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Old 28th September 2006, 07:51 PM   #31
Nordic is offline Nordic  South Africa
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Not everyday we read about a Darwin award winner before he even received his award.

Ever notice how almost regardless how strong an everyday magnet is you can still slide objects along it... I dont think the "suction is your problem, but the random forces while driving with no friction for holding the magnets in place wont work... slippage...
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Old 28th September 2006, 08:22 PM   #32
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Quote:
Originally posted by Nordic
Not everyday we read about a Darwin award winner before he even received his award.
The only thing missing is for him to say "hey y'all, hold my beer and watch this!"

I_F
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Old 28th September 2006, 08:39 PM   #33
Aengus is offline Aengus  Canada
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Well, I'm going to jump back in here for three reasons.

1. Despite the doomcrying by a couple of folk who think that this can't possibly work, apparently on a priori grounds, and who - presumably as good Aristoteleans - don't want to see it tried, I see no reason why this shouldn't be an interesting experiment; provided, of course, it follows the safe methodology kelticwizard described.

2. Early on (post #2), the link I provided points not just to rare-earth magnets, but also to a high-friction material intended to prevent lateral sliding. Using some such material would probably be a good idea - as would making sure that no dust, etc., gets under it.

3. And, despite my interest in this qua experiment, I should point out that my car has no rain gutters and the roof-rack people have no problem providing mounts that hold a rack on while I transport a sixteen-foot boat on top.
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Old 28th September 2006, 09:59 PM   #34
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May I repeat once more that magnetic ski-racks are old fashioned stuff. It works. I have used them with no problems for transporting skis, no ladders, however.
http://www.fabbrisrl.com/eng/home3portasci.htm
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Old 29th September 2006, 12:31 PM   #35
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Wilfried:

I didn't mean to skip over acknowledging you the first time. Thank you for posting those two links which illustrate the magnetic cartop rack principle is being used in commercial products every day. Am presently looking for a quick freeware program to translate the German site-this is painful to admit because I took two years of German back in college, and all I can remember from it is "Wo ist der Bahnhof"? (Where is the railroad station?)

Your input has been extremely helpful.
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Old 29th September 2006, 12:56 PM   #36
Wizard of Kelts
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Aengus:

Thank you for the post above, as well as your previous posts.

When I started this thread, I asked for both pro and con responses to this. I was hoping the con responses, if any, would be from:

A) Engineers who would do a couple of quick estimated calculations of the forces involved and give their honest opinion about whether it would work with materials an amateur can likely get.

B) People who perhaps do not do the calculations but who have worked with magnets extensively. Certainly Schaef's posts, about his lack of success of using magnets to hang a bulletin board on the wall would fall into the category of people with special experience with working with magnetic applications.

In other words, I did not mind responses advising against it, in fact I welcome them, if at least the people advising against it, like Schaef, have some special knowledge or experience dealing with magnetics on some level.

However, the most vociferous opposition and snidest comments seem to come not from the people who have actually worked with magnets, but from people who appear to have no special knowledge or experience with them particularly. I wonder if these fellows plan on giving the Darwin Award to those companies which are already successfully producing magnetic cartop carriers. Especially since the Darwin Award comments came AFTER Wilfried pointed out these products and companies.

Oh well, isn't that always the way.......
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Old 29th September 2006, 01:08 PM   #37
Wizard of Kelts
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Tool49:

Your suggestion to use decal material between the magnets and car surface to prevent scratching is well considered. After all, decals work by friction, so gluing the magnets to the decal material adds an extra demension-friction-to the magnetic force.

The decals I have handled seem to have a vinyl feel to them, which I hope is the case. Most clear flexible plastics are hard to glue, but vinyl is easy to glue. Most glues will stick to it easily. Just as a side note-if you ever have a project which requires clear plastic film for anything, don't use just clear plastic wrap-use Saran wrap. It's vinyl and so most glues stick to it. The normal clear plastic food wrap has few glues which stick to it well.
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Old 29th September 2006, 01:44 PM   #38
Schaef is offline Schaef  United States
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Okay, I'll jump back into this, with a couple of thoughts.

First, I didn't look at the commercial magnetic racks, but a set of skis are a lot lighter than a sheet of plywood (or a ladder) so there are less forces involved.

Second, I'll agree that experimenting in a safe or quasi safe (meaning only the driver is in danger) situation is not a bad idea. In fact, if you do this, I would love to hear the results.

Next, on to the scuff problem, a thought occurred to me, someone had mentioned something about using neoprene as a buffer, this may not be a bad idea. Another thought would be to use something like a router mat or its generic equivalent, namely anti-slip rug stuff. This should provide both the buffer you want and, since its anti-slip, should help with the lateral movement problems. Certainly a better idea than some simply plastic. I'll have to ask some chemical engineers I know that work for a company that makes a neoprene clone what their thoughts are on something like that.

I still have several concerns about this. I'm still not sure about the holding power of even the strong magnets on the thin metal of the roof of your car, and the whole mass and inertia of the cargo on a sudden stop worries me. The starting, not so much, as you can control that, but a sudden stop, you can't always control.

So, if you do try it, let us know the results. Oh, and I still say no, but I tend to over-engineer things.
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Old 29th September 2006, 03:28 PM   #39
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Quote:
Originally posted by Schaef
I'm still not sure about the holding power of even the strong magnets on the thin metal of the roof of your car.....
I'm leaning toward the idea of temporarily removing the interior roof liner of the car and attaching large magnets of equal or greater size as the carrier pad's magnets to the underside of the roof at the point the carrier pads contact the car. This will double the holding power of the magnet attached to to the carrier pads. Of course, then I reattach the interior liner.

I'll probably attach the magnet on the underside of the roof with Bondo, which will harden and conform to the contour of the roof's curve. Without that, two powerful magnets coming together might tend to flatten the roof at the meeting point!

Also, as this is diyAudio, how appropriate that I just hit the tag sales this weekend and come back with a bunch of people's old speakers and use the magnets from those? Just a thought.....
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