Monthly Archives: September 2017

I Completed Assembly of the SatNOGS Rotator

I completed assembly of the SatNOGS rotator this morning. If you haven’t heard of SatNOGS before, it’s an open source ground station and network for receiving satellite transmissions. So far, I’ve built the rotator and it’s quite cool. From the picture below you get the general idea. It consists of 3D printed parts for the mechanical components and some simple electronics, including custom PCBs.

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This was a group effort with Walter Anderson and Bill Reed. While based on the version 2 design, we made a few improvements along the way. Most obviously, we changed the case. While the SatNOGS mechanical assembly instructions include a case in the bill of materials, that case isn’t ideal as you’re cutting a lot of additional holes. So, Walter designed a custom case to be laser cut from 1/8″ acrylic. you can find the necessary files on Thingiverse.

As written, the design calls for 32mm PVC pipe. Not only is 32mm PVC pipe difficult (impossible!) to find locally, it’s not the greatest material in the sun. So, we replaced the PVC tube with a 1-1/4″ OD fiberglass tube from McMaster-Carr.

Finally, we found the set screw in the worm gears couldn’t hold the work gears in place and thus the work gears would pull out of the bearings. We resolved that problem by adding a shaft collar acquired from McMaster-Carr to hold the worm gear in place. You might be able to identify the shaft collar in the picture below.

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From the software side, I haven’t installed the SatNOGS client that would make my station part of the worldwide network. Instead, I have installed the software components needed to control the rotator locally and point to satellites under control of my Raspberry Pi. In brief (very brief), it consists of:

– Installing gpredict (sudo apt-get install gpredict) and configuring it with a rotator on localhost, port 4533. Gpredict is a satellite tracking program.

– Installing rotctld (sudo apt-get install libhamlib-utils). Rotctld is a software daemon that provides a network server to control a rotator on a serial port.

– Starting rotctld withsudo rotctld -m 202 -r /dev/ttyACM0 -s 19200 -T 127.0.0.1&. This command starts the rotator control daemon identifying the rotator as a model “EasycommII”, on the specified serial port.

We’ve been thinking about leading a group build at Dallas Makerspace. If you’re interested in such a build, please let me know.