Servo Stock 3D Printer Brings Closed-Loop Control To Reprap 56
A limitation of current (affordable) 3D printers is their use of open loop controllers and stepper motors which limits reliability (drove the motor too quickly and skipped a step? Your model is ruined) and precision (~300 steps per revolution). A new project, Servo Stock instead uses cheap RC Servomotors combined with Hall Effect sensors, using a closed-loop controller to precisely position the extruder. The Servo Stock is derived from the delta robot Reprap Rostock (which is pretty cool even with stepper motors). The sensors give a resolution of 4096 ticks per rotation, and the controller can currently position the motors to within +/-2 ticks. They've also simplified the printer electronics by driving as much as possible from the controlling computer using Bowler, a new communication protocol for machine control. The Servo Stock also includes sensors for the hot end, presumably to be used to control the filament feed rate and temperature. The hardware models are fully parametric, allowing reasonably straightforward scaling of the design. Source for the hardware, firmware, and software is available.
A note on the video: the extruder platform is tilted in the video, but a project update indicates it was fixed by making the support arms more rigid.
Move along nothing to see here. (Score:4, Insightful)
Pretty much all lies from the start.
First off, almost nobody is missing steps in their cheap 3D printers. They simply do not move fast enough for that to happen. And if they are missing steps you have a bigger issue, usually lots of friction somewhere.
Secondly, 200 steps per rotation is normal for motors. However, the drivers everyone is using do 16x microstepping, good for 3200 steps per revolution. Accurate steps per revolution. That's better then 4096 +- 2 steps.
You also lose the close coupling between the 4 axis that you need (the feed stock of the material is also an axis that you need to control), which is a big deal in running accurate prints.
The cheap hobby servos will also have mechanical play, which will cause vibrations to be transferred to the head, which will result in a reduction of print quality.
I'm also willing to argue that it's more expensive. But I didn't do the math on that part yet.
(Who am I to say so? Just a guy who has been working at Ultimaker for 2 years. Kinda know what's needed for quality 3D printing at a low price and what's not)