In the last Veritasium video, we explained that wireless inductive charging worked almost like an electromagnet in reverse. In your standard elementary school electromagnet, you run a current in a coil of wire wrapped around a nail to induce a magnetic field (check out the discussion of the first video if you don’t know what I’m talking about). Induction works the opposite way where a quickly moving or changing magnetic field is able to produce current. You can use this effect to essentially beam power over air gaps as demonstrated in the first video.
Now lets take this concept one step further. We’ve already established that there is a relationship between electric current and magnetism that can be manipulated to work in both directions. Can we use the principles of induction to produce a magnetic force in a non-ferrous conductor like copper or aluminum? What do you think? Here’s a hint: think about the “levitating barbecue” from the first video. Intuition will tell you that copper and aluminum are not magnetic. That’s why the simple demonstration in these new videos will surprise you:
And here’s a further explanation from a professor at Nottingham University:
So it is possible to produce a magnetic attraction in copper and aluminum. The key to the process is that the conductor has to be a circular shape and the magnet has to pass through the center of it at a decent speed. Here’s an easy way to think about it: picture the copper tube as the coil of wire around the nail in that same elementary school electromagnet that you built. In the discussion for the first Veritasium video, we talked about how the current flowing in a circle through the coil causes a magnetic field in the nail because of the right-hand rule. The current is supplied to the coil of wire by the battery. With the magnet in the pipe demonstration, we obviously don’t have a battery. So how does the copper pipe produce an electromagnetic force? The answer is that we are adding energy to the system through gravity. There are two separate processes happening:
1. The magnet falls through the pipe. We input the energy to the system by lifting the magnet up to the top of the pipe. As gravity pulls it to the bottom of the pipe, it’s picking up speed. As we’ve already discussed, the moving magnetic field produces a current in the pipe.
2. The current in the pipe flows in a circle like the coil of wire on the nail and battery electromagnet. This produces an electromagnetic field in the opposite polarity of the magnet falling through the pipe. That’s why it resists the magnet’s motion and it takes longer for the magnet to fall than the chunk of aluminum.
You could say that dropping the magnet through the copper pipe is making an electromagnet powered by induction. It’s kind of neat to see both processes demonstrated in one simple experiment. If you can wrap your mind around this then you pretty much understand why electric motors are also generators based on the magnetic phasing or rotation direction.
If you’re a typical car guy, you probably don’t find driving hybrids very interesting. I don’t blame you. But just because the driving experience is usually sterile and unengaging shouldn’t undermine the fact that some serious engineering goes into making them work. This is a breakdown of the 2nd gen Prius transmission by an instructor at Weber State University where they work with Toyota on degree programs specifically having to do with the Hybrid Synergy Drive system.
The transmission is responsible for blending 3 different power input/outputs. The engine provides power to drive the car and to recharge the batteries, but it also requires power input to get started after it’s been turned off at stops. The two permanent magnet AC motors are referred to as Motor-Generators (MG1 and MG2) because they can easily be switched between propulsion and regeneration. MG1 is the smaller of the two electric motors and it acts as a starter, alternator and mainly as a generator fed by the engine power to recharge the battery pack. It’s also responsible for driving the car in reverse since that doesn’t require as much power. MG2 is the larger electric motor that is directly connected to the car’s wheels. It helps propel the car and is also responsible for regenerative braking. The engine and the two electric motors are tied together with a planetary gear set (ring gear, sun gear and planetary gear carrier). The video does an excellent job explaining how that works using the actual parts from the transmission.
The basic hybrid transmission architecture found in the Prius drive train was developed by a Japanese transmission company called Aisin and it is used by both Ford and Toyota. Does that mean that a Ford hybrid and a Toyota hybrid will get the same gas mileage since their hybrid systems have similar components and formats? Nope. Getting the best gas mileage is a complex puzzle of matching the power and torque requirements of the car with the efficiencies and operating points of the gas engine and electric motor. The gas engine is the most efficient at constant rpm and load like on highway driving. The electric motor provides better low end torque but it still has an optimum load and rpm. The planetary gear architecture basically allows an infinitely adjustable blend between the electric motor and the gas engine but you still need to know how to efficiently use it. When is the best time for the generator to use the engine power to recharge the battery pack? How low can the battery charge go before it needs to be recharged? Will using the electric motor’s low speed torque give the best overall gas mileage once the battery pack has been recharged? Should the gasoline be used to charge the battery or will more work be done if the same gas is burned to drive the wheels? It’s up to the software engineers to program the drive train controllers to figure out what the best combination of power input and output is for any situation the car sees. A good portion of the car’s price tag goes into the R&D and data crunching to figure these things out.
Check out Motor Trend’s latest episode of Head 2 Head. They take a look at the Toyota Prius V and the Ford C-Max hybrid. The guys do their usual excellent reviews of the cars, but the interesting part begins when the discussion turns to the gas mileage. Both cars didn’t get what the EPA rated them for and the Prius got the better real world mileage despite the C-Max having the better rating.
Even on a regular gas car, your mileage can vary massively based on where you drive the car (hilly terrain, higher elevations, traffic etc.) and how you drive it (pedal input smoothness, braking early, coasting etc.). The purpose of the EPA testing is not to tell you exactly what kind of mileage you will get, but to give you a standardized comparison between different cars. If you’re shopping for a hybrid, the emphasis really shouldn’t be on flat MPG figures as the Motor Trend guys have demonstrated. Your mileage will be based on how flexible your hybrid drive systems is. The car that will return the better gas mileage is the one that can consistently be the most efficient in a wide spectrum of driving conditions. It’s all in how the controls system (electric motor and gas engine blending) software is tuned.
The Motor Trend guys suspected that the Ford C-Max was tuned to rely on electric power up to a higher speed specifically to do better on the EPA test which ironically made it perform worse in real conditions. This result enforces story a few years ago about Prius drivers who would try to drive slower in an effort to keep the transmission from turning on the gas engine. This technique ended up giving the drivers worse gas mileage because it was completely depleting the battery pack. The system would then have to turn on the gas engine and run it at full recharge through the generator which reduced the overall mileage. The moral of the story is to do your research. What you want to look for is gas mileage consistency. What are other owners getting? Are people in different situations getting similar mileage or do the results vary a lot? My advice would be to put less emphasis on the EPA numbers and high score mileage numbers and try to find the hybrid that returns the least deviation in mileage numbers among a large number of owners. What you need to find is which automaker’s engineers did the best job programming the hybrid system to react to real world driving conditions. It’s a whole new ballgame for evaluating how well cars work. Now you have to look at how well the car is bolted together as well as how refined and effective its software package is.
The Nissan Deltawing finally got a chance to prove itself two weeks ago coming in fifth at the Petit Le Mans at Road Atlanta. The car survived two collisions, one at Le Mans and one during practice for Petit Le Mans, before finally getting a chance to finish a race and showing the world what it could do.
The entire Deltawing concept has revolutionized how people think of race cars. The car has proven that it has competitive speed while using half the power, fuel and tires thanks to greatly reduced aerodynamic drag and a well thought out design. Now we get the privilege to see how it drives and to understand the engineering that makes it work up close thanks to Chris Harris and the DRIVE channel. Harris takes the car around Road Atlanta for 5 laps to get a feel for its character before having the its creator, Ben Bowlby, guide him through the suspension systems. They touch on a few interesting engineering concepts. Watch the video and we’ll talk about them afterwards.
Jay Leno’s Ecojet is a project that’s been two and a half years in the making with the help of his garage mechanics and industry friends. The goal was to build a high performance car powered by a turbine burning soy bean oil based biodiesel. Like engines, turbines turn thermal energy into rotational mechanical energy. Instead of compressing air and fuel for detonation, the expansion of heated air turns a fan-shaped turbine on a rotating shaft. The most common automotive application is a turbocharger that harnesses the thermal energy of exhaust gasses. It’s work is then used to compress fresh air to force into the engine’s cylinders. Turbines are only used for direct mechanical drive in heavy duty applications like tanks, trains, ships and helicopters. They’re a lot more efficient when they can stay spun up at high rpm’s. Piston-cylinder engines are generally more efficient for the stop and go duty cycles seen in cars, but that’s not to say that turbines were never used in cars. Check out this vintage promotional video for Chrysler’s turbine car program from the early 60’s. Jay Leno owns one of the 50 cars that were made available to the public.
Hopefully you have built one of these simple electromagnets somewhere along your journey to become an educated human being. If you understand the basic principle of how an electromagnet works, then you can understand how wireless inductive charging works. In an electromagnet, the flow of electrons (current) causes a magnetic field. The magnetic field forms at a right angle to the direction of the current (the right hand rule). That means as the current flows in a circle around the nail (the fingers of your right hand wrap around the nail), the magnetic field forms along the nail (your right thumb points in the direction of the magnetic field) putting the poles on either end of the nail. If you’ve built one of these basic nail magnets, then you intuitively understand this already.
Here’s the really cool part. This relationship between current and magnetism works in reverse. A fluctuating magnetic field will also create a current in an otherwise dormant wire. Sustain the situation and you will eventually produce enough current to charge a battery. This is usually done with two coils of wire similar to the ones you wrapped around that nail to make an electromagnet. One of the coils is hooked to a power source and the other coil is hooked to whatever it is you’re trying to charge. The coil connected to the power source becomes an electromagnet that is switched on and off at very high frequency. This transforms the electrical energy into a usable form of magnetic energy. When the second coil is in range of the fluctuating magnetic field of the first coil, it transforms the magnetic energy back into electrical energy like an inverse electromagnet. Rapidly turning the electromagnet on and off allows you to broadcast energy as a magnetic field that can travel through the air without a physical wire connection. Check out this video from Veritasium to see how these principles were first discovered and a rad magically illuminated floating grill that would be perfect in a science nerd man cave.