Accurately aligning axes of centres or rotation for parts

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nohspamjose
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Accurately aligning axes of centres or rotation for parts

Post by nohspamjose »

FreeCAD v20.1 on MacOS10.16

Please will someone point me at a tutorial or help me understand how to set up composite objects?

I am modelling a pan an tilt head on a dolly that runs on a track, so I need:
  • 1 a composite object for everything (part)
     1.1 a composite object for the dolly assembly (part) - I won't detail this more
      1.2.1 a composite object for the tilt assembly (part)
       1.2.1.1 stepper motor (part)
       1.2.1.2 gearbox (part)
       1.2.1.3 a composite object for the pan assembly (part)
        1.2.1.3.1 stepper motor (part)
        1.2.1.3.2 gearbox (part)
        1.2.1.3.3 a composite object for the camera (part)
         1.2.1.3.3.1 cylinder stand (part)
         1.2.1.3.3.2 camera (part)
         1.2.1.3.3.3 lens (part)
     1.3 a composite object for the stand (part)
      1.3.1 stand-a (25,10,45), with a 4mm hole on the y axis at 12.5,10,352 (part)
      1.3.2 a stand-b (25,10,45), with a 4mm hole on the y axis at 12.5,10,352 offset on y by 55mm (part)
With this arrangement, I can set
  • y offset for 1 and everything moves down the track
  • angle around y for 1.2 and the tilt, pan and camera tilts
  • angle around z for 1.2.1.3 and the pan and camera pan
Fine with this but understanding how to align rotations axes, using the edit>placement>tasks/centre seems unintuitive and much too complex, needing a complete understanding of the interplay between all the origin and offsets and coordinates. If these are set right at the outset before the assembly is moved, then perhaps it's simplified a bit but if I try later, when I want to modify or add something, it fries my brain.

I'm specifically looking to align the tilt axis (that goes through the stand and the sides of the tilt gearbox) and also the pan axis that goes through the top of the tilt gearbox and the side of the pan gearbox

Is there a simpler way or is this a usability nightmare waiting to be solved?
FWIW - I'm a usability/UX consultant

Thanks,

Greg
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PanTiltTravel.FCStd
(245.3 KiB) Downloaded 20 times
freedman
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Re: Accurately aligning axes of centres or rotation for parts

Post by freedman »

In the tree, drag the Pan_tilt Part container (yellow icon) into the dolly. Now when you use Transform to move the dolly the pan tilt will move with it. This is a basic grouping of parts, is that what you mean by composite. No one here knows the word composite so maybe do some research and try a different word.
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thomas-neemann
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Re: Accurately aligning axes of centres or rotation for parts

Post by thomas-neemann »

nohspamjose wrote: Mon Sep 26, 2022 9:07 pm ...

is this a solution for you?

https://www.youtube.com/watch?v=2VZC2XpBxak

phpBB [video]


edit

the axis of rotation is not correct yet. I can also make a video about it if you want
Last edited by thomas-neemann on Tue Sep 27, 2022 8:34 am, edited 1 time in total.
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nohspamjose
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Re: Accurately aligning axes of centres or rotation for parts

Post by nohspamjose »

Thanks for your prompt feedback. Sorry, I used composite in its vernacular form (plain English) as it is a word that describes the assembly of subordinate things, so it would be unambiguous and reduce the chance of me accidentally calling it something less clear but also not part of the FreeCAD lexicon. What do you call a parent part that has child parts?

I constructed the text hierarchy before I realised I could attach my FCStd file - I probably should have removed the text version after attaching the file.

I'm sorry I muddied the water with the part hierarchy but I wanted to illustrate the construction of parts, so that my query about how to manage global origins, the local origins of 'composites' (assemblies made up of other parts) and the origins of the composite's child parts but...

primarily: how to move the origin of what I've called a composite (and you're about to reveal the correct name for), so that when I apply a pan angle to the composites (tilt part or pan part), they turn accurately on a carefully placed axis and not a guessed approximate placement of the axis

If you open the file and apply an angle to the tilt part, you'll see that the axle moves relative to the side part. I want the y axis of the origin to perfectly align with the centre of the axle part in the tilt part

Thanks
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Re: Accurately aligning axes of centres or rotation for parts

Post by thomas-neemann »

nohspamjose wrote: Tue Sep 27, 2022 8:27 am ... axis ...

here is a suggestion with the right axis of rotation


https://www.youtube.com/watch?v=AdTOMeyLQzA

phpBB [video]
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papyblaise
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Re: Accurately aligning axes of centres or rotation for parts

Post by papyblaise »

It is true that words change from one language to another
in French, a whole is a set, the elements are subsets (direct children, nephew or nieces)
Me, before starting to draw, I think for 5 minutes to know what should move in 3D, and remain fixed or just in translation, and I will place the main object which must move in 3D at the center of the universal coordinate system, and all the other "children" by this same UCS, so the assembly will be without finding a good position
relative movements during an animation will be simpler since always in relation to the UCS
your drawings are "finished" but it would be easier to take each of the "children" to replace them in relation to the UCS without redoing everything, but it will save time compared to trying to align all the planets and their moons respectively at a time "T"
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Re: Accurately aligning axes of centres or rotation for parts

Post by nohspamjose »

Thanks Thomas,

I'm not quite sure what you're showing me there but the grids look useful. Do they represent the local coordinate system of the item selected in the tree? I was slightly confused by this feature only appearing in the Architecture workbench, because if it's the answer I think it might be, I'd expect it to be front and centre in the Part, Part Design and Assembly workbenches too.

Thanks for the hint
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thomas-neemann
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Re: Accurately aligning axes of centres or rotation for parts

Post by thomas-neemann »

nohspamjose wrote: Tue Sep 27, 2022 9:37 am ....

it is possible in arch and in draft. not in part and partdesign. but you can mix the wbs
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nohspamjose
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Re: Accurately aligning axes of centres or rotation for parts

Post by nohspamjose »

Thanks papyblaise,

I think I did that. Perhaps not perfectly but at least for the pan/tilt motors and gearboxes.
For example (a subset of the bigger task),
  1. I created a pan part
  2. created two cubes (motor & gearbox).
  3. moved the pan stepper motor relative to the pan gearbox
  4. dragged the two cubes into the pan part (maintaining their relative positions)
  5. perhaps at this point, I should have tried to move the local origin to the pivot point for the pan part and not wait until I'd constructed the Dolly AND Tilt AND Pan AND Stand AND Camera? What do you think?
  6. applied position translations to the pan part
It would be great (more usable) if actions like this were less work order dependent?

Thanks
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papyblaise
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Re: Accurately aligning axes of centres or rotation for parts

Post by papyblaise »

not in part and partdesign
not true
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