1. a plank to form the base
2. several 6 inch nails
3. wire
4. a tin can (as a source of sheet metal)
5. tape
No magnets. But it worked perfectly fine when connected to a dry cell. Adventurous science lad that I was, I decided it would work better when connected to AC. So I attached a power cord and plugged it in.
A loud vibration ensued, and then it burst into flames. My mom wasn't happy.
Three holes were punched in the house by the branches, 1-2 inches in diameter. What to do, what to do. I took a coke can, slit it and unrolled it into sheet metal. Then cut a disk bigger than the hole, and epoxied it into place. Worked like a charm, and cost nothing.
I've used coke can metal for shingles and flashing, too. They don't rust.
"Good judgement comes from experience; experience comes from bad judgement."
I commend your excellent use of bad judgement there, WalterBright (despite your mom's lack of enthusiasm)!
Mine was a bit fragile, and the first gust of wind shredded the sticks and plastic film.
But it was still fun!
As a teen I built a flame thrower. No, I'm not going to explain how to build one. My dad told me that God looks out for little boys, because otherwise they'd never survive to adulthood.
When I was 9, I found a book of his "Rocket Manual for Amateurs". The opening sentence was something like "if you're fascinated by things that burn and explode, this book is not for you." Who could resist a teaser like that? I promptly read it cover to cover. He wouldn't let me buy any of the necessary materials.
Translation… ‘read me now!’
All big generators have an exciter coil that is used to generate the magnetic field. It has the advantage of allowing voltage regulation through adjustment of the field, rather than after the fact, which would be far less efficient.
In both motors and generators, there is an efficiency hit related to the need to supply power in order to generate the field, but when you scale up the system, it actually becomes more efficient to use the electromagnet. With the rare-earth mineral shortage, it makes even more sense.
That and not having huge strong magnets is nice when doing maintenance.
A permanent magnet motor uses permanent magnets on the rotor, but an electrically excited synchronous motor has an electromagnet on the rotor. This requires a rotating electrical contact which has normally been made with slip rings and carbon brushes. These wear over time and need replacement.
Most large electric generators are externally excited synchronous generators using carbon slip rings, so it's a well understood field.
This can be made contactless using inductive coupling and a rectifier - since inductive coupling needs AC but the excitation coil needs DC - at the expense of some efficiency.
You can see the efficiency difference - Renault claim 92% efficiency but permanent magnet motor EVs have touted efficiency over 95% in the motor.
It's like how laptop power bricks used to be big and get hot, and now they aren't and don't.
They've been used to great success since we had the needed power electronics to drive the electric trains of Europe.
The lower efficiency means a lower range for the same battery, which is why the companies that have used them in the past, like Tesla, have abandoned them.
Permanent-magnet motors have the highest possible energy efficiency, followed by electrically-excited synchronous motors, than by the induction motors mentioned by you.
Both permanent-magnet motors and induction motors do not contain parts that need frequent maintenance, while this property is more difficult to achieve for electrically-excited synchronous motors.
And some heat which must be dissipated or else they will dethrone the BMW as the leading burning car. /s