Tag: 3D printed

SatNOGS News – January 2017

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SatNOGS community has been busy over the last couple of months, with many exciting updates on projects to share with you!

 

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Rotator v3.1

First and foremost, the 3.1 version of the SatNOGS rotator is soon to be finalized. If you are already working with a v3 keep in mind that upgrading to 3.1 is pretty straightforward, on the meantime feel free to share your build progress or finished ground stations with our community We got have some stickers to send to SatNOGS ground station operators. We really hope that lot’s of people get to install their own v3.1 rotator and hook up to the SatNOGS network, and we are working on a way to get the v3.1 rotator design to as many people as possible.

New UHF antenna

We published a new UHF 8 turn helical antenna design.  Documentation and step-by-step build process is now public so everyone interested can build one on their own, using readily available tools and materials.

Updates on SatNOGS DB

Our crowd-sourced satellite database, SatNOGS DB, is expanding and will soon be powering Csete’s gpredict through it’s API. In the meantime we deployed new functionality that allows SatNOGS DB to visualize telemetry data captured using the SatNOGS Network of ground stations.

Events

We really appreciate people participating in the SatNOGS project, either in our community website,  our IRC/Matrix chatroom, the SatNOGS Wiki, populating the SatNOGS database and our source code repositories but we also enjoy meeting people interested in SatNOGS in person.

linuxconfauLast week on Linux.conf.au taking place in Hobart,Australia, Scott Bragg’s gave a great talk titled “Decoding Satellites With SatNOGS“. It was a great overview of the SatNOGS project and the ways you can get involved.

shrAijm8_400x400Since most of the core SatNOGS team lives in Europe most of us will attend FOSDEM in Brussels,Belgium this February. There Manolis Surligas is giving a talk “SDR for Space the Open Way” focusing on the Software Defined Radio RF frontend and the GNU Radio module operating it and will be introduced in the coming versions of the SatNOGS client.

Stay tuned for more detailed updates, and as always … keep hunting satellites!

 

 

Extreme conditions considerations – Radome

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In order to achieve global coverage, a network of Ground Stations would have to have nodes in places that are not entirely friendly environments. Desert hot, ice cold, gusty, monsoon rainy, mountain dry and forest humid could be some descriptions of possible locations SatNOGS would have to survive in.

Apart from the obvious networking considerations (internet connection and power) which are not in the scope of our project (and are dealt with existing solutions), SatNOGS has some physical constrains, especially around wind and water.

The relatively compact design, our current antennas and the targeted IP55 protection marking are indeed a slight advantage on moderate wind and rainy situations, but we had to do more to ensure reliable operations on rainy and windy hilltops and locations.

The way to protect antenna tracking mechanisms (especially dish antennas but not only) has been long known in the industry and in military. The name of it Radome (Radar-Dome). Radomes provide weather protection (ice, heat, rain, wind) especially combined with an environmental control system, and ensure uninterrupted operation for moving tracking mechanisms.

After extensive search on the webz we could not find any DIY and/or Open project for a Radome, so we decided to design, build and document one for SatNOGS.

We started with the desired shape and size. A geodesic dome (3V frequency) provides a good approximation of a sphere (less air drag) while not requiring large amounts of material. For the size, we modeled SatNOGS with a typical antenna setup (Helical and Yagi) and calculated the extremes. We ended up with a sphere of 1.5m radius, 1.2m from the ground.8103441414183780536

 

The material selected for construction is PVC tubes for struts (cheap and light-weigth) and ABS connectors (3D printable and durable). The Base is an aluminum (L channel) pentagon that can be bolted on the ground. It is important to emphasize that all materials (except the base pentagon) are non-conductive and dielectric. If Aluminum (or any other metal) was to be used, Quasi-Random patterns would have to mandate the design to avoid interference with the RF signals. For the outer surface many materials were considered, and Shrink Wrap seems to be the most cost-effective, easily applied and durable solution (check here for examples).

Gathering all materials is not hard, especially when you have access to a 3D printer. The overall cost is just below 130 USD.2728161414186279380

 

Construction is pretty straightforward. You start with the pentagon and work your way to the middle. Then you start from the top working your way down, until you are left with two hemispheres. Once those are connected in place you lay out the shrink wrap and using a heat gun you apply it in place.

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Depending on the materials you would choose, some bonding might be needed between connectors and struts. (epoxy glue would do just fine). Shrink Wrap would take care of the final rigidity of the structure.

Unfortunately shipping times for shrink wrap as not as fast as we expected so we only finished the skeleton of the radome and we are waiting for the final layer to apply it by next week. (an new log will be posted for this!)

The end result is really impressive taking into account resources used. The structure is really light-weight so 2 people can fit it on SatNOGS by lifting it and lowering it on top of it. Then you would secure the pentagon on the ground and you are ready to go!1304161414187677993

 

Designs (CAD and STLs) are available in our repo, and once the shrink wrap arrives we will be posting a detailed how-to guide.

 

 

Portability for SatNOGS ground station

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Most of the times you would want your ground station to be stable. Secured on a metal beam on top of a building, protected, homed and zeroed where no-one and nothing could disturb it. That is the ideal situation.

For those of us though that like adventures and want to carry a ground station with us on a field trip (DXing, Iridium flare hunts or even mountaineering) having SatNOGS be portable would be a huge advantage.

Luckily (actually… by design) the main gear mechanical assembly is a lightweight box with 3 beams sticking out. Easily carried even as a backpack. Antennas can be detached and especially the yagi ones, disassembled and carried as a long beam. But where would you put your ground station on? That called for a tripod!

We did have a tripod design (v1) early on (check designs here) but it was not really easily constructed and not easily deployable. So we focused on a new design.4056311414017834614

Version 2 is much more easily constructed, considerably more stable and totally portable as it collapses in a single beam. We tested it dozens of times on the field over the past couple of weeks and it is stable enough to allow reliable operations for a typical SatNOGS setup (UHF and VHF antennas mounted too). The cost of it? Aprox 15 USD 🙂

Designs and models can be found in our github repo here.

Bill of materials here. And guess what? We love documentation 🙂 So here are some step by step instructions to build it yourself!

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SatNOGS going Helix

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An important part of the instrumentation of our ground station is the Antennas. Early on the SatNOGS team designed and constructed 2 Yagis for UHF and VHF bands. The UHF Yagi design was essentially a cross Yagi design trying to address the circular polarization issue. Based on the experimental operation of the ground station we were sure we can do something better.

Satellites are tumbling and turning, thus if the transmission of the transponder is done in a single dimension polarization you better match this polarity to get the optimum gain. (if not you will loose 30dB) (check here for details). We decided that a Helical antenna would give SatNOGS a better chance for an optimal reception, so we needed to design, document and build one.

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There are a couple of theoretical models for Axial-mode Helical Antennas. Most notable are the Emerson one and the Kraus. We decided to go for Emerson, given our wavelengths, construction constrains and overall size. As we were going for UHF band 437Mhz seemed like a popular frequency for satellite communications and we centered around it. As for the circular polarization we designed a Left-Hand one (as we already had a Right-hand cross-Yagi design).

Dimitris worked on a modular and extensible design that can be used on other bands too. 3D printed parts and off the self items is the classical recipe that we followed. The result is a sturdy and easy to construct antenna. Initial tests are showing improvements compared to our cross-yagi UHF which is a win!

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The design can be found here, bill of materials here and a detailed documentation on how to build here.

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Optimization of the antenna is crucial. We invested considerable amount of time towards that and there is always room for improvement in matching, constructions and details [1]. More NEC calculations will follow and we expect more fixes as we go.

[1] http://users.ece.gatech.edu/~az30/Downloads/HelixAPMagazineSubmission.pdf

SatNOGS Ground Station v2

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The time we’ve all been waiting for, has come. We are proud to release v2 of SatNOGS Ground Station (Tracking Box) with many upgrades and fixes from the previous version. Notably:

  • Redesigned Axis Gear Assemblies. They are now smaller, more robust and reliable based around a much more powerful NEMA 17 Stepper Motor. The two assemblies are now structurally connected, making the whole assembly much more rigid. Also we redesigned the Worm Gear for improved printability on 3D printers.
  • Integrated electronics. We designed and built a new PCB to house all electronics (Arduino, and Stepper Drivers) along with an additional PCB as a PSU for voltage regulation and neater cable management. (see previous post)
  • Reworked stepper driving code, featuring a much cleaner code, acceleration and deceleration in movement, stop functions and early opto-homing support. (see previous post)

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Tripod and On-board computer (TP-Link) stayed the same, with developments on them coming down the road.

A detailed Bill of Materials is available here.

We have also compiled a detailed construction guide, with step by step instructions on how to assemble the Ground Station Tracking box for both Mechanical and Electronics components.

http://satnogs.dozuki.com/c/SatNOGS_Hardware

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All Designs and 3D printable files can be found here and all PCB files for our electronics shields can be found here.

Development does not stop with v2, and we are already working on the homing/zeroing code that will enable the homing parts we included in v2 to function. Moreover based on more testing we are applying to v2 and feedback from the community, we expect minor fixes to be released soon.

 

We can’t wait to see v2 out there, built by others, so get started and/or provide feedback!

Axis homing tests

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Using the first version of satNOGS hardware we figured out that some times due to various reasons (software, mechanical or power malfunctions) the rotator might end up in an unknown position.

At that point, the only way to resolve that situation was to manually reset the rotator to home position (pointing at the north with zero altitude). Therefore, since we wanted the rotator to operate without human supervision, we decided that an automatic homing system was crucial.

At first thought we tried an IMU, which turned out to be too noisy and affected by the rest of the systems so we ended up with a pair of opto-swithes which are manually set at the first run.

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The mounts and activators of the switches are designed in a way that they remain modular and independent of the rest of the tracking hardware so that they can be fitted in previous or future versions.

Our intention is to write two homing functions in the arduino code

The first one, which is already written, is called when the arduino boots for the first time or after power loss. In this function, the rotator scans around the current location until it finds home position. Below you can see a video in action:

The second one runs after every tracking job or on demand through the serial interface and just moves the tracker to the home position. This way, whenever a new traking job begins the user knows that the job starts from zero position.

You can check the code in our repo, and the designs for the hardware too.

It was always our intention to have SatNOGS ground station as unattended as possible in terms of operation. We are now much closer to it!

Gears… gears everywhere!

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Working towards v2 of the Ground Station Gear Assembly, the SatNOGS hardware team has experimented with various gear designs. All of them where designed and 3D printed from scratch focusing on ease of reproduction and excellent mechanical operation and properties.

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The new gear assembly (which is almost identical for both Azimuth and Altitude) sports a much thinner and compact design, driven by a much more powerful NEMA 17 Stepper motor.

Failing was part of the process. As you can see in the pics above, 3D printing a worm gear can be a monster of its own. After careful calibration and fine-tuning (layer heights, cooling, leveling, infill settings etc)  on our 3D printer we were able to consistently reproduce worm and matching gears. We even experimented with acetone abs curing, which (based on the results we are seeing) we believe should be the default for our gears moving forward.

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v2 of Ground Station is around the corner, and we will be posting later this week with full documentation, designs and instructions on how to build. Till then, back to gear-craze!

New design and NEMA17 motors

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Despite the fact that NEMA 17 stepper motors were considered our best choice, at the time of our first design some old NEMA 14, spare parts from an old Rep-Rap, where available so we stuck with them. Last week, we received our new motors and did some tests. The first test was to find the optimal torque without overheating the (also new) drivers. Although we have some results, tests will be continued and we will come up with some numbers probably by next week.

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Additionally we are working on the new rotator design. We placed the motors on top. This way we managed to decrease the profile of the design a bit and also now the device is a lot more serviceable. Now you don’t need to remove everything if you want to access the motors or the worm gear. We are also trying different designs in order to improve the connection between the stepper shaft and the worm gear.

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