#linuxcnc-devel Logs

Mar 25 2018

12:09 PM pcw_home: rene-dev yes 7I74 will work with type I serial pulsecoders
12:16 PM pcw_home: type I are RS-422 (1 TX pair for request, 1 RX pair for data) type II are RS-485 (1 TX/RX pair for request and data)
01:36 PM andypugh: pcw_home: While we are talking about 8i20, I found a strange quirk yesterday. With an unconnected motor running flat-out, if you set the 8i20 current to zero it continues to run at full speed. Friction on the pully stops it instantly, but it does look as if the 8i20 is still supplying currrent up to that point.
01:36 PM andypugh: (Maybe some sort of back-emf resonance thing?)
01:46 PM pcw_home: I think its possible a resonance thing with large angle steps
01:51 PM pcw_home: probably fixable by running the servo thread faster (or lowering the current loop gain)
02:04 PM pcw_home: andypugh I know you experimented with some laser control hal code, what do you think is the best way access motion synced laser data?
02:07 PM pcw_home: an external file and halstreamer and a hal only data path or embedded somehow in the gcode (allowing arbitrary motion data painting with a surface length vector)
03:15 PM rene-dev: pcw_home thanks! I had some communication problems, but it turned out just to be too much voltage drop on the 5v. the older encoders draw a lot of current
04:31 PM pcw_home: those encoders are pretty amazing, maintaining absolute position on a few 100 uA
04:31 PM pcw_home: (from the battery)
04:32 PM pcw_home: if you turn them when on battery power you can see the current go up as they
04:32 PM pcw_home: increase the power up/down sample rate to not miss counts
04:39 PM rene-dev: yeah, very cool :)
04:39 PM rene-dev: do you know how exactly the crc works?
04:45 PM pcw_home: yeah
04:51 PM pcw_home: CRC5-ITU, MSB first (over 76 bits)
04:56 PM pcw_home: not sure about type II
05:01 PM rene-dev: over all 76 bits, so you include the crc in the calculation, and it should return 0?
05:03 PM pcw_home: I think so, its been a while
05:05 PM rene-dev: do you check the crc in the fpga or dirver?
05:06 PM pcw_home: Yeah 0 over 76 bits: http://freeby.mesanet.com/fabsread.pas look at then end of softcrc
05:07 PM pcw_home: The hardware doesn't check, the driver could but does not currently
05:09 PM rene-dev: yes, looks like it calculates over all bits
05:13 PM rene-dev: do you know how abs encoders differ? do they just always set the index found bit, and return a abs position?
05:17 PM pcw_home: They have a power fail bit (is that your index found?)
05:18 PM pcw_home: that gets (set or cleared not sure) if they ever lose main and battery power
05:23 PM pcw_home: note that they all have a absolute commutation track (10 bits) that does not depend on the battery
05:34 PM rene-dev: yes, I found that. there is one bit that clears when it passes the index