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.
So I promised that I’d have something cool coming up, the major ’secret’ project I’ve been working on is an Autonomous Surface Vehicle entered into a AUVSI competition. While I will eventually do a full writeup with pictures and descriptions of various hacks that we have done, and the general construction of the boat, however I’m to tied up with actually helping the team with getting the project complete and working for the competition.
The competition itself is held at Virginia Beach, at the Founders Inn hotel under the Association for Unmanned Vehicles Systems International. Starting on July 19th onwards, each night at 10pm the officials have said that a ‘recap’ video will be posted. As well, at some point there will be a live webcast set up… more details as they come.
In other news, I have finally popped my ham radio cherry while on this road trip. My friend had his FT-897 set up in the roadtripmobile with a 2m magmount antenna ontop of the van, I managed to make my first contacts as a ham on repeaters on the way down towards VA beach. Since his radio and mine (FT-857) are fairly similar with the multifunction display driven controls, it wasn’t terribly hard to make contacts, unfortunately there were issues with the power wiring to the radio, so my apologies to anyone that was speaking with me and got cut off.
So as I prep for a roadtrip, the thought of timelapse occured to me. I have already made some random timelapse test videos using my old Canon Powershot A40 and the software that came with it, however portability was always an issue.
Today, that is no longer an issue, I built in a few hours a frame to hold my old camera and a servo motor, and controlled the entire setup using a Arduino. The setup includes a LCD for display purposes, but in general is meant to quickly satisfy the need to do timelapse for the roadtrip drive. I plan to improve this a little bit, perhaps add a LM317 vreg so the entire setup is self-contained and powered off a 12V wall-wart or battery pack, however time is at a premium.
So I have been fairly recluse from the 4hv.org community and blog posts in general, all I can say is that I am working on a damn cool project, which when concluded will have a nice writeup.
Ok I lied, I can also say it involves a smegload of Arduinos.
Thanks to www.spiffie.org for the donated *duinos by the way.
So I’ve been busy over the last few days on a few projects.
First, a quick and simple wood frame for 3x 1W solar panels I purchased for $9 a piece. I plan to add a shunt controller, or at the very least a simple LM317 regulator set for 13.7-13.8V, because the solar panels are happy putting out a unloaded 23V!.
Yet another quick and dirty project, during my post-exam cleanup I decided I wanted to build a stand for my printer to sit on so that I can store stuff (ie: paper) underneeth it. Just old spare MDF from Ikea furniture. Always a good hack for anyone with flat pack furniture that they can’t be bothered to sell.
Another project that is unfortunately a bit of a failure is a big rackmount power supply I built. Using a beefy transformer it supplies 13.8VDC regulated, at high current (20-40A). Unfortunately the transformer I used was a microwave oven transformer, re-wound for low voltage. The transformer contains a shunt, and the laminations are welded together, shorting them and creating a ton of wasted power, and high idle current. Testing with a proper meter, I found out that the idle current is 6A, with a power factor of 0.12! Once I replace the transformer, the power supply should be rock solid and reliable.
Enough of that rant, the technical details:
The power supply uses 42000uF in the smoothing filter, 2x ISOTOP/SOT-227 dual diode modules for rectification, and 4x 2n3055 pass transistors with a LM723 regulator. The inside is a bit of a rats nest, however it works well and even *with* the voltage sag due to the transformer being very lossy, I can push at least 20A within a range of 12-14V. Note that using fuses is a very good idea with a power supply that has a very large short current, and the fuse block is mounted behind the front panel (those 2 screws on the right).
Future additions include: more binding posts, and a volt/current meter setup, along with the replacement transformer.
Last but not least, new gear! I’m studying for my amateurs license, and I’ve already picked up my radio, and a cheap (as in free) tuner.
So I’ve recently vanished from the face of this blog due to exams once again. Never again will I underestimate how much biochemistry there really is (read: over 100 hand written pages of biochem study notes). Regardless, I am now free to relax a bit and update the blog once again! Onto business I suppose.
First things first, since the last rogowski coil update, I haven’t gotten it functioning properly yet. I suspect its due to the fact that I foolishly omitted any form of burden resistor (standard practice with current transducers is to place a resistor of a few ohms to a few hundred to reduce the voltage output). The opamps may be fried, however I have hope that they are still functioning, and as such I will try to modify the integrator to work…
Moving on, tons of projects for the summer:
The capacitor bank: I have done some more work on it, reconfiguring the SCR pucks to parallel and the stud diodes to antiparallel to both increase the current capacity (each puck at about 5.5kA for 8.3ms, derate for maybe 8-9kA) and catch all the ringing. My previous design would have failed spectacularly since the configuration was essentially a boost converter with nowhere for voltage to go.
I’ve been fiddling with a tiny ZVS flyback driver I built, unfortunately the capacitor I had on hand was insufficient, so at some point I will have to do a revisit.
I’ve acquired 3x 1W solar panels for $9 a piece, and they’ll provide just enough power to trickle charge a SLA battery, granted its nothing much but every bit counts, especially if you want to go QRP with a small radio and limited power supply for amateur radio.
Plans for a 3 tesla coil symphony using polyphonic MIDI driven by Ableton Live + a multichannel sound card.
A few arduino projects including a voltage/current meter and a MIDI control surface 9either mixer style or DJ style).
A simple analog signal switcher (ie: powered by 4051 CMOS) or mixer to combine audio outputs from devices to a computer, and a complementary mini-mixer to buffer/isolate audio input from a computer to devices.
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.
So one of my next projects is going to be a (slightly insane?) 3kJ electrolytic capacitor discharge bank using a mishmash of 450V caps. My current collection is as stands:
I plan to purchase another 4-6 of the Aero M capacitors as cash becomes available, inverter grade capacitors stand a better chance at surviving extreme current discharges. I will likely replace the 4 Chemi-Con caps with 4 more inverter grade caps, and eliminate the CDE caps completely (save them for another project, perhaps a multi-stage CG).
The capacitor bank will be switched by a Powerex C397 Hockey-puck SCR rated for 5500A non-repeating surge current, and I will likely invest in some beefy stud diodes to place in-series on the opposite leg of the capacitor bank to minimize the ringing that will occur due to voltage reversal in inductive loads.
The reason for the series diode is that for any inductive load, there will be significant ringing resulting in voltage reversal. Electrolytic capacitors do not tolerate reverse voltages, especially when swinging from -300 to +300 in rapid succession. A example LCR simulation based on a can-crushing coil results in some… interesting figures.
All in all this should be an interesting project, having a 3kJ capacitor bank will allow for some experiments in coilguns, railguns, magnetic launching, magnaforming, can crushing, and wire exploding.
Ok, so 9am classes on Monday, not the best thing – especially when fighting the tail end of a cold.
First and foremost – people need to watch where the hell they are walking. This is a long ongoing rant of mine, but as a greater aspect, people no longer seem to give a damn about other people by basic consideration at all. When you walk down a hallway people now expect you to move out of their way, its rediculous. When the hallway is narrow to 2 people and you can’t move, they ram through anyway and give you dirty looks as a result. I don’t want to seem like a jerk, but I think that this general lack of respect for other human beings is due either to generational and/or racial change, *or* that corporate media has brainwashed people to care about nothing other than consumerism.
Moral of the story: Watch where you are walking, especially when you are smaller than the person infront, and they honestly don’t care if you get knocked over cause you didn’t move…
Edit: Also, girls with TNA bags: no one gives a damn, you look stupid and your bag takes up on average 1-1.5 body widths (2 if you are overweight).
So it turns out there are a whole collection of songs on biology and chem… a select choice for any chem students (or mol. bio). A is for Alanine – Good for any student stuck memorizing amino acid residues
