EVODYNAMICS Ultimate Suspension Data Thread
Feb 20, 2014, 02:32 PM
#46
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I've got some more good track data I will share here along with a bunch of thoughts I've had pertaining to the discussion. Working hard to get some customers cars out the door first. 
Mar 5, 2014, 08:11 PM
#47
Just curious. Spent most of my professional life as a controls engineer and the linear pot is a relic I haven't seen used in modern equipment in more than 20 years. So why is it still used in this application? Cost? Simplicity? Not knocking this thread, this will be great info.
Mar 6, 2014, 11:08 AM
#48
Just curious. Spent most of my professional life as a controls engineer and the linear pot is a relic I haven't seen used in modern equipment in more than 20 years. So why is it still used in this application? Cost? Simplicity? Not knocking this thread, this will be great info.
What are the other alternatives for linear position sensing in an application like this? The magnetostrictive sensors look awesome, but they also look big and expensive.
Mar 6, 2014, 12:52 PM
#50
a LVDT would be the industry standard. They're just not as cheap as linear pots.
Just haven't seen linear pots used in a long time. But they are cheap, and easy to come by.
Mar 6, 2014, 03:56 PM
#51
You could also go to a rotary pot mounted on the chassis and drive it from a link on the arm.
Linear encoders are fairly expensive. Rotary encoders on the other hand are much more common and can have very high resolution. Considering you would have to use only 1/3 or so of the range, that high resolution would be needed. You would also need a curve fit equation to deal with the nonlinearity of the linkage. Pretty straight forward though.
Digital would be the way to go due to the noise environment, not sure how many automotive DAQs will deal with digital data though? This is where the PLC/FPGA type control of the high end systems comes into play...
Linear encoders are fairly expensive. Rotary encoders on the other hand are much more common and can have very high resolution. Considering you would have to use only 1/3 or so of the range, that high resolution would be needed. You would also need a curve fit equation to deal with the nonlinearity of the linkage. Pretty straight forward though.
Digital would be the way to go due to the noise environment, not sure how many automotive DAQs will deal with digital data though? This is where the PLC/FPGA type control of the high end systems comes into play...
Last edited by 03whitegsr; Mar 6, 2014 at 04:01 PM.
Mar 27, 2014, 01:21 PM
#52
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I have very little experience when it comes to controls, but would it be possible to design a system using 3 axis accelerometers to measure such things? By placing acceleromters at different points, you may even be able to derive position changes of certain suspension components, deflection of arms, hardpoints, strut towers, all while being overlayed on steering angle and g force. Its a much more complicated approach, but boy would it be comprehensive. Of course, i agree that using a pot to develop a baseline and starting point for damping would be the first step.
In my SAE days, we didn't touch the paper or computer unless we had tire data first. Then we decided on natural frequency 2nd, chose a roll gradient 3rd, and worked backward from there on everything else. Moral of the story, tire data is king and the suspension should be designed around it instead of being considered an afterthought as is common with most people who mod production cars.
In my SAE days, we didn't touch the paper or computer unless we had tire data first. Then we decided on natural frequency 2nd, chose a roll gradient 3rd, and worked backward from there on everything else. Moral of the story, tire data is king and the suspension should be designed around it instead of being considered an afterthought as is common with most people who mod production cars.
Last edited by hispanicpanic; Mar 27, 2014 at 01:24 PM.
Mar 27, 2014, 03:25 PM
#53
I have very little experience when it comes to controls, but would it be possible to design a system using 3 axis accelerometers to measure such things? By placing acceleromters at different points, you may even be able to derive position changes of certain suspension components, deflection of arms, hardpoints, strut towers, all while being overlayed on steering angle and g force. Its a much more complicated approach, but boy would it be comprehensive. Of course, i agree that using a pot to develop a baseline and starting point for damping would be the first step.
Measuring relative deflection of hard points isn't going to happen with accelerometers. The deflections you'd see would be absolutely tiny relative to all of the other accelerations experienced from driving around. And even if you did have the precision to measure that, your measurements would still be swamped by the vibrations running through the car from the motor, etc.
Mar 27, 2014, 05:53 PM
#54
Evolved Member
You couldn't really pull absolute positioning data from such a system, but it would be feasible to pull shock rough velocity out of such an arrangement. I'm not sure how accurate or precise it would be, though. The unsprung mass in particular can see some very high accelerations, so you'd need to have enough accelerometer dynamic range to handle the massive bump accelerations while still being able to measure the smaller relative difference between the top and bottom of your strut, for example. You would absolutely have to compensate for drift and integration error by forcing the average shock velocity to zero over time, though, which is also going to color your measurements somewhat.
Measuring relative deflection of hard points isn't going to happen with accelerometers. The deflections you'd see would be absolutely tiny relative to all of the other accelerations experienced from driving around. And even if you did have the precision to measure that, your measurements would still be swamped by the vibrations running through the car from the motor, etc.
Measuring relative deflection of hard points isn't going to happen with accelerometers. The deflections you'd see would be absolutely tiny relative to all of the other accelerations experienced from driving around. And even if you did have the precision to measure that, your measurements would still be swamped by the vibrations running through the car from the motor, etc.
Mar 28, 2014, 08:12 PM
#56
I have very little experience when it comes to controls, but would it be possible to design a system using 3 axis accelerometers to measure such things? By placing acceleromters at different points, you may even be able to derive position changes of certain suspension components, deflection of arms, hardpoints, strut towers, all while being overlayed on steering angle and g force. Its a much more complicated approach, but boy would it be comprehensive. Of course, i agree that using a pot to develop a baseline and starting point for damping would be the first step.
In my SAE days, we didn't touch the paper or computer unless we had tire data first. Then we decided on natural frequency 2nd, chose a roll gradient 3rd, and worked backward from there on everything else. Moral of the story, tire data is king and the suspension should be designed around it instead of being considered an afterthought as is common with most people who mod production cars.
In my SAE days, we didn't touch the paper or computer unless we had tire data first. Then we decided on natural frequency 2nd, chose a roll gradient 3rd, and worked backward from there on everything else. Moral of the story, tire data is king and the suspension should be designed around it instead of being considered an afterthought as is common with most people who mod production cars.
You couldn't really pull absolute positioning data from such a system, but it would be feasible to pull shock rough velocity out of such an arrangement. I'm not sure how accurate or precise it would be, though. The unsprung mass in particular can see some very high accelerations, so you'd need to have enough accelerometer dynamic range to handle the massive bump accelerations while still being able to measure the smaller relative difference between the top and bottom of your strut, for example. You would absolutely have to compensate for drift and integration error by forcing the average shock velocity to zero over time, though, which is also going to color your measurements somewhat.
Measuring relative deflection of hard points isn't going to happen with accelerometers. The deflections you'd see would be absolutely tiny relative to all of the other accelerations experienced from driving around. And even if you did have the precision to measure that, your measurements would still be swamped by the vibrations running through the car from the motor, etc.
Measuring relative deflection of hard points isn't going to happen with accelerometers. The deflections you'd see would be absolutely tiny relative to all of the other accelerations experienced from driving around. And even if you did have the precision to measure that, your measurements would still be swamped by the vibrations running through the car from the motor, etc.
Physics says you should be able to work out velocity and position from an accelerometer data stream. However, as construct says, there is so much going on thinking through the math and calculations required makes my head hurt. Right off the bat, separating vibrations, resonances, tire noise, etc, etc from the actual movement would be near impossible.
It's way easier ,mathematically to start with real time positional data and derive velocity and acceleration from that.
May 10, 2014, 11:36 PM
#59
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the car runs hoosier A6s in 275 35 18 on the track usually. although we also have a set of R888 in the same size mounted as well (usually used for practice events and we used them in the endurance we just did)
Feb 3, 2018, 06:24 PM
#60
Bumping this thread up from the grave. I'm interested in putting linear shock pots on my Evo so I may scientifically tune the damper settings, as well as measure aerodynamic forces.
1. Any more data sets from different data settings?
2. Photos of shock pot mounts (especially fronts)?
1. Any more data sets from different data settings?
2. Photos of shock pot mounts (especially fronts)?
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