Hi all,   I'd like to know where the cheapest place to get reprap

Hi all,
I’d like to know where the cheapest place to get reprap parts and can I replace/how much can I replace the electronics with a Raspberry pi (given that I have one of those)?

RaspberryPi doesn’t have a good moto controller available for it as far as I know. I’ve had a little success using one to put my printer online and then feed the gcode over usb to the Ramps board, but as far as I know there is nothing you can buy right now. Gertboard is coming sometime this year. I haven’t been keeping track of that space though so there could be a lot I’m not aware of.

RasPi + Ramps is working perfectly for me. The Pi has been discussed a couple of times as a potential replacement for the Arduino, but the verdic basically is that it runs a non-realtime OS, which can not directly control the printer.

Why is that though? Excuse my low-level ignorance but the device has output pins on the main-board, what is stopping me writing a program for my RaspberryPi that controls devices attached to those pins directly? Is the issue one of latency and timing unpredictability?

When an AtMega gets an interrupt it jumps into the corresponding routine and executes that code right away, blocking everything else for that time (except other interrupts with a higher priority). On the RasPi, the code you run needs to go through I/O schedulers, fight over CPU time with the kernel and other software that runs on it and can generally not be relied on to execute any given command at the very specific time we tell it to.
So to exaggerate a bit, while the Arduino will instantly stop when an endstop is triggered, the RasPi might happily keep on going for a bit because your software is not getting the resources it needs to process that signal.

Fair enough, I understand why timing is everything when controlling real-world devices. Is that just a software issue though, as it’s easy enough to run another OS on a raspberry pi?

Many x86 Linux distros offer a realtime kernel.
For the RasPi, there is some experimentation going on right now, so i’d expect that sooner or later we’ll have a usable realtime kernel as well. At that point, we’ll have to see how well it works and whether or not the Gertboard can do what we need.

Tim, if you get rid of the OS entirely, and run you code on the RPi “naked” or “bare metal” , then you will probably get what you are after ( ie fast, reliable I/O with no unpredictable latencies), but then you are going down a much, much harder path that no ohter reprapper has been down yet with the RPi. Good luck. here’s a hint: http://www.raspberrypi.org/phpBB3/viewtopic.php?t=10167