Procrastinatus

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Archive for the ‘Projects’ Category

DIY Robot-boat at AUVSI’s Autonomous Surface Vehicle Competition 2009

Posted by aonomus on June 24, 2009

So the major project that I have been involved in recently was working on an autonomous surface vehicle (ASV) that was entered in AUVSI’s 2009 ASV competition. Given a small team (6 people, 2 builders), under $1000, and about 30 days we built what would be considered a feat of bodging and hacks based on extreme ingenuity and resourcefulness.

Note that of the four people in the photo above, it consists of (from left to right) a comp sci masters student on exchange, a political science student, a broadcast technician, and a chemistry/biology student.

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Posted in Arduino, Autonomous surface vehicle, Electronics, Projects, Robotics | Tagged: , | Leave a Comment »

Cap Bank – Rogowski Coil

Posted by aonomus on January 29, 2009

So before I really get started with my capacitor bank, I decided I would design on paper all the instrumentation so I could characterize the capacitor bank discharges. In order to measure current over time, either current shunts (DC), current transformers (AC), or rogowski coils (AC, pulse) can be used. The advantage of a rogowski coil is that it is equivalent to a air-core current transformer allowing for much faster response to changes in current flow. Also, due to construction, a rogowski coil can be opened and closed for placement in temporary positions.

Yesterday I finished my constructing my rogowski coil, however it still requires an active integrator to make voltage proportional to current. I used RG6 coax cable, stripped the outer sheet, braid, and foil, then wound 30AWG magnet wire evenly around the dielectric. The magnet wire was attached to braid and core at either end, heat-shrinked, and luer-lock syringe fittings were placed on the ends to allow for the coil to be placed around an object.

A major key to being able to construct a accurate rogowski coil is that the windings must be absolutely even, and remain even as the coil is bent and closed. It is easier to wind a coil on a straight segment of dielectric, heatshrink, then bend, instead of attempting to precision-wind around a torroidal coilform.

The luer-lock fittings prior to attachment.

The completed rogowski coil, note the heatshrink around the coil and BNC connector on the end.

Closeup of the joint where the coil closes. I didn’t have small enough heat-shrink so I had to wedge some tiny pieces of balsa wood in to keep everything snug and secure.

Once I had the coil built I gave it a test, first using a small motor, and a second test using my old coilgun.

I used a induction motor fan wired up to 120VAC for the first test, it didn’t seem to be affected by an un-centered conductor, however I may still build a plexiglass support so that under higher-voltages there is no risk of arcing into the coil (the heatshrink + enamel can only stand so much).

The test setup and waveform (sine = 120VAC, other = current).

The second test was performed using my old 430J coilgun, I looped the coil around the heavy cable from the stud-SCR and tested a few voltages. I captured the waveforms using a soundcard oscilloscope program and got some data, however the higher powers generated voltages exceeding the max rating of the soundcard, causing clipping.

The 3 test waveforms captured at increasing capacitor voltages, note the last test at 430V caused significant clipping of the current waveform.

And also, 2 videos (the last 2 tests)

Posted in Capacitor Bank Mk 1, Electronics, Projects | Tagged: , | Leave a Comment »

Mini project – Vacuum tube retro

Posted by aonomus on December 29, 2008

So I was browsing through Active Surplus (downtown Toronto on Queen St.) and saw (like any other trip there) these gigantic cardboard boxes full of vacuum tubes. Apparently they were $1 a piece, but I never asked before. I came home with 5 tubes and 5 matching sockets and went to home depot to buy a prime (read $2) piece of wood.

I drilled evenly spaced 1″ holes (just a hair under the size of the tube socket base) and mounted the sockets, then added ‘feet’ to give it more presence.

I plan to look up the datasheets on the tubes and find out the fillament voltages, with any luck they will all have matching filament voltages so I can power them all off a 6.3V or 12.6V power supply (perhaps just a LM317 set for an appropriate voltage) to get warm glowing tube goodness. A bench test with 6V and 12V shows that this does actually work.

Note for photographers: this was a super low light photo, I had to take 2 separate 15 second exposures at both 200 and 400 ISO and composite them to get a decent looking photo…. in real life the tubes are no where near as bright.

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Ever so busy…

Posted by aonomus on October 26, 2008

Well, as usual I vanish off the face of the internets due to being too busy, but at least I have plenty of juicy things to show you guys. I’ve finished off my solid state tesla coil (SSTC), made most of my spectrum analyzer, and been doing leatherworking on a Halloween costume. This post is very image intensive so for the sake of anyone with 56k I’m going to separate it from the main page.

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Posted in Audio Spectrum Analyzer, Electronics, High Voltage, Projects, Tesla Coils | 2 Comments »

Coilgun goodness!

Posted by aonomus on September 3, 2008

So I just finished lashing together and test firing my coilgun, I’ve tested it with 400V at 4800uF using a nice sized coil. For now its experimental, however I may add more windings or simply just increase the capacitor bank size.

Photos follow:

At the moment, the coil (18AWG 32 windings x 4 layers) heats up after a few firings and is connected to the capacitor bank which has been tested up to 400V. The firing circuit is simply a 9V battery, a 82ohm resistor and a pushbutton switch connected to the SCR.

The charging circuit is connected directly to the charging circuit, however I should have a DPST or DPDT switch to physically disconnect the bank from the charger.

The SCR is mounted onto a short flattened copper pipe with 2 other holes for mounting.

My next step is to build a much larger bank of 200V or 300V capacitors as they are more available to me. Using bigger SCRs or multiple paralleled SCRs may be an option to increase pulse current and faster charging can be obtained via directly rectifying AC mains. 200V or 300V capacitors are usually used when 120VAC is rectified to 170VDC, thus they are more commonly available.

Energy is obtained via the formula E=0.5CV^2, since C = 4.8×10^-3 and V=400, E=384J, however by decreasing voltage to 200V, E drops to 96J and in order to obtain the same energy, capacitance must nearly triple. Substituting a 400V cap bank for 200V is a fairly poor choice, however some coilguns have been designed so well that efficiency is good. Losses in this particular coilgun are in the projectile shape/size sticking in the barrel at times, and also likely back-EMF losses.

Now for the comedy gold:

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