Rainbow Astro RST-135E
Rainbow Astro is a Korean company that has its origins in robotic engineering. They produce a line of telescope-mounts using strain wave gear or harmonic drive motors. These motors are known to combine a lot of torque in a small package, are very precise in their movement and have almost no backlash, ideal properties for an astronomical mount. In the case of the RST-135E, the mount weighs only 3.4 kg, but can hold a 13.5kg rig unbalanced or 18kg balanced. The Rainbow Astro was one of the first to bring out such mounts, but harmonic mounts have become very popular, with many options available.
The RST-135E includes an encoder on the RA axis for better tracking performance. In contrast to the GM1000HPS, this mount can not be used unguided. The precision is not good enough for that, and also an encoder on the DEC axis is missing. Pointing accuracy is very good. After a polar alignment, syncing just one blind plate-solve is often enough to put any selected target right in the middle of the field of view. There is a native INDI driver for the mount, so it can be fully controlled through KStars/Ekos.
The claim to fame for this mount is its portability. One can carry it in a backpack and set it up in minutes. Portability and versatility are the two main reasons why this mount was added to the observatory. It forms the basis for the travel rig, but also works well in the solar rig and even in night-scape photography for meteors for example. The Perseid meteor shower for example was photographed using this mount. It combines a lot of use-cases which make it a very versatile addition to the observatory.
Specifications
Mount Type: German Equatorial or Alt/Az
Weight: 3.4kg
Payload capacity: 13.5kg (no counterweight), 18kg (counterweight)
Tracking: encoders on RA axis only
Guiding: requires separate guide scope
Electronics: Hand controller (HUBO-I)
Connectivity: USB
Hand Controller
The hand controller (HUBO-I) plugs in through an ethernet-cable. The menu-system is not very intuitive, but with a bit of practise you can find all relevant options. The most important function is the homing function, a long press on “0". With this function the mount calibrates its position and parks the mount in a fixed home position. Each time when turning off/on the mount, this homing needs to be done, otherwise the mount can show some weird behaviour and erratic movements.
Losmandy Saddle
The saddle is screwed on the mount using M8 bolts, spaced 35mm apart. This is not a very common connection, and most standard Losmandy/Vixon saddles cannot be used. ADM has a saddle that fits, but it is rather large and can crash into the mount in extreme positions. An alternative is this one, shown in the picture above. It has a solid build, and keeps the setup nice and compact. Currently the Saddle Powerbox from Pegasus Astro has found a permanent place on the mount.
Counterweights
A counterweight is not strictly necessary for most setups. The motors can easily carry serious loads. However, when the whole system hangs on one side of the tripod, there is the (perceived) risk of the tripod tipping over. And as the center of gravity is constantly changing, flexure in any part of the setup will lead to worse tracking performance. So when a regular rig is mounted, it is good practise to roughly balance over the DEC axis and add the separately sold counterweight to get more balance on the RA axis.
Vixen saddle
If size and weight is critical, and the telescope can be mounted using a Vixen saddle, it is hard to beat the standard Rainbow Astro saddle. One main knob to hold the telescope and a smaller knob to further secure the base-plate.
Altitude setting
The scale on the altitude setting is not very precise. To speed up polar alignment, an extra marker has been added to the mount specifying the correct altitude setting for the location of the observatory. Polar alignment remains necessary, but using this little help makes for a good initial starting point.
Arca Swiss saddle
When using the mount in combination with a regular photo camera, a typical connection plate is of the Arca Swiss type. ADM has an Arca Swiss type saddle that can be screwed onto this mount. On the mounting plate there is a total of eight holes, so the saddle can also be placed perpendicular to the regular telescope pointing position. Depending on the camera/lens connection this may be important.