Tech Explained: Data Acquisition – Racecar Engineering

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Information acquisition a broad subject – on trendy race vehicles, there are oceans of knowledge recorded over a run, from lots of of sensors measuring portions from airspeed by way of pitot tubes, gasoline stream with ultrasonic sensors, trip heights by way of lasers and far in-between.

Instrumentation in a trackside context permits engineers to know what state the automobile is in at a selected second and make performance-related adjustments to enhance drivability, tyre efficiency, dynamic response of the automotive, and assess and improve driver approach.

Right here, I’ll cowl a couple of strategies used to course of and visualise the information and contact on how they’re analysed to supply significant assessments into the automobile dynamics and driver’s enter within the lap.

Kicking off with the subject of roll stiffness, you’ll recognise this one from the springs & dampers article.

Roll Stiffness Distributions

With damper potentiometers or, higher but, laser trip top sensors, it’s attainable to know the quantity by which the chassis is rolling in response to lateral acceleration.

 By measuring spring compression, potentiometers permit us to know the roll angle induced by elastic weight switch. Moreover, mixed with laser trip top sensors, an commentary of the tyre deflection brought on by geometric weight switch may also be made.

Utilizing some easy maths, the linear displacements measured by this instrumentation are used to determine the roll angle for every axle on the automotive at a given lateral acceleration.

Roll angles skilled by every axle are very indicative of the roll stiffness distribution of a race automotive

Roll angles can then be associated to one another utilizing the idea of a roll angle ratio. The roll angle ratio skilled by the chassis provides an understanding of the roll stiffness distribution of the automotive, which, as you learnt from the earlier article on chassis, is a parameter used to tune the race automotive’s stability. 

Plotting this knowledge on an X-Y scatter chart permits us to know that the entrance/rear roll angle ratio, on this case, is round 0.65, which allows us to recognise that the automobile has a forward-biased roll stiffness distribution.

Scatter charts are a good way of visualising relationships and correlations in knowledge. Proven right here is the entrance vs. rear roll angle knowledge. From this, the gradient may be understood.

There’s no magic quantity to search for, however utilizing driver suggestions and knowledge of tyre degradation over a run, a ‘goal’ roll ratio that gives the very best efficiency for a selected race automotive may be understood – a necessary reference for a chassis setup.

When making roll stiffness adjustments to affect stability, the intention is to take care of the overall roll stiffness (i.e. roll gradient) and alter the quantity of this stiffness distributed between every axle.

Understeer Angles

Staying with the topic of chassis stability, one other nice metric to quantify is the deviation of the steered angle to the best ‘Ackermann’ steering angle at any second.

The Ackermann steering angle is calculated in regards to the wheelbase and the cornering radius and is, subsequently, a operate of velocity and lateral acceleration. For instance, if the Ackermann steering angle for the surface wheel in a given nook is 5deg and the steered angle is 7deg, the understeer angle is +2deg. Damaging values of understeer angle point out oversteer.

Ackermann angle illustration displaying its relationship with wheelbase (WB) and nook radius (R)

Recording the instantaneous understeer angle and additional but averaging it all through a lap is a robust device to know the stability of the chassis for a given setup which is useful in quantitatively assessing setup adjustments. Nonetheless, secondly, we are able to use it to judge and predict tyre degradation over a stint. A pattern of accelerating or lowering understeer angle as gasoline is used and tyre put on is effective suggestions into preliminary setup targets.

The understeer angle is an efficient method of understanding the stability of a chassis.

Observe: The calculations of Ackermann angle are an assumption and reduce in accuracy because the tyre slip angles construct in the direction of a peak and the tyre transitions from linear to non-linear character, however for these functions are adequate to point what’s occurring.

Damper Histograms

Histograms are comparatively easy diagrams that permit visualisation of the frequency at which a selected variable happens, organised inside discrete intervals.

In our case, damper histograms are a method of displaying the time which a selected damper spends at discrete damper piston velocity ranges. This metric helps perceive the dampers dissipated vitality in each compression and rebound strokes over a lap or observe part.

Damper histograms are helpful to know the relative time a damper spends at numerous piston velocity intervals.

Low-speed damping, which covers shaft speeds of as much as round 0.15m/s, is primarily involved with physique management in displacement modes of roll, pitch and heave. In distinction, high-speed actions of > 0.15m/s may be thought of as major enter from the observe floor, affecting unsprung mass and the related variations involved patch loading.

As most motorsport dampers are 4-way adjustable (excessive and low-speed rebound & compression), this sort of visualisation permits us to think about the damping motion in every velocity vary and make changes in the direction of optimising efficiency in every of them.

A shorter, wider histogram signifies free low-speed damping with comparatively excessive damper velocities. In distinction, a taller, slimmer histogram profile tells you that there’s extra time spent at decrease damper speeds. For a given automotive and observe, this is able to point out comparatively excessive damping charges.

There’s no proper or mistaken form for a histogram; the profile to goal for is determined by the appliance at hand. At a minimal, it’s logical to infer that environment friendly shock motion dissipates an equal quantity of vitality in compression and rebound stroke. For many instances, what ought to be focused is an asymmetrical profile – a histogram is a helpful device in guaranteeing that damping ratios are well-matched left-right and front-rear.

Driver metrics; Throttle %, curvature, braking effort

In addition to the automobile behaviour, measured knowledge permits the driving force enter to be quantified and analysed. By relating these portions to automobile dynamics concept, it’s a highly effective device for suggestions and to develop the driving force to make sure they’re getting the very best from the race automotive; listed here are a few of the vital ones.

Throttle %

The % of a lap which the driving force spends at full throttle is a necessary metric on two fronts. All different issues being equal, if a driver is spending extra time at full throttle, their common velocity can be greater, which might recommend a decrease lap-time.

Utilizing this metric, we are able to examine driving strategies over totally different laps and consider the evolution of a automotive’s efficiency over an occasion – rear tyre degradation could be a straightforward one to identify via a decrease time at max throttle.

The typical throttle % may also be used to evaluate numerous setup adjustments. It may present a extra rearward aero bias as profitable in addressing some traction points, or some damping changes are settling the rear finish to permit the driving force to get on the ability earlier.

Curvature

The inverse of the cornering radius (1/R) defines the curvature adopted by the automobile. It follows that curvature is excessive when the cornering radius is low, so we are able to deduce that conserving curvature as little as attainable implies that the driving force is making the nook as ‘huge’ as attainable, carrying as a lot velocity as attainable and taking the quickest strains via a nook.

For the reason that optimum line via a nook can hardly ever be checked out in isolation attributable to its dependence on the subsequent observe characteristic, the curvature isn’t a device to point out you the best line, nevertheless it does permit sensible assessments to be made.

Comparability:

Evaluating the curvature hint between two drivers at a selected nook or single driver practising strategies is a good way to visualise the strains taken. With sector occasions, we are able to quantify the faster line by turn-in and apex places.

Plotting curvature permits driving types to be assessed for tempo. Low common curvature over a lap usually correlates with low lap time.

Consistency:

Plotting the typical curvature achieved by a driver relative to lap quantity is an efficient method of understanding how constant the driving force is all through a race. Most often, a decrease common curvature signifies a faster lap time.

This isn’t an exhaustive checklist and merely scratches the floor on what’s attainable with knowledge evaluation. Nonetheless, it references the connection between the significance of knowledge for automobile dynamics and clear efficiency outcomes in design and growth.

On the observe, it’s the function of the Race Engineer, Information Engineer or Efficiency Engineer to work with the information from the automotive to narrate to the basics of car dynamics and implement adjustments to the setup to get the behaviour appropriate for a given session.

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