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What's wrong with this picture?

by frazelle09
Tags: heater, parabolic, solar hot water
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frazelle09
#1
Jun12-14, 03:34 PM
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P: 12
We are working on an electronic solar hot water heater.

We had it working but decided to change the way the aluminum tube was connected to the frame by running a 7" bolt through both the alum tube as well as the support (see photo 02, bolt at top). We thought that it was going to act as a pivot but, now, when we try to run the heater the 3 ft. threaded rod wants to bend/deform. We've already gone through two plastic/rubber spiders linking the threaded rod to the 1 amp motor.

Since we are not mech. engineers we don't have a clue as to what is causing this thing to get bent out of shape.

Any help would be greatly appreciated. If you need more details, pics, etc. please just ask.

Here is a link to our area in Appropedia for more photos, description, etc.

Have a great afternoon! :)
Attached Thumbnails
motor_assembly_01.jpg   motor_assembly_02.jpg  
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Travis_King
#2
Jun12-14, 04:01 PM
P: 826
The rod/alum tube is free to slide in the bracket you've made with the plastic rollers? Doesn't look like it. I'd check how tight that bracket is against the main rod. If you look at picture 2, I would venture to guess that as the bottom of the pivoting rod moves left, the sliding bracket on the positioner is clamping the rod and being displaced downward (following the arc of the rod about it's pivot).

A three foot span requires very little force at the center to deflect it.

I would also check horizontal alignment. Everything should be moving about the same vertical plane.
frazelle09
#3
Jun12-14, 08:49 PM
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P: 12
Ok, Travis_King. We really appreciate your input and will see if it's binding. At least it's pretty simple setup and should be fairly easy to fix. Maybe some more space between the plates/bracket that surround the rod would be in order...

Thanks again and your input makes us very happy. This is a great forum!

Have a super evening! :)

Travis_King
#4
Jun13-14, 10:34 AM
P: 826
What's wrong with this picture?

Ideally the rod should be touching only the rolling surfaces. It should not come into contact with the plates.
frazelle09
#5
Jun13-14, 10:57 AM
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P: 12
Thanks, Travis_King. Wow, i hadn't expected another response - lol.

Yes, last night before i went to sleep i was "imagining" that i would need to check to see if there is some sort of spacer on either side of the rollers. i was also thinking that perhaps the rollers that we had purchased were not really up to the task. We had to change the rollers in the other "bearing" - we call it a jalero (instead of balero) because our son "invented" - his first name is Jalál. It is the one that the collector hangs from, but this one used to contain the same type of rollers, but the angle of the collector would reflect the sun in such a way that it melted part of the plastic rollers. So i got some 1/8" (i think they are) regular, metal bearings. A little more expensive, but i'd rather pay a little more and not have the stuff melting.

Nuts, boy did i get carried away. Anyway, thanks again on your further thoughts. We'll keep you updated on how things are going.

And, have a great morning! :)
frazelle09
#6
Jun14-14, 12:19 PM
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P: 12
O.k., i went upstairs this morning and disassembled the rod and slider (i guess that's as good a name for it as anything). i also removed the poor threaded rod. i'll have to buy another one since it's permanently bent. You were correct Travis_King -- the inside of the aluminum slider plates presented scratch marks where the rod scraped against them.

After disassembling the slider i started checking eBay for the bearings that we used in the Jalelero - the homemade bearing that carries the load of the collector. Those bearings are only 1/2" wide but my alum rod is 3/4". We used shower rollers in the old slider - a total of 8, 2 per bolt in order to obtain the "proper" width.

to be continued.

But now, it looks as though we will need to rebuild/reconfigure the slider so it doesn't bind. As i mentioned i was checking out eBay and noticed that there are also LM8UU 8mm Linear Ball Bearings for sale. If they are long enough to separate the plates, do you think they would be a good choice to replace the shower rollers?

Have a super morning! :)
frazelle09
#7
Jun14-14, 02:02 PM
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P: 12
Perhaps instead of "building" something, we could just use this SCS20UU 20mm Liner Motion Ball Units Series Pillow Block Slide With Bearing and run a round rod through it instead of the square one we are currently using...

Any thoughts?

Have a great afternoon! :)
Attached Thumbnails
scs20uu linear motion ball pillow block slide w bearing.jpeg  
Travis_King
#8
Jun16-14, 12:37 PM
P: 826
That would probably work. But you may be able to make your design work as well.

Your two main issues are this:
1. As you know, you've got to stop the bar from binding. You could add some slide-plate material in the slider to facilitate this. But more likely you'll need to redesign the slider in such a way that the rollers rotate freely and easily (from the looks of the first picture, the rollers seem to be rubbing on the plates as well). You also need to ensure that all faces of that rod are touching rolling surfaces. Or buy one of those things and a new round connection rod, that would work and might be easier and cheaper in the long run.

2. All of the loads are being transferred through that threaded rod. In similar mechanisms, the slider is typically mounted on one or two high strength rods/beams (above and below the threaded rod) so that the only forces the threaded rod sees are axial. Basically this idea (in principle) ]
frazelle09
#9
Jun16-14, 01:14 PM
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P: 12
Wow, Travis_King - we really appreciate your comments. Nothing like reading your comments to confirm that for this type of project it's better to have some knowledge of engineering than not - lol.

We'll take your wonderful ideas under advisement (like they say) and see what more trial and error reveal.

Actually your photo was what i was looking at yesterday in place of the rod and slide-plate assy. (w/o the threaded rod of course).

Well, here we go - cross the border and off to Lowe's in El Centro.

Thanks again and we'll keep you informed and - have a great day! :)
elegysix
#10
Jul8-14, 10:16 PM
P: 314
Quote Quote by frazelle09 View Post
We had it working but decided to change the way the aluminum tube was connected to the frame by running a 7" bolt through both the alum tube as well as the support (see photo 02, bolt at top). We thought that it was going to act as a pivot
How was it originally mounted?
Was it fixed to pivot there before?
How is the threaded rod attached to the guide? Are threads on the guide fixed or allowed to rotate to compensate for the angle of the tube?

It looks to me like the guide stays aligned with the tube as the angle between the tube and the threaded rod changes, so if your threads on the guide are welded square (fixed and won't compensate for the angle of the tube) they will pinch/bend/torque the threaded rod. On your picture here (http://www.appropedia.org/File:Aluminum_guide.jpg) the guide is nice and square with the threaded rod, yet on the one you posted on the thread, there's a nasty angle between them.

By the way I'm no engineer, just a bored physics guy. So King probably knows better than me. cheers


EDIT: sorry I didn't realize this was old. Didn't mean to necro
frazelle09
#11
Jul8-14, 11:46 PM
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P: 12
elegysix... Thanks for posting and offering suggestions (and questions - lol).

At this point we're trying to do away with the rectangular contraption with the little plastic wheels and are trying something else. We're just going with the long alum. tube. The threaded rod has a 2" steel piece threaded on it which has a 1/4" threaded hole in it. We're trying to make a 1/4" x 6" channel in the alum rod through which we will run a long 1/4" bolt which will loosely bolt it to the steel piece. i need to find some place around here that can finish the channel that i've started with a bunch of 1/4" holes using my inexpensive drill press.

As some sort of clarification, the rectangular piece in the photo has a bolt in the middle of the right hand side. It's the same bolt we'll be using but instead of using the rectangular contraption, we'll just run it through the alum rod - hopefully - lol.

i think you are very correct - we've got to really make sure that the items that should be perpendicular are square, etc.

As soon as i get the new rod finished, i'll upload a photo of it.

Again, thanks for chipping in. Any help is really appreciated, especially from bored physics guys...

Have a great evening! :)
elegysix
#12
Jul9-14, 01:12 AM
P: 314
Quote Quote by frazelle09 View Post
We're just going with the long alum. tube. The threaded rod has a 2" steel piece threaded on it which has a 1/4" threaded hole in it. We're trying to make a 1/4" x 6" channel in the alum rod through which we will run a long 1/4" bolt which will loosely bolt it to the steel piece.
I think that will work. That'll take care of the angle problem and the variable distance.
Let's just hope the tube can handle it.
frazelle09
#13
Jul9-14, 12:14 PM
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P: 12
Well, it's Wednesday - i went up the street about 6 blocks to the local iron-worker (he also bent our parabolic ribs) and he had a machine with what looked like a one foot, thin abrasive wheel on it and made short shrift of the holes i had made, creating the channel on both sides. Cost: $2.00 and an explanation of the heater. Foto below.

i still need to file down a couple of places, but it was worth it. Now on to connecting the lower part/extension where it will connect to the parabola and setting it into the box, running the sun seeker wires up the rod and reconnecting everything.

Have a super morning! :)
Attached Thumbnails
square_alum_rod.jpg  


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