shackspace Infrastructure: OR4 Room Rearrangement
shackspace recently got a full-body scanner donated and we needed some space to set it up. For this we needed more space in room OR4.
Together with dritter, lotho and domyos we moved around some tables, cleaned the laser cutter coolant tank and re-filled it with fresh water.
shackspace Infrastructure: Laser Exhaust Fix
The shackspace laser cutter had a bit of a suction problem. The low pressure side of the big air pump connecting the pump to the cutter was soft and unstable and fell in on itself when the pump was running.
I’ve replaced the tube with a big flexible clothing dryer tube and got an angle and reduction piece to connect the lower diameter high pressure side to the exhaust going out of the building.
With help of dritter I then mounted the pump itself on the underside of the laser cutter table to clean up the mess under the table a bit.
Works like a charm and suction power is greatly increased.
Project INFRA #5: Light Barrier Breakout
The results are most excellent! I’m very pleased with how the boards turned out.
The price was reasonable bordering on low. However, the low priority international shipping did take around three weeks. But you get what you pay for :)
Experiment: Resonant Inductive Coupling
Because the automatic drip irrigation system on the balcony needed power - at least some of the time - I decided to do some quick and dirty experimentation with resonant inductive coupling.
The basic idea is to have two coils of similar dimension (the simple case).
Drive one coil with an AC signal - in my case this was done using a function generator and hold the second coil close to it.
For optimal power transfer, make sure the receiver coil is resonating at the frequency you’re using to drive the sender coil.
The most difficult part if you don’t have to have a LCR meter at hand, is finding out the inductance of your - probably - hand-made coils. Luckily there’s several methods to measure this if you happen to have some other tools at hand. I’ve used method two outlined in this handy howto.
To design the resonator circuit for the receiver, there’s also a nifty little calculator.
I somehow didn’t manager to get this setup to drive a LED on the receiver end, but that might be down to either too little drive strength or me screwing up the receiver circuit. Probably the latter.
However, I was able to get a nice strong coupling at least on signal level when measuring it with my scope.
shackspace Infrastructure: Spray-Etch Tank Heater Fix
The last time bronsen and I wanted to use the spray-etching machine the heating element broke in a spectacular fashion (smoke, blown fuses, everything).
I’ve ordered a new heater (thanks Timm for pitching in) and now only hat to somehow mount it in the tank. This wasn’t straight forward since the old mount broke as well.
However, we do have a laser cutter at shackspace!
I grabbed a caliper and quickly measured out the key dimensions needed for a mount. I cut the mount from four millimeter PMMA (Plexi) and also cut four mounting slots in the base plate of the etching tank.
The mounts slide right over the heater’s glass tube and then slot into the base plate. Everything holds together by itself as long as you don’t lift the base plate. This allows for easy maintenance and replacements should the heater break again.
Project INFRA #4: GPN14
bronsen and I went to GPN14 a week ago and learned a few very valuable design-lessons.
1) The coils using ~10 loops of 2.5 mm² NYM wire don’t cut it. We can’t feed enough current through them to produce any serious magnetic field.
2) Thinner wire but also more loops results in way better magnetic performance.
3) Using pieces of threaded rod as ammo we did science (a bunch of measurements and some math) and determined there’s an optimum distance between coil-center and projectile-center paired with an optimal trigger-pulse duration to fire a single stage coilgun. It doesn’t seem to matter much how long the coil and/or projectile is.
4) Record muzzle velocity was 3.8 m/s (not really much)
5) We need better coils (more loops, way more loops)
We did some preliminary trials with a double-stage coilgun. Results weren’t really what you could call a break through, we’ve only gained around 0.4 m/s in muzzle velocity. Probably the hand-tuned timing is off.
Timing will be replaced by proper real-time calculations in the next iteration. As a preparation for better speed measurements, we’ve already soldered simple light barrier breakouts that come with the required resistors and can be simply hooked up to the Arduino board which we’re using currently for prototyping.
In other news, we’ve decided to name the project INFRA. Short for infuanfu rapid accelerator. There’s also some code on Github which is almost certainly no use to anyone at this point.
Project INFRA #3
The borosilicate glass tubes arrived! So did the light barriers.
I quickly soldered a prototype on a piece of perfboard and hooked it up to my oscilloscope to measure the falling speed of anything I drop through the glass tube.
A rough calculation tells me I’m in the ball park and there should be enough accuracy to scale up to higher speeds which will be required for the actual coilgun setup.
Timing will later be done using an Atmel Atmega32U4 (probably) with options to go nuclear using a CPLD or maybe even an FPGA. No reason not to go insane ;-)
After all, I’ve got those components still around form a previous project.
Updates will follow.
Project Fronius Repair #3
The first batch of replacement components arrived and I started replacing a few here and there.
In the process of doing that I removed one of the larger circuit boards and noticed huge black smoke stain on the back. Turns out that one of several APT5010JVR power mosfets died.
On Digikey those go for 36 EUR. On Ebay however you can get them for as cheap as 14 EUR. Well, you do pay with longer shipping time (3 to 4 weeks).
Time to wait again…
Project INFRA #2
The second iteration of the coilgun project yielded in one awesome decision and one bad decision.
First the awesome decision: bronsen (who joined me in scaling up the coil gun) and I decided to get a proper high power capacitor. Specifically the Maxwell BCAP3000 that comes with a whopping 3000 F (note: no milli or micro here, proper Farads) capacitance.
It takes a “while” to charge it up (read: long minutes to few hours) depending on how much current you can provide.
However, the short circuit current of this beast is at around 10 kA thanks to a mere 0.28 mOhm ESR. Enough to use it for spot welding and melting of nails.
The bad decision we made was using 16 mm PVC tubing as a barrel.
The extra power we got from the huge capacitor was not enough to produce a magnetic field strong enough to get anywhere close the power we had with the small capacitor bank in the first iteration.
Also, with a capacitor of this size, we would not be able to simply shut down the magnetic field by waiting for the cap to discharge. It would simply take too long and produce way too much heat in the process.
So a means to actually switch such a high current was called for. The most powerful FET we found at Digikey was the IXYS IXTN600N04T2. It’s able to switch 40 V and up to 600 A. So we got a few :3
To measure the projectile speed and time the switching of the coil we decided to go for the bare bones solution using IR LEDs and suitable photo darlington detectors.
To attach the homebrew light barriers to the PVC tube, I quickly designed a clip-on holder in Inkscape and used the shackspace laser cutter to cut a prototype from birch plywood.
The light barrier turned out to be sub-par for the task. Especially the holes that had to be drilled into the tube were a bit tricky to manufacture. The most difficult part was sanding down the edges of the holes inside the PVC tube so that the projectile wont get stuck.
The next iteration will change two things:
- Replace the PVC tube with a borosilicate glas tube. It’s transparent so no holes have to be drilled.
- Replace the 16 mm sized tube with an 8 mm sized tube. This will result in a stronger magnetic field.
- Replace the homebrew light barrier with off the shelf 8 mm light barriers. No tricky alignment or mounting issues.
Practical Data Projection
Easterhegg is over and we had some printouts with personal data left. Mostly lists of names and a few notes taken during the event.
To make sure no personal data ends up in the wrong hands we decided to take the most fun solution and employed the process of rapid oxidization paired with mechanical agitation of the carbon fallout to ensure proper information disposal.
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