[mtraven]

I'd be lost without people like you!

I think we are on the same page in terms of the big picture theory of how this all should work. I do pretty well in conceptualizing electronics systems, I struggle significantly at determining the exact components (sizing caps / resistors ect).
Where did we land on using the SAMD21 at the primary controller (vs the sub axis controllers)?

I'm a little perplexed at it's purpose, considering that the SAMD21 is available in a QFP,

well ****, when you make me think about, I see how silly it is.

re: bldc motor sensor vs sensorless: that remains unclear. I have two of these motors, used for electric steering in cars. That black case at the end, holds a driver of its own. The first one had been wired wrong & let out the smoke and then I thoroughly destroyed it trying to take it apart. In taking it apart, I found a small ceramic magnet at the end of the shaft. It only has two poles, but I suppose with 3 hall sensors 120 degrees out of phase, that would probably get the job done. The thing is, I cannot find the sensors! So I am hoping to use the one I destroyed to workout the pinout of the good one and build a driver for the second.

and the rest to an expansion header in case you think of anything you want to add later.

good call

I would suggest having a look at the schematic for the Arduino M0

this is helpful, I need to continue to study it.

A programming header for flashing the bootloader

never been successful at this, but I have only tried in an effort to repair chips. honestly I am not sure I totally understand what bootloaders do, it is fair to think of them like the operating system of the chip?

re: crystal - a bit confused here, I understand the relevance of 32.768 khz, but I thought the oscillator was responsible for timing cpu cycles....but how does a 32.768 kh produce a 48 mhz cpu cycle?

re: precision voltage reference: is a zener diode sufficient for this, or is that not considered to be a precision reference?


encoder: these are hedl 5540 encoders. Looks like 500 lines of resolution. optical. That seems both sufficient for accurate positioning and not too high that the pulses are difficult to process. Would you agree? datasheet

the spindles: I would like to work out what kind of speed I can get out of the spindles. the motors are maxon 248530 (EC series) --maxon's documentation is normally really good, but there is nothing on this motor, its as if it never existed. I have an email into them.
The spindles are made by GMN they have different serial numbers (r339423 & r337051) and the common marking of TS 25x56 -s6. Not finding any info on those either. The TS is a class of spindles with a max 20k rpm. I think the 25x56 is ID and OD of the bearings, no idea what s6 means.

It seems like developing these boards is gonna take a bit, I was thinking about ordering a SAMD21 dev board to start familiarizing myself with it, thoughts?

I did some more breakdown on the machine, one unsettling discovery: the lead screws have no rear support bearings on any of the axis! Back end of the screw is just hanging in the air. wtf ? That's the sort of thing I expect from harbor freight machines, not a precision dental mill that cost tens of thousands (when it was new). So I guess I will add that to the TODO list.

[mtraven]

Check the voltages with respect to the system ground with a multimeter (and on the encoder connections; be sure to rotate the encoder while watching the meter). For protection, you could put some unidirectional TVS (Transient Voltage Suppression) diodes across the inputs if you want. Also, by setting the values of the resistors in the voltage divider high enough, excess current would be limited should a spike occur.

I will have to put the whole thing, at least the electronics, back together to test it. I was planning on doing that anyways, although I don't have full control of the machine, but I can get it to run its homing sequence. Observing what the stock system was doing will be useful. Wouldn't that be a good place to use my new old scope? And on the voltage divider, your saying if my desired ratio was 2:1 that could be accomplished with a 2k & 1k, but doing it with 20k & 10k or even bigger, will help limit spikes?

Re: the opamp schematics. It's probably possible to combine some of those stages; but I did it the way I did so that the signal processing proceeded in distinct steps

personally, I like that, much easier for me to understand. Still need a couple clarifications though. So I know the rail connections are not shown on diagrams, those would go to the +12 and -12v source from the driver correct? Is the ground in you schematic, 0V (the same 0V that provides the reference input)? Also, you had recommended the lm324, I chip I happen to have in inventor. Its a quad opamp, so I just need one of those to do the circuit you drew right?

*1*

I'll cook up a schematic that shows what I mean when I get a chance.

that would be cool, but don't post it just yet. I think you have given me enough for to work it out and I would like to try to do that on my own, but I'm sure i'll need your answer key soon enough.

output signals: Still a bit perplexed by this, but lets see if I have it right. So one of the inputs is ALWAYS a 0V ground reference, lets call it setpt2. Would that just be a connection to the ground of the arduino? Then setpoint 1 is the result of the circuit you drew, when 0> spins one way, <0 spins the other. That is all determined by the positional feedback PID loop. That sound right to you?

(I'm guessing that if they are replaceable, they wouldn't be cheap)

no they are not, saw a few used on ebay for $100. But new, they go for $250-400 each. Kind of mind blowing to me, its just a DC motor driver..so like an H bridge and then current limiting and such. If that happened, I would probably replace with something else, or consider building my own driver. But lets try to avoid that! On the note of these old ass electronics--that embedded pc is listed in many ebay auctions, usually in the $2000-$3000 range! The pc, even in 2003, is rather humble but also very specific. So is this just legacy cost? It would be cool if I could sell that to help fund some more advanced features of this machine.

with low-cost jewelry cleaners...

yah that what I have, maybe I will just try using it for the final cleaning, after I have gotten most of the gunk off it.

I got my sam21d dev board yesterday, damn that samd is small! I was feeling good about soldering after watching videos, but the scale was not quite there in the tutorials. Anyways, the board was $12 and at my front door in 24hours. it seems unlikely that I will be able to buy the components & have the boards printed for less than that, so I am debating whether I should just go with the custom sheild approach. I think I will do that for at least the first one anyways, see how it goes and decide what to do for the others.

I noticed you use the "XXXnn_t" variable format, I discovered that with my last big arduino project and I very much prefer that.

I am just curious, are you a teacher or something? You seem very patient and are quite good at explaining. I starred at the schematics you drew for like an hour and gained nothing, then you gave me that nice narrative in your last post and things starting clicking fast.

My soldering station project has rolled over into another day, so I will finish it tonight and then get going on the prototype axis card.

Are there any other forums you would recommend to discuss this stuff? I am very thankful to have caught your very knowledgeable eye, but you seem to be the only one.

[norwich]

coincidentally I'm working on the same project. I have made some progress. For ease of programming, I have an arduino controlling each axis to do PID control as an output to the motor drivers (in current mode) and they receive an input of step / dir like a normal stepper driver would. I'm then using estlcam to control each axis, but you could easily sub for GRBL. I'm not done yet, but I do have the control prototyped and working on one axis, and I'm able to successfully control from estlcam. I'm in the process of building mounting everything to a new frame now. If you're interested in details / code I'd be happy to share.