- When people are talking about high end suspension tuning, you'll often hear the
term damper pot being thrown around.
The term damper pot is an abbreviation for damper potentiometer and all it really means
is having a sensor that measures the position of the suspension as the car moves around
the circuit.
There are multiple types of damper pot that can be used to measure suspension
position, most commonly this is either with a linear or a rotary potentiometer.
A linear potentiometer simply measures the change in a linear position whereas a rotary
potentiometer measures a change in angle.
Depending on what you've got available, and the space you've got to work with inside
your car, will depend on which of those two systems you go for.
This is an example of two different sizes of damper pot, both linear potentiometers.
This is where you've got one end which moves inside of this housing and there is an ouput
here that would be run to your logger to spit out a position at each point the logger is
measuring the signal in time.
If one of these sensors is mounted in parallel with a damper you would typically have one
end attached to the upper part of the damper and the other to the lower, then when the
damper is changing position, moving up and down, the sensor moves with it and sends
that signal back to the logger.
These don't have to be mounted in parallel with a damper, it's just as relevant for them to
be attached to a suspension point so in that case, you would typically have one part
of the sensor attached to the sprung mass of the car, as in the chassis, and the other
attached to something like a suspension arm.
As long as you know the mathematical relationship between each part of the
suspension and the damper, it doesn't actually matter where the sensors is placed, you can
always calculate the position of any and every part of the suspension as long as you
know the measurement of one point.
This of course relies on the assumption that all of the suspension components are rigid
and generally this is a pretty safe assumption as long as the suspension is well built and
well serviced.
There are lots of different uses for having damper potentiometer data.
One of the most obvious ones is just to know how much your suspension is
actually moving as you move around the circuit and go through different manoeuvres
like steering and braking and accelerating.
This is really useful information when you're diagnosing handling problems on your car.
Another useful way you can use damper potentiometer data is to estimate the
level of downforce you are getting from your aero on your car.
As long as you know the stiffness of your springs and bump stops and when in the
suspension travel your bump stops engage, if you know how far they're moving
and you know the stiffness of each one of these elements as well as the motion ratio between
the wheel and the damper at each end of your car, you can get a pretty good
estimate of how much downforce your car is generating on track.
Another way you can make use of damper potentiometer data is by estimating ride height
at different points on track.
So if you know the relationship between say your front splitter and the chassis and how that
relates to the suspension, you can create a simple math channel that would show you
splitter height at each point on track.
In cars with really effective aero floors like a large front splitter with a diffuser built into
the front of it, the proximity from the splitter to the ground is a really critical component
in tuning the aero behaviour of the car.
If you can calculate the ride height of the splitter above the track at each point on
the circuit, it is a really useful thing when it comes to tuning your downforce and diagnosing
handling problems that can be caused when the splitter gets too close to the ground
at some point on track when you're braking.
Damping forces in a conventional hydraulic damper are proportional to the velocity
that the damper shaft is moving at.
In order to calculate velocity, we need to do something called differentiation of
the position.
All that really means is taking the difference in position from one time step to another and
taking the difference in those two positions over a known time step, you can calculate
velocity.
In order to get really good velocity data from your damper potentiometers, that
damper signal needs to be logged at quite a high frequency.
Typically this logging frequency is between 250 and 1000 Hz so that means the logger
would be recording each position signal between 250 and 1000 times a second.
Once you've logged the damper position data at a high enough frequency, this allows
the differentiation to be smooth, meaning that you've got a relatively continuous
velocity profile coming from each damper potentiometer you've got fitted to the car.
Once we know the velocity of each damper at all points on the circuit then this tells
us quite a lot about the damping forces we're using in the car.
With these velocities we can start to do some pretty simple statistics.
Usually we're making use of a velocity histogram for each corner of the car.
The histogram is simply telling you how much time each damper is spending in
which velocity ranges and in which direction it's moving.
Typically this is characterised as being either low speed or high speed compression
and rebound.
Because we know dampers are most sensitive to velocity, if we know the velocities
they're moving, that tells us quite a lot about the forces they're providing
if we know the velocity ranges they're using.
Making use of damper speed histograms is not just useful for tuning and understanding the
performance on track, it's also a really good tool to understand if there's been a mistake
with the settings or damage has happened inside the damper that's stopping it working.
This is because you can usually compare one corner of the car to the other, say the
front left to the front right and if you see something really skewed or different on the
damper histogram, this tells you that there's a problem with that damper.
That's really useful because it's a really quick way to pick it up while you're actually
running on track without needing to remove the damper and have access to a damper
dyno to understand if it's something different with that damper.
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