#4 veered off course and came close to #9. Should have taken the route shown as the blue line.
#5 too high up the hill close to the control
#12 running along the highest point of the hill would probably have been better
14.5.2013 Firmaliiga, Salmi
#1 when initially lost, should have continued to the road, re-located on map, and would have found control much quicker.
#6 approaching the control from above would have been better.
21.5.2013 Firmaliiga, Laakso
#6 the organizers had placed this control incorrectly - more than half of the field did not find it.
#9 only major orienteering mistake here - looking for the control on the wrong hill for about 3 minutes before re-locating using the road.
#12 someone had stolen the control flag! By itself the small EMIT-control taped to a tree was hard to find.
#13 should have approached control from above, not below.
Here's how the wedge looks like. It consists of a fixed plate that attaches to the tripod, two fixed side plates that bolt to the bottom plate, and a moving plate that tilts about 10 degrees. The wedge is designed so that the centre of gravity of the MiniTower is positioned straight over the middle of the tripod.
The extra 6mm hole in the side-plates is for an M6 threaded rod through the mount which should provide precise azimuth-adjustment. I did not complete this feature (for example a rotating nut in the fixed plate would be needed).
Setting up grub-pc (1.99-27+deb7u1) ... (pass0:ahcich0:0:0:0): READ CAPACITY(10). CDB: 25 0 0 0 0 0 0 0 0 0 (pass0:ahcich0:0:0:0): CAM status: CCB request was invalid (pass1:ahcich1:0:0:0): READ CAPACITY(10). CDB: 25 0 0 0 0 0 0 0 0 0 (pass1:ahcich1:0:0:0): CAM status: CCB request was invalid (pass2:ahcich2:0:0:0): READ CAPACITY(10). CDB: 25 0 0 0 0 0 0 0 0 0 (pass2:ahcich2:0:0:0): CAM status: CCB request was invalid (pass3:ahcich3:0:0:0): READ CAPACITY(10). CDB: 25 0 0 0 0 0 0 0 0 0 (pass3:ahcich3:0:0:0): CAM status: CCB request was invalid (pass4:ahcich4:0:0:0): READ CAPACITY(10). CDB: 25 0 0 0 0 0 0 0 0 0 (pass4:ahcich4:0:0:0): CAM status: CCB request was invalid camcontrol: cam_lookup_pass: CAMGETPASSTHRU ioctl failed cam_lookup_pass: No such file or directory cam_lookup_pass: either the pass driver isn't in your kernel cam_lookup_pass: or ada0p1 doesn't exist camcontrol: cam_lookup_pass: CAMGETPASSTHRU ioctl failed cam_lookup_pass: No such file or directory cam_lookup_pass: either the pass driver isn't in your kernel cam_lookup_pass: or ada0p1 doesn't exist Generating grub.cfg ... Found background image: /usr/share/images/desktop-base/desktop-grub.png Found kernel of FreeBSD: /boot/kfreebsd-9.0-2-amd64.gz Found kernel module directory: /lib/modules/9.0-2-amd64 done
Some orienteering maps I haven't had time to post before now.
1.5.2013 Myrbacka. Overall very good orienteering on a fairly easy course.
#3 lost a few seconds looking for the control at a big stone when in fact it was a hill
#9 should have found a quicker/better route on top of the hill at #5
#11 slow out of #10 since I did not find the path immediately
2.5.2013 Olars. Again quite good! Maybe slightly harder course.
#1 maybe a bit too careful at the start
#3 very slow close to the control - went for the wrong feature inside the control-circle
#7 did not have very good control/feel for the distance along the #6-#7 path. should have kept up speed better along the path.
#10 amazingly, the huge detour right around the hill resulted in the best leg on this course! Fast running on the road/path, then very carefully into the control which looked hard to find on the map.
4.5.2013 Salmenkallio. Ugh - many mistakes (five out of twelve legs) - and they were out of maps so had to use a hand-drawn map.
#3 circling around as I was looking for the control on top of a ridge or at a saddle, when in fact it was much lower down. Wrong interpretation of height contours..
#5 BIG problems. It should have been easy to run along the path and look for the right cliff features on the right and find the control 50m from the path. I managed to climb the hill much too soon and circle around on top of it. Dead last in the split-times!
#6 veering off compass course to the right, which resulted in unnecessary distance. Blue line shows a better direction.
#11 somehow I was afraid of the green area and decided to run around it, but made a much bigger loop than necessary. Should have run right through(blue line) the green thick area!
6.5.2013, Pirttibacka. This should have been a familiar map... but made bigger mistakes on three out of twelve legs. (numbers refer to the control-codes on the map)
#30 Aaargh! How is it possible to start towards the first control at 90-degrees to the right direction??
#6 wanted to run along the path and find the less steep opening in the hill (blue-line). Didn't run far enough and instead circled around #19
#14 my route is direct but the second half is slow going through an area with many details. The blue line probably shows a route which is easier and more fool-proof to implement.
I've been cranking out parts for this Crimp-Clamp-Tool over the past few days:
(design inspired by Lindsay Wilson's site, which has more information on the seal-off technique)
It's used to permanently seal vacuum-systems that are pumped through a ~10 mm diameter copper tube. The jaws of the tool compress the tube and "cold-weld" the tube walls together which seals the tube.
The top and bottom clamps are milled from 20x40 mm steel bar. The bottom clamp has slots that secure two M12x100 bolts in place, and 6mm holes for M6 screws that hold half inch Thorlabs rods that guide the top and bottom clamps. The top clamp has 12mm holes for the bolts, and half inch holes that I opened up with a boring head so the Thorlabs rods (about 12.66 mm diameter) fit accurately.
The jaws are 3.125 mm diameter carbide rods (the shaft from old used PCB milling bits). They are held in a V-groove on a rod-holder part that bolts to the top/bottom clamps with M5 screws. I glued the rods to the V-groove with Loctite Hysol.
Here's how the crimped tubes look like. The first test resulted in a jagged edge, while the second test produced a nice straight cut. We will test how vacuum-tight these are with a Helium sniffer later.
#15-#16 a long pause to read the map on top of the first hill
#16-#17 a small correction to the south just before the control
#18 had a reasonable plan and executed it OK.
#19 again a long pause to read the map
#20 found the swamp instead of the lake didn't have a good plan when leaving #19
#21 again poor planning running up/down hills instead of around them.
I have no time for this kind of jackassery and have marked my Prime membership to not renew.
Honestly, their "free" video selection was pretty poor anyway, and I rarely watched it, but it was one of the items that made a Prime membership feel like it was worth more to me.
A fairly easy course with lots of running along roads and paths.
Right at the beginning on #2 I searched for it on the wrong hill - on the wrong side of the road/path ?!?
#3-#4-#5-#6-#7 nothing to report. Running speed is enough for top-10 placings
#8 the GPS-path looks ok but speed was slow.
#9 right after #8 the compass seemed to just rotate around and I wasn't confident enough to run by the map alone. Very slow and shaky going to #9.
#10-#11-#12 more fitness required to keep up speed in the forest and uphills
#13 again an easier control and better speed
#14 lost concentration and headed in the wrong direction. Lots of open areas with freshly cut trees (compare to 2012 map)- hard to tell how well the map corresponded to reality here.
Update3: Here's what happens if you disconnect the master from the switch. The slave clock runs off on its own, with about 5ppm drift compared to the reference clock. Once the fiber is connected again it takes a few seconds to re-sync and lock on to the master clock.
Update2: two different measurements, on the left with a short 2m fiber, and on the right with a few hundred meters of fiber to a WR-Switch, and a few hundred meters back.
Update: an improved measurement now shows some promise:
Testing White Rabbit at work. These are fancy network-cards connected by optical fiber which allow synchronization between the cards at better than 1 nanosecond level. My first results are a bit strange:
This is in "grandmaster" mode where we input a 1 PPS and a 10 MHz signal to one of the cards:
A second result in "free-running" master mode:
Just in time with the start of spring in northern Germany I happened to take another week of holiday for working on PyCAM again.
I started on Monday with some previously reported issues (handling of special characters and whitespace in the “recent files” list) and some involuntary easter egg process settings that were revealed only ofter some specific activities.
(The default view is zoomed up close but clicking and dragging with the mouse buttons will zoom/pan/rotate the object. There's still plenty to be done with materials and lighting but being able to share FreeCAD models through a browser is very cool.)
Still lots of snow on the ground, and a temperature just barely above freezing this evening.
The first red (slow) bit between #19 and #20 could not be avoided - just too much snow for running. A bigger mistake on the #11-#12 leg where clearly the better choice after the bridge would have been to run up the hill. Instead I continued north along the stream looking for the small and steep trail up to the control - which was of course completely covered in snow and invisible. Having not learnt much from this I then sort of repeated the same mistake on #25-#24 where my route is direct, but very slow because of snow up to knee-level or above. A small U-turn on #23-#15, but it probably did not cost much in terms of time lost.
My timing-receipt from the EMIT-system shows strange split-times. We'll see if those are corrected in the final results.
We've been playing with a blue laser at 461 nm in the lab lately. If tuned to just the right frequency (wavelength) neutral Strontium atoms will strongly absorb the laser light. Shortly (5 nanoseconds) after that the atoms emit at 461nm also, allowing us to see them:
The atoms originate from a hot "oven" at the right. It glows dark red because it's heated by driving a 5 A to 7 A current through it. The cloud of absorbing atoms glows at 461nm in the centre of the picture.
We can scan the laser frequency by adjusting the current through the diode-laser that produces the light. If the frequency is too low or too high we'll see nothing as the light will just pass through the cloud of atoms without interacting. On each side of the correct absorption frequency we'll see different parts of the atom cloud light up. This happens because the atoms stream out of the oven in slightly different directions, so they experience a different Doppler shift and will react to light with a wavelength slightly to the blue or red from the centre of the absorption-line at 461nm.
When slowly scanning the laser frequency over the absorption-line we got these nice videos. One with a narrow beam and one where the laser beam was expanded.
These were shot with a Canon DSLR so be sure to view them in HD on youtube!
To that end, here's the fingerprint of my key, which is also uploaded to sks-keyservers.net:
Orienteering again! All of the snow isn't really gone yet, but the orienteering season kicks in anyway.
This was a 3km easy sprint course where the opportunity for making large errors was quite small. In sprint-O keeping out of the prohibited areas (e.g. back-yards, in green on the map) of the map is a challenge - there are lots of DQs for this in competitions.
I'm not sure how bad going off the map is considered. At the top of the map between #9 and #10 there was an open path where I, and everyone else, ran, but according to the GPS-trace it might be just outside the printed map.
One of the most productive areas at the Raumfahrtagentur is the textile workshop. As we strive to get as close to the bits as possible in our production methods, a longtime goal was to get dress patterns directly from the digital file to the fabric.
A projector at the ceiling with a mirror projects the CAD drawing made in QCad onto the table. That makes it easy to retrace the cutting lines with chalk directly on the fabric.
I'm going to build an enclosure for my CNC mill to keep coolant and chips from going all over the floor. It took about ten minutes to model the mill table in FreeCAD but modeling all the aluminum extrusions was looking like a lot of work. Fortunately it isn't necessary
More and more vendors are providing CAD data in their online catalog. As long as they provide data in one of the non-proprietary formats, it should import very nicely into FreeCAD.
McMaster-Carr's catalog is legendary and many of their products have CAD data associated. You can download in a bunch of different formats that are compatible with FreeCAD, HeeksCAD, or probably any other CAD system on the planet.
Just click on the part number . In the item detail pop-up there's a CAD link that will take you to a page where you can get 2D and 3D CAD models and also see some dimension data online.
Misumi's site is maybe even better. Misumi will custom cut aluminum extrusions without a setup fee. The nice thing is they also provide custom CAD data for the parts you specify. For example, if you want a 330 mm extrusion, they'll cut it, but you can also download a 330mm model to use in your design.
In the design at the top of the page, I used three different length pieces and played with them in FreeCAD to verify that things would line up on the table the way I wanted.
I wish all vendors provided this, along with detailed specs, schematics, and illustrated parts lists. If you know other noteworthy vendors, drop a comment.
I made this aluminium bit on the lathe/mill today. It holds a blue laser-module from dealextreme. The brass barrel measured about 11.81 to 11.84 mm in diameter so I first drilled a 10mm hole, then opened it up slowly on the lathe until the module just fit the hole. There is an M3 set-screw to hold the laser module in place. Four long M2.5 screws clamp the aluminium part into contact with a peltier-element and the copper heatsink. A thermistor for temperature measurement and feedback control will be glued to the aluminium part as close as possible to the peltier.
Temperature control of the laser diode should provide for rough tuning of the laser wavelength. We want the wavelength to be about 405.2 nm, to be used for photoionization of Strontium.
Aside: A few years ago I tried to order some of these 405nm laser-pointers to the university. It was impossibly difficult because the shipments were stopped by the customs. Negotiations with the radiation-safety authorities did not help. It's simply forbidden to import non CE-approved laser-pointers - it doesn't matter if you are a researcher or work at a research institution. The story is completely different for laser modules (this is exactly the same product as the laser-pointer, but without the pen-like shape and the battery holder). Apparently these are classified just as "diodes" or "electronic components" and there are no problems getting them through customs.
3D printed parts always have this rough, structured finish where you can see and feel the printed layers very clearly. Various methods have been tried out to get to a nice polished finish. The most promising so far has been treatment with a SMD hot air desoldering station, but thats a lot of manual work and does not always give really nice results.
So a few days ago at http://blog.reprap.org/2013/02/vapor-treating-abs-rp-parts.html came along an interesting description for using acetone vapor to achieve a nice and smooth surface. Initial trials using a small glass and a minor amount of acetone looked promising, so we ordered some labware and raided the Raumfahrtagentur Biolab for a heatplate with precise temperature control.
Safety warning: acetone and especially acetone vapor is combustive and a fire risk. Only work in a well ventilated place and have a fire extinguisher at hand. Do not heat on an gas stove. Read the safety warnings regarding health risks for acetone. Don´t Panic.
This is our current process description, to be changed and updated as we find out more.
You can see clearly how high the vapor has risen
Apparently the smoothing continues for a while after removal, until the acetone vapor has vanished. Cover acetone cylinder again and wait a couple of hours for your objects to become hard again.
First series of controlled experiments with test bodies. 5 minutes is sufficient for proper smoothing. Touch-hard after about 30 minutes sitting. Apparently a little bit of shrinking occurs (less then 0.5mm on 20 mm diameter / width). The test bodies were printed with 3 outer layers and 40% infill, the print was rather sloppy and imperfect. Next series with more infill and / or more outer layers.
OpenScad file with the test bodies attached.
$ printf "%f\n" 1.23 1.230000 $ LC_ALL=de_DE.UTF-8 printf "%f\n" 1.23 1.230000 $ env LC_ALL=de_DE.UTF-8 printf "%f\n" 1.23 1,230000
If we push a current through the resistor we'll get a voltage of across it. Now as the temperature changes the resistance will change by where is the temperature coefficient of the sensor. This will give us a signal
Here's a table with some common values for pt100 and 10k NTC thermistors. The sensitivity is determined by the sensor type. What limits is self-heating of the sensor which probably should be kept to a few milli-Kelvins in most precision applications. Thermistors with their higher sensitivity are an obvious choice for high-resolution applications, but the lower of a pt100 sensor can be compensated with a larger since most pt100 sensors are physically larger and thus have lower self-heating. pt100 sensors require 4-wire sensing, slightly more complex than a 2-wire measurement which is OK for a thermistor.
|Sensor||Resistance||Sensitivity (divide by R to get alpha!)||Dissipated Power P||Noise-Equivalent-Temperature
|pt100||100 Ohms||0.391 Ohms/C||100 uW (I=1mA)||3 uK|
|NTC Thermistor||10 kOhms||-500 Ohms/C||9 uW (I=30uA)||0.9 uK|
I conclude that it is not entirely obvious how to choose between a pt100 and a 10k thermistor. The thermistor is intrinsically more sensitive, but with good thermal contact to its surroundings self-heating in a pt100 sensor can be minimized and the same noise-requivalent-temperature achieved. In any case it looks like Johnson noise limits resolution to 1 uK or so in a 1 Hz bandwidth. If we AD-convert the voltage at 24-bit resolution (16M states) we can get a reasonable measurement range of ~32 K by matching 1 LSB = 2 uK.
Does anyone know of similar back-of-the-envelope calculations for other sensors (Thermocouples, AD590)?
Here's an experiment I've done recently:
(Time-lapse of ca 18 hour experiment. Bottom left is a spectrum-analyzer view of the beat-note signal. Top left is a frequency counter reading of the beat-note. Bottom right is a screen showing the a camera-view of the output-beam from the resonator)
This is a measurement of the thermal expansion of a fancy optical resonator made from Corning "Ultra Low Expansion" (ULE) glass. This material has a specified thermal expansion of 0.03 ppm/K around room temperature. This thermal expansion is roughly 800-times smaller than Aluminium, around 400-times smaller than Steel, and 40-times better than Invar - a steel grade specifically designed for low thermal expansion.
Can we do even better? Yes! Because ULE glass has a coefficient of thermal expansion (CTE) that crosses zero. Below a certain temperature it shrinks when heated, and above the zero-crossing temperature it expands when heated (like most materials do). This kind of behavior sounds exotic, but is found is something as common as water! (water is heaviest at around 4 C). If we can use the ULE resonator at or very close to this magic zero-crossing temperature it will be very very insensitive to small temperature fluctuations.
So in the experiment I am changing the temperature of the ULE glass and looking for the temperature where the CTE crosses zero (let's call this temperature T_ZCTE). The effect is fairly small: if we are 1 degree C off from T_ZCTE we would expect the 300 mm long piece of ULE glass to be 200 pm (picometers) longer than at T_ZCTE. That's about the size of a single water-molecule, so this length change isn't exactly something you can go and measure with your digital calipers!
Here's how it's done (this drawing is simplified, but shows the essential parts of the experiment):
We take a tuneable HeNe laser and lock the frequency of the laser to the ULE-cavity. The optical cavity/resonator is formed between mirrors that are bonded to the ends of the piece of ULE glass. We can lock the laser to one of the modes of the cavity, corresponding to a situation where (twice) the length of the cavity is an integer number of wavelenghts. Now as we change the temperature of the ULE-glass the laser will stay locked, and as the glass shrinks/expands the wavelength (or frequency/color) of the laser will change slightly.
Directly measuring the frequency of laser light isn't possible. Instead we take second HeNe laser, which is stabilized to have a fixed frequency, and detect a beat-note between the stabilized laser and the tuneable laser. The beat-note will have a frequency corresponding to the (absolute value of the) difference in frequency between the two lasers. Now measuring a length-change corresponding to the size of a single water-molecule (200 pm) shouldn't be that hard anymore!
Let's say the stabilized laser has a wavelength of (red light). Its frequency will be (that's around 474 THz). When the tuneable laser is locked to the cavity we force its wavelength to agree with where is an integer and is the length of the cavity. I've drawn only a small number of wavelengths in the figure, but a realistic integer is . We get and , very nearly but not quite the same wavelength/frequency as the stabilized laser. Now our photodiode which measures the beat-note will measure a frequency of .
How does this change when the ULE glass expands by 200 pm? When we heat or cool the cavity by 1 degree C the length changes to 300 mm + 200 pm, and the wavelength of the tuneable laser will change to
. Now our beat-note detector will show . That's a change in the beat-note of more than 300 kHz - easily measurable!
That's how you measure a length-change corresponding to the diameter of a water molecule!
Why do this? Some of the best ultra-stable lasers known are made by locking the laser to this kind of ULE-resonator. Narrow linewidth ultra-stable lasers are interesting for a host of atomic physics and other fundamental physics experiments.
The first design is a single transimpedance-amplifier (TIA) using an ADA4817 and a 1 MOhm resistor. This isn't a great design, since the op-amp is much too fast compared to what is needed/required here. The second design is a 7 kOhm TIA (AD8597) followed by a ~140 V/V gain non-inverting amp (ADA4817). This gives the same total effective gain of ~1 MOhm.
These circuits were designed for a 2 V output with a 2 uA photocurrent produced by about 5 uW of HeNe laser light at 633 nm. The output will hit the "roof" (the positive rail) at about 12 uW of optical power.
The agreement between simulation and experiment is not very good. I suspect my extremely simple LED-test is to blame. I should build a VCSEL circuit which allows testing these and other photodiode receivers to much higher frequencies.
I assembled and tested the latest photodiode-amp today. I tested the frequency response using a red LED driven directly by an Agilent function-generator with an offset of 1.2 V and a 600 mVpp sine-wave. The LED datasheet doesn't specify a rise-time or bandwidth, but I'm hoping it is fast enough to test this 2-3 MHz receiver. I do have some small VCSELs that should be very fast and suitable for testing photodiode receivers up to 500 MHz and beyond.
The signal from the LED caused a 3 V output swing, which explains the slightly lower observed (large-signal) bandwidth compared to the simulated (small-signal) bandwidth. Some of the difference between the simulated frequency-response and the measured one is probably explained by stray capacitance which slightly lowers the bandwidth.
A revised version of the circuit and PCB for a photodiode amplifier, to be used in PDH-locking (Pound-Drever-Hall) as well as RAM-nulling (residual amplitude modulation) in a laser experiment I am doing. The changes compared to the first prototype are:
Here is a schematic and simulation results produced with the free version of NI Multisim from Analog Devices. The design is for roughly 1 MOhm of transimpedance gain in total, here split between 7 kV/A transimpedance gain, and 144 V/V for the non-inverting second op-amp. At 1 kV/A of transimpedance gain a 5 uW optical signal at 633 nm (HeNe laser!) that produces a 2 uA photocurrent will result in a 2 V output signal. The AC analysis shows very slight gain-peaking for the transimpedance-stage (red trace) and a -3 dB bandwidth of >3 MHz overall (green trace).
The first op-amp used in the transimpedance stage only needs to have a bandwidth slightly exceeding the transimpedance gain bandwidth (the feedback resistor R1 together with the compensating cap C1, the capacitance of the photodiode C2, and the input-capacitance (not shown) of the op-amp form an RC low-pass filter). The AD8597 is marketed as "ultralow distortion/noise" and is fast enough (10 MHz). The second non-inverting op-amp needs a high gain-bandwidth-product (GBP) since we are amplifying ~100-fold here. The ADA4817 has a small-signal bandwidth of 1 GHz and GBP~400 MHz, so should work OK here.
A voltage of only 14 mV over the transimpedance-resistor is not ideal. The Johnson noise (which in principle a good designer can control/minimize) in the resistor will dominate over the shot noise (which we cannot avoid) in the optical signal. For shot-noise limited performance the rule of thumb is to make the voltage drop at least 51 mV (which will make Johnson and shot noise equal). Without tricks however that is not possible as here we have both a weak signal (2 uA of photocurrent), we want a high gain (1 kV/A in total), and we want to go fast (~3 MHz bandwidth)! If you relax any of those requirements (more power, less gain, slower response) it is straightforward to build a shot-noise limited amplifier in one or two stages.
The PCB, fresh from the mill:
Far right is a 3-pin TO-18 socket for the photodiode. Right-middle are the two op-amps with their feedback-resistors/caps, as well as two de-coupling caps for both +5V and -5V. Left-middle are 7805 and 7905 voltage regulators, and the BNC output-connector is far left. All the surface mount components are mounted on the top layer of the board, while the through-hole components are bottom-mounted. Resistors and caps are 1206-size. This PCB should fit the earlier enclosures I turned on the lathe.
Hopefully I will have time to assemble and test one or two of these next week. I should measure the actual frequency-response and compare it with the simulated one.