[WIP - idea stage] MagLev

[fred67]

First (for the something-th time) I want to thank @LegoMonorailFan for starting the WIP thread on Monorails.  I am hoping to finish cleaning up my new space and get back to work on it, because I had an idea I wanted to implement that I was hoping would give us smooth running monorails that can go on inclines.  Instead of going off on that tangent, though, I was searching youtube for LEGO monorails, and ran across a few MagLev videos, demonstrating magleve using LEGO.  I found two interesting ones:

The problem here is that, while the poster talks about curves, he hasn't posted one (in fact, this one was nine years ago).  The other problem - the elephant in the room, is that this is not propelled down the track by anything other than pushing it.  Cool concept, but how can we make it work in LEGO?  So I kept searching, and trying to noodle through how MagLev trains are propelled (and ran across some interesting videos on "aerotrains, but I won't digress).  I looked them up and saw the general idea is using a linear induction motor over magnets to propel the train - the same way a rail gun works, and how Busch Gardens Cheetah Hunt roller coaster gets launched (for the record, I've been on it several times, and it's absolutely awesome).

Then I ran across this, which actually is using a LEGO "car" with magnetic linear induction to move it - theirs is much more complicated than I would want; it's also far too bulky, although I think a smaller Arduino or Raspberry Pi controlled solution would work. 

So, I wondered, how could an electronics idiot like me make magnetic propulsion work?

Well, in the future I hope to dig in to using an Arduino or Raspberry Pi; I have an electronics book, which came with a bunch of little components to play around and learn, so I should probably do that, too - so many hobby ideas, so little time.

But in the meantime, I wanted to come up with something that anyone could do.

I asked, in the General LEGO Questions forum if anyone could come up with a way to do something like this:

I have magnets on order - both 3/8 inch neodymium magnets on order and magnetic tape (both "A" and "B" poles).  The idea is that the neodymium disks would be put along the track (alternating poles), as the "real" method would do, but instead of a linear induction motor, I'd fabricate a magnetic "worm" drive by arranging the magnets inside the LEGO 2x2 bricks in a corkscrew pattern; the axis of rotation would be along the track.  Each brick would have 4 magnets, alternating poles.  I measured the inside space, and believe the magnets would fit just perfectly, and would be locked in by the piece that attaches below it.  That would essentially give three stages, at any given time, assuming it worked (if the magnets are strong enough), would actually give fine control over speed and direction.

You still need a LEGO motor, and that disappoints me - mainly because of the noise, but it seems like it should function.

My example solution is kind of bulky; in another thread, @JACKATTACKS suggested using this:

Instead of the round 2x2 plates in order to achieve the 45 degree offset twist required by the middle piece.  A second one would do another 45 degree twist to get the third brick back to being aligned with the first one.  In either case, these would both require glue to make sure pieces could not spin off their alignment with the other bricks.

@MAB suggested I just use round 2x2 bricks, but I was being somewhat secretive about what I wanted to accomplish, and it wouldn't work for two reasons: first, you still wouldn't (in the interior of the brick) get a 45 degree offset middle piece; second, the round bricks have no interior space for the magnets.

HOWEVER, after also ordering the matched magnetic tape, I figure I CAN use the round bricks - and just wrap the tape, in pair, helically  around the 2x2 shaft.

Other thoughts: my preliminary idea is to have outside containment/guides; it's based off of this:

 

Two is better than one, right?  So why not have both attraction AND repulsion floating your train?  I was also thinking - again, for testing purposes, of just building up on train track; that way I'll have fairly easy curves to deal with, and the track will help keep everything aligned.

Ultimately, I think this won't work well, and I'll probably end up with magnetic tape on bottom of the cars, and on the track.  However, I'm hoping it works because I'd like to ultimately go back to monorail, and do maglev monorail:

Then the top of the track could have the drive magnets.

Anyway, wanted to throw this idea out there; I have two sets of magnets (discs and tape, and a bricklink order on the way.  I was hoping some of you electronics hobbyists could suggest ways of doing a small linear induction motor - it would be awesome, fast, and quiet.

Edited May 9, 2018 by fred67

[Trekkie99]

This could potentially be awesome!!! Because what's better than a Lego maglev or a Lego monorail? A Lego maglev monorail of course! 

[Hod Carrier]

That’s an ambitious but exciting project. 

One observation I’d make is that using your worm drive will require the train to carry both the motor, power source and controls, and that’s going to be quite a heavy mass to levitate. I wonder if you would have more success by taking the more challenging route of building a linear motor into the track with electromagnets and controlling the speed of the train through Arduino.

As a fellow electronics idiot I understand the challenge you’ve set yourself. I wonder if, as well as researching the necessary electronics components and skills, you should also give yourself a grounding in the relevant physics and maths. Experimentation will obviously form a major part of your research, but having some underpinning physics knowledge may open some short-cuts to you.

Unfortunately I don’t have any further expertise to offer. All I can do is wish you luck with this project and I look forward to seeing how it develops. 

[fred67]

Yup... @Hod Carrier I understand the concepts, if not entirely the math, and am already trying to plan around the probably failures.   One of the things I do is use the 9v (square battery) adapter instead of the giant LEGO battery box, so that saves a LOT of weight.  After experimenting with the levitation itself, I was going to make three small cars (smaller is better to handle curves); one with a 9v battery, one with the motor, and one with the drive (connected by a universal joint).  I do not think it should be that bad, although I will likely resort to having the magnetic tape on the underside of the train and top of the track, as most of the videos so far have done. 

I've also been thinking a lot about the track, as I've run across a few more interesting videos:

I've seen other videos using this concept, as well, and I wonder if metal LEGO train track - if not LEGO, then something ME models OLD metal track (which had solid metal rails, as opposed to metal plated) would work.

This guy built a heavy duty LEGO car (on a home made track); he's using a lot more powerful magnets than me, though.  To magnetize a decent length of track with magnets that strong would cost way more than I'm willing to sink into this.

The concept is sound, though, and if I can do it with much lighter weight, I think it will work.

 

Edited May 10, 2018 by fred67

[Man with a hat]

Very interesting. I was thinking of building a Maglev (monorail is so 90s) but then just a simple hidden wheel motorisation. 

But taling it to a realiseren Maglev would be awesome. Good luck and I am looking forward to your results. 

[fred67]

I had my first fail - the magnets I ordered (and I swear I measured) did not fit cleanly inside bricks.  The idea was that the small neodymium magnets would fit in, for example, a 2x2, and then be held in place with another plate or brick attached to the bottom.  So I had to use 1x1 round to space it; the magnets moved too freely inside.  Those suckers are super strong, though.

I'm afraid I will need to then sacrifice a few bricks, even for testing.  So I will need to glue magnets.  I am getting magnetic tape, which will come with adhesive on one side, but I want to test both.  Also, the plans in diagrams will not work - any shift out of equilibrium, and the mock car just stuck to the closest opposing pole.... so each side will need to be the same polarity, top and bottom.

At the same time, I'm still organizing my space, and still wanting to make the monorail work, also.

[Hod Carrier]

Sorry to hear about your setback. It's clearly a hard nut to crack otherwise maglev would be everywhere by now.

I have to be honest and say that I think you might have to take the same pseudo-levitation route taken in both of the videos you have included in your original post. Casting my mind back to playing with magnets as a child I can recall that the force of repulsion is incredibly unstable while the force of attraction is stable, directional and very strong. Reading more deeply into magnetic levitation threw up Earnshaw's Theorem which explains this phenomenon and has implications for the use of ferromagnetic materials in magnetic levitation. Basically, it is not possible to create stable magnetic levitation of a body in free space against the force of gravity using permanent magnets.

Pseudo-levitation (where the movement of the object to be levitated is constrained in one or more direction) is possible, as your linked videos show. The length of the car prevents the magnets from flipping it end over end, while the guide structures (either built onto the car as in the space monorail or into the track as in the Arduino controlled sled) stop it from being thrown over the side.

I fear that the diagrams you have referred to may be slightly misleading. I think their intention was to explain the forces involved rather than to give a DIY guide to building a maglev using household materials. My understanding of existing maglev systems such as Transrapid is that these use electromagnetic coils in both the track and the train for lift and propulsion. Lift is achieved using the force of attraction rather than repulsion and the strength of the magnetic forces are automatically adjusted in response to measurements of the air gap between the train and the track to ensure a constant, safe ride height. Clearly this is going to be difficult for the home hobbyist to replicate, though.

An alternative system that has been the subject of experiments going back more than 20 years is Inductrak. Unlike Transrapid, this does use permanent magnets arranged in Halbach Arrays on the underside of the train to provide both lift and stability. Wire coils or stacked copper or aluminium plates are built into the track and, as the train car passes over them, this induces a current in the trackthat in turn generates a repulsive magnetic force that acts against the magnets and lifts the car. The advantage of this system are that it does not require any external power source to achieve lift and that the arrangement of magnets makes it inherently stable. The downsides of Inductrak are that it does not provide for propulsion and that the train must achieve a certain speed before achieving lift-off. Again whether or not this can be replicated in LEGO form is open to question.

[fred67]

Thanks for the reply.  For levitation, while the neodymium magnets are much stronger, I think I will use the magnetic tape.  My current thoughts are something like this:

Although I think a lower center of gravity, and wider magnets - the hope is that it will stay stable both vertically and horizontally.  Unfortunately, my room is a giant mess as I try to clean up and reorganize my entire parts collection.  I'm actually working on that right now.  It got much worse than I thought it would.  I did receive my A/B magnetic tape, though, and really want to play with it.

I will not try to do anything like Inductrack - that's far beyond just wanting a maglev for my city.  Ideally I could use neodymium magnets with metal track to pull the train using the old 9V speed regulator.  It would have to be a radically different design to hold the cars up, but it would be cool on so many levels, including not needing a motor on the train.  It would cause problems trying to switch, but a loop could work.  I have to research the physics behind the linked-to video above (how to make a simple linear motor). NOPE.  Requires conductivity across the rails.  I will keep looking.

Edited May 15, 2018 by fred67