Author Topic: Worm thoughts  (Read 476 times)

Paul L

  • Jr. Member
  • **
  • Posts: 99
    • View Profile
Worm thoughts
« on: March 09, 2016, 09:42:35 AM »
Hi Everyone,

   It's been a while since I've posted, so I thought I'd dust off the keyboard and share a few thoughts here.

   I've been hoping for the last few years that someone here would come up with an accurate, easy to do diy worm gear for all these stepper driven heliostat designs.  It's becoming increasingly clear that it's not going to happen, and that it's not a trivial task do accomplish, so I am begrudgingly abandoning hopes of that happening.

   I've been thinking again lately of the tensegrity design I had posted on the forums a few years ago (http://cerebralmeltdown.com/forum/index.php?topic=357.msg1504#msg1502) and am thinking about building a small test version.  What originally put me off ever pursing it years ago was the problem with the "bail" not working as the original designer had intended.  What I plan to do now is mount small steppers directly on the tensegrity structure where the bail would have gone.  Most likely 28byj-48 motors since they are readily available and inexpensive.  Since they run with very little power, I plan on chaining a handful of them together for azimuth control and running several mylar mirrors simultaneously, while another stepper controls all or their altitudes,.

  The problem with this idea, I imagine, then would be the holding power of the 28byj-48's.  A large mylar mirror with a small gust of wind would throw alignment of these small motors out.  My solution is to use another fairly common piece of equipment - guitar tuning pegs or gearheads.  They're cheap, small, readily available, are self locking and have great holding power. The gearing ratio on them would also bump up the accuracy of the heliostat considerably - I believe the most common gear reduction is 12:1.  The are remarkably accurate when under tension, but there is some slop when changing direction (at solar noon say, or while pulling off the limit switches)but I assume one could account for those few extra steps in the coding.  Graphtech, a company out of Vancouver supplies tuning pegs with even higher gear ratios - I've contacted them - gave then a brief overview of this site -  and they've graciously sent me a few 39:1 tuning pegs to experiment with.  They seem to be of better quality than the standard pegs I've purchased off ebay, though I assume they'd be quite expensive to buy. 

While I haven't had time to play with this idea yet, I hope to "fairly" soon.  That being said, I'm expecting my first child in...a few days ago, so I'm guessing my free time will be in short supply in the near future.  Just thought I'd throw the idea out there and see where all of you will take it, since it could be applied to any stepper heliostat design, not just 28byj-48s.  Hopefully someone on the forums here will give it a go and post about it!

Cheers,

Paul


Paul L

  • Jr. Member
  • **
  • Posts: 99
    • View Profile
Re: Worm thoughts
« Reply #1 on: April 23, 2017, 07:58:57 AM »
Just a quick update on this idea:  It works really well as far as moving power is concerned.  I hooked up a 5v 28byj-48 to a common tuning peg, and attached it all to a lazy susan bearing which would act as the azimuth.  I stacked a three foot tall pile of textbooks on it, and it had no problem moving the whole thing, which was really amazing to me seeing how the running voltage was 5v, and roughly 200mA if I remember correctly (I did this a few months after the original post, so it's been awhile).  I'm guessing the books weighed thirty lbs.  It's slow but it works, and the resolution was pretty darn good!  The only drawback is the play when the motor stops - it's really sloppy.  There would have to be some kind of resistance to pull against the heliostat to tighten everything up.

I did take pictures with all the pieces I used, but I can't seem to find them now....I'll post them if I come across them.

This would most likely be the cheapest way to build a heliostat  - I think the motors, couplings, and tuning pegs came to less than ten dollars - per heliostat!  And it's not just a toy, it can move practical amounts of weight, including, I would guess, full sized mylar mirrors (4'x8').