Seeing in radio frequencies
  • chironexchironex March 20
    So it took me and my friend 2 months, but we managed to build our first radio telescope. LINK
    Easily my favorite part of the whole project was at the end when we were left with an image of something, in a frequency that you will never be able to see. We were able to see satellites over 35,000km away, glowing as bright spots in the sky. To really drive the point home, we took a 360 visual image and then overlaid the radio image on top. In this way we could literally see the ring that surround the earth. 

    I feel like, and other variations at other frequencies would be awesome to have in something like the hololens. Being able to look around and feed in data from telescopes like this, would make staring at the sky super interesting

  • ThomasEgiThomasEgi March 21
    That's pretty darn cool. If you want to build such a system again in a DIY way, I'd have a whole set of ideas which would increase stability/accuracy of the mechanics while cutting back on 3d printed parts pretty much entirely. 
  • I want one. I'm half tempted to build one of these with a friend. Do you think you could use enough of these to create a near real-time image of the sky, and then pass that to one of those VR headsets?
  • chironexchironex March 21
    Thanks :) If you've got a 3d printer, i'd actually advise using MORE pieces, not less. Increasing the torque at least double would be ideal. And using a worm gear in the bottom set. Or if you've got a machine shop laying around, im sure there's better ways to do it. 

    Do it! this was super fun, though if you do, maybe consider getting at leasta  90cm dish. That's the minimum requirement to see the milk way. Or use a different style antenna. If you just want to see the satellites though, this is fine. For the live image thing, if you had 7, all scanning a different bit of the sky over and over, it'd take about 3-5 minutes per image. So not quiet real time, but pretty close. Again, you'd want to use a bigger dish or you won't see anything fun. But it would be really cool. I mean that's sort of what they do at the really big observatories. Though they're looking for more specific stuff. I think it'd be really cool to try.  We're planning a few big community projects to collaborate with people all over the world to do large scale stuff.
  • ThomasEgiThomasEgi March 21
    A few mechanical suggestions from my end. 
    Use proper bearings for the vertical axis (azimuth?). I'd suggest UCF type bearings. They cost about 10 per pcs bucks depending on where you get them. Easily found on Ebay. Pillow bearing blocks might also be an interesting alternative. Proper bearings are vital to get a more rigid setup, which again is vital to operate the entire thing under non-ideal environments, such as wind loads etc.
    I recommend two of those bearings or the vertical axis to lock down all undesired motions. If you can use a metal rod instead of a broomstick, i recommend that too.

    As for the elevation bearing I have no handy recommendation. Ballbearings work but would be a bit too much effort to get in place. Bronze bushing and a steel rod could work out okay. There are also a number of dry running polymer based bearings for such a task. Again, 2 bearings would be the way to go, preferably spaced apart as far as reasonably possible (my recommendation would be > 5cm )

    Now for driving the thing. Using specially printed gears with low backlash for the elevation is a nice idea, but in this particular situation it has no benefit over cheap off the shelf parts. The gears are under permanently pre-loaded by the weight of the dish. So you never deal with backlash so no need to reduce it.
    I'd also recommend to mount the small thread further away from the rotation axis to give it a bigger lever effect. This will reduce load on your gearing and motor, giving you more accuracy and  a ted more stiffness. Best option would be to run it along a circular surface (similar to oil pumps), that way you get a linear relationship between steps and elevation.

    Controlling the azimuth is a bit trickier and there are more options. The wormgear idea is one option. Another would be to avoid gears as those suffer from backlash (and in this case it does affect the operation). One alternative would be to construct a disk (maybe 30 to 40cm diameter) and run a timing belt around it and the motor, with a small tensioning mechanism. The disk doesn't need groves like other timing pulleys. If you are good with a limited amount of rotation you can even screw it to the disk in one place.
    You could also try to work with friction gearing. Use a disk on the azimuth pole again (printed/wood/metal, all works) and simply press the stepper motor axis against it (preferably with something rubbery on one side). Rubber-paint on the disk , or shrinking tube on the motor might already do the trick. I'd try the timing belt first tho but if you'r on a budget, worth a shot.

    Once you get your mechanics to be rigid and non-wiggely you can, and should, go big. Reason being simple: bigger the dish, the more narrow your beam. Not only will the signals you pick up be stronger, you also get a higher "resolution" when scanning the sky.
    So yes size does matter, I'm not kidding: https://en.wikipedia.org/wiki/Effelsberg_100-m_Radio_Telescope 
    I've had the honor to climb that thing halfway up during a guided tour. It's darn amazing. Not quite within the DIY budget but crazy cool.

    What else to say. Signal measurement: keep the noise out and away. At this stage the receiver amp is probably the part that benefits most from improvement. Not only would a proper circuit itself help, but also properly designed encasing to block noise, proper power supply (no switched stepup, at least not without very good linear regulators and filtering). Moving radio emitters out of the way (away from behind the dish too).
    Just the many little things there are. But yeah, keep up the work, continue hacking! Next time you have such a cool thing going on be sure to drop some note on IRC so i can throw in my 2 cents.
  • ThomasEgiThomasEgi March 24
    Talking about 3d printed gears. If you are looking for a gear with low backlash and higher gear ratios on smaller space, you may want to explore eccentrically cycloidal gears.
    https://www.youtube.com/watch?v=9l9QMz67J0c

  • chironexchironex March 25
    Thats a really sweet gear! No idea if I'll use it in a telescope, but if nothing else I want a set just to have.
    We'll be starting work on our next telescope in the next few months, so when we do I'll be sure to hop on the IRC. thanks :)

    Also for the next one we'll be using an SDR and a more custom set of amplifiers and filters rather than simple off the shelf parts so we can get a better image. We also want to get a 10 foot dish to improve the resolution by a lot. Should be the bare minimum to detect pulsars as well, so it could be pretty sweet if everything works
  • JupiterJupiter March 26
    This looks to be a great project guys, good work on that chironex. Id love to see this sort of thing somehow made smaller, I don't know a ton about how radio telescopes work, but if you had a smaller antenna dish, what are all the he downsides? Could you possibly work around the small dish problems if you had a computer that filtered out unwanted noise? Or would there be too many signals that you simply wouldn't receive at all, I mean at all at all, not like, too little to be useful to a human looking at the incoming data.

    EDIT: I mean small, like, a diameter of a few inches, maybe 6 at most. Intended for carrying around.

    As a side note, as amazing as the Hololens is (in more ways than the obvious) I feel it's best use is for overlaying images on top of reality, not full VR experiences, there are other cheaper solutions for that. That said, if you could somehow keep a liveish feed, overlay that on top of an actual view of the night sky, that could be cool too. Though the Hololens itself wouldn't function well outside as it relies on its own visual light vision to properly track its position and orientation as well as it does. (I have one.) That said, I was skeptical about the technology for the longest time. Then I bought one, and although I have yet to fashion a practical use for it, it is the coolest thing since the iPhone first came out.

    EDIT: I completely forgot I wanted to ask...
    What IRC server/channel are you talking about? Is there a biohack.me IRC I don't [read: need to] know about?
  • ThomasEgiThomasEgi March 26
    there's ##biohack on freenode
  • chironexchironex March 26
    You can't really make it smaller and have it still be useful. It's not really a carry around kind of thing. The smaller the dish, the lower the resolution. Anything much smaller than what we used would be functionally useless. That's why I'd suggest having these set up in a fixed location and feeding the data to you over the internet or something.

    Ya I got to try the hololens recently. While the flaws are still large and it needs more work, it was so fricken cool. I'm excited to see where the tech is in 3 years. That'll be when I buy one.
  • ThomasEgiThomasEgi March 28
    btw, just for the fun of it, can you put an usb-wifi stick in the focal point and run a scan. Not directed at the sky of course. Would be interested to see wifi signals seeping out of windows, or houses in general (depending on the distance).  Maybe even color-code the strength by ssid.
  • chironexchironex March 28
    Thanks :D 
  • chironexchironex March 28
    We built a very directional yagi that was tuned to 1.4ghz. Could see detect wifi signals nice and clearly. The problem would be all the reflections. Would make getting a clear image difficult. But still worth a shot. I'm gonna build more of these tracking rigs so i can do more stuff like this. I wanna do LIdar and Sonar imaging, then move on to more difficult stuff
  • ThomasEgiThomasEgi March 28
    if you are into reconstructing geometry, don't miss regular photogrammetry. OpenMVG and OpenMVS as well as meshlab might be of interest