General discussion  - 
Here is the latest release of the ServoStock, a PID controlled Delta printer. We have finally integrated the g code parser and the linear interpolation stack. All parts are printed on a Printrbot Plus. 

I also deployed the rotated arm kinematics. You will notice we have a 100 mm arm width and a 50mm tool plate diameter. This is possible because 2 of the arms are rotated 90 degrees. This allows for a much stiffer tool plate without sacrificing x,y and losing 100 mm of z only. I think it would be interesting to see how a mill would do...

We are on track for 160mmx160mmx300mm (120mm circle by 300mm) for ~$350 assembled. 

Now to integrate the canvas audo print bed and auto tip calibration...
Whosa whatsis's profile photoMike Miller's profile photobob cousins's profile photoKevin Harrington's profile photo
The effector does not appear to stay parallel to the build plate throughout the range of travel...
Hmm, yeah, off to the right? I looked at it again, and it is the ball joint hitting a limit and warping the mechanism. It is a work a in progress...
Cool, just so long as its not an oversight in the theory. 
just a controls engineer failing at structural design...
Honestly, more useful than anything would simply be a DC/Encoder based solution as a replacement to steppers.  If someone would simply come up with that, I think a lot of people would be interested.
With step/dir signaling so that it can be used without firmware modification, and preferably in a Pololu driver formfactor so that it can also be used without electronics modification (using two of the stepper output pins as outputs to the motor, and the other two as inputs for the encoder). If you orient those pairs as inner/outer, you should even be able to maintain the ability to reverse direction by flipping the connector.
I'd settle for a driver + DC motor with encoder that was cheaper than a pololu + stepper. Firmware and electronics can change to suit, a drop in replacement could come later.
How do cheapa$$ printers do it? Sure, the $35 machines are subsidized, but VERY high resolution 2D CNC control can't cost a whole lot more than, what, $20 a unit? (considering they also have to mount a printhead and make a plastic case...lets assume all major CPU stuff is offloaded to the PC)
So just as clarification, we are a controllers company and this printer is just to show of the new electronics/firmware/PC software pipeline.  We based the axis control around the magnetic orientation encoder, a 12 bit SPI based absolute encoder. Each control axis (at 4096 ticks/rev resolution and with motor, magner and cable) is around $15. The motherboard is coming in around $45.

  Since it is SPI, each axis requires 2 digital outputs, on running a servo pulse, the other the slave select for the encoder. they all use a common SPI bus as well. 
So a little over $100 for 4 DOF on a shared bus? 
+Kevin Harrington
$15 per axis sounds nice :) I'd love to get hold of 6 of these for a Sextuperon. Might be interesting to develop an interface board for existing RAMPS type setups.
It has 8 channels on the main board and an additional 32  with the expansion header (to be released later). It also has 3 heater/sensor pairs for up to 2 hot ends and a heated bed. 

As for the RAMPS setup, the controller requires an SPI bus and 2 I/O per axis, so there is no easy to set that up. Our board is in the price range of an arduino with an 80mhz Pic32 and a new in-protocol bootloader. 
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