Mini-Bot Mangets

[UrizenII]

Although we are not currently using them, we are considering using neodymium magnets from an old hard drive, but I have a question about the legality of these. The magnet itself is obviously allowable, but our problem is the way the magnet is mounted to a non-explicitly permitted material; like I said, the magnet is from a hard drive, so it is incredibly securely mounted to a piece of material that acts as a magnetic insulator. I don't want to try to take the magnet off the mount because I am afraid we'll break it, so my question is this: would it be legal to leave the magnet as is and use it on the minibot, or would it not be permitted since the material it is mounted on is not on the list of allowable materials and so is technically illegal?

[EricH]

I'd suggest that if you err, you want to err on the side of caution. If you choose to go the non-caution route, develop a backup plan that can be installed in an hour or two at competition; the inspectors are likely to figure that illegal materials connected to legal materials are still illegal.

You could also try to get the magnets off... but there are some things that may just be really really unsafe/not smart/impractical. What's the mount like, other than really secure?

[UrizenII]

Originally Posted by EricH

I'd suggest that if you err, you want to err on the side of caution. If you choose to go the non-caution route, develop a backup plan that can be installed in an hour or two at competition; the inspectors are likely to figure that illegal materials connected to legal materials are still illegal.

You could also try to get the magnets off... but there are some things that may just be really really unsafe/not smart/impractical. What's the mount like, other than really secure?

That is exactly what I was thinking. Our currently functional robot is going to remain unaltered as the backup, and we are going to test a new minibot with the magnets. However, as Tristan said, trying to remove these magnets will not only be next to impossible, but it will also be incredibly dangerous and unwise.

Tristan, thank you very much for the golden response. It perfectly addressed the question and was incredibly helpful. Your point about the magnets from a "sold as" point of view is puzzling, as you are exactly correct. I know the magnets in question were some that my Dad removed from an old hard drive, and I don't think it's going to be possible to find a vendor with these exact magnets. In that case, it is a modified hard drive, which would be illegal. I'm going to post this in the Q&A per your suggestion and see what kind of results I get. Thanks again for the great input.

Edit: I just searched around on the FIRST Q&A Forum and found someone who asked essentially the same question I did. Here is the response from the game design comittee:

Per Rule <R92>, magnets are permitted. All other materials (i.e. mounting plates) must meet requirements presented in Rule <R92> to be used on the MINIBOT.

I gather from this that the mounting plates are therefore illegal because they are not explicitly listed as an allowed material in Rule <R92>. This really bites because, like Tristan said, these magnets are nearly impossible to remove from the mounting plates safely and without breaking them. Bummer. Any suggestions?

[philso]

The magnets from a hard drive can be sheared off their mounting plates relatively easily. Use a large screwdriver to apply the force to the side of the magnet and tap the handle until the magnet pops off. Sometimes, a small part of the magnet remains stuck to the backing plate. The magnet might break into several pieces if you are not lucky. With the going price of dead hard drives being pretty low, you can afford to try this a number of times. All the magnets I have removed seem to be attached with some sort of cyanoacrylate.

Heating the backing plate with a soldering iron may also work. It will not get the magnet hot enough to damage it. I have put these magnets onto red hot steel as part of a heat treating process and they still work fine.

Phil

[Tristan Lall]

Originally Posted by philso

Heating the backing plate with a soldering iron may also work. It will not get the magnet hot enough to damage it. I have put these magnets onto red hot steel as part of a heat treating process and they still work fine.

You're right about that Curie temperature; I'm not sure what I was misremembering, but I was significantly off. It's Sm-Co that has the higher Curie temperature, and Nd-Fe-B that has a lower one, but still over 300 °C. (See here.)

Also, if the glue is cyanoacrylate, a good soak in acetone might help to loosen it enough to pry off easily.

Edit: I removed the erroneous portion of the comment in my post above, lest anyone get confused by it.

[UrizenII]

I took the magnets home and my Dad and I managed to remove them without significantly damaging them (a little of the protective outer covering came off, as it got stuck to the mounting plate) by wedging a putty knife under the magnet and tapping it with a hammer to break the seal. Now it's just a matter of trying to figure out how to mount these magnets to the minibot without hurting anyone or magnitizing every tool in our work area in the process! Thanks for the help, guys!

[philso]

The ones in the hard drives I have opened up were not that big so they are not likely to do any real damage, unlike the larger ones.

They are really handy for magnetizing screwdrivers. It makes the screws stick on the end all by themselves, freeing up one of your hands.

Just make sure you don't put the magnets in the same pocket you have your wallet since they may wipe out your credit cards. You may want to put them in your wife's purse for the same reason...

[sumginazu]

My team and I were considering using magnets on our minibot, but we are concerned that they will induce a charge in the pole when the minibot moves. Has this been a problem for anyone using magnets on their minibot?

[jskene]

We're using fairly strong magnets and have not encountered this.

[philso]

We attacked a bunch of dead hard drives this afternoon. We broke 5 of them by trying to shear them off by striking them. We broke another one by trying to shear it off by applying pressure with a pair of vice-grips.

We got two off intact when I found an industrial heat gun at work. It took about two minutes of heating on high. The magnet shifting with a gentle tap means that the glue has been sufficiently weakened. The magnet can then be removed when cool (as my son found out).

Hope that helps.

[nighterfighter]

Originally Posted by philso

We got two off intact when I found an industrial heat gun at work. It took about two minutes of heating on high. The magnet shifting with a gentle tap means that the glue has been sufficiently weakened. The magnet can then be removed when cool (as my son found out).

Hope that helps.

Make sure you don't overheat the magnet.

Overheating a magnet makes it turn from a cool magic hunk of metal into a useless hunk of metal.

[Jstack14]

I am not exactly sure which type of magnets we use, but what i do know is that they are pretty strong, but probably not as strong as some teams use. When mounting them, we are incredibly close to the pole, less than 1/16 in. This has allowed us to have a relatively safe and light magnet and still have enough traction for a sub 2 second minibot. We used two total, however only one really applies traction, the other makes sure we track straight up the pole.

[philso]

Hello Matt

Perhaps soaking in solvent is the way to go even though it would be much slower.

I just read a datasheet for some neodydmium magnets last night and they indicated the magnets would start to lose magnetic strength above a surprisingly low temperature. I don't recall the exact number but it was something like 80C. I am sure the industrial heat gun gets hotter than that since we were charring the solid maple workbench with the blast. Unfortunately, I don't recall which manufacturer posted this data (it was pretty late).

We also noticed that the pulling force of the magnets that we measured seem to decrease to a fraction after removal from the backing plates. This observation applied to the ones we heated as well as the ones we sheared off. We suspect that the backing plates are some sort of high-permeability steel and they concentrate the magnetic flux. They look rather thick for the mechanical stresses involved.

Another strange phenomenon we noticed is that the magnets seem to be magnetized in zones along the arc. The pair of magnets from one hard drive would stack nicely but magnets from another (different brand/model) would only stack with an offset. In the past, I had noticed this same effect with strips of flexible magnets.

Since we could not get the pulling force we needed with the magnets from the dead hard drives we now have some on order from an online supplier.

[Nathan Streeter]

1519 is using two Neodymium magnets also...

As always, be careful with high-strength magnets! I do recommend using a smaller magnet at a closer distance (partly for weight, but primarily for safety). We didn't have any trouble mounting ours ~.125" from the pole, and the two of them have only 23 pounds of force each!

Here's the link for the ones we used:
http://www.kjmagnetics.com/proddetai...884DCS&cat=173

Some recommendations:
- Use ones with countersunk holes... they make mounting them a charm!
- Mount closer to the pole (3/16" or less), to minimize the weight of the magnet you have to lift and reduce the danger from having a higher-strength magnet.
- Not that important, but the narrower your magnets are the more of the magnet is at the minimum distance from the circular pole.
- Spread them out over the length of the minibot, if possible. This will help create a longer moment for your resistance to the minibot driving up the pole at an angle. We relied more on near-perfectly balanced weight to achieve a straight ascension.


Best of luck, the magnets really made our design possible!


And here are some links of our minibot climbing:
Climb Only: http://www.youtube.com/watch?v=3Ht0gHEOb14
Slowed Down Minibot Race at GSR: http://www.youtube.com/watch?v=Dl55U1PuDKM

Thanks to Joe Barra from Team 20 for posting (http://www.chiefdelphi.com/forums/sh...59&postcount=1) the second video.

[Tristan Lall]

That answer about the plate on the back of the magnet strikes me as a little bit odd.

If a magnet is defined as a pure chunk of magnetic substance, then to use ordinary rare earth magnets, you'd have isolate the actual magnetic material by removing the plating—because plating material is not on the allowable materials list. (That's a horrible idea for many reasons, and would be an absurd ruling.)

But if a magnet can have other stuff attached to it, what's permissible? A fridge magnet has a label, or paint—and indeed the "magnet" part is really a polymeric substrate with ferromagnetic inclusions. And as noted above, rare earth magnets are almost always plated.

So why can't hard drive magnets have a backing plate? They're still magnets, aren't they? Or are we reverting to the absurd definition I gave initially? I'm not seeing a middle ground either—the rules don't imply anything about the definition that might be used to discriminate between different varieties of magnets.

On a related note, FIRST has been quite consistent this year in defining components in terms of the way they're sold. It would follow that if these things are sold as magnets, then they would be considered magnets. So, is there a vendor that sells these (as COTS items, to the public), either after having salvaged them from hard drives, or as the supplier to the hard drive manufacturer? If you can find such a vendor, I think it's pretty clear that FIRST's ruling is not correct for all cases (again, unless we're falling back on the discredited definition).

But if you can't find a vendor selling the exact hard drive magnet you want to use, then from a material utilization perspective, you're actually using a modified hard drive (which is not in <R92>). At that point, you need to know whether or not FIRST is operating with a dualistic definition—something like "either it's sold as a magnet, or is inherently a magnet"—or if they're just picking one criterion and sticking to it. You might therefore want to ask the Q&A.

If this were to come up at inspection, I'd say giving the team the benefit of the doubt would be appropriate. I'm not sure how to interpret FIRST's intent based on that Q&A, and I don't think we can expect that of a team in this circumstance. (The team shouldn't suffer because of a rule that was not clear, and for which they executed a reasonable attempt at compliance.*)

By the way, odds are it's not going to be possible to remove that magnet from its plate without something horrible happening to the magnet. It's probably epoxied to the plate, and there aren't many solvents that can dissolve that in a reasonable time. Rare earth magnets are very brittle, so trying to shear it off will probably snap something. Same goes for machining the plate off, except maybe by grinding. And when heated past a certain temperature—like if you tried to torch the glue off, or if you let it get too hot while grinding—they'll demagnetize. Then, even if you get it off, you'll probably lose the plating, meaning the magnet will corrode. And did I mention that magnetic dust is pretty hazardous (both because it's magnetic and will stick to things, and because it's chemically toxic when ingested).

But while I'm on the topic, remember that ferrous metals can be turned into magnets. (Yes, I'm looking at you, Vex sheet metal!) Most magnets are made the same way—using a powerful electromagnet, and a sintered slug of randomly magnetized rare earth or ferrous alloy—so it's not an illegal process. And that theory works in mundane ways too: want to bet that the backing on your hard drive magnet is made from steel—a ferrous metal.

(This of course raises the question of whether FIRST meant to say "permanent magnet", or whether any magnetized substance—like in an operating electromagnet, or a slug of iron next to a permanent magnet—will do.)

*When I say "reasonable attempt at compliance", I mean that they read the rule, attempted to determine its meaning as written, came to a plausible conclusion given the rulebook (this is the key; clearly incorrect interpretations are worthless), and successfully executed a design that complies with that meaning. This is certainly not a validation of the idea that they should be passed for giving it a good effort, even if noncompliant.