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Canopy/Hatch magnets

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fly boy320/02/2019 23:47:09
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3672 forum posts
22 photos

Hi all, decided to try magnets instead of bolts ( looks better) to hold my hatch down. It's a long cover 17x1/12 inches. Never used magnets before. How do I know what strength or pull would I need. Strong enough to ensure safety of hatch, but not so strong that I cannot remove it lol. Perhaps I need to slide it off ?. Thanks. ps due to the length I may have to use say 3 pairs, would the pull strength be added together ?

PatMc21/02/2019 00:07:37
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4387 forum posts
527 photos

I usually use some sort of tongue at the front & a pair of magnets to hold at the rear. I use pieces of soft iron (tin plate is fine) fixed to the model, this gives adequate hold power & you don't have the bother of ensuring opposite polarity that would be the case with magnet to magnet.

Toni Reynaud21/02/2019 08:44:30
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423 forum posts
58 photos

Try these people for the magnets. https://e-magnetsuk.com 8mm ones are good with tinplate (or a flat headed nail trimmed for length), 6mm ones are useable in pairs.

Other than that, what PatMcC says is good. However, I tend to use the magnets in pairs when I want a stronger hold. Take a pair of magnets with at least two layers of THIN polythene between them and epoxy into place in previously prepared rebates on the airframe and hatch.

Geoff Parkes21/02/2019 08:51:07
108 forum posts

I buy mine from Hobby king, they sell round or square various sizes as cheap as chips, never had one fail, as mentioned above use them in pairs, with a dowel or tongue locating the front, most ARTF,s have the tongue fixing as standard, I also epoxy the magnets in because if used in pairs they can take some pulling apart.

ken anderson.21/02/2019 10:06:22
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8637 forum posts
779 photos

FB3....slec sell the magnets also...……. I've also used the ones from broken B/less motors....

ken anderson...ne...1...magnet dept

Geoff S21/02/2019 12:49:58
3591 forum posts
14 photos

I've bought them via eBay and use mostly 6mmx1mm but bigger ones are available. They're all much of a muchness as regards strength ie strong!

The method I use is as Pat says a tongue at one end and magnets at the other. You can use a bit of mild steel on one side because it's tricky making sure 2 magnets are of the correct polarity to cling together but 2 magnets do work more positively. I find covering the magnets with very thin ply doesn't affect the attraction and holds them in place.

Geoff

Toni Reynaud21/02/2019 14:26:48
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423 forum posts
58 photos

I like the idea of the thin ply. Actually getting magnets to permanently stay somewhere, even using epoxy, is not always successful. A thin ply cover will work wonders. Also plus one for the use of magnets removed from old motors.

Edited By Toni Reynaud on 21/02/2019 14:27:29

Simon Chaddock21/02/2019 17:30:50
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5695 forum posts
3028 photos

Remember the attraction force is proportion to the square of the distance so two magnets actually touching require a serious pull to separate hence the advantage of a thin covering to secure the magnet and reduce the pull a bit.

The other way is to use small but deep circular magnets which give a reasonable area for the glue to hold on to.

I like the audible "click" as the two magnets surfaces actually touch then I know the hatch is secure.

.

PatMc22/02/2019 00:11:52
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4387 forum posts
527 photos

Re fixing the magnets -
I usually use medium cyano with 5 or 6 mm button magnets.

As an alternative more solid fixing - some time ago Maplins used to sell magnetic contacts as paired N & S magnets with a flexible copper wire fixed to the rear. When I used these I soldered the wire to a scrap of PCB after gluing the magnet in place. A bit dearer than normal button magnets - id-34-0915:dev-c&gclid=Cj0KCQiAtbnjBRDBARIsAO3zDl-Rbbrxw_xWBXnWzQRD3PiIG1_idcREZ8k8kKDLUlsnF3Z0pbBe62kaAi1AEALw_wcB">now available from here & here.

Another method is to fix one magnet to the rear former of the hatch & the other to the fuselage former as shown in the rough sketch below. The hatch mounted magnet is positioned to be slightly above the position of the fuselage one so that it's being permanently pulled down when in place. The advantage of this method is that the magnets are not being pulled out of their fixed positions when the hatch is being removed.magnets.jpg

 

Edited By PatMc on 22/02/2019 00:19:44

Former Member22/02/2019 01:49:59
3577 forum posts

[This posting has been removed]

Callsign Tarnish22/02/2019 13:19:15
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100 forum posts
1 photos

I use magnets quite a lot and now buy them from Amazon, plenty of choice.

RC Plane Flyer22/02/2019 13:32:34
712 forum posts
22 photos

On my last purchase of hatch magnets there was a slip of paper to advise not to let magnets touch each other when used in hatch situation and advised cover one touching suface with masking tape. Worked well so far

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