Month: March 2008

WordPress 2.5

WordPress 2.5 is out, and I've upgraded. Most of the shiny new stuff is on the admin side only, and so the outward look of the site remains.

The upgrade went smoothly, with the usual tweaks to style.css for the ever changing header image and to put the blog title in the left upper corner.

I've started tagging my posts, and there's a new tag-cloud at the top of the sidebar. I'll use it as a way of sub-categorizing posts without actually creating new categories. Once it's been in use for a while it will be useful for searching too.

Another recent update to the site is the list of WWW-links in the sidebar ("Anders' Web tips"). It's an RSS feed of the links I mark as 'shared' in google reader. Hope you like them!

Hard disks are not forever

Just had a 2-3 year old SATA drive fail on me. If you're reading this, go and take backups of critical data. Do it. Now.

This is the cnc-mill controller machine so hopefully no critical data was lost. Some notes on the EMC2 install process, just in case I need to do it all over again sometime soon...

  • Install WinXP on a 50 Gb NTFS partition
  • Installed Ubuntu 6.06LTS from CD. Manual partition, 50 Gb for root file system, 2 Gb for swap.
  • Ubuntu update manager suggests 301 updates (278M) to install. I'm in Finland, but strangely my sources.list points me to au.something servers. Reboot.
  • Install EMC2 using emc2-install.sh. Reboot.
  • 'latency-test' shows reasonable jitter values - good.
  • Configure X to enable 1280x1024 resolution: 'sudo dpkg-reconfigure xserver-xorg'. Answer lots of techy-questions, remember to add the correct screen resolution and the correct keyboard (pc102). I wasn't able to log in the first time I tried this because I had chosen an incorrect keyboard type/layout.

VFD control board

This small PCB is going to sit between the M5i20 optoisolators and the VFD that runs the spindle on the mill.

Starting from the lower edge of the card there are three outputs that drive optoisolators on the VFD through BC337 transistors. On the VFD they are wired to Forward Start/Stop, Reverse Start/Stop, and External Fault.

The next signal goes in the opposite direction, from VFD to EMC. The VFD has a general purpose analog output which can be programmed to monitor motor current, power, etc. Since the m5i20 doesn't have analog inputs I'm using the V-2-f converter AD654. It's hidden below the board since it was only available in surface mount. As seen below it seems to work nicely. I designed the output to be at 1000 Hz with 10V input, but I'm only supplying 12 V to the AD654 which means the output goes all funny somewhere after 8 V input. Maybe the VFD software can scale the 0-10V output, or I can put a voltage divider in front of the AD654 to get maximum 8 V input. I need to come up with a HAL config that reads a general purpose IO pin and figures out the frequency (think big green/red pyVCP spindle load meter in AXIS).

The top two connections are for the frequency reference, a pulse train, and for an NC E-stop relay.

This card together with a spindle encoder should allow for rigid-tapping.

Clear skies - Finally!

It's been cloudy almost every night for about three weeks now, but finally today a half-decent sky-watching night. The moon is full, so my moon pictures were predictably quite bland. I tried to search for some messier objects, but with a poor finder-scope and 25mm being the widest eyepiece that didn't work out too well (even with Stellarium on the laptop right beside me...). Here's the best of around 10 shots of Saturn.

102mm refractor, f=1000mm (~F/10), 2x Barlow, Canon 20D, 1/3 s exposure at ISO100

Timing build_kdtree()

Drop-cutter requires a fast way of searching for triangles under the tool. A kd-tree (4-dimensional in this case) is suggested by Yau et al. I've tried to implement one here (look in trunk/Project2). Just ran some timing tests using Stopwatch() on it, and indeed the build_kdtree() function which takes a pile of triangles as input and generates a kd-tree seems to run in O(N*log(N)) time as it should.

I've never drawn this type of plot before, and I was surprised at how close N*log(N) is to N - in a loglog plot they are almost equal!

This is a recursive function. I wonder if there's a good way of multi-threading recursive functions? My laptop is dual-core and a modern desktop PCs is likely a quad-core - so let's try to write these things multi-threaded from the start.

Next up is a function for doing the orthogonal range-search for triangles that lie under the tool. That's supposed to run in O(N^(1-1/D)+K) time, where D is the dimension of the tree and K is the number of reported triangles - so O(N^(3/4)+K) in this case. I'll try to get that done during the weekend.

E-stop circuit

This is the E-stop circuit I am going to use when upgrading the cnc-mill to servo control. The idea is to use a wire-OR circuit (series connection of NC switches) for things that cause an E-stop followed by a wire-AND circuit (parallel connection of relays) for things I want to happen at E-stop.

The E-stop out signal from EMC is wired to the top right of this board (labeled E-stop IN...). When this signal goes high it closes the rightmost relay which has +12V wired to it. The 12 V then goes through a series of NC switches, which I've here just shorted out with the black wires. In reality the black wires will be replaced by one E-stop button on the main enclosure, one E-stop button on the jog-pendant, X/Y/Z limit switches, NC servo-amp fault relays, and a VFD NC fault relay.

When all is well +12 V is supplied to the three other relays, and these provide NC or NO outputs. One is used to tell EMC everything is OK (E-stop IN signal in EMC), one is used to enable the power switch of the axis servos, and one is spare for now.

This should make the machine reasonably safe. If any of the E-stop buttons are pressed, a limit is tripped, or the servo amps/VFD are not feeling well we should go into E-stop, and that will cut power from the servos. EMC will also notice this and I'm relying on EMC to shut down the coolant pump and the VFD.