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Falcon Rotator and Optec TCF-Leo. A match made in ... a 3d printer

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#1 deonb

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Posted 26 August 2020 - 10:38 PM

I ordered a Pegasus Falcon Rotator and TCF-Leo Focuser, thinking that they would fit over each other. Unfortunately they don’t. The motor cover of the falcon rotator bumps up against the sides of the TCF-Leo, no matter which way you turn the TCF. You’d think they’d fit looking at it, but they just don’t. Short by maybe 5mm.

 

i.e.

Rotator 7.jpg

 

So, what to do… What to do...

 

Well, throw out the motor cover of the Falcon Rotator of course, and give it a different cover with a “notch” instead:

Rotator 2.jpg

 

Now it fits nicely. You can see based on this picture where the stock motor cover would bump up against the TCF-Leo:

Rotator 3.jpg

Curious minds may wonder why do this...

 

Well, glad you asked! The combined backfocus of the:

a) The Optec 17803 Celestron C11/C14 adapter (7mm negative backfocus)
b) Optec TCF-Leo set to its middle position (56000 of 112000)
c) The Optec 17804 Optec 3000 to 2” ring
d) The (modified) Falcon Rotator

 

is 64.75mm. In comparison, a moonlite litecrawler is 74.3mm set to an equivalent out-travel (4.45mm). That makes this combo over 10mm thinner. It’s also marginally cheaper, and more readily available - I received both parts with overnight shipping (Optec directly + HighPoint). Finally, you have 2 separate parts that you can split across 2 scopes if you want.

 

Full setup:

Rotator 6.jpg

The image train above is somewhere between 145mm and 146mm after the Celestron 0.7x reducer (which I just use to show here as a spacer since the back of that reducer is equivalent to the back of the SCT). It  includes 36mm of spacers. 31mm between falcon rotator and OAG, and 5mm between EFW and camera. This should hopefully mean a Celestron OAG would also fit instead of a ZWO OAG.

There is some additional space available between the TCF-Leo and the Rotator that can be claimed if you do a Precise Parts custom “Optec 3000 deep receiver” to “Falcon Rotator (54mm)” adapter.

Overall, it's a very simple modification. Remove the marked screws, remove the rotator plate (to get to a screw under it), and finally slip the motor cover out from the back.
Rotator 1.jpg

3d printed design on:
https://www.thingive...m/thing:4580838

One caveat – my top-most screw in the design doesn’t line up with the hole in the rotator. For now I’ve put in only the bottom screw, which holds it in place. I’ll redo it later.
 
Feel free to take/copy/modify my design for any purpose, including commercial. Hint hint @PegasusAstro... if you ever feel like making a metal version of this, put me on the list smile.gif.


Edited by deonb, 26 August 2020 - 10:40 PM.

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#2 SonnyE

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Posted 26 August 2020 - 11:18 PM

Youz guyz and your 3D printers!

 

I no gotz one, but I thank you for sharing your design!

 

Very nice!grin.gif



#3 evansg

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Posted 12 October 2020 - 10:01 AM

Hi Deonb and thanks for the recommendation!

 

Based on your observations we have redesigned the motor cap. A couple of customers checked this thread and they expressed a similar request as their telescope equipment was colliding with the original motor cap of the Falcon Rotator.

 

Unfortunately we cannot provide a metal redesigned motor cap at the moment as we have our production running with the current design.

In the future we are going to replace it with the new one.

 

For anyone who owns a 3d printer and has a similar issue I strongly encourage him to download and print the redesigned /shorter motor cap

 

Download the STL 3d file from here: 

https://pegasusastro...otor-cap-v2.zip

 

For more information you can contact our support email. support [ a t ] pegasusastro.com

 

Regards,

Evans


Edited by evansg, 12 October 2020 - 10:08 AM.

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#4 deonb

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Posted 20 October 2020 - 11:59 AM

Hi Deonb and thanks for the recommendation!

 

Based on your observations we have redesigned the motor cap. A couple of customers checked this thread and they expressed a similar request as their telescope equipment was colliding with the original motor cap of the Falcon Rotator.

 

Unfortunately we cannot provide a metal redesigned motor cap at the moment as we have our production running with the current design.

In the future we are going to replace it with the new one.

 

For anyone who owns a 3d printer and has a similar issue I strongly encourage him to download and print the redesigned /shorter motor cap

 

Download the STL 3d file from here: 

https://pegasusastro...otor-cap-v2.zip

 

For more information you can contact our support email. support [ a t ] pegasusastro.com

 

Regards,

Evans

Thanks! I like the thinner lip you have on it, and the better cutout for the motor.

TBH though, not a lot of home fused deposit printers will get M3 threads right with any degree of reliability. I have a fairly high-end printer (TAZ5) and it got only 1 of the two holes. I'll get Sculpteo to run it using laser sintering, which should work. It's cheap ($20) but it takes a couple of weeks to deliver, so isn't as useful as printing at home.

However, I was actually thinking of reducing the lip to a completely flat 1.5mm lip with a countersunk hole in it for a 6mm M3 screw, and then use a nut on the inside of the rotator. I think the hole will have to cut a notch out of the body for the screw head, but it should work. That will allow me to change the OPTEC-3000 -> 2" -> 54mm train into a very short (3mm) OPTEC-3000 -> 54mm part, which I can get made by PreciseParts. That should squeeze out another 10mm or so of backfocus.

I wished there was a simple way to just mill this out of 2x2x2 aluminum on a 3-axis CNC, but I can't think of one. 

 

Hopefully your next run of the Rotator will put the screw-holes in a different location to avoid the lip altogether smile.gif


Edited by deonb, 20 October 2020 - 12:05 PM.

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#5 Mikehuerto

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Posted 01 September 2021 - 04:08 AM

Hi 

 

I am thinking of buying one of these for my SW 14" GOTO Dobson, do you guys have any feedback on how well it is performing?

 

My main use would be to  cure rotation effects for long stacks. Would it also allow for longer sub-exposures - since there is less rotation movement?  My current exposure length is limited by both rotation and poor tracking of the mount. I can currently can do 1-4 secs, at 8-15 secs I start to see elongated stars. Just be good to get some authentic feedback. I have found very few user reviews of this item on the web. 

 

Best

 

Mike



#6 deonb

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Posted 01 September 2021 - 09:14 AM

Hi 

 

I am thinking of buying one of these for my SW 14" GOTO Dobson, do you guys have any feedback on how well it is performing?

 

My main use would be to  cure rotation effects for long stacks. Would it also allow for longer sub-exposures - since there is less rotation movement?  My current exposure length is limited by both rotation and poor tracking of the mount. I can currently can do 1-4 secs, at 8-15 secs I start to see elongated stars. Just be good to get some authentic feedback. I have found very few user reviews of this item on the web. 

 

Best

 

Mike

If you can only do 8-15 secs, that's not rotation effects yet - that's mount tracking.

 

The Leo is REALLY smooth. Smoother than my mount movements. But I've never actually tried it to counter earth rotation - I've always used an EQ mount for that.

 

There is a OPTEC user group on groups.io if you want to ask there if anybody has tried it.


Edited by deonb, 01 September 2021 - 09:14 AM.


#7 Mikehuerto

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Posted 01 September 2021 - 11:00 AM

If you can only do 8-15 secs, that's not rotation effects yet - that's mount tracking.

 

 

Yes  - correct there are two things going on with my setup - poor tracking leading to elongated stars at longer exposures, and field rotation during live stacking. Its the latter I hope to correct with the rotator I do live stacks of 100s to 1000s of 1-4s frames. the rotation effect  becomes obvious after about 10 min, you can see the field rotating as a series of shadow frames during live stacking. I therefore keep most integration to 5 mins (see my astrobin in signature). The field rotator would allow me to use the entire FOV on longer stacks instead of having to crop out the rotation shadows. 

 

But thanks for the feedback, on the rotator performance.Very much appreciated.

 

I've meanwhile checked with Fillipo on Astrobin. He has a 23 inch Dobson!  And he is getting great results. As for me, the main advantage for him is to get rid of field rotation and allow him to use the entire FOV.  see. https://www.astrobin...sers/filiscoop/

 

I'll be ordering today!!

 

Clear Skies 

 

Mike


Edited by Mikehuerto, 01 September 2021 - 11:08 AM.



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