Trinamic controllers idea

Disclaimer: this is basically thinking out loud. I suspect the idea would not add any features not already present in current electronics packages, and definitely won't be cheaper than what exists. I'm just curious if it would be a viable system or not.

So I was reading about the Tbone beaglebone cape (over here: [forums.reprap.org]) and while I have mixed feelings about the board, the Trinamic chips are interesting. I was reading more, and found out about the TMC429 chip, which allows control of up to three steppers through a single SPI interface. Send position and configuration data through SPI, and it generates step/dir pulses for the three steppers, and has integrated switch inputs for endstops. I know people like to ask if they can control their 3D printer with a raspberry pi; but is this actually a way it could be done? Two of these (and either traditional pololu sockets or TMC2660 for more SPI configurability), and you have your three axes and three extruders, all through the pi's SPI. Since the pi itself isn't generating the pulse trains, it's no longer necessary for the pi to be working in real time. The one thing is, though, that the chips don't seem to have a buffer, so I think the SPI commands would have to be fairly timely. It seems like this would make the basis for an electronics package that was more easily portable to other microcontrollers/single-board-computers (just need something with SPI). And yes, I haven't mentioned temp control or other outputs, because I haven't given them any thought yet.

Does this seem like a viable idea? Any pros/cons you notice that I haven't?

Thanks for reading my brainstorming!

It doesn't look like it does coordinated motion -- you can "Drive motor 2 to position 1000", but you'd need to externally re-calculate the ramping math to tell motor 1 and motor 3 how to move to make the hotend interpolate between the points in a straight line.

Supporting lookahead seems like it would need V_start and V_end, but that doesn't look like it is supported in positioning mode.

Some people have managed to run their printers on Beaglebones, search the deltabot group on Google.
[groups.google.com]

I can't be of much help, but maybe that will point you in the right direction.

Oh, good point DaveX, you'd have to calculate and set the acceleration and speed with each move, as well as the positions. Plus like you said, it assumes you start and stop at V=0, so you'd have to come to a stop at the end of every segment like the really old firmwares. I wonder what sort of uses this chip is put to, you need a microcontroller to use it, and it doesn't do anything that a microcontroller can't do, even a cheap, low-power one.

Quote
TopherMan
I know people like to ask if they can control their 3D printer with a raspberry pi;

For me personally the good thing is, that by using the T-Bone board i can control the 3D-printer with a Beaglebone-Black, which i consider being way better than the raspberry pi and which is anyway the preferred mainboard for my next 3dprinter-project.

The T-Bone then offers several additional features like the stallguard (homing without endstop switches), higher accuary by 256-times microstepping, or higher acceleration with s-shaped ramps and some more.