Mill with digital scales

[irving2008]

I've done the read a dxf, pick out lines arcs and circles then stitch lines and arcs together into shapes (fudging the ends slightly so they meet up properly). Also the expand/contract it bit to get the tool path.

No G-Code planned, it goes straight to my box of tricks and turns the handles. I have a wicked arc drawing algorythm my brother wrote, any start point, any end point, either direction. I just call it and it gives the next pixcel on the arc. I tried it drawing circles on screen, then had to add a delay between pixcels so you could actually see where it started and which way it was going :D

Sounds interesting... so lets see some pics :)

My preferred small quantity supplier has to be Rapid Electronics.

Thanks, I'll go investigate

40 volts is very close to smoke if you're using a transformer, suggest you do something clever in the PSU to protect it.

Yes I know. Go to do a back-emf dumper and some sort of voltage limiter (not a regulator as such) - looking at some ideas that combine the two. Don't want to use a series regulator cos of the losses involved at 6A+ (if all 3 axis active) but thinking along lines of series/shunt MOSFETS (got a couple of samples rated at 120A, 200V and 0.003ohm Rds, so even at 10A its not going to get warm if turned fully on!)

[Robin Hewitt]

Sounds interesting... so lets see some pics :)

I could do a movie of me slaving over a hot PC but apart from that there is little to see yet.

Now working on the command protocol, having a slight snag with a worst case fast traverse doing 2 steps in one axis and 1 step in the other. It's a baud rate thing :D

[irving2008]

My preferred small quantity supplier has to be Rapid Electronics.

Thanks, I'll go investigate

Well I priced the parts for my controller from Rapid - they came out about 3% more expensive than Cricklewood and didn't have a couple of parts but had some better options on others... Only sell resistors in packs of 100 though.

[Robin Hewitt]

Well I priced the parts for my controller from Rapid - they came out about 3% more expensive than Cricklewood and didn't have a couple of parts but had some better options on others... Only sell resistors in packs of 100 though.

That's a surprise because they are having a sale at the mo'. I ordered a hundred quids worth yesterday and it was on my desk by 10:30 this morning :D

[irving2008]

Robin,

Have you seen this thread on CNCZone discussing PIC-based DRO capbility using cheap chinese scales?

regards,
Irving...

[irving2008]

I guess, seeing as you posted there tonight, the answer is now yes :)

[Robin Hewitt]

I guess, seeing as you posted there tonight, the answer is now yes :)

Absolutely, thanks for the heads up :D

I'm not sure he isn't introducing too many delays, that scale data gets very stale very quickly. I suppose it all depends on what he is trying to achieve.

I made the data input, scale reading and motor stepping completely interrupt driven. There is a sort of housekeeping program that looks for new devices and button presses, but all the vital stuff happens automatically in the background without the slightest intervention apart from Pause and Abort. It's as close to real time as I can possibly make it. I find PC's are a bit too handy at turning the interupts off.

[irving2008]

Absolutely, thanks for the heads up :D

I'm not sure he isn't introducing too many delays, that scale data gets very stale very quickly. I suppose it all depends on what he is trying to achieve.

I made the data input, scale reading and motor stepping completely interrupt driven. There is a sort of housekeeping program that looks for new devices and button presses, but all the vital stuff happens automatically in the background without the slightest intervention apart from Pause and Abort. It's as close to real time as I can possibly make it. I find PC's are a bit too handy at turning the interupts off.

Using a PC for anything truly real-time is hard - actually its not the PC of course, but Windows that is the issue. There are good real-time extensions for Linux and there used to be a pretty good real-time extension for Windows too but I don't know what happened to it - http://www.directinsight.co.uk/produ...urcom/rtx.html is something similar though. I've done projects in the past with single board and single chip solutions with tiny real-time kernels such as iRMX, embedded Linux as well as solutions based on WindowsCE, stuff you couldn't begin to make work reliably under Windows.