We now have a working stacking shield for Arduino MEGA that fits all the electronics for our Mendel into one tight little package. We have been posting our work and source on the RepRap Wiki here. There has already been significant development and testing for the Arduino MEGA and Pololu A4983 stepper driver for RepRap control, and we have our Mendel running on this set up now. It is far optimal, but an improvement all the same I think. 

Adrian has his Pololu Electronics that we loved, and several other people have been using the Arduino Mega and Pololu stepper drivers. Dissidence is working on almost the same thing on his blog. Joaz at RepRap Source is using the Arduino MEGA to control the ShaperCube. His firmware is quite stable and available on GitHub. We had the Arduino MEGA prototype shields in stock so we went down the road of knocking off Adrian's design with our own optimizations including - smaller total footprint, access to potentiometers, more mosfet outputs, standard power jack, cleaner installation with less wires, and less connections to add to the cost and failure opportunities.

One of our favorite tricks was placing the capacitor and resistor needed for each driver under it. We are also using connectors that I remember from hobby servos. They are 2.54mm pitch connectors that claim a rating of 3A.  The shield I have has room for an additional stepper driver or pair of mosfets. The eagle design includes both :) We are about to start printing tests of a housing for the electronics.

One of our main goals is to make this board on Mendel. This board is drawn up on Eagle with as fat of traces and wide of gaps. This is our first PCB design, so comments and criticisms are welcome. One issue we are trying to resolve is protection for the mosfet circuits. The heater wires became shorted during testing due to careless connection at the tight quarters of the heater terminal block and the mosfet branded my finger tip pretty good. The honking big mosfets are dangerous unwatched I think, especially mixed with cheap brick style power supplies.

Again, our source files and progress on instructions / notes is at http://reprap.org/wiki/Arduino_Mega_Pololu_Shield.

BTW, sorry for the lapse in blog entries (and the non stellar quality of this one, we do have a nice camera - just more concerned with production than promotion at this point). We've been a little preoccupied making sure everybody's orders go out the same day, and adding new COOL PLA COLORS, and electronics, individual components, etc. Hope you forgive us :)