Category: Informatics

LinuxCNC servo tuning

John Candlish

I’m fairly satisfied with my servo tuning results.  Pretty much within a 10 micron bound at the path reversals with acceleration set to 800mm/s2 and velocity at 300mm/min.

The deviation from the planned path is within a couple of microns during the constant velocity sections of the motion.  I think I can reduce that further by compensating for the error measurements I’ve made of the analog drive system.

An analog +/- 10V signal commands the velocity of the servo drive.  That signal is derived from a filtered PWM source.  Sweeping the signal range while measuring the servo velocity gives a scatter graph like this:

Applying the mean to a sliding bin of size 0.1mm/s shows that both axes have very similar responses once the gain has been nulled.

Overall the velocity of the servos are within 0.3mm/s of the commanded speed over a range of +/- 67mm/s.  (2000rpm @ 2mm/rev).  While very good, this error feeds into the PID loop, and is quite characterizable, so there is room for improvement.

 

Here a short video of the test system running.  The first portion shows the high speed performance  while following the ‘EMC AXIS’ path.  The second portion shows holding a tolerance of better than 20 microns over a simple path programmed at 300mm/min.

 

The first part of that video should probably have been in slow motion.

 

Fixing the WordPress multisite master hostname

John Candlish

There is an unfortunate design choice in WordPress, where the ‘Network Admin’ site is assigned to the www. hostname of a wildcarded domain.

This is a poor choice because almost invariably the Site administrator will want to assign the www. hostname to an IP address available on the internet.

To allow master.example.com to be the Network Admin default site it is necessary to change the

files of your WordPress installation.

As of WP-4.4.2 the change looks like this:

Then also define the constant COOKIE_DOMAIN in wp-config.php.

If you are correcting this from a default installation it may be necessary to also adjust the database, as documented here ==> How to change a Multisite primary domain, and elsewhere.

Migrating the cyrus-imapd backing store

John Candlish

Migrating the cyrus-imapd backing store to a new server, while at the same time changing the mailboxes domain, can be a bit tricky. The following procedure works for me.

These notes are for Kolab’s version of cyrus-imapd (2.5~dev2015021301-0~kolab1.1).

Stop all the services on the target machine that might interfere with the migration.

Make a backup of the target machine’s LDAP database. Delete the target DN ou=People,dc=(the mail domain), it will be restored in a later step.

For a new migration stop the target cyrus-imapd service and clean the directory structure.

Restore the DN ou=People,cn=(your domain) that you deleted above. Kolab will notice the change in the LDAP directory and recreate the mailbox structure in the cyrus-imapd spool files.

Now synchronize the backinstore with imapsync.

Imapsync might have a problem finding the mailbox folders. Notice the difference specifying a domain can make.

My gnupg public key

John Candlish