Objective: This series of articles presents the design of a mobile satellite ground station. The basic idea is to build a custom low-cost and mobile rotator for satellite tracking and pointing a parabolic dish for C-band communication with a satellite. Part 1 will cover the design concept.
Recommended Prerequisite articles to read
One of my ongoing projects is the concept of a ‘mobile and low-cost ground station’ for C-band communication. The focus of this write-up is on the embedded systems part of the project. Hence the communication part will not be covered.
The idea is creating a custom rotator that can be used with parabolic dishes of between 60 cm to 120 cm in diameter. The bottom line is to have a simple cost-effective solution that is also mobile in the sense that it can be loaded onto a car/mini-truck to wherever the tracking of a satellite may be necessary. At my current institution (Kyutech), there is an industrial-grade S-band ground station that is shown in the cover image. The idea is to build a portable version of it for a small-sized dish. This is part of a larger satellite project whose details are not necessary here. A high-level block diagram of the design is shown in the figure below
With such a task, it was a challenge visualizing how the end-result would look like. Luckily, a couple of amateur radio operators have designed their own antenna rotators such as the work of Tom Doyle that provided me with a starting point concept. Nevertheless, most of these designs are for VHF/UHF Yagi beam antennas as opposed to parabolic dishes. A 120-cm parabolic dish is much heavier and would need a quite strong base/rotator. Hence the rotator would need to be robust enough to handle such weight but simple enough to build and meet the low-cost objective.
One of the greatest challenges in such a design is to have a strong base that can also achieve azimuthal rotation with minimum friction. This requirement was the first thing I had to get right. It also had to be a cheap and simple option since it is just a small (but critical) part of the whole mobile ground station. I spent quite a while looking at diverse options to meet the above requirements and finally found a perfect match. This is in form of this turntable on Amazon. It has greased ball-bearings that make its rotation under load extremely smooth. It can handle over 200kgs load. The deal is sealed by the price-tag: 1200 Yen ($12). I couldn’t have asked for a better option.
Whilst the turntable is sufficiently strong, it requires robust support off the ground and for attaching the rotary mechanism. I settled on these angle bars from a local Nafco hardware section. They are cheap enough and allow for flexibility in the design.
With the azimuth base and support bars having been identified, it was now easier to start working on a design concept built around the chosen turntable. One of the greatest advantages of our times is in the amount of information resources and tools available on the internet. If properly utilized, an individual can achieve much more within a remarkably short time compared to yesteryears. I settled on the Autodesk Fusion 360 CAD software since it is free for educational purposes. More so, there are a couple of tutorials available on its use. Within a week or so, I had mastered the general flow of designing on the software and I commenced working on the rotator design.
One of the objectives of the project is to be low-cost. Hence the design should be simple enough that it shouldn’t need production with specialized machines or factory. Hence in the design I ensured that the only “manufacturing” needed would be drilling of holes and cutting materials to size. My institution workshop is more than capable of doing that. This meant that I couldn’t use complex gear system for the rotary part. Hence a motor+chain+sprocket mechanism is adopted.
On this design, there were two iterations. The images below represent the initial iteration. However, here the support structure had not yet been identified i.e. the angle bars were not yet considered. It was more of a concept design than an assembly ready design.
In the next iteration, I aimed to make the design robust by incorporating the angle bars and using metal plates to offer rigidity. The images below show an assembly ready CAD design for the basic rotor structure design.
Some of the design drawings are shown in the image slider below. As can be seen, it’s mostly about dimensions and holes, hence simple enough for production.
With the above design and drawings, I acquired the aluminum plates and had them cut to size and the holes drilled at the workshop. The metal plates that will be used are thin aluminum plates (~1.5mm thickness). Some of the parts from the workshop are shown below
The other parts will be described in part 2 of this writeup.