The Real Reason Tesla Developed The Plaid Motor!

What is it that makes an electric car so fast? And more specifically - what is it that makes the Tesla Model S Plaid the fastest accelerating production car that has ever hit the road?

Well, honestly it’s a lot of different factors all combined together - but at the heart of the Plaid is the trio of very special electric motors - and to a similar degree the battery pack - but we already talk a whole lot about batteries on this channel and we have never really taken any time to explore electric motors, specifically the very innovative electric motor designs implemented by Tesla. Which is a shame, because they are really neat.

And while there is a lot of high level engineering going on here that we won’t even try to explain because we’re not nearly smart enough to do that - it’s actually not too difficult to gain a basic understanding of what’s going on inside a Tesla motor, even an advanced design like the Plaid. So let’s get into it.

Nikola Tesla’s Design

Alright, we all know that Tesla the company is named after Nikola Tesla the human, right? Nikola was an inventor and engineer who lived during the late 1800’s and early 1900’s, his work revolving around electricity and magnetism. He invented things like the radio, the remote control and his namesake tesla coil. But the real reason that Tesla the car company took on his name is because Nikola invented the induction motor - an alternating current motor powered by electromagnetic induction.

Again, that sounds really complicated - and it is - but we can simplify. And it all starts with magnets.

So, a quick and easy experiment we can all relate to - if you have a compass, you know that the needle will always point North. The magnetized needle will always be aligned with the magnetic field of the Earth, the North pole of a magnet will always seek the North pole of the Earth by attraction. But if you place a magnet close to your compass, then the needle will spin to align with that magnet because it’s now the strongest force of attraction. And if we take that magnet and move it to the other side of the compass, the needle will spin over to that side and follow the magnetic field. By moving the magnet around the compass, the needle will continue to spin. So we just induced rotation using a magnet. Very cool.

Now on the other side we know that magnets can create very strong push as well, or the opposite of attraction. We’ve all tried to press two magnets together only to find that there is an incredible force preventing you from doing that.

An electric motor is just harnessing that power of push and pull to spin the rotor. But you can’t get a constant rotation without introducing electromagnets to the party. And that’s where things get freaky.

So, a material like copper is extremely conductive, but it is not magnetic - that is, until we flow an electric current through the copper material, at which point it becomes an electromagnet - so this is a non permanent magnet, if you take away the electricity, you also take away the magnetism. This gives us incredible control over the magnetic field. A magnet like the one on your fridge is called a permanent magnet, because it has a physical north and south pole that are… well, they’re permanent, they can’t be changed, you have to physically rotate the magnet to rotate the magnetic field. But with an electromagnet, the magnetic field will follow the direction that the electrons are moving through the conductive material - so if you reverse the flow of electricity, you reverse the poles of the magnet. So electromagnets can swing both ways, depending on what kind of juice you give them. Now you don’t have to physically turn the magnet to reverse the poles.

Inside the Electric Motor

OK, so now we can go inside our induction motor, where there are two key components - the stator and rotor. The stator is the outer ring of the motor and the rotor is the inner center that does the spinning - Stator, is stationary. Rotor, is rotating.

In this application, our rotor is an iron core surrounded by rows of permanent magnets that run lengthwise - for simplicity right now, let’s just say there are 4 rows and these magnets are evenly space around the ring: top, bottom, left and right - and each quarter of the ring has an alternating pole, so they go North, South, North, South as you go around.

The stator is a tube of electromagnets, made up of many coils of copper wire that surround the entire ring, also running lengthwise - each coil of wire is an individual electromagnet - therefore each one can be turned on and off and have its polarity flipped just by controlling the flow of electricity into each coil.

So by placing the rotor inside the stator, we have a magnet within a magnet - a permanent magnet inside an electromagnet. Now anytime you put two magnets near each other, there will be a natural push and pull, the opposite poles will pull towards each other and the like poles will push away. But once that initial alignment is complete, the rotation will stop. All we have to do to maintain that rotation is to constantly move the North and South poles of the stator magnets around the outer ring. And again, we do that by controlling the direction that electrons are flowing through the coil of wire. So by moving the South pole of the stator around in a circle, it will pull the North pole of the rotor along with it - and conversely at the same time the South pole of the stator will push the South pole of the rotor as it moves around that ring.

That constant force of push and pull will spin the rotor, and the faster you move that magnetic field around the stator, the faster the rotor will spin.

This is what we’re looking at when we see the Tesla T logo, it’s a cross section of an electric motor, the top curving line is the stator ring and the pointy T shape is a slice of the rotor.

Hopefully that made sense and it was at least mostly accurate - I’m not saying this is a textbook worthy explanation, but it should be enough to get the main point across.

Inside Tesla’s Plaid Electric Motor

OK, so now that we’ve qualified all of that, we can talk about what makes the Tesla Plaid electric motor so special.

There’s more to making this car so fast than just having three motors instead of two, if it were that easy, then everyone would do it, it would also mean that the Rivian R1 with 4 motors would be the fastest vehicle in the world - but it’s not. 

We know that the defining characteristic of the Plaid design is that the rotor has a carbon sleeve, this is how Tesla describes it on the product website. And during the Plaid launch event at Tesla HQ in 2021, Elon talked up this carbon sleeve technology a lot. Typically a rotor would just have a steel sleeve around the outside, this is the first one that Elon knows of to use carbon composite.

So what we have here is actually an incredibly tight wrapping of carbon fiber threads around the outside of the rotor - imagine the rotor is like a bobbin being spooled up with thread, or a fishing reel even, if that’s more familiar to you. And the carbon fiber thread is soaked with epoxy so that it hardens into a solid mass.

Elon says that Tesla does this wrapping process under extreme tension - they actually had to build a new machine that was capable of wrapping the threads tight enough - and the reason that they do this is because the material of the rotor will shrink in low temperature, but the carbon fiber will not, so the carbon actually has to be compressing the rotor to prevent a separation from ever happening when the rotor contracts.

So why even bother to do this? Well, just like how the rotor can contract, it can also expand - not only at elevated temperature, but also under elevated force, such as when the rotor is spinning at 20,000 RPM. The centrifugal force on the rotor would actually cause it to grow outwards, Elon kind of insinuated that it would even fly apart if it wasn’t being held together by the wrap.

But the reason that we don’t want the rotor to expand is because we want to keep the distance between the rotor and the stator as small as physically possible. Getting back to our own experience playing with magnets, we know that the force of the attraction and repulsion between two magnets gets stronger the closer the magnets are to each other. And that force is what spins the rotor, so maximum force occurs when the rotor is as close as possible to the stator. But if we know that the rotor is going to expand outwards at maximum power, then we’re going to have to widen the gap between the two to account for that expansion. If the carbon fiber wrap is preventing the rotor from expanding though, then we can keep that gap much smaller. And we’re talking about microns here, this is a tiny, tiny measurement, but it makes a difference to squeezing the absolute highest performance out of your motor. This allows the Plaid to continue putting max power down all the way through its range. If you look at the power curve of all previous Model S motors, they start off super strong, but actually lose power as the speed of the vehicle increases. Plaid does not do this.

The Munro Teardown

So we can look over to Sandy Munro and his engineering company to get a glimpse of what the inside of a Plaid motor actually looks like - these guys have probably one of the coolest jobs ever, they just take cars apart all the way down to their base components and look at how they work.

And Sandy has done this teardown procedure with the Model S Plaid. So there are a few very interesting discoveries that he made.

Let’s start off with the inverter - this is a component that we didn’t talk about in the basic explanation, but this thing is like the brain of the motor - the inverter controls the flow of electricity into all of those magnets, and in doing that, it precisely controls the speed and operation of the motor.

What’s interesting is that we can actually see that the inverter board inside each of the model S Plaid motors actually says Model 3 right on it. And Sandy goes around demonstrating that every Tesla motor, whether it’s in a Model 3, Model Y or Model S Plaid, has the exact same inverter - the housing is the same on each motor, and the circuit board is very nearly identical, with only one significant change on the Plaid, that we’ll get to in a second.

So when we talk about Tesla prioritizing efficiency in their production lines, this is what we mean, the same basic component goes into every car, they don’t even waste time changing the printing on the board, they all say Model 3 - this is the inverter that Tesla invented for the Model 3, and they liked it so much that they implemented it into every single motor in the lineup.

The slight modification to the Plaid inverter board is actually an explosive fuse - this is really cool. The fuse is actually a tiny bomb that will fire two pushers straight out that will physically break two of the bus connectors that link the power from the inverter to the motor. So, I’m not sure what exactly would cause this to fire, but if something catastrophic happens to a Model S Plaid, this explosive fuse will physically break the electrical connection to the motor and make perfectly sure that the motors go completely dead in an instant.

Sandy also found that all three of the motors in a Plaid vehicle are exactly the same, again, this is the most efficient choice for production.

He talks a bit about the advantage of having two motors in the rear - yes there is more power, but there is also more simplicity. By using one motor per wheel there is no need for a differential. When you have one motor powering two wheels, the power has to travel through a differential before it can hit the drive axles, because the car can’t go around a corner if both wheels are spinning at the same speed, the inner wheel has to turn faster, the differential allows this to happen using a set of gears. But every time you put something in between the motor and the wheel, you are introducing an opportunity to lose energy, either through friction or through the gear set.

So the only thing between the Plaid Motors and rear wheels is a single gear box, and that is a necessity - Tesla doesn’t have a transmission, there is only one, set gear ratio - but you can’t just have the motor connected directly to the wheel, there needs to be a gear reduction first. On the Plaid motor, this is actually a different reduction ratio than on a standard Tesla motor in a Model Y. Munro found that the Plaid has a gear ratio of 7.54:1 - while the Model Y has a gear ratio of 8.996:1.

It’s also interesting to see that the stator inside the Plaid motor is the exact same component as the one inside the Model 3 and Y motor - again, maximum production efficiency.

The rotor, however, is significantly changed. Not only is there the carbon fiber wrap, but there is also a totally different assembly underneath. So, Tesla is using these star shaped laminate sheets to make up the iron core of the rotor, all these thin strips are stuck together to form one solid part. Munro found that there are 529 of these stars making up the core. And this core creates 6 rows of magnets around the rotor. The magnets are then capped off by another laminated piece, just tons of thin strips all compressed together to make one solid - and if you look at the caps on top of the magnets, they actually look almost exactly like the Tesla T logo. These caps don’t connect to the core of the rotor, they are just held on by the magnets themselves. And this is a design that Sandy and his crew have never seen before inside an electric motor, they seem kind of baffled by it, but they say that Tesla claims this laminated star construction and floating caps gives them 25% more power and torque capability.

And on top of that, the permanent magnets used inside the Plaid rotor are significantly more powerful than your average electric car motor, even significantly stronger than Tesla’s standard motor. So Munro did a little, unofficial, practical test - just by measuring how much force was required to pull a bolt away from the magnet. They did this test using rotor magnets from a BMW i3, a Mustang Mach E rear motor, a Model Y rear motor and the Plaid. They found that the Plaid required 151 newtons of force to pull the bolt away, while the Model Y required 112 newtons, the i3 required 93 newtons and the Mach E just 81 newtons. So your magnets inside the Plaid rotor are nearly twice as strong as the magnets found inside a Mustang Mach E rotor - and they are over a third more powerful than the rear motor in a dual motor Model Y or Model 3.

And that’s about as much as my feeble brain can handle for one day - so hopefully a lot of you learned some new things from this video today - this is the first time we’ve really gone in depth with this topic, and it is a complicated one, but I think that knowing these things just makes it even more enjoyable to be an electric car enthusiast.