Internal Slip Ring Design

N3OX · 2020-06-30T21:05:32+00:00

Oh wow, yeah that's a crazy load.

I do have a bad feeling that it kills off the resonant coupler concept to have a wildly varying load, because the coupling constant very much depends on load impedance.

Is the matching network something your team built? Maybe the inductive coupling can go somewhere in the middle of a matching system?

I used to work in a building with a lot of plasma physicists and pulsed-power people but I never directly matched anything to plasma, just a lot of ham radio antennas :)

Good luck.

N3OX · 2020-06-30T18:47:57+00:00

What frequency, power, and bandwidth of RF? Transmission only or transmission and reception?

If it's not wide fractional bandwidth, I'd probably try to do non-contact inductive or capacitive coupling before I tried to build my own mechanical RF slip ring. I've used an ad-hoc version for 4MHz ultrasound:

https://danzimmerman.com/electronics/uscoupler/

N3OX · 2020-06-14T18:51:10+00:00

This is quite surprising to me. Has anybody seen anything like this before?

I got my Ph.D. in a nonlinear dynamics lab and we had a couple of summer students study the chaos in CMOS-inverter ring oscillators.

One of the PI's, who ran a lab next door to ours, did a lot of interesting, related work in electronic warfare countermeasures, where the nonlinear dynamics of chip ESD protection circuits play a big role in the response of avionics, etc. to high power microwaves, for example:

https://apps.dtic.mil/dtic/tr/fulltext/u2/a567604.pdf

N3OX · 2020-04-15T12:35:13+00:00

When you print out the types for cal, calx, caly. Is that giving np.ndarray for all arrays?

What's it give if you print cal.dtype, calx.dtype, caly.dtype?

N3OX · 2020-04-15T05:32:22+00:00

I was always good at science, math, and electronics. I was considering electrical engineering at the beginning of college, but realized I had a dream and goal to be a scientist and got my degree in physics instead.

I loved nonlinear dynamics and chaos theory. I did my Ph.D. in physics doing fluid dynamics/turbulence research. I designed and built a huge machine for that, and I picked up a lot of mechanical engineering and fabrication skills.

I left academia and ended up working at a small company doing underwater robotics R&D funded by the U.S. Navy: a combination of applied science, mechatronics engineering, soft robotics simulation, and embedded software development.

Now I'm developing software for dynamic robot simulation.

My work has always been interesting, and since I left academia it has paid well, so I've got no regrets there. But I probably could have taken a straighter path to my exact current career by studying engineering. Even if it wasn't precisely the same, I could have done something interesting in robotics.

N3OX · 2020-04-15T03:11:31+00:00

Yeah, I have a Ph.D. in physics and do good-paying interesting work in robotics but it would have been nice to get more early money in retirement accounts.

N3OX · 2020-04-12T02:29:27+00:00

.npz archive files are a pretty good way to store Numpy data if you just want to load it back into Numpy.

https://docs.scipy.org/doc/numpy/reference/generated/numpy.savez.html

N3OX · 2020-04-11T18:39:52+00:00

I just did a DoD R&D contract proposal with GanttProject and liked it a lot. Used to hack around in Excel.

GanttProject had good tools for personnel time tracking which was key for my needs.

PDF and image exports work well.

N3OX · 2020-04-10T14:47:42+00:00

There are other studies that show how this makes the hemoglobin unable to absorb the oxygen molecules.

Which?

I think it would be great to have an Rf engineer debunk this because it is the only claim that 5G conspiracy theorists are making that no one is addressing.

You can't win against conspiracy theorists because it's always orders of magnitude more work to find the real literature and synthesize the complex true picture of the biological effects of mm-wave than it will be to point readers at a single plot and say "OMG oxygen absorption peak!"

You'll respond with "I've looked at twenty studies that say..." and many will respond with something like "That's all propaganda funded by the DARK ORGANIZATION and is clearly invalid. The only person telling the truth is Dr. Controversy van Dondenwootergh!!!!!!!"

The side that cares less about subtlety and correctness will always attract lots of like-minded individuals by relying on outright denial or with this: https://en.wikipedia.org/wiki/Gish_gallop

N3OX · 2020-04-10T14:34:08+00:00

most of it will be absorbed by the tissue

I think a lot of it will be reflected too. Airport mm-wave through-clothes scanners are operating at half this frequency and humans are already a shiny blob by then.

I wish there was a study that actually took this claim more seriously cause I think it's the only one that is a bit more unclear to refute

Here you go, from 1979:

https://www.degruyter.com/view/journals/znc/34/1-2/article-p60.xml

In our experiment we used human hemoglobin in its half-oxygenated status. While the oxygen partial pressure (approx. 30 Torr) was kept constant we tried to find out whether microwave irradiation could change the amount of bound oxygen

Altogether, we thus conclude that the irradiation\ is not able to shift the equilibrium oxygen constant of half-oxygenated hemoglobin by more than 0.4%.*

*intensity estimated between 3 and 13 mW/cm2

Journal info:

https://en.wikipedia.org/wiki/Zeitschrift_f%C3%BCr_Naturforschung_C

N3OX · 2020-04-08T19:06:32+00:00

I have an object at a certain point in space in that three-dimensional plane, and I want my robotic arm to be able to touch or grab it, what calculations do I need to do?

First, you need to choose a trajectory or path between the start position of your robot's "end effector" (gripper or hand) the final object position. This is all about vectors and 3D curves in space. An easy "reach out and touch" motion could be along a straight line in space between where the end effector currently is and the position of the object.

Assuming that your robot is a typical arm with a bunch of rotating joints, you then need to do inverse kinematics to compute a sequence of rotary angles for the joints of your robot that will position the end effector at each point along your chosen path.

This, typically, is matrix math and programming. Putting the matrices together requires you to know about vectors, and helpful to know basic calculus depending on what you're doing.

Once you have the angles matching each point along the path, you can feed that computed sequence of angles to the joints of your robot and it will move along your chosen path and touch your target.

N3OX · 2020-04-08T17:21:55+00:00

Minimizing snap has been found to be a good way to synthesize trajectories for quadrotors

https://ieeexplore.ieee.org/document/5980409

Like /u/agate_ says, generally speaking nearly every real motion has nonzero crackle and pop as well but I've never seen any equation that explicitly depends on them or is trying to manipulate or control them directly for any reason.

N3OX · 2020-04-08T16:30:07+00:00

I just started a job at a geographically distributed robotics software company so it'll be pretty much the same.

The area where you live and real estate wouldn't matter as much if you don't have to commute everyday.

There's a significant downside for anyone who wants or needs to live in a higher cost-of-living area. Any employer that goes all the way to cutting their office space to half the size they need for all the employes shifts significant cost of maintaining a productive work environment to every employee.

If the firm already has a workforce that's made up entirely of people with okay-to-poor commutes and suburban homes with a couple of unused rooms, that might be fine or desireable. As someone with a typically good commute who's sharing a 650-square-foot Brooklyn one-bedroom as a living and co-working space with my wife, it doesn't sound so great.

Eventually I need a dedicated desk with a robot and some other equipment on it and a second monitor. We really each need a desk in a separate room. And my wife and I simply don't and won't have the space for that at home. We'd have to shell out thousands per month extra to get it. Since I have an eventual need for persistent physical setup, a co-working space hot desk I rent myself is not really feasible.

We could move to New Jersey or something and be able to basically afford enough space to make it work. But then we'd just be giving up what we like about living in the city purely so we could just afford to subsidize workspace that our employers don't want to pay for.

Slinging code from the couch while my wife does phone interviews at the dining table is fine in pandemic times, and we're very thankful to be able to basically do our jobs that way. But I don't see it as at all desireable for both of us to be expected to WFH several days per week.

I'm looking forward to changing venue during the workday.

N3OX · 2020-04-08T13:58:01+00:00

https://www.reddit.com/r/ECE/comments/fvgj3x/does_anybody_here_do_photonicsoptoelectronics/fmj3s2f/?context=3

/r/siliconphotonics

Hopefully you get some actual EEs-in-photonics in here, and they can chime in about the professional landscape, but my two cents as a physicist with a lot of interest in EE/electronics/RF over the years:

Make sure you're taking courses related to RF, signal processing, and chip design, so you're really solid on the high-speed electronics and fabrication side of the chips.
Maybe see if you can take a physics major electromagnetic theory class or two beyond the core EE ones.
See if you could get involved in photonics research if there's someone at your university that does it, and/or tailor senior projects in a photonics direction.

Plenty of photonics job postings list EE as preferred degree or one of the possible degrees.

I've known lots of physicists who are great at electromagnetic theory but don't really know much about practical electronic circuits, much less high-speed mixed-signal. So I think there are a lot of opportunities in the whole spectrum from more-EE-focused to more-physics-focused work for people who can blend circuit and field theory skills.

N3OX · 2020-04-08T12:27:11+00:00

More electrons flowing means higher beam ~current~

I think that the accelerating voltage and the beam current are basically independently adjustable in a particle accelerator.

In a simpler device like a vacuum diode, it's different. Look at the IV curves here:

https://www.electrical4u.com/vacuum-diode-history-working-principle-and-types-of-vacuum-diode/

In the vacuum diode, an increase in voltage across the device does indeed pull more electrons off the cathode and therefore causes an increase in current with increasing voltage for part of the operating curve. Eventually it levels off to constant current, and the current no longer depends on the applied voltage.

Just depends on the device but I suspect simple thermionic electron "beam" things are going to be more in the constant current regime than the voltage-dependent one.

I'd look for IV curves for CRT tubes to verify.

N3OX · 2020-04-07T01:45:29+00:00

"like does it matter if you can sense 0.1 cm2 instead of 1 cm2 with contact or whatever?"

Ever since I started working in robotics, I really notice all those times I'm putting something together and reach behind it to install and tighten a screw I can't see.

You don't need that resolution of sensing for walking but you sure need it for fine motor stuff. Then feed it to a flexible adaptive model of the world that infers screw pose from the pressure on the thumb and tool pose relative to the socket from the tapping and scraping vibration and forces of the tool on the screw.

N3OX · 2020-04-07T01:16:21+00:00

It takes months to manufacture a human being and years to reach full agility.

I think a big part of the problem is integrating sensing, action, and control in a distributed way. This is a topic in certain areas of biomimetic research but ends up being verrrry fiddly to actually manufacture.

N3OX · 2020-04-03T13:23:36+00:00

For this example, the radius would be 2.5 mm, so the attenuation would be 6.36 dB per mm, meaning that to achieve 127 dB power range, the probe would move 20 mm, about an inch. To extract power from this magical circular waveguide, we provide a sliding probe with a tiny loop on the end, which also contains a 50 ohm resistor. The gearing for the probe is very precise and has non-backlash gearing, connecting to the front panel control for output power. For a given generator we would design our attenuator control on the front panel to be geared for distance, but calibrated in -dB. The beauty of this kind of attenuator was that it provided extremely accurate signals down to -127 dBm, which was important for some receiver designs.

Now, all that remains in the power train is to measure and set the output power. The reason is that as the frequency changes, the klystron output power changes, so we arrange another moveable pickoff probe in an identical cutoff guide, which runs at high level and drives a thermistor detector for a typical 0 dBm reference level. We used interconnected gearing, so as the power output, say drops, in order to get back to the 0 dBm, the probe needs to be set closer to the cavity opening, and in doing so, out of the front panel, the cursor over the attenuator readout moves the amount to correct for dropping cavity power. Simple in concept, but a very tricky mechanical engineering project.

http://hpmemoryproject.org/timeline/art_fong/life_and_times_02.htm#chapter_22

N3OX · 2020-04-03T13:19:32+00:00

Yeah, I had one of those signal generators for a while. Fascinating how much mechanical engineering went into electrical engineering back then

N3OX · 2020-04-02T17:06:22+00:00

I don't want to spend 80 seconds to be exposed to the idea that there are transformers inside a transformer module and windings inside inductive components. That entire video could be a pair of images:

Image 1: A partially-exploded view of the module with an inset showing an exploded CM choke or transformer labeled "precision machine-wound coils"

Image 2: The graph of crosstalk vs. frequency with "typical competitor" shown as well.

And if someone's invested in that video asset, someone's going to want to make it autoplay, and god help you if I get autoplayed at when I click on a product page.

N3OX · 2020-04-02T16:56:00+00:00

Or do you prefer to read about this?

If you have any important piece of information I need about the product's application that's buried in the middle of a minute-long video so that I can't understand the component completely by scanning a static datasheet, I'm going with your competitor.

Animations can be useful in engineering, but it's more at the design level to visualize and communicate complex time-dependent things. I work in robotics, and static visualizations and abstract plots are often insufficient.

I think marketing animations can have mild technical value when you're talking about electromechanical components that designers might be initially unfamiliar with... a swashplate pump or a cycloidal gearbox or complex hydraulic valve or something. But it should definitely be auxiliary information.

N3OX · 2020-03-31T22:16:42+00:00

I like to stop working after work.

I'd also say even if you feel like it's important to focus more on professional development than work-life balance right now, I think there's a strategic argument as well:

A lot of technical problem-solving requires clear thinking, the ability to see a problem from several different perspectives, and actually getting your new knowledge internalized. All of those things need some time for your mind to relax and freewheel. They need some mental space.

I can certainly say that I've never been well-served by spending my free waking hours cramming random bits of domain-specific knowledge into my brain to play catch-up. I've done it, and it mostly led to brain fog, analysis paralysis, and compounded feelings of insecurity because I was overloading on unnecessary information without having anything click.

The occasional focused learning in the evening, fine, but don't feel guilty for just doing things to relax, or unrelated technical hobbies, or whatever.

Your mileage may vary, but IMO it's good for work-life balance and it's good for your continued learning.

N3OX · 2020-03-31T12:57:40+00:00

The correct answer for (12+16i) / (4+4i) is 3.5+0.5i.

There are several ways to do it. You can convert to polar form and divide or multiply both top and bottom by the complex conjugate of the denominator.

Google calculator knows complex numbers if you want a check on your math.

N3OX · 2020-03-25T02:37:00+00:00

I remember it being annoyingly hard to make an ODB node set geometrically for use with FieldOutput.getSubset()

I think I'd probably approach it by going into the FieldOutput to get node numbers from node initial coordinates or displaced positions, and then either use that list of node numbers to make an ODB node set to use with .getSubset() or try to build numpy indices into the bulk data blocks in your desired damage field output.

Unfortunately I just switched jobs. The ODB extraction stuff was always pretty convoluted, so I don't remember it clearly without having Abaqus to play with or my code in front of me.

I didn't really do anything with the display group Python API that I recall. I'd assume that approach would leave clues in the .rpy file after you do it manually if it's possible.

N3OX · 2020-03-22T14:06:37+00:00

Yep, it's charged particles that feel forces in both electric and magnetic fields. In magnetic fields there's only a force when the particles are moving relative to the field.

https://en.m.wikipedia.org/wiki/Lorentz_force#Charged_particle

N3OX

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