The Magnetic Pull of Experimentation

Deanne writes:
The magnet experiment is one of my favorites. Here are the basics of our exploration:

Rare earth magnets - commonly referred to as “NIB” magnets (neodymium-iron-boron):
NIB magnets are extremely powerful for their size. Everyone that came anywhere near the magnets had to keep fingers, cell phones and computers at a safe distance. The downside of NIB magnets is that they are very brittle and can shatter if dropped.

The scientific principle of Lenz’s law:
When a magnet is moved towards a coil of wire, it induces a current. The direction of current that is induced is such that it opposes the change in magnetic field that created it.

Translation to modern roller-coaster brakes: When you move a conductive, non-ferrous material, such as aluminum, by a really strong magnet, eddy currents set up and a force is produced that opposes the direction of movement.

The Halbach Configuration:
Klaus Halbach discovered a configuration of magnets that creates a concentrated magnetic field on one side by arranging the poles. Originally, he designed the configuration for particle accelerators.

Our tests:
Behind the scenes, we explored the possibility of using electromagnets and NIB magnets, but the elegance and simplicity of a passive rare earth magnet braking system (that requires no back-up generator) won us over.

The electro-magnet exploration involved magneto-man style electromagnet boots and gloves. It was so hilarious that the entire camera crew was brought to tears.

After a successful ramp test, it was time to get serious about the math and figure out a force versus velocity profile for the magnetic configuration we built.

Magnet braking systems have many fine-tuning adjustments that can be made. You can modify any of the following variables to alter your applied braking force:

Size of magnets (i.e., 1-inch cube, 2-inch cube)
Arrangement of magnets (standard stack, Halbach array, double Halbach array)
Air gap distance between magnets
Thickness of the aluminum fin

But, the braking force applied by the magnets is not a constant! The braking force due to Lenz’s law varies depending on the applied force, so I had to test multiple data points to get a trend curve.

Force is mass times acceleration, so I had to either change the mass or change the angle of the ramp. Changing the mass is much easier, so that’s what we did. 

We did two series of ramp tests – the first was with a single Halbach array of 1.5-inch magnets.

It was a very basic physics model:
We had an inclined plane at 30 degrees  (sin30g = .5g)
And a sled with “x” sandbags (mass in slugs = x lbs/32.2)

I plotted a graph of each sled’s velocity versus the applied force.
Fapplied = .5mg
v = distance/time

Using these points, I found a trend curve and then extrapolated what the final speed would be for a final applied force of 250 pounds (going straight down).

(My model took into account rolling friction as well.)

At low velocity, magnetic drag is linearly proportional to velocity. All of our tests were at low velocity, and my plot was linear, so I knew my data was looking good.

But our single Halbach configuration resulted in a final speed that was a bit too dangerous and/or fun (depending on how you look at it).

After referencing predetermined trend curves for changing magnet size, configuration and air gap, I decided to revise the system to use a 2-inch double Halbach configuration.

Then we repeated the test (which you don’t see) and calculated our approximate final test velocity – which was 3.1 feet per second.

But everything is in theory; we had to take it to the final test.

We dropped Chuck (275-pound load with the sled) at a descent rate of 3.4 feet per second. It was a nice controlled descent.

The test was a successful, calculable, proof of concept. The magnet design could be tweaked in a number of different ways to create whatever size escape pod that you want. We brainstormed many ideas of how to make larger-capacity pods with a variable design that adjusts fin engagement based on the applied load. These are just two of the many ideas we had to implement this on a manufactured system.

If I had to do it again, I would choose a faster descent rate. (Chuck was a little too controlled going down the tower.) And I would experiment with alternate pod designs for larger capacity loads.

Question:
What’s your take? How would you have used magnets to escape from a high-rise?

Comments

[Fairmount]

OK, this was probably the best episode so far. Not because you invented a practical solution for getting people out of burning buildings, but because the magnetic thing with skateboard wheels was cool and did what you wanted it to do. Reminded me of myth busters.
You know, if you changed the whole premis of the show, I think you may be able to avoid a lot of the critisism that you've been getting. Instead of the show being about scientists who use cutting edge technology to try and make the world a safer place, make it all about scientists who use cutting edge technology to invent really cool stuff! The magnetic thing that you created could have just been about creating a fun and cool way to get from your bedroom to your kitchen! It would have been a total success and people wouldn't be gettin all upset about this being a totally impractical way to get people out of a burning building, which it is.
It's clear that none of the stuff you've done in previus episodes will never be implimented in the real world. That is why most people feel like this show is a waist of money and time and get all angry and stuff.
It's not too late to make a change. In fact, your viewers will be greatful and respect you for it. It would show that you care about what your viewers think!

[Tim R.]

Deanne,

I thought it was a great demonstration, and a succesful feasibility study. My concern is in the robustness and durability of the strategy, so here goes:

Is there any way of substitututing a more durable and fire resistant material, like a graphite composite, for the Aluminum?

Next - Is there some way of making the rail structure flexible? A conducting cable or -set- of cables kept in a housing that can be uncoiled and thrown down from the roof of a building?

The plan forming in my mind is a strategy involving large cable drums kept on the roof of the building, that are fed through sturdy, spaced brackets much like those that hold life boats on a large ocean liner. These cables can be uncoiled and inspected for sturdiness and electrical properties on a routine schedule.

The platform could be a simple fabric seat arangement, and with a bracket that could be secured about the cable. These brackets would contain the Halbach arrays as well as cable guides and tensioners to feed the cables through the approximate center of the array. It could also include an augmenting mechanical hand brake (For when you reach the bottom).

There are some real advantages here that people may not have thought of-

1) In a multi-story building you can have more than one platform on the array at a time, meaning on a high-rise you could have access points every five floors.

2) The platforms can be stored off site, and it would be quite easy to drop these on the roof with a Fire Department Helecopter, or even feed them in a window. It would be far less time consuming and difficult than moving people around - If you drop one it's no great disaster

[Jonny]

OK, I fell asleep and missed half the show yet again.
What I did see was an escape mechanism for only a few, important people. Aside from the design, the application is impractical. You have potentially 100's if not 1000's of people in high rise buildings. The real world chance of someone waiting for the "life boat" to reach capacity before launch is near zero. Maybe I missed the part where the "pod" goes back up.
As far as someone posting here about having the fire department deploy these with their helicopter.... LOL. Really, do you have any idea how many fire departments actually have a helicopter? How do you get people to effectively deploy these in an emergency with an erratic state of mind? They will be focused on the helicopter, and probably killed by the dropping pod.

Just some things to think about.

[Tim R.]

1) In a multi-story building you can have more than one platform on the array at a time, meaning on a high-rise you could have access points every five floors.

Please note that "array" should have been "Cable"

Come to think of it, as long as the cable is well protected Aluminum might do - Maybe the stuff high tension electrical wires are made of - Should be strong enough.

[shayne]

This was a fascinating show. The Halbach arrangement of the magnets was genius! this configuration should be used in some of the free energy or permanent magnet motors that are being designed. I would have used a simple wrist strap connected to the magnetic device and a single rail as the delivery or descent vehicle then just hook it on and step off.Then adjust the descent rate so you could go as fast as you needed to go without splatting at the bottom.

[Tim]

Finally a decent episode.

[Wrenchy]

What a waste of time and money. What a waste of aluminum.
Yet another episode of overgrown children with expensive toys and absolutely NO IDEA of what they are doing.

Tim R. You should apply for a job with the team. One more useless and inane idea couldn't possibly do any more damage to the show....

[todd]

Wrenchy...the experiment worked you complete moron.
Enough said.

[Wrenchy]

Timmy,
I certainly hope you'll be first on board the mickey mouse rollercoaster ride when the fire breaks out.
As for myself and the rest of civilization with their cerebrums intact, we'll be in the stairwells.

Until then I anxiously await their next pointless & retarded "experiment". Hmmm, maybe parachutes or bat-man costumes....or just rollerskate down the side of the skyscraper?

Quit being such a poor sport, you can ti-vo it and be the only person on earth to have the 6 or 8 episodes of Smushed Lob ever made! Yay!

[Steven Cage]

Was impressed by this episode, but it got me to thinking. Dividing into two teams with two separate proofs of concept, but they both had the right idea, you just needed to combine the two.
on the final proof of concept they'd need to take the track and start by drilling small holes at the top, growing progressively larger to increase the speed of decent, then reverse at the bottom so it'll sloww then gradually back down.
They'd have to computer model it to make it work right, but you should get a much faster overall descent without any increased discomfort or danger.
Just a thought.

[PleaseStop]

The best way to safely get people out of burning buildings is keeping things up to code and having a good floor plan for each floor. You guys were better off making a poop shoot for people.

[Michael]

Did any thought whatsoever go into getting the thing back up to the top of the building? Or is this just a VERY expensive disposable one-time use escape pod?

Sure it worked, and proved that you can get people safely to the ground using magnetism. But why would you?

[Dave Samuels]

The use of the Halbach array in this manner was very intriguing to me. Another very practical use for this might be to replace your rocket idea to stop a trailer. I would think that large trucks could use a mechanism like this to slow their descent down steep grades. (Does this work using an aluminum disc?) Then, the Halbach configuration could be used like a winchester drive head - as the speed gets higher, the unit could be engaged by gradually moving the array more over the disc. Partial for less braking, all the way for maximum braking, and every place in between. Another option is to control the gap, closer for maximum braking and wider for less braking.

Lastly, you mentioned that you purchased these 50lb rare earth magnets for about $50 each. Where can I get some for that price? I have a practical use for an adjustable counterbalance for our observatory when guest astro-imagers add camera gear of varying weights. Using a collection of magnets my be an easy way to add/remove weight.

Thanks
Dave

[Norm Kelly]

Loved this episode. Wasn't too interested in the whole fire escape thing though. The concept intrigued me. Have been doing a lot of research about NIB magnets. Was also wondering where they can be purchased for about $50.
Second question: if the array slowed the sled on the way down, would the exact same array, without modification, make it easier to lift the sled back up the aluminum? Does the array/aluminum combination make the sled lighter & slide back up the building easier?
My interest is in other uses for this technology, not for fire escapes. I'm thinking that shows like this one are to get creative juices flowing in areas other than the specific idea presented on the show. If this technique can be applied to other challenges, such as the roller coaster braking system, maybe some good comes out of this experiment.
If the slide back up is made easier because of the array, I already have an idea that may work for a challenge I've recently experienced. If the up-trip is not easier, my idea falls apart. I just don't know where to find information about this or interpret what I've already found to know if the up-trip is positively affected.
Any additional info is appreciated.
Thanks for shows such as this.
Norm

[Kelly]

Deanne-

Two quetsions:
1) your degree is honorary, isn't it?
and,
2) Who wrote your blog entry for you? You don't come across as capable of uttering anything without prefacing it with"Way";i.e "Way bigger', "Way hotter".

[shawn]

i would like to know what size and strength the magnet's were that you used on the show, and where you bought them or who you bought them from. And the price of them.

[Dave]

I liked it. Dont see why everyone is getting so heated

[Rick]

The magnet array will become very hot if lots of weight is decellerated over long distances. A means of keeping the magnets cool, below the Curie temperature, would be part of the design. If the magnets get near the Curie temperature, then the magnet quickly looses field strength. Maybe a phase change material, like wax, could be added around and through passages in the magnets. The temperature of the magnets should be monitored versus time, just as you monitored the velocity vs time.

[Chris]

Ever notice they never answer posts here for people to see? This utter disrespect for their audience is another reason people are mad. Instead of listening to people and taking hints, they make an initial post and let us waste our time asking questions they never answer.

[Thomas George]

HI Deanne,
Just watched the the Magetic high rise escape system. It was just fantastic. It really had me biting my fingers.
A suggestion I would have is to use a steel/(other) rope instead of a alumnium flat, assuming a situation like 911, where it would have got distorted.
the comments about the impracticality of this system is nonsense, taking into consideration the deperate state of mind of a man waiting to escape the seemingly inevitable disaster. KIndly can I have more details about the magnets power and loading calculations.
Keep creating wonders like this.
Regards,
Thomas