Well, here is the update.
I picked up some new stepper drivers from Pololu to experiment on. I also wanted to test out a .NETMF based one so I picked up the Fez Panda II.
Well, the Panda was a pretty nice board. Notice the "was"? Well, one of the joys of getting older is that my eyesight is not that great any more. While testing out a servo, I plugged into the wrong row on the breadboard and fried the poor little board. Ooops. Oh well.
My first impressions of the board were actually pretty positive. There are some things I prefer about the Ardiuno, and some about the Panda. The panda is faster and has more memory. It also has a built in SD card slot. The IDE has more features but I don't really put that much of a plus in its favor. C# isn't too bad and the ability to print debug statements is an advantage. If I were going to build a graphical interface for an LCD and stuff like that, it seems to be a pretty robust set of tools. That said, I wasn't impressed enough to wait and buy another one to work with. Maybe later for some other project.
I was doing some tests with the Pololu stepper drivers and so far I really like them better than EasyDriver boards I was using. The EasyDrivers were OK, but they began failing and I was down to one working board out of the 6 I had bought. At present, I don't have enough code to think about going with something besides grbl for a real machine. It is a lot more complete but I have been taking some of the code and converting to the Arduino IDE. The main reason I am going that way is to be able to switch boards more easily. The grbl code is pretty deeply tied to the 168/238 and I would like to move over to the Mega. I was testing out my ideas for writing directly to the ports to sequence the steps and that worked as planned. Actually, better than I had thought. I was having to increase the delays to allow the motors to keep up. In the 1/16 step mode, I was down to something like 90 microsecond wait for the motor to respond.
Now, I need to start doing some work on the communication. The plan I am working on is to lighten up grbl by using a pre-processor on the host computer side to be able to do things like units conversions and configuration storage on that end rather than keeping it on the arduino. I have been working with switching the stepping mode kind of like a transmission to switch between rapid motion and real cutting. I won't really be able to tell that much until I have some mechanical motion to see what it is really doing. Right now, I am just sending a fixed number of steps and directions. Some of the ideas I have for the motion control are not as sophisticated as grbl but I really don't think that some of the stuff that they do is totally necessary. At cutting speed, the motion will be slow enough that a simple acceleration scheme might be more economical. Of course I might be wrong, but I already have grbl installed on another board and I don't have to depend on my ideas.
The other thing that has been occupying me is I finally got my mini-mill from Harbor Freight. I had to reorganize my garage to be able to set it up and that was a lot of work. How this relates to this project is to be able to work out some of my ideas for linear motion. This week I will be able to get it all set up and actually see about cutting some metal. I will be tight on space for a few more weeks until I can get the boat out of the way in the garage.
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