FarmerTy Posted June 2, 2016 Share Posted June 2, 2016 Got a question for the ARC brain trust. I'm working on making a cheap DIY frag rack with a magnetic scraper and some eggcrate. I've actually made one before and want to improve on the design. I've been playing the scenario over and over in my head and to me, it makes more sense to add the rack to a bottom of a magnetic scraper than the top. My reasoning would be that that either scenario would create a fulcrum at the bottom of the magnet but it would be more resistant to flipping down and dumping all my frags on the sand if the rack was placed at the bottom of the magnet to minimize leverage. Aim I correct in this line of thinking? It's been awhile since my last physics class. Link to comment Share on other sites More sharing options...
FarmerTy Posted June 2, 2016 Author Share Posted June 2, 2016 I'm an idiot... in the end it doesn't really matter. Just flip it and test it in real life and report back which way holds up more weight. I still think my original hypothesis will prove correct. Link to comment Share on other sites More sharing options...
BornToHula Posted June 2, 2016 Share Posted June 2, 2016 Seems like a logical plan. I never had a problem with it tipping over when the eggcrate is on top though - but I didn't have many large frags. Link to comment Share on other sites More sharing options...
Dan H Posted June 2, 2016 Share Posted June 2, 2016 I think your hypothesis is correct. The bottom position would have the shortest distance to the fulcrum point generating the smallest moment of inertia. Its been almost 20 years since my statics class so I'm probably off. Link to comment Share on other sites More sharing options...
FarmerTy Posted June 2, 2016 Author Share Posted June 2, 2016 Seems like a logical plan. I never had a problem with it tipping over when the eggcrate is on top though - but I didn't have many large frags. That was my original problem was it kept tipping over when the rack was on top. Now, I'm also working with 3/4" thick glass so it does present some problems with magnet strength and my rack was loaded. Link to comment Share on other sites More sharing options...
FarmerTy Posted June 2, 2016 Author Share Posted June 2, 2016 I think your hypothesis is correct. The bottom position would have the shortest distance to the fulcrum point generating the smallest moment of inertia. Its been almost 20 years since my statics class so I'm probably off. That makes absolute sense. Thank you for the visual bud! Link to comment Share on other sites More sharing options...
Juiceman Posted June 3, 2016 Share Posted June 3, 2016 I used old Tunze and Jabao Pump mount magnets to make mine, it's done pretty good Sent from my iPad using Tapatalk Link to comment Share on other sites More sharing options...
Sascha D. Posted June 3, 2016 Share Posted June 3, 2016 In the past I had used a medium mag to make a frag rack on 3/4" glass. I mounted the diffuser to the top of the magnet, using spacers and glue to level the mount. My original design was 12" long and had about 6-8 spaces front to back. It would tip forward and separate the magnet if I loaded it with hard corals. I addressed the problem by reducing the depth by half and increased the length to 18". The increase in length eliminated the pitching, but created a new problem where the rack would sink 1-2 cm per day when full. Link to comment Share on other sites More sharing options...
+FluxCapacitor Posted June 6, 2016 Share Posted June 6, 2016 My laymans/easy fix for all of this would be to use stronger magnets. Then it wouldn't really matter what the weight it was supporting did to a fulcrum on the low side of the magnet. If that's not possible add more of the weaker magnets and make more attachment points for the frag rack... although that could be expensive if the magnets you're using are from a magnetic scraper. http://www.harborfreight.com/10-piece-rare-earth-magnets-67488.html Those are nickel plated so I don't know how desirable that would be for a reef tank. It may be fine, I haven't researched what that metal will do in a marine environment. The magnets there are cheap and they could easily be super glued to something (minding the polarity of course ). I also found these and they sound like they're pretty strong: Link to comment Share on other sites More sharing options...
FarmerTy Posted June 6, 2016 Author Share Posted June 6, 2016 My laymans/easy fix for all of this would be to use stronger magnets. Then it wouldn't really matter what the weight it was supporting did to a fulcrum on the low side of the magnet. If that's not possible add more of the weaker magnets and make more attachment points for the frag rack... although that could be expensive if the magnets you're using are from a magnetic scraper. http://www.harborfreight.com/10-piece-rare-earth-magnets-67488.html Those are nickel plated so I don't know how desirable that would be for a reef tank. It may be fine, I haven't researched what that metal will do in a marine environment. The magnets there are cheap and they could easily be super glued to something (minding the polarity of course ). I also found these and they sound like they're pretty strong: Screen Shot 2016-06-06 at 9.57.08 AM.png Thank you for the feedback. Simplicity was the focus and not wanting to modify anything was ideal in this situation. It seems to be holding just fine currently. Link to comment Share on other sites More sharing options...
FarmerTy Posted June 6, 2016 Author Share Posted June 6, 2016 I've used neodymium magnets in the past for my stand build and they are very strong for their size. I still wouldn't trust the epoxy coated ones though in the water as the coating scratches easily, hence why I didn't want to add magnets or modify the mag flat to accomplish this. The goal was just to understand the optimal placement of the egg crate material for the most resistant application for this DIY frag rack. Link to comment Share on other sites More sharing options...
victoly Posted June 6, 2016 Share Posted June 6, 2016 The real question is, don't you have a frag tank? Link to comment Share on other sites More sharing options...
Sascha D. Posted June 6, 2016 Share Posted June 6, 2016 The goal was just to understand the optimal placement of the egg crate material for the most resistant application for this DIY frag rack. I wasn't smart enough to answer your original question, so I made up my own and answered it in this thread. I'm an idiot... in the end it doesn't really matter. Just flip it and test it in real life and report back which way holds up more weight. I still think my original hypothesis will prove correct. So...how did the test go? I believe it prevent the tipping because the force will be redirected from the magnetic connection to the joints connecting the magnet to the crate. The question is, can you make the joint strong enough for long-term use? Link to comment Share on other sites More sharing options...
FarmerTy Posted June 6, 2016 Author Share Posted June 6, 2016 The real question is, don't you have a frag tank? You mean this thing? You must be mistaking me for another Farmer. [emoji6] This magfloat frag rack was for pieces to heal a bit before transferring to the frag tank. Link to comment Share on other sites More sharing options...
FarmerTy Posted June 6, 2016 Author Share Posted June 6, 2016 The goal was just to understand the optimal placement of the egg crate material for the most resistant application for this DIY frag rack.I wasn't smart enough to answer your original question, so I made up my own and answered it in this thread. I'm an idiot... in the end it doesn't really matter. Just flip it and test it in real life and report back which way holds up more weight. I still think my original hypothesis will prove correct. So...how did the test go? I believe it prevent the tipping because the force will be redirected from the magnetic connection to the joints connecting the magnet to the crate. The question is, can you make the joint strong enough for long-term use?It works. I've made one before so I wasn't worried about the joint holding. I was just looking for optimal placement of the connection joint to minimize the leveraged force on the magnet. My initial guess was correct and I appreciate everyone who contributed to my physics question of the day. Haha. Link to comment Share on other sites More sharing options...
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