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

Advice on track design for DIY dome

  • Please log in to reply
9 replies to this topic

#1 althor74

althor74

    Lift Off

  • -----
  • topic starter
  • Posts: 6
  • Joined: 14 Sep 2015

Posted 24 May 2021 - 10:07 PM

Hello,

 

I'm looking for advice on a design for a wheel track for my 10' DIY wood dome. I'm having some issues keeping it it rotating evenly due to imperfections in not having a perfect circle. The previous attempts I've made by adding guides either on the outside of the dome or guides up against the wheels have added too much friction and uneven binding which simply have made my easy-to-rotate dome very difficult to rotate. Since I want to motorize and automate the dome soon I want something better. I think my best solution is to install a track of some design that will be very close to round, and then have a V or U wheel which will sit in that track. It should be pretty easy to locate the center of the dome, then attach a string to that point and draw a nearly perfect circle on the bottom of the dome where the track will be mounted as well as the platform that the wheels sit on. Then I can install the track and wheels on that circle, esuring that the wheels are turning on a true circle and will not bind or shift. My two design options I'm considering are with a V wheel and a T shaped track, or a U wheel and a piece of round conduit. I'm planning for 12 wheels, which should be more than enough to handle the weight, but I could do more if needed. Advantages/disadvantages I can see are:

 

V wheel

- I'd use a 1-1/2" steel track which should be very durable and then support that with two aluminum 1/2" brackets which would be screwed into the dome (with notches cut every foot or so to allow for the bend).

- This design would allow for a perfectly smooth surface for the wheels to sit on (as opposed to screws or holes discussed below)

- It'd be super easy to bend to my perfect circle shape

- Not sure if it's a negative, but it would have only a tiny area of contact on the wheels. However that's what the V wheels are designed for.

- Something like this https://www.amazon.c...y/dp/B085C2SVNP

 

U wheel

- I'd use a 3/4 metal conduit as my track

- I'd either attach it with screws (which would cause a tiny bump every time a screw crossed a U wheel). Or more likely drill a hole larger than the screw head, and then a smaller hole through the other side of the conduit and then the screws would go through the conduit and hold it to the dome from the inside (I would still have a tiny notch left that might cause the U wheel to slightly sit in, but this should be a lot less friction than screw heads)

- It'd be fairly easy to bend to shape, but more work to get perfect than the flat steel track mentioned above.

- It would give me more surface area for the round conduit sitting on the U wheel. Everywhere I read I hear that bigger and flat wheels that provide more surface contact is better.

- Something like this https://www.amazon.c...g/dp/B08XZBR4TK

 

Below I attached an image showing kind of what each track would look like, with conduit and U wheels, or the track I'd assemble for a V wheel. I'm interested in feedback on which is the better track system. OR if I should be considering something totally different. Thanks!

Attached Thumbnails

  • Observatory Wheel Track Ideas 2.jpg

Edited by althor74, 24 May 2021 - 11:09 PM.


#2 duck

duck

    Ranger 4

  • -----
  • Posts: 322
  • Joined: 11 Jun 2020
  • Loc: madera ca

Posted 24 May 2021 - 10:36 PM

I used separate rollers for the vertical load, which is pretty large.  Radial location was with horizontal wheels running against accurately rolled flat iron.



#3 Christopher Erickson

Christopher Erickson

    Skylab

  • *****
  • Posts: 4,027
  • Joined: 08 May 2006
  • Loc: Waikoloa Village, Hawaii

Posted 25 May 2021 - 01:56 AM

Unless you have a fairly precise way to make or bend the track, it will never give good results.

 

Instead I would suggest stationary, hard plastic or metal rollers, facing up onto a hard, flat metal or metaloid (aluminum) surface. Side rollers to maintain concentricity.



#4 mark77

mark77

    Viking 1

  • *****
  • Posts: 841
  • Joined: 28 Jun 2015
  • Loc: PA

Posted 25 May 2021 - 01:40 PM

I agree with Christopher, unless the V/U tracks are perfect, they wont work.

 

I use flat wheels upside down, then I have roller blade wheels on the inside keeping it in place.  At any given time, at least some of the roller blade wheels are NOT touching.

 

The bottom ring of my dome is 6 inches wide and flat.  The reason for the wheels being upside down is so that you dont get dust/dirt/dead bug build up which increases the rolling friction.

 

Go to this link and scroll down to the very last picture   http://www.skychario...dome/index.html

 

Mark



#5 appicloudy

appicloudy

    Explorer 1

  • -----
  • Posts: 75
  • Joined: 14 Feb 2018

Posted 26 May 2021 - 09:26 PM

Hello

 

My solution ( and it may be a bit late for you ) was to have 6mm thick ( 1/4 inch ) aluminium laser cut for the bottom ring of the dome then the Tee shaped ribs were attached ( welded ) to the ring along with a flat bar section of about 75mm by 6mm ( 3" by 1/4 inch ) was welded to the ring using the ribs as spacers to get a uniform distance from the inner edge of the ring.

 

This created about 25mm ( 1 inch ) from the inner edge of the ring to the inner face of the flat bar, to the bar I attached a 50mm ( you work it out ) flat belt, the ring rides on regular ball bearings. The drive pulley is held against the toothed belt by a heavy spring, two idlers at 120 degrees at fixed and hold the dome in line so it does not crash into the dome.

 

The last thing the ring / drive pulley and idlers do is they are effectively over part of the ring, this stops any chance of the dome lifting in heavy winds.

 

I must be heavier than I think as in even very strong winds the dome has not shown any indication it was about to lift.

 

The dome has been rolling for 3 years on the aluminium ring and as yet the ring is not showing any wear, steel would have been more durable but hard for an amateur to weld steel to aluminium.

 

Ed


Edited by appicloudy, 26 May 2021 - 09:26 PM.


#6 kathyastro

kathyastro

    Soyuz

  • *****
  • Posts: 3,515
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 27 May 2021 - 07:03 AM

The "T" cross-sesion of the Exporadome ring system works well.  Fixed, upward-facing wheels support the upper ring, and out-ward-facing alignment wheels keep it centred.

 

The dome has shown no tendency to lift in high winds.  However, since this photo was taken, I have added some aluminum passive restraints that curve over the top of the drive ring.  I also can install turnbuckles to hold it down in hurricanes.

 

P1090858-800px.JPG


Edited by kathyastro, 27 May 2021 - 07:04 AM.


#7 MHamburg

MHamburg

    Vanguard

  • *****
  • Posts: 2,461
  • Joined: 21 Jun 2006
  • Loc: Brooklyn, NY/Berkshires, MA

Posted 27 May 2021 - 09:48 AM

 

Hi 

As it was the first dome I ever built, I made plenty of mistakes. Not only did I fail to make a perfect circle in the X axis, but I also failed to keep the base ring level (the y axis). I also designed the base ring to ride on the inside of the angle iron which constituted the base ring. Therefore, I had various and very annoying issues with rotation. Finally, I came upon a good retro fix as shown in the image. Supports that could move both radially and vertically compensate for all the irregularities. In addition, the base ring now rides on the vertical edge of the angle iron thus eliminating any binding surface,

Michael

 

 

 

Attached Thumbnails

  • 2018-11-18 10.10.43.jpg
  • 2018-11-18 10.07.21.jpg
  • PICT4403.jpg


#8 MJB87

MJB87

    Gemini

  • *****
  • Moderators
  • Posts: 3,071
  • Joined: 17 Feb 2014
  • Loc: Talbot County, MD & Washington, DC

Posted 27 May 2021 - 10:37 AM

 I also can install turnbuckles to hold it down in hurricanes.

Could you provide some details on how the eyebolts were fixed to the dome?  I'm concerned that without the proper fittings the wind could just rip the dome off the eyebolt.  How much of a metal (?) backing do you have on that eyebolt on the outside?  Thanks!

 

Marty



#9 kathyastro

kathyastro

    Soyuz

  • *****
  • Posts: 3,515
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 27 May 2021 - 11:25 AM

Could you provide some details on how the eyebolts were fixed to the dome?  I'm concerned that without the proper fittings the wind could just rip the dome off the eyebolt.  How much of a metal (?) backing do you have on that eyebolt on the outside?  Thanks!

 

Marty

There is no metal backing.  The eyebolt just has a washer and a nut holding it.  The heavy poly of the dome is darned near indestructible.  I once attempted to rotate the dome using the motor, forgetting to remove the turnbuckles.  The motor had enough torque to bend the bolt, but did no damage to the dome.  (That wouldn't happen these days: I use a stepper motor with less torque, and there is a signal that tells the controller that the turnbuckles are installed, so it will refuse to rotate.)

 

The main function of the turnbuckles is not so much to resist the wind as to prevent the wind from lifting the dome. If the dome doesn't lift, the wind isn't going to rip it off anything.


Edited by kathyastro, 27 May 2021 - 11:26 AM.


#10 MJB87

MJB87

    Gemini

  • *****
  • Moderators
  • Posts: 3,071
  • Joined: 17 Feb 2014
  • Loc: Talbot County, MD & Washington, DC

Posted 28 May 2021 - 10:08 AM

Thanks.  Looks like a good solution.




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