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INDI Library v2.0.6 is Released (02 Feb 2024)

Bi-monthly release with minor bug fixes and improvements

DIY Flatfield Dustcover with RPi

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hi Magnus_e,

Thanks for your fast response, please dont try to do anything now! I think I found the error.
I think I have a faulty libindi installation... I will report back soon :)
--= human, without Windows™ =--
pls excuse my bad english! :)
6 years 11 months ago #16030

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Ok. Let me know how it turns out.

This was a funny coincidence. Yesterday I 3d printet the first prototype of the printable dust cap :)
I have to figure out how to get better finish when printing with supports (this was my 4th print), but hopefully It wil turn out nice after some dev.

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6 years 11 months ago #16031
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Wow, that looks quite nice! I might consider 3d printing too if my aluminium cap idea fails but I dont own such a printer, and printing 4 ore more prototypes via online service might get very expensive...

I managed to get the ServoBlaster Cap work. Absolutly no errors during compilation! Servo moves as expected in indi :side:
It was indeed a faulty indi installation. Maybe I forgot to do "make install"... I will double check in future to prevent mass panic ;)

I can now order the aluminium sheet for the dust cap and will try to get it all on the scope.
--= human, without Windows™ =--
pls excuse my bad english! :)
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Last edit: 6 years 11 months ago by pauledd.
6 years 11 months ago #16032

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Good to hear it works :)

The picture was first print of the protltype, and 4th print total. I finished assebeling my Prusa mk2s yesterday :)

The aluminum version you ar making should work just fine, I think.
If I remember correctly I installed the prototype from the tutorial in my observatory in November and it still works great (and that one is held togheter only with tape and glue.)
Proud owner of Observatory 17b - A remote Linux observatory.
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Build thread @ SGL: Starting summers observatory project
6 years 11 months ago #16036

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wow. I love the dust cover design. would you share your STL files? i'll need to resize, but this would be a great start.
6 years 10 months ago #16607

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Hey.
I uploaded the files to thingiverse :)
I updated the original thread I had on the 'Dark Cap' so It won't hijack @pauledd's thread

indilib.org/forum/ekos/1452-feature-dust....html?start=12#16659
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6 years 10 months ago #16660

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Hey Magnus, this cover looks awesome, nice work.
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6 years 10 months ago #16662

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I made "some" progress with my dustcover. I decided to make parts of it made of wood because that was the easiest. In the course of this I realized that I was maybe wrong with the assumption that my littly tiny servo would have enough power.

I left the EL-Flatfield Foil away to just concentrate on the dustcover. The cover itself as baseplate for the foil was made of acrylic glas.




Its weight is about 150g. Some tests showed I would need about 800g force to lift the arm. That approx. matched my calculations I did before:



However this does not work. I can unpark the cap but the servo never reaches the end position and stays making noise.
I tried to increase the servo voltage up to 6.7 Volts but it still doesn't reach the end position. I dont know whats wrong here because with that 3.8cm servo arm it should be able to handle up to 1.2Kg on that arm.

Before I consider to buy another stronger servo I'll try to replace the dustcover with an aluminium one, 0.5mm thickness, that should give a weight of about 20cmx20cmx0.05cmx2.6g= 52g and that should give a load on the servo of about 52x4.73= 245g, one third of my current weight.

Here's just a short video of my dustcover in action, looks good but doesn't reach end position and continuously makes noise.

--= human, without Windows™ =--
pls excuse my bad english! :)
Last edit: 6 years 9 months ago by pauledd.
6 years 9 months ago #17387

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Great work, and nice to see you are making progress :)

Something you can try to be 100% sure that it is a weight issue is to see that your servo in fact can move further with the lid disconnected (just remove the bolt that is connecting the brass / anodized servo horn to the wood linkage.

The reason for this is that from watching the video I'm not entirely sure if the lid stops when it has past the point where it's the heaviest, or just after.
(When I think about it, you don't have to unscrew anything. Just point the scope at the zenith. If it fails to move at all or if it opens to the expected position, it's the weight for sure).

However it might be servo centering. When you hear the bussing at the most open position, and it stops to move then it is binding.
There is three ways a servo can bind.
1. The object that is being actuated reaches a mecanical endpoint, and can move no further.
2. The object being moved is to heavy and the servo motor is skipping.
3. Internal binding.

If the weight test above do not proove it's the weight (i.e servo motor skipping) then it's allmost certanly internal binding.
Servos work at a PWM pulse from 0.5 - 2.5, at least some of them! There is no standard that ceeps a servo from actually woriking in PWM range 1.0 - 2 as an example.
If you tell a servo to go to PWM 0.5, and it has internal limits at 1, then the servo will appear to bind, even if it is not binding at an endpoint or skipping from overload.

If you have not done so allready, you can disconnect the servo horn completely, and try to Park / Unpark while encreasing / decreasing the (Max travel limits [set open travel (ms), set close travel (ms)]) in the Calibrate tab. You should aim for the limits closest to 0 and 3 that you can acchieve while the servo makes no sound at the endpoints. You should do this while the (Preffered travel limits [set open limit (%), set close limit (%)]) is set to 100, 100

After that set your close limit to 90 - 95%, park the cap and attach your servo horn and linkage while the lid is closed against the telescope. (Then you have 10 - 5 % to work on when the lid is connected to the servo, to ensure that it can close fully). Leave your preferred open limit at 100%, as it does not look like your setup will bind.

Hopes this helps to determen if you need new servo / lighter lid, or if you can calibrate it out, (not sure if I explaned thiswell enough on the github readme, so tought I'll go into some detail :) )
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Build thread @ SGL: Starting summers observatory project
6 years 9 months ago #17397

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Thank you Magnus_e for your detailed ideas!

I am nearly 98% sure its a weight issue. The cap moves fully if the scope is slightly off the home-position so that the cap is not in its "heaviest position". I currently discuss my torque/weight calculations on a physic-board and its a little bit more complex than I thought.
Someone presented a formula to get the caps torque when its opened at 90° degree (the most heavy position):

Where
Mk: is the needed cap torque
m: is mass of the cap
g: Gravitational acceleration (9.81)
l: length of the cap (diameter)

With that formula he got about 13Ncm force needed to move the cap.
My motor has 46Ncm divided by 3.8cm of the servo arm that makes ~12Ncm.
I have no confirmation yet that its the right way to calculate it but it seems my motor
specs missed the caps torque very close. So I am quite shure replacing the acrylic cap
with 0.5 or 1 aluminium will do the trick. I will order two sheets of it, its quite cheap.
--= human, without Windows™ =--
pls excuse my bad english! :)
Last edit: 6 years 9 months ago by pauledd.
6 years 9 months ago #17398

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you might try a count weight along the plane of the flap.
provided you have clearance along the OTA, then only a very small weight would be required.
Last edit: 6 years 9 months ago by Rob Jones.
6 years 9 months ago #17400

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This would of cource depend on the orientation of the scope when unparking.
I park my scope at alt +1, so a counterweight would not work when unparking the cap at that position.

However... You could add a spring to the equation. Fasten it so the spring is slightly tensioned when the lid is at it heaviest. This might cause the lid to not stay completely closed when the servo is not powered, so possibly not a god idea? Ebay id for some springs 281291676039
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Build thread @ SGL: Starting summers observatory project
6 years 9 months ago #17401

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