Mini-Bot Mangets

[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.