Friday, April 2, 2021

The Real Science Behind Controller Drift

If you’ve ever had ghostly inputs into your control stick cause you to fail to catch a rare bug, miss a precision jump, or fall off the edge of a cliff into a bottomless void, you might be a victim of control stick drift. It’s annoying, notoriously hard to fix, and seems to be a growing problem. If you want to know why it happens (and how to fix it?), we’ve got to understand more of the science behind how your controller actually works. Fundamentally the thing that makes any and all of your electronics work is right in the name: electrons. Moving electrons from place to place is how we generate electrical current, and that current supplies the energy that allows our devices to run. [poilib element="accentDivider"]

How Your Controller Works

Underneath the plastic or metal shell of your device is its electric skeleton: the circuit board. Whether it’s your phone, your computer, or your game controller, all the critical parts that make your electronics function live on that circuit board. A circuit board is designed to send current to different places to accomplish different goals. To make a signal when a button is pressed, for example, or power lights, or sense the position of a thumbstick. These boards are carefully designed so that the current can only flow along tracks of conductive material (usually copper), and nowhere else. [widget path="global/article/imagegallery" parameters="albumSlug=the-evolution-of-the-playstation-controller&captions=true"] That current has to be precisely controlled, because if it runs unrestricted it burns through your energy supply incredibly fast and generates a ton of heat, which can damage the components and leave your device broken and useless. We limit that electric current’s flow by putting either resistive elements or gaps across the circuit board. Gaps make a break in the circuit, so that the current will only flow if something is inserted to complete it. Resistive elements still conduct current, but they slow and reduce the overall current that moves along that particular path, so we can send different amounts of energy to different parts of the circuit board depending on the job we need accomplished. Essentially, the more resistive material energy has to flow through, the lower the current. For example: if you press down on a button, a conductive element is brought into contact with the circuit board. That fills in a gap and completes the circuit allowing current to flow, generating a signal that reports the button has been pressed. That particular kind of input is either on or off, represented by a signal that reports either 0 or 1, which we call a digital signal.

Drift Happens

For a thumbstick though, we need to know not just if it’s been pressed, but by how much and in which direction. We need a signal that is analogous to the input, which is where we get the term ‘analog stick’ from. We accomplish this in electronics by varying the amount of current generated for different stick inputs. When you press your control stick, you’re actually turning two small wheels underneath it in an electrical component called a potentiometer. Those wheels are in contact with a track of resistive material, and act similarly to how the buttons fill in the gap in a circuit; the difference here is that it’s not just an on or off signal. [ignvideo url=""] The amount of resistive material the current has to flow through is determined by the orientation of the wheel, and a small piece of metal called a wiper that moves with it, choosing where along the track the connection to the circuit is made. Remember, the more resistive material in the circuit, the lower the current. If you jam the stick to the side, it turns the wheel all the way, such that the entire resistive track is used to complete the path for the circuit. If you just nudge it a little bit, the wiper moves to use only a small part of the track’s surface for the path the current will flow over. Every different orientation results in a different amount of current, and a unique signal. Your controller registers the current values from each wheel, and reports those as the x and y positions of your stick. It then turns that information over to the game console to move forward, spin your camera, or do whatever the game designers want that stick motion to represent. When working properly, there’s a 1-to-1 relationship between the current being reported and the position of the stick. When we’re experiencing stick drift, something is causing that current value to change when we’re not actually changing the stick position. [poilib element="poll" parameters="id=dbb28af4-fe41-420f-85c4-5f92eb12cb12"] This could happen for countless reasons: there could be something like dust or skin flakes along the resistive track or on the wiper, which would change the flow of current between the contacts in an unpredictable way. The conductive material along the track could be damaged from wear and tear, which would change the resistance across certain parts of it, triggering a bad signal. There could have been an error in the manufacturing process causing issues with the track right out of the box; without taking the controller apart and physically testing the signal from the potentiometer, it’s nearly impossible to tell. With more and more reports of drift popping up day after day, there’s got to be a systemic problem happening somewhere though. Nintendo has been facing backlash over Joy-Con drift for years, last year Microsoft had a class-action lawsuit filed against it for Xbox controller drift, and now Sony is facing its own legal trouble after PS5 DualSense controllers are showing the same issues only a few months after launch. If you dig around a little bit you can find complaints about drift on Valve’s controllers too; it seems almost universal. Personally, I’ve had 3 PS4 controllers start to drift, and both of my Joy-Cons, left and right. The weird thing is, I’ve got a half dozen GameCube controllers that have been kicking around for 2 decades that I still use occasionally for Smash, and I’ve never had the same issues. I don’t think Nintendo forgot how to make functional controllers; this feels like a fault of newer hardware.

Why Are Newer Controllers Drifting?

If you crack open a DualShock, Xbox, or Switch Pro controller, you’ll find the same basic potentiometer design in all of them. The folks at iFixit have done some investigative work and tracked down the make and model of potentiometers found inside the PS5 controller and discovered they’re rated for 100,000, or 2 million ‘cycles’, depending on the exact model used. ‘Cycles’ is a little vague, but seems to mean one full motion of the stick along one axis. Rough math from iFixit suggests that could work out to be just a few hundred hours before the potentiometers start to wear out and you could potentially drift. Their analysis is really good and I think it gets to the most likely reason we’re seeing drift problems become so prominent; the design used in modern controllers has a fundamentally limited lifetime, and that isn’t clearly advertised. When it comes down to it, to me this seems like both an engineering and a communication issue. There’s a common adage that shows up in engineering circles; your design *needs* to be 3 things: good, cheap, and reliable. You only get to pick 2. Controller manufacturers seem to have focused on the first 2, and let the 3rd fall off. [ignvideo url=""] We expect modern controllers to have high precision. We want to be able to gently nudge the stick when we’re sneaking, and then jam it forward when we’re running, and have that be accurately representing in-game. That fine-tuned feedback requires a high level of sensitivity, and that makes it vulnerable to the problems we’ve talked about. Controllers also need to be affordable. If you look online for replacement potentiometers, you can find them for only a couple of dollars. It’s possible that there are higher quality potentiometers available that could stand more wear and tear, but those will be more expensive and drive up the price of the unit. When you're already charging $60, $70, $80 dollars for a controller, that’s a big ask to make of your customers. So what we’re left with is this middle ground where we have high sensitivity, *relatively* lower cost, but the looming possibility your controller could start malfunctioning without any warning. I think if we had more clear communication from hardware manufacturers about how long controllers were expected to last, we could avoid some degree of this backlash. Do they really expect them to start giving out after a few hundred hours of use, but just don’t advertise it? Most controllers come with a standard one-year warranty, but one year could mean wildly different usage times depending on what your play habits are. [widget path="global/article/imagegallery" parameters="albumSlug=best-pc-controller&captions=true"] I think the Joy-Con drift is where this hurts the most. Their potentiometer design is a bit different, but still works on the same fundamental principles we’ve been talking about using a variable resistance and current to relay stick position. A big difference though is their potentiometer sits flat underneath the thumbstick, compared to other controller’s having a vertical orientation, which seems to make them especially vulnerable to dust and grim getting inside and mucking things up. Having your Joy-Con start to drift feels especially galling when we’ve had decades of Nintendo’s consoles and controllers being made of ‘Nintendonium’; being famously durable and long-lasting. There’s the impression that as long as you take good care of your controllers, they should last indefinitely. That clearly just isn’t the case with this technology. All that said, it’s pretty clear going forward that something needs to change with how the controller manufacturers handle this. From my perspective, there’s a few different routes they could take, none of which are particularly good solutions:

How Companies (Might) Be Able to Fix Drift

They can redesign how we track motion from analog sticks; focusing on using higher quality potentiometers that don’t wear down as easily, and trying to design them in such a way to be more isolated from dust and other contaminants. That would definitely make drift less common, but probably wouldn’t fully solve the problem. There’s also other technologies they could use besides potentiometers: something like the Hall Effect can track stick position using magnetic field sensors without making physical contact, avoiding the wear and dust problems entirely. Of course, controllers seem to have converged to the same basic design starting about 20 years ago, so that sort of drastic change would involve a lot of engineering work and probably come at an even greater cost. Another option would be to make controllers more modular so you could easily swap out the potentiometers once they start going bad. As a general rule, manufacturers really don’t want you opening up your controllers and potentially damaging the internal parts. Nintendo especially uses really uncommon screws, seemingly out of spite, just to make sure you can’t get into your hardware easily. I could, however, imagine something like the jumper-pack on the N64 that was designed so users could swap out internal components without needing to open up the system and expose its guts to the elements. The last option, and the least popular one I’m sure, is to just be more explicit about expected lifetimes for controllers. If we knew controllers were really designed to last 1000 hours, or whatever the number might be, we could at least plan ahead and not feel like we’re just rolling the dice on how long before our controllers start malfunctioning. That would give us a standard to hold the manufacturers accountable to as well. If their devices start failing any earlier, and drive a bigger discussion about what we should expect to pay for something that has a finite lifespan. That obviously isn’t going to win them any good will, but might be the path of least resistance to help deal with these mounting lawsuits they have on their hands. There’s not a clear answer, but the more consumers push back, the sooner they’ll have to stop kicking the can down the road and find a solution. [poilib element="accentDivider"]


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