Four dimensions are so three weeks ago...

It has an extra DDA variable that is the feedrate. This means that if you send it:

G1 X85.3 Y75.8 E18.3 F2495.4
G1 X85.5 Y75.5 E18.7 F2575.9

For the second move it accelerates linearly from 2495.4 mm/minute to 2575.9 mm/minute as it moves from X85.3 Y75.8 E18.3 to X85.5 Y75.5 E18.7. That is to say, it treats the F values in exactly the same way as it treats X, Y, Z, and E. (This is not how GCodes conventionally work, of course, so you can turn this behaviour off by commenting out a line in the firmware that says

#define ACCELERATION_ON

)

Of course you can have the machine move at constant speed as well if you want. You do that simply by setting the feedrate first:

G1 F2575.9
G1 X85.5 Y75.5 E18.7

That will do a move at a constant 2575.9 mm/minute, as you would expect.

The latest Java host software in the repository now supports all this (again you can turn it all off by setting Accelerating false in the preferences).

There is one final firmware upgrade needed to finish this work off: buffering the moves in the micro-controller (as Zach and co. are doing with their code). At the moment there is a barely-perceptible pause between moves, which means that accelerating to high speed hits a momentary barrier at the end of the acceleration. As the whole point of all this is to make the machine move much more smoothly, that's got to go.

Accelerations allow the machine to work faster and more accurately at much lower motor currents, or maybe even with smaller cheaper motors. Or maybe even with motors we print ourselves, which Forrest is working towards...