Mini-Bot Mangets
 

Our team was thinking about using some magnets for our mini-bot. What strength magnets did you use, and did you have them mounted on so that they touched the pole or like 1/2" away from the pole?
Thanks

Re: Mini-Bot Mangets
 

We're using one of the 2" and one of the 0.75" versions of these magnets: http://www.magnet4less.com/index.php?cPath=1_95 . These seemed to be the least expensive ones we found. With 3:2 gearing (gearhead:wheel), they work fine. When we tried 2:1, we need more traction, so we will probably be going larger or adding additional magnets.

Keep your distance at least 0.25" from the pole, as these are very strong Neo magnets. If you're touching the pole, your minibot won't be going anywhere. Also be careful handling them, since there is a large pinch hazard. On a flat surface, the 2" one can support 200 lbs.

One other item to consider - since these have an intergral steel cup, there may be some question about their legality. They are marketed as "cup magnets", so we think they are safe, but you might want to order some without the cup (not as strong) just to be safe.

Happy hangin' !

Re: Mini-Bot Mangets
 

Our team is using neodymium magnets, which a very strong rare earth magnets. as for distance, go with jkessler's description. good luck!

Re: Mini-Bot Mangets
 

Currently, we are using one rare earth magnet from McMaster-Carr. Mcmaster might not be the cheapest, but you should be able to get it next day.

Re: Mini-Bot Mangets
 

Joe,

Most schools would not allow neodymium magnets in the hands of a student and some schools will not allow them on school property at all!

The pinch hazard you mention becomes critical if you loose your grip on the magnet as it approaches a ferrous object (such as n EMT pole). The magnet will accelerate to very high velocities in the inch or so of "free fall" and can shatter into thousands of shards at near ballistic velocities.

A warning from Edmunds Scientific on "high quality" neo magnets sold for educational use in classrooms:

Depending on the size and strength of a rare earth magnet, some may be physically impossible for a human being to hold onto if it comes close to a ferrous component. I actually had this happen to me years ago. I bought a neo magnet and brought it close to a sheet metal locker at the school. The device literally ripped out of my fingers and dented the locker. It was also a real @#$$% to remove from the locker...

Mentors should monitor the handling of these devices very, very closely and teams should expect intense scrutiny from robot inspectors if these are used on a minibot (or hostbot for that matter).

JMHO,

Mike

Re: Mini-Bot Mangets
 

As said above, I will again warn you and anyone using these magnets:

THEY ARE EXTREMELY DANGEROUS. I HAVE NEARLY LOST MULTIPLE FINGERS MANY TIMES, SINCE I WORK WITH THESE MAGNETS A LOT OUTSIDE OF ROBOTICS. THEY MUST BE HANDLED WITH EXTREME CARE AND KEPT AWAY FROM COMPUTERS, PHONES, ELECTRICAL COMPONENTS, ETC. THESE ARE NOT TOYS, I REPEAT, THESE ARE NOT TOYS!

just wanted to make sure people know how dangerous they can be, but at the same time, they are quite useful, which is why i work with them a lot. the last thing i want is to see people get hurt by these things. safety is always first. be careful, and good luck everyone!


p.s. i know people who have actually had to get fingers, toes, and even entire hands amputed because they were fooling around with neo magnets. even with a hand in between, they will pull towards each other with a MASSIVE amount of force. Actually, 2 neo magnets larger than only a few centimeters can snap together with enough force to break fingers like toothpicks.

Re: Mini-Bot Mangets
 

Instead of using one or two giant neodymium magnets, use a larger quantity of smaller magnets. It's much safer.

The ones we are using only have a max pull of about 3.5 lbs each, and can easily be pulled apart with your hands.

Re: Mini-Bot Mangets
 

We are using two magnets scavenged out of a defunct hard drive mounted about .125 from the pole. Plenty strong and plentiful.

Re: Mini-Bot Mangets
 

we used half inch magnets with a pulling force of 15 lbs each. We mounted them so they would stay a half an inch from the pole.

Re: Mini-Bot Mangets
 

We use a 52 (i think) pound pull neo magnet. It's about 1/8 in away from the pole. Were using a bracket to hold the magnet in place to make sure it doesn't travel at all, somehow ultimate velcro wasn't able to hold the magnet in place. These magnets are wicked strong though... can't with one in my pocket at the work computer without it completely distorting the screen :eek:

Re: Mini-Bot Mangets
 

Make sure you remove the plate: http://forums.usfirst.org/showthread.php?t=16822

Re: Mini-Bot Mangets
 

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?

Re: Mini-Bot Mangets
 

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?

Re: Mini-Bot Mangets
 

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.

Re: Mini-Bot Mangets
 

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: 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?

Re: Mini-Bot Mangets
 

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

Re: Mini-Bot Mangets
 

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.

Re: Mini-Bot Mangets
 

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!

Re: Mini-Bot Mangets
 

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...

Re: Mini-Bot Mangets
 

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?

Re: Mini-Bot Mangets
 

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

Re: Mini-Bot Mangets
 

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.

Re: Mini-Bot Mangets
 

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.

Re: Mini-Bot Mangets
 

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.

Re: Mini-Bot Mangets
 

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.

Re: Mini-Bot Mangets
 

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.