note: the title should say ‘Twinstar,’ lol…can’t seem to edit that out😀
It seems that every other day brings a new mount on to the market these days but, beyond the sales pitch, there are often no real-world data on which to make purchasing decisions. With that in mind, I thought that it might be useful to document my first few weeks with a recently purchased Twinstar FG-80 friction mount.
Unlike many of the other recent announcements, the FG-80 is a friction-drive rather than a harmonic-drive and is also aimed at the high-capacity rather than low-capacity end of the market with a max stated 80kg payload. In this respect, it appears to be a direct competitor to the JWT Trident, with very similar pricing, just over EUR4000, depending on options. Guiding performance is quoted as ‘+/- 0.5 arcsec for unlimited time’.
Despite receiving the mount earlier in the year, I have due to weather and other limitations only had it out under clear skies for less than a week in total…so these are very much initial impressions. The FG 80 is an impressive beast and appears both well designed and well engineered. It is super quiet (if you have light-sleeping neighbours). One of the main attractions of the FG-80 for me, apart from the payload capacity, was the ‘integrated electronics’ incorporated into the mount saddle. On each side of the saddle there are 8 x 12V DC outlets (max 4A per port) and 7 x USB-3 outlets.
📷 Saddle power.jpg
📷 Saddle USB.jpg
This makes for very minimalist cable runs - I just have one 20A power supply to the entire mount, then everything is powered from that via the integrated hub on the saddle. Similarly, I have a mini-PC mounted on top of the scope and can communicate with everything via the integrated hub. For my set-up this results in just 2 cables between the mount saddle and the base but this could reduce to one if you had your PC mounted on the base.
I purchased the FG80 with the intention of using it with my C11edge SCT on there operating at native focal length but, assuming the initial setup at 2800mm would be challenging, I first put a RASA8 on there. This uses an external guide scope and ASI Air for control. The FG-80 utilizes EQMOD ASCOM drivers and so it is simply a matter of selecting ‘EQMOD with SkySafari’ in the ASI Air and everything communicates straightaway. I was literally up and running with initial polar alignment completed within 30 minutes🙂
The ASI Air of course only incorporates a very stripped-down version of PHD2 and so there are very few options for honing the guiding behaviour but I have to say that, with minimal mods (mostly just increasing the RA aggression), the mount guiding with this relatively light rig (~10kg ) looked pretty good, hovering around 0.4 arc seconds total RMS (ignore the dither settings as this was not set correctly for this experiment). RA error somewhat larger than Dec but all well within the image scale of the RASA setup (1.2-1.9 arc seconds per pixel, depending on the camera used).
📷 RASA guiding.jpg
Buoyed by this initial success I am now, cloud permitting, playing around with the heavier C11 edge on the mount - this using an OAG for guiding and PHD2 running with NINA. There was, as I anticipated, some initial angst in setting this rig up but I have to say this was entirely due to operator error (as a lifelong Mac user I would rather poke my eyes out with blunt sticks than deal with COM port issues on a PC - what century are we living in again?🙂).
Once resolved though, I again found the mount to be very well behaved. This is a heavier payload (~ 20kg) albeit still nowhere near the stated load capacity of the mount. Total RMS for this scope is hovering around 0.35 arc seconds. The main issue again is the somewhat higher RA variation compared to Dec but both seem pretty good to me – at least for my Bortle 5 skies on the edge of a major city and are actually better than I have seen with any of my other mounts.
📷 C11 guiding.jpg
I am still playing with guiding parameters (again blunt sticks come to mind..) but the performance so far has been very encouraging. So far I really like the FG-80. The only negative I can think of thus far is that I do miss having a hand controller but, to be honest, I’m not even really sure why – I barely use the ones that I do have on other mounts. It’s probably just reassuring in case you want to take over the mount in a hurry…
Anyway, that’s just an initial look but I hope this helps anyone looking into the friction drive market segment…bit by bit just a little more information out there.
cheers, Jon
