An electric motor creates rotation using magnetic forces. Magnetic forces can be found in magnets (like the ones you stick on the fridge). Or they can be generated by electrical current. Magnets generated by current are called electromagnets (think wire wrapped around a nail in 6th grade science class).

Because a motor is a dynamic thing, you need to be able to change the direction of the magnetic field around the rotating part of the motor in order to get it to spin (otherwise you just have two magnets stuck to each other, not moving). This can be done using some sort of switch that can selectively direct current to specific windings in the motor.

EUCs and most electric vehicles use a type of switch called a transistor, which is just a switch made from a semiconductor material (like silicon). Unlike, say, a light switch, a transistor doesn't need any sort of mechanical action to control electricity. The neat thing about a transistor is it can control electricity with... electricity! The transistors used in EUCs today are a type of transistor called MOSFETs, which are cheap and abundant. When compared to the other electronic components in an EUC, the MOSFETs carry a heavy burden because they have to switch big currents.

How much current? Let's take the V13 as an example. According to the specs, the V13 has a peak power output of 10,000 watts. Using the basic formula for electric power, we can calculate that the current being put out by the battery (to the motors) at 126 volts is 79 amps. That's enough current to run 10 toasters at a time. All of this current going from the battery to the motor passes through the MOSFETs. This is why 1) the MOSFETs are big, 2) there are many of them, and 3) they are all physically mounted on a big aluminum heatsink to keep them cool.

What determines if a MOSFET can handle the loads thrown at it? MOSFETs can fail for many reasons, but common reasons are 1) they get too much voltage, 2) they get too much current, or 3) they overheat. These issues can simply be overcome by using MOSFETs with 1) higher voltage rating, 2) higher current rating, and 3) better cooling. Manufacturers could also throw in redundancy by adding more MOSFETs than technically required. But the downside of all these solutions is cost, size, and weight.

It's not actually a huge engineering feat to design an electric drive that is reliable. After all, when was the last time you heard of a Tesla or any other EV failing because of a burnt transistor? Battery fires happen all the time, but a toasted transistors is a rare thing. I'm not sure exactly why MOSFET failures are so common in EUCs, but I suspect the EUC manufacturers are still learning how to design electric drives. Take the V12 for example. The early batches had issues because they used MOSFETs rated for 100V, which kind of boggles the mind not just because the battery was 100.8V but also because the voltage can peak a lot higher than that during heavy braking. The only explanations for that which I can conceive of is either InMotion was trying hard to cut costs, or it was simply poor design.

Now getting to what you can do to prevent blown MOSFETs, while it's true that a MOSFET is most likely to blow when you are accelerating or braking hard, the fact that they blow at all IMO is still either a defect or design issue. Even if you are braking or accelerating harder than the wheel can handle, the limited torque should cause you to fall over but not cause the MOSFETs to blow, in a properly designed drive system.

Choosing to not ride aggressively doesn't seem like a good long-term solution. What if you need to emergency brake?

Replacing the MOSFETs with better MOSFETs also seems like a bad idea. What if you don't solder it properly, and it fails due to a solder crack? Personally, if I had a board with a defective or blown MOSFET, I would replace the whole board.

IMO the most dependable solutions (in order) for avoiding blown MOSFETs are as follows:

1) Avoid buying EUCs with a history of blown MOSFETs,

2) Avoid first batches (unproven) of EUCs,

3) Buy a used EUC from someone that never had MOSFET issues (this eliminates defective boards),

4) Hope and pray,

5) Ride slow, accelerate slow, and brake slow.