AgitatedPancake
Frobot
We've dabbled in shock/damping theory a few times recently, but don't have a dedicated thread to really dive into the details (that I'm aware of). Let me first say that I'm not an expert here by any means, just a nerd learning nerdy things so please, ask questions along with me! But better late than never, let's get a thread going. As I'm currently imagining this thread, I think the theory is far more helpful than specific "my truck has this tune and it's good" style discussion. I'm going to skip emulsion shocks for the sake of simplicity, but you're welcome to bring them up if you so desire.
The kinds of things that would be awesome to bring to this thread
- Documents: Patents, PDFs, college/ASE papers, etc
- Cutaway models with functional descriptions
- Videos: Helicopter footage, onboard videos with suspension focus to interpret
- Shock Dyno Charts: footage is even better, but correlating force curves to certain valving/features would be incredible.
- Anything else you find relevant, use your own discretion
I'm going to call mechanical shocks "dumb" shocks for simplicity, and anything implementing computer control is a smart shock.
Most "dumb" (mechanical) shocks are velocity sensitive. They have no idea where they are in the shocks travel range, but the force they produce is directly impacted by the piston speed. When the shock is moving slow, it's easier to cycle (low force) because the fluid is moving slow enough to take the free bleed path. When the piston starts moving faster, it can't free bleed fluid fast enough and some of the fluid is forced through the valve stack at much higher resistance (higher force). So by tuning the free bleed and the primary shim stacks, the force created by the shock can be tuned for the different speed regimes.
Bypasses are the primary "dumb" shock that are not only velocity sensitive, but also position sensitive. They still have all of the velocity sensitive tuning of the above basic shocks, but also now have the ability to change force not only based on piston speed, but also on piston location. External bypasses do this with the visually obvious bypass tubes, and Internal bypasses do the same with reed valves instead of poppets (different mechanisms to accomplish the same results due to packaging reasons) but concealed by the outer body that supports the coil springs. They are true to their name, they literally allow a bypass path for the fluid to travel from one side of the piston to the other without going through the primary shim stack. So a "full stiff" bypass essentially has all of the tubes closed off completely, and is forcing all of the fluid through the primary shim stack. Then the bypass tubes can be opened incrementally to soften specific areas of travel from there.
There are other types of position sensitive devices that companies use to create stiffer "bump" zones such as moving the reservoir mounting point lower on the body (vs the cap), or king with their needle and seat mechanism, but those can be discussed in more detail in follow up replies.
Then there are "smart" shocks, that have electronic control devices that help the shocks create the right amount of force for any given scenario. Some electronically tuned shocks effect primarily the compression valving, others impact rebound. But the idea is they are run by a computer that is observing variables such as shock position, vehicle speed, accelerometers, steering wheel position, brake/gas pedal positions, as well as reading mode selections (comfort, sport, etc) by the driver.
Many (most?) electronic control devices are implemented between the main body of a shock and the reservoir. I find this fascinating to be honest. At full extension the entire shock shaft is exposed. When fully compressed, the shock shaft takes up volume that is normally used by fluid. So the only way the shock can move, is if that displaced fluid has somewhere to go, the reservoir. When the entire shock body is 100% full of fluid like normal, if you were to plug the reservoir hose the shock would by hydrolocked and unable to move in any direction at all, like a hydraulic ram. What this also means, is that you can apply valving to the fluid going back and forth between the main body and reservoir just as you would apply normal valving on the piston. This is how the Fox DSC (manual), IQS (manual) , Live Valve X1/X2 (electronic) work as well as the Icon system and others.
So that covers some of the various basics of how control can be applied via shocks, based on velocity, position, or other parameters from the vehicle (to be covered in far more depth in follow up responses!). Then we have to figure out what we're actually asking them to do. I've seen discussions on Skyhook control theory, Groundhook control theory, is our use-case unique or does it fit directly into a category? In basic terms, we're looking to keep the chassis as stable as possible (because any rocking/bucking motion are inherently unstable), and keep the tires on the ground as much as possible.
I'll come back later with more details about some of those individual topics, but just wanted to get a foundation of the basics to get the ball rolling
The kinds of things that would be awesome to bring to this thread
- Documents: Patents, PDFs, college/ASE papers, etc
- Cutaway models with functional descriptions
- Videos: Helicopter footage, onboard videos with suspension focus to interpret
- Shock Dyno Charts: footage is even better, but correlating force curves to certain valving/features would be incredible.
- Anything else you find relevant, use your own discretion
I'm going to call mechanical shocks "dumb" shocks for simplicity, and anything implementing computer control is a smart shock.
Most "dumb" (mechanical) shocks are velocity sensitive. They have no idea where they are in the shocks travel range, but the force they produce is directly impacted by the piston speed. When the shock is moving slow, it's easier to cycle (low force) because the fluid is moving slow enough to take the free bleed path. When the piston starts moving faster, it can't free bleed fluid fast enough and some of the fluid is forced through the valve stack at much higher resistance (higher force). So by tuning the free bleed and the primary shim stacks, the force created by the shock can be tuned for the different speed regimes.
Bypasses are the primary "dumb" shock that are not only velocity sensitive, but also position sensitive. They still have all of the velocity sensitive tuning of the above basic shocks, but also now have the ability to change force not only based on piston speed, but also on piston location. External bypasses do this with the visually obvious bypass tubes, and Internal bypasses do the same with reed valves instead of poppets (different mechanisms to accomplish the same results due to packaging reasons) but concealed by the outer body that supports the coil springs. They are true to their name, they literally allow a bypass path for the fluid to travel from one side of the piston to the other without going through the primary shim stack. So a "full stiff" bypass essentially has all of the tubes closed off completely, and is forcing all of the fluid through the primary shim stack. Then the bypass tubes can be opened incrementally to soften specific areas of travel from there.
There are other types of position sensitive devices that companies use to create stiffer "bump" zones such as moving the reservoir mounting point lower on the body (vs the cap), or king with their needle and seat mechanism, but those can be discussed in more detail in follow up replies.
Then there are "smart" shocks, that have electronic control devices that help the shocks create the right amount of force for any given scenario. Some electronically tuned shocks effect primarily the compression valving, others impact rebound. But the idea is they are run by a computer that is observing variables such as shock position, vehicle speed, accelerometers, steering wheel position, brake/gas pedal positions, as well as reading mode selections (comfort, sport, etc) by the driver.
Many (most?) electronic control devices are implemented between the main body of a shock and the reservoir. I find this fascinating to be honest. At full extension the entire shock shaft is exposed. When fully compressed, the shock shaft takes up volume that is normally used by fluid. So the only way the shock can move, is if that displaced fluid has somewhere to go, the reservoir. When the entire shock body is 100% full of fluid like normal, if you were to plug the reservoir hose the shock would by hydrolocked and unable to move in any direction at all, like a hydraulic ram. What this also means, is that you can apply valving to the fluid going back and forth between the main body and reservoir just as you would apply normal valving on the piston. This is how the Fox DSC (manual), IQS (manual) , Live Valve X1/X2 (electronic) work as well as the Icon system and others.
So that covers some of the various basics of how control can be applied via shocks, based on velocity, position, or other parameters from the vehicle (to be covered in far more depth in follow up responses!). Then we have to figure out what we're actually asking them to do. I've seen discussions on Skyhook control theory, Groundhook control theory, is our use-case unique or does it fit directly into a category? In basic terms, we're looking to keep the chassis as stable as possible (because any rocking/bucking motion are inherently unstable), and keep the tires on the ground as much as possible.
I'll come back later with more details about some of those individual topics, but just wanted to get a foundation of the basics to get the ball rolling
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