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## Electrical engineering

### Course: Electrical engineering>Unit 9

Lesson 2: Hair dryer

# Compare the hair dryer motor to the one you can build

In this video we compare our hair dryer motor to the motor we built. Created by Karl Wendt.

## Want to join the conversation?

• I still don't really understand, why does the ring of wires spin? Is it repelled by the magnets?
• Actually, it is repelled by one magnet and attracted to the other since they're at opposite polarity. When there is electricity in the coil, it forms an electromagnet that aligns with the two permanent magnets that are already aligned with each other. When it gets to that position (the circle of the coil of wire will be in the same plane as the circles of the permanent magnets), the inertia keeps it rotating.

Now the critical piece happens: the electricity turns off, which allows the rotation due to inertia to continue through the point where the electromagnet would have been in opposite polarity if the electricity had not been turned off.

If the electricity had not been turned off, the coil would have settled quickly to the position where the magnetic field is aligned. And this will happen if you let it run long enough since the insulation will eventually wear off all the way around.

They way the electricity gets turned off is that the clear insulation on the leads that go through the washer is only removed on one side, so that if you magnified the wire and looked at it on end so that it looks like a circle, only the top side would be scraped, and the bottom side would still have the clear insulation on it. So electricity only flows every other time the coil faces up, which it does twice per revolution- imagine that one of the pieces of tape holding the coil together is white- when white is on top of the video, electricity is on, and when it's on the bottom, electricity is off.

Maybe think of it like a tether ball- you can throw it only once every time it comes around, until it wraps around the pole and stops and then this example doesn't make sense anymore.

This switching process is called 'commutation', and there's a way to make it so that it works better. Instead of turning it on and off, you make it so that it's always on, but positive and negative are switched so that the magnetic field is no long just on or off, but on and then flipped so that it's always being pulled to the opposite side.
• How can you tell the difference between north and south poles?
• Actually the magnetic SOUTH pole is at the "top" of the world, which is why the north of your compass points towards. Opposites attract.
• could this motor(2 of them) power a small cart that weighs 1.5 pounds at the greatest with no load? and would it go faster than it would now? right now, there is a small solar panel that powers 4 wooden wheels and the actual motor. The motor and the solar panel probably weigh 2/3 of the car.
• Almost any battery-powered motor of this type could outperform your solar panel-powered motor by an order of magnitude. This is the case for 1 to 16 batteries. Depending on how you apply the batteries, your car could move fast, slow, or backwards. We'll also remember that very many batteries, may be too much weight and cause the wheels of your car to have more friction than the motor can resist. We'll remember that using zero batteries means your device is not using battery power.
• how do brushless motors work?
• im guessing it has to have no electromagnet to start it spinning
• if you put something around the motor (exept for the propeller) to protect it from water and connected it to a mini boat would it propel it in the water?
• Yes it would. This is in fact the most difficult facet in the design. Too firm a seal will be difficult for the motor to turn due to the increased friction on the shaft of the propeller. The trick is to place the motor above the water line so the seal isn't so critical (water won't tend to flow into it). The shaft of the propeller is not inline with the motor shaft and is placed below the water line. The shaft of the motor is then connected to the shaft of the propeller with gears which can be submerged. This is similar to an outboard motor setup. Outboard motors also don't like to be submerged. The outboard is above the water and mechanical links turn the propeller below the water.
• Is there a way to make it waterproof?
• Maybe you could use batteries, then make none of the water interfere with the circuits!
(1 vote)
• please make a separate video on working principle of DC/AC motors and generators.
(1 vote)
• Hello Zubair,

Agreed, but it will take time.

For what it's worth, a discussion of AC motors requires knowledge of RL plus RC circuits along with a solid foundation in transformers and phasors.

Ref: https://en.wikipedia.org/wiki/Phasor

Regards,

APD