The RST-135 is a new mount from a Korean company called Rainbow Astro which seems to be a subsidiary/ sister concern of Rainbow Robotics.
Rainbow Robotics is known for their endeavors into Robotics and more specifically their HUBO2 robot. So these folks seems to have a background in robotics which is quite relevant here.
The RST-135 is a different kind of mount to most you or I have used in the past. It uses Strain Wave Gears which are a type of Harmonic gear. This video explains the functioning pretty well: https://www.youtube....h?v=bzRh672peNk. These gears are used extensively in industrial and robotics applications and are incredibly robust as they are designed for 24/7 365 day operation. With the company's background in robotics I think this was probably a natural transition for these guys.
This is not the company's first mount. They have a whole line of mounts but started using harmonic drives in their last mount the RST-150. That mount was a bit more expensive as it used (more expensive) drives from a Japanese company. For the newer mount they have managed to source a less pricy drive which was brought the price of the mount down quite a bit.
So, what is special about this mount? Well quite a bit due to the harmonic drive used in the mount.
Harmonic drives are incredibly strong so they can be really small yet drive very large loads. You also don't need counterweights and there is almost no backlash. This yields a small lean mean machine when it comes to making a mount.
The one downside is that the drive has meaningful periodic error. But it is slow and very easy to guide out. But it also means you are limited in the length of the unguided exposures that you can use.
Here is the value proposition as I see it:
- Only 7.3lb
- 30 to 40lb payload capacity
- No counterweights required up to 30lb - saves dead weight and eliminates another of my pet peeves...
- No need to balance (Absolutely love this - I can add remove accessories or change OTA without worrying about counterweights. Balance issues in AP are one of my pet peeves. For visual in Alt Az this is ideal as well)
- Can be used in Alt Az and EQ mode
- Even if your polar alignment is slightly off it can compensate
- Little or no backlash - this is under appreciated but is a critical factor for guiding
- With guiding total rms error can as low as 0.40” which is very impressive
- Unguided - lets do some math. I saw the manufacturer state some where that the PE was about 20” in 420 or 430 seconds. Assuming it is 20” peak (not peak to trough) in 400s then with a sampling of 2” you should be able to get ~40s unguided exposures. If peak to trough then double that... approx 80s.
If I think about it, this is very close to the definition of my ideal imaging mount.
In this running thread / review I post my evaluation of this mount. Goal is to tease out max capacity, tracking accuracy, ease of setup / polar alignment etc. Here is what I will cover:
- Unboxing & accessories / cables etc.
- Ease of Setup & Polar alignment
- Guided and unguided imaging:
- Widefield: using AT60 and the RedCat 51
- Long FL imaging: using EdgeHD 8 and EdgeHD 9.25 scopes
- Tease out maximum real world load capacity for imaging
- Will evaluate it in EQ and Alt-Az modes
- Go to accuracy using 1, 2, 3, 4, 5 point alignment models
- Max weight for visual e.g. can I push it to a C11 (~27lb OTA / 30lb with diagonal and EP) with counterweights? - this will likely come later as I don't have a C11 on hand
- Tracking at higher magnifications (this is somewhat more dependent on the tripod but I have sometimes seen oscillations due to motors as well but I don't expect that from this mount)
So lets begin with the unboxing pictures...
Edited by Astrojedi, 01 July 2019 - 01:11 PM.