Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Swing balance arms

  • Please log in to reply
4 replies to this topic

#1 hakann

hakann

    Surveyor 1

  • -----
  • topic starter
  • Posts: 1779
  • Joined: 06 Aug 2015

Posted 24 May 2019 - 12:40 PM

I thought I can do a own thread of the design of a ‘floating’ swing balance arm ( for a 18 pt mirror cell )

First question.
One can think about ; what is the gain from a centre hole based balance arm ?

 

Ok, low mount as arm inside the frame, but one can has the same low mount in a centre hole arm to in a frame.

 

Next.
What is the most easy way in machining ?
I would say both is pretty equal if one do a CNC billet frame.

 

I thing about the swing arm is axial supports, as glue the mirror to triangle is not a real good idea.
But maybe the arm will be ok in centre my mirrors weight even at tilt ?

 

What will the angle best be at, I has been into 30 degree.

 

Next is diameter on bearings vs reaction.
Is a smaller diameter better than a bigger ( ex OD/10 mm vs a OD/20 mm ) ?

 

Both a centre based arm and this swing arm will work the same as adjust the triangle.
But what should the gain be in the swing.

-Just some thought’s.

Attached Thumbnails

  • CN10.jpg

Edited by hakann, 24 May 2019 - 12:44 PM.


#2 Oberon

Oberon

    Mercury-Atlas

  • -----
  • Posts: 2916
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 24 May 2019 - 06:51 PM

Although the dwg above is a clever design that is likely to work well enough in practice, it doesn’t obviously offer any benefit over more traditional arms that pivot in the center, and has the at least theoretical disadvantage of increased bearing stiction. If we think a center bearing risks stiction, then two bearings doubles that risk, and now without the leverage to overcome it. So risk of stiction may have increased by an order of magnitude.

 

However...find a practical way of replacing those 2 bearings with 2 flexures one each at say 45 degrees either side of perpendicular and we may have found a unique new solution, a compact flexure that works.


  • PrestonE likes this

#3 hakann

hakann

    Surveyor 1

  • -----
  • topic starter
  • Posts: 1779
  • Joined: 06 Aug 2015

Posted 25 May 2019 - 10:54 AM

Oberon,

One problem I see here on the swing arm is beside stiction is the axial force.

The one on picture don't has that problem as mirror is more or less stick on the triangles.

Anyhow if a mirror weight 10 kg it's 3.3 kg on each arm in load.

It can be bearing that the swing arm can fall down at and work as a axial bearing.

 

On the idea you was into, any ideas you can put up ?

Attached Thumbnails

  • CN10.jpg


#4 MitchAlsup

MitchAlsup

    Soyuz

  • -----
  • Posts: 3898
  • Joined: 31 Aug 2009

Posted 25 May 2019 - 12:45 PM

Oberon; the advantage is that the arm may support the mirror with greater stiffness.

The classical pivot in the middle arm has bending moments.

This new design goes a long way in removing those bending moments.

 

Hakann, you are going to want the sliding pivots to be supported with ball bearings for minimum friction.



#5 hakann

hakann

    Surveyor 1

  • -----
  • topic starter
  • Posts: 1779
  • Joined: 06 Aug 2015

Posted 25 May 2019 - 01:29 PM

Mitch, did you mean as I drawed the 'axial bearings' ?

 

And yes, you has a point that this swing arms will be stiffer as 2 rest points ( that's one good aspect.


Edited by hakann, 25 May 2019 - 01:39 PM.



CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics