World's Simplest Electric Train [video] | Hacker News Reader

World's Simplest Electric Train [video]

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360 pointsTuring_Machine54 comments

I have some old Ladybird Classic books[0] that I inherited from my father, who had them when he was a kid in the 60s. I remember one of them included something like this. It may have been [1]. I can't imagine a modern childrens book encouraging kids to take apart batteries or attempt their own electroplating :-)

[0] https://en.wikipedia.org/wiki/Ladybird_Books#The_classic_Lad...

[1] http://www.ebay.ie/itm/VINTAGE-LADYBIRD-BOOK-Magnets-Bulbs-a... (several pics of inside)

Nice demo! Quick back of the envelope calculation for the current to overcome dynamic friction:

I = mu_friction * Mass * grav_acc / (Turns_per_length * Area * Br_magnet)

Say Mass=0.1kg, coil at 600 turns per metre, hand-wave mu_friction=0.2, and a rare-earth retention Br=1Tesla, gives a current of 3A. Maybe more to chug along, would deplete a 2000mAh battery in about 30 minutes. Wire looks about 20 AWG, should get quite hot.

Which would theoretically use more energy, levetating the "train", or overcoming the friction?

(I"m not suggesting this design can levitate, just curious about the trade-off.)

The train never levitates.

Levitating.

Since overcoming the friction can be achieved through approaches like coating the wire in ultra low friction material which will consume no power to operate.

Same principle, different application (an electric engine): http://www.youtube.com/watch?v=zOdboRYf1hM, http://youtu.be/CoXboA8Ax7Q (or zillions of other videos)

Almost as interesting, this video of a Stirling/Heat engine using just an empty can, sticks and heat for power source:

https://www.youtube.com/watch?v=FCjYZT6FJm4

And a very simple motor using just only a battery and wire:

http://www.youtube.com/watch?v=vCSvNyHorgo

Could a design such as this work in the real-world, for a real train?

It seems to me that this could be feasible, since the power source is on the "car" itself, and the coil (infrastructure) wouldn't be that expensive to build (apart from the materials, of course). Or is it just too inefficient?

I don't know much about electronics/electromagnetism, admittedly.

A variation where the power source is in the track exists in the real world, http://en.wikipedia.org/wiki/Linear_motor#Train_propulsion

Also never forget the implications of the Square-Cube Law http://en.m.wikipedia.org/wiki/Square-cube_law

Can you explain what you mean by this? I can't find mention of its implications to electricity.

Probably that as you scale up the size linearly, the volume, and thus weight goes up as the cube, but the surface area goes up as the square.

Since this design relies on closing the circuit by having the magnets rub the wire, as you scale up you have an area in contact with the wire (surface area) going up as X^2, but the downforce due to gravity going up as X^3.

You could add wheels and metallic contact brushes to scale it up. Keep in mind copper is really expensive, and you'd be scaling that up nontrivially too, or the current would fry the wire (I'd think the mass of the copper would go up as the cube too, at least to accelerate at the same rate--acceleration depends on the mass since F=MA, and the mass of the train went up as the cube).

Why I do not know anything about how this works. I thought myself how to code but each time I see this stuff I struggle with the feeling that I can't seem to find a reasonably DIY knowledge builder for basic science branches like this.

How do you start? Help please.

A while ago I would have told tou to buy "the art of electronics", and the student manual that accompanies it, and some cheap electronic test equipement and power supply and a bread board and a selection of useful components, and to then spend an hour or so each week ploughing through the book.

Today there are probably better ways.

Depending on the depth you're interested in, Khan Academy has some pretty good videos on the topic:

https://www.khanacademy.org/science/physics/electricity-and-...

There are some great Arduino tutorials on basic microcontroller usage. They give you an idea on the basics of electronics.

We were taught this stuff in school, although I didn't think of that application then :-) I mean that current running through a coil induces a magnetic field.

Maybe just start with a physics school book?

Edit: in fact current running through a wire induces a magnetic field (actually, just electrons moving, with or without a wire), I guess the coil just gives it direction and kind of amplifies it (it's been a while).

*taught :\

Buy this. - Getting Started in Electronics - by Forrest M. Mims, III. - http://www.w5yi.org/catalog_details.php?pid=34&sort=21

It is thoroughly excellent and the electrons all have little faces.

Anyone have a neat explanation for how it works?

Magnets are serving two purposes; First one as contact point for the coil and completing the solenoid, and the second one to push the battery. Metal coil is generating magnetic field.

http://en.wikipedia.org/wiki/Solenoid

http://en.wikipedia.org/wiki/Ampère%27s_circuital_law

I'm not sure but it looks like the same effect of a homopolar motor: http://en.wikipedia.org/wiki/Homopolar_motor

When the train is placed completely within the copper coil, the circuit is closed. A current flows from the +ve end of the battery, round the local part of the coil, back into the -ve end of the battery (the magnets are conducting).

This circulating current generates a magnetic field. Proper orientation of the head and tail magnets leads to both magnets being pushed in the same direction because of their interaction with the generated magnetic field.

This is the force that drives the train.

We may properly guess that the handedness of the helical copper coil determines the direction the train takes? (left hand rule and whatnot) Connect two loops of opposite handedness and perhaps the train will alternate direction? nahh, probably just get stuck at the transition point.

Is this also the first real perpetual motion machine? That thing looks like it could go on forever. Or is it limited by the current in the battery? If it is, could the motion provide back the energy to the battery somehow, and would it be a net positive?

The motion depletes the battery, no different than a toy car motor. Yes, you could theoretically provide energy back to the battery. No, it would not be a net positive. It would deplete the battery faster, for a net loss because of unavoidable conversion inefficiencies.

Edit: if you saw this video, realized there was a battery involved, and your first thought was "Perpetual Motion Device!", you might be delusional or severely misinformed. For your own sake, please research the topic a bit more and avoid echo chambers.

This comment would be better without the second paragraph, which is needlessly personal and meta.

The first paragraph is splendid.

I agree the second paragraph is personal and meta, and I don't like it either.

But if I ever go down a rabbit hole and end up detached from reality, I would love to have someone to tip me off. It's like pointing out someone's fly is open.

Maybe OP is perfectly sane and just got confused on the physics of this system. Maybe they are very young. Or I misread their comment. In that case, OP has my deepest apologies.

It's just that perpetual motion is a well known trap for intelligent people; and expressions like "first real perpetual motion machine" and "provide back the energy to the battery somehow" make me worry that a fellow human being is going down the wrong path.

Thanks for clarifying the helpful intention behind the comment. That does make sense. Probably all it needed to do was make the intention a bit more explicit, so it wouldn't be mistaken for one-upmanship.

By the way, your reply was so neutral and respectful that I didn't realize you were the original commenter. That's remarkable, so thank you.

Quite an unnecessary, mean-spirited, and mistaken edit.

OP, your confusion is perfectly normal. I came here to post that my dad would think this is a perpetual motion machine. He simply is not familiar with the physical laws that make such a thing impossible and likes the idea of it.

Please stop downvoting higherpurpose for being curious and asking a question like this. We all lack knowledge in different areas, that shouldn't prevent us from positively participating because we fear repercussions.

I would rather see that people are prevented from participating when they have nothing very insightful to say. This policy prevented me from posting some stupid comments and I think this made HN better. You should stop and think before submitting your comment. Otherwise HN will change into another slashdot where stupid uninformed comments are rampant. If there are no repercussions to people who don't think before posting, there will be more people, who don't think before posting ;).

Sure, I can induce that if it is a battery, it is being used as a power source. Others may induce that it is simply a thing with north and south magnetic poles. While I understand I am contributing to the phenomenon, HN threads often derail and become critiques about what HN should and should not be.

A question was asked. That implies a lack of knowledge. Given that lack of knowledge, how is one to know if the question is regarded by people who do have that knowledge as "stupid"?

I wouldn't downvote it, but "Is this also the first real perpetual motion machine?" indicates that the one asking the question is familiar with the terminology, and even knows that all known perpetual motion machines aren't real. If so, in this forum, I think we can assume that (s)he also can google that term and make some deductions from what (s)he finds. It is not as if (s)he does not have Internet access.

"I googled, and found differing opinions on whether perpetual motion is possible. Is this an example that shows that it is?" would be a better question. It still would surprise me that there are people on HN who would pose such a question about such a simple device, but it would show some intelligence and a will to make an effort to learn. The OP still may have both, but the way the question is posed doesn't show it.

You're right, stopping and thinking before posting is important. (You can also think after posting, and edit!) We want reflective comments and votes as opposed to reflexive ones. But we also want HN to be a place where people are welcome to ask simple questions.

There are many reasons for this. Not everybody knows the same things. It can be surprisingly valuable to go over the basics even when you already know them. And then there's the "stupid question" that so often is far from stupid—often everyone else in the room is wondering the same thing. It usually isn't obvious in advance whether a question is deep or shallow.

Asking simple foundational questions out of interest isn't a problem around here. The finest conversations always welcome them. It's the intellectually petty discussions, where people try to one-up each other with displays of knowledge, that can't handle them.

Anyone else notice the Berta Lovejoy comment? :D

I wonder who made the stupid decision to remove the downvote feature in the YouTube comments. I heard that they couldn't implement it because Google+ only has upvotes, but why they don't simply allocate another column in their database is beyond me.

If I had a dollar for every time a manager said "Just put another column in the database"...

But seriously, I doubt it was a technical reason. Probably wanted to drive more positive behavior.

http://www.reddit.com/r/OutOfTheLoop/comments/2g99vg/who_is_...

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