Paul Jeffrey
Premium
Ahead of a big December update for RaceRoom Racing Experience, Sector3 Studios physics developer @Alex Hodgkinson has written up a great blog post explaining some of the physics changes coming to the sim.
Many of you will be aware of the world Alex has undertaken at RaceRoom Racing Experience since starting with the studio in recent years, having been one of the key individuals to bring a range of new and impressive physics and force feedback developments to the simulation, and it looks like a few more changes are on the way this month too... as Alex explains in his recent blog posting below:
...
Tyre Models
No version/empty cell
Pre-2017 development. Not really sure about the method here and didn't really dig too deeply in to it, so there's not much to say.
V1 (2017)
This was my first attempt at making a tyre generator tool for RaceRoom in excel. It's actually built on something I started for rFactor in around 2009, adapted to suit RaceRoom. It's quite basic truth be told as all tyres use the same core characteristics. Slip angles, slip reaction and grip curves are all exactly the same across the different tyre sizes. Different tyre weights are accounted for, and affect unsprung weight as well as the spinning inertia of each corner.
V2 (2018)
Built on the work above, this version takes into account a few more criteria in order to generate each tyre's character. The slip curves are updated to match some findings, which actually give a narrower operating window than previously. Cars are more responsive, but grip drops off more quickly.
V3 (2019)
With this update tyre construction becomes more of a factor. How much the optimum slip angle changes as the tyre loads up is now calculated per tyre size and according to tyre construction. In addition, each tyre's vertical stiffness (how much it compresses as downforce builds, for example) is particular to each individual tyre width, sidewall height, construction and weight.
We added flat spots at this point. Each tyre is divided into radial segments which can wear down at different rates depending on how they're treated during the tyre's life.
Also started to implement different compounds with differing characteristics other than the obvious grip and wear rates. Harder tread compounds tend to have softer construction as they operate under less load. If soft compounds had the same construction as hard compounds, they would feel mushy as they're under more load.
Different compounds also have differing grip drop off at different wear levels, an example of which is below:
V4 (2020)
Moving from V3 to V4 was the biggest step of all. Until now, optimum camber was a set value - tyre grip peaked at whatever that value was set at and dropped of either side. With V4.0, that code was re-written. Now the optimum camber changes according to how much load is on the tyre. The greater the load, the higher the optimal camber. So we can now take two different cars, one heavy and one light, fit the same sized tyres to them and simply due to the different loadings the camber requirements will be different. Nice stuff!
Slip angles are calculated per tyre, and are related to tread width, aspect ratio, sidewall height and construction. Now if we change tyre sizes on a car, the characterises change slightly.
The final big thing was a creation of a new slip curve generator. This now adjusts slip/grip curves slightly per tyre to account for different characteristics. As an example, for the same construction, a taller sidewall will tend to flex a bit more initially but then be more progressive as load increases. Lower profile tyres will flex less initially, so slip angles are lower, but then drop off is a bit steeper afterwards.
In other words, now we're getting really close to just punching in a tyre size to our calculator and getting something completely bespoke out.
V4.1 (2020)
This is really just a small tweak on the V4.0, as the .1 suggests. I had a re-think on how to calculate slip ratios and applied it. Gives the calculator tool a wider operating range which will allow a larger range of tyres to be generated without having to 'fudge' at any point.
The following cars will be updated with the new tyre model:
Engine Maps, Throttle Maps, Turbo Updates & More
I'll start by going straight in; when the December update drops, your driveline tuning page will look like this:
With two new new additions:
Engine Braking Reduction:
This is something we always had to tinker with behind the scenes. The real power of this became apparent when we started to look at dialling out some tricky behaviours from some of our cars. Namely the off-throttle any-speed unrecoverable spins, also known as instabins. Some of us rarely had any trouble with such behaviour whereas others were very vocal. It turned out those who had little issue with it were naturally keeping a little bit of throttle applied at corner entry to keep the car stable. Those who regularly spun were completely off the accelerator pedal on entry.
This lead us to realise that some drivers would benefit from a little bit of throttle being applied in order to reduce the engine braking and keep the car stable, even when they were not pressing their actual pedal. We also realised that would not suit everybody as agility is sacrificed. Thus the answer was to make it adjustable and that's when this slider was conceived.
More clicks/higher values here will decrease the engine braking and make the car more stable when not pressing the accelerator pedal.
It's worth mentioning that the name engine braking reduction was decided on as the normal English idle adjustment doesn't translate well to other languages, as it intrinsically linked to when the engine is at tickover revs and thus easily confused.
Porpoising and How to Stop It Happening
Porpoising
Verb
To move through the water like a porpoise, alternately rising above it and submerging.
"the boat began to porpoise badly"
or in our case to drive along the road, alternately rising and diving.
This is a phenomena which is specific to cars which rely heavily on ground-effect to create downforce.
A ground effect car uses a sculpted lower surface in order to create an area of low pressure beneath it. This low pressure area causes the car to be 'sucked' down towards the ground:
The forces generated by ground effect are immense. At the peak of their development in the early 90s ground effect Group C cars were producing more than double the downforce of anything that's racing today.
However, ground effect development is far from plain sailing. This style of downforce generation can be hugely sensitive to the pitch, yaw and roll of a car's body. So much so that a Williams F1 engineer once admitted that if the ride height changed as much as a few mm, downforce generation could drop by as much as half. One of the biggest issues that GT, Prototype and Touring cars have with ground effects is when the front of the car gets too close to the ground. Air flow to the underbody is cut off, which quite literally switches off the downforce. This is less of an issue with single seaters as air can flow more freely around the front of the car given that the front wheels are not enclosed.
This sudden switching off of downforce causes the car to jump upwards as the springs are no longer being compressed by the huge downforce. Once the ride height has risen up and the airflow has re-attached, the downforce builds quickly again, forcing the car back towards the ground and the whole cycle starts over. To an onlooker, the car can be seen to be physically jumping up and down, like a Porpoise swimming in the sea. Pay particular attention to the high speed sections in the video below, especially this section to see what this looks like inside RaceRoom;
Aerodynamic solutions
So how do you solve it? For the first race teams to experience it, it was a real conundrum. Considering how much downforce the GTP cars of the late 80s and early 90s were making and how stiffly they were sprung to keep them from scraping the ground, the porpoising effect was incredibly violent.
Once they had worked out that the route cause was cars running too close to the ground, they increased spring rates and damper rebound settings. The stiffer springs would increase the ride height at speed, and the rebound would stop the car from springing up so violently should the underbody stall. That however was a less than ideal solution as it dramatically increased the load and also the load variation of the tyres, meaning mechanical grip reduced and tyre failures became more frequent. Some teams also used very small bump rubber gaps meaning the cars had effectively no suspension at speed.
Something better was needed.
One example is the Nissan NPTI team's solution of installing front diffuser vents, shown in the picture below above the car's headlights. Referred to as BASSholes, they syphoned off the airflow from inside the front wheel arches even when the splitter was running extremely close to the ground, thus reducing the possibility of total downforce loss. Louvres placed over front wheel arches are a more common solution which is still seen nowadays and which performs a similar task.
The most common solution applied to most flat-floored race cars since the mid/late 90s is to scallop out the centre section of the splitter, highlighted below in yellow. Air flow in though this scalloped out section will not be blocked off should the rest of the splitter touch the ground, so downforce production can continue.
Third Springs
I'm often asked what the third spring on a race car is for, and this is it's intended purpose; to hold the car at an optimal ride height so that the underbody downforce production can remain optimal and consistent.
Look at the picture above and you'll see that the third (central) spring is connected to both suspension pushrods as well as both left and right damper/spring assemblies. There's also a pivot on that connection which means the left and the right damper can move independently, but should a force act on both left and right damper the central spring is also compressed. So any force pushing the car down towards the ground equally on both corners of an axle needs to compress left spring, right spring and central spring.
This now means that there's no need to run exceptionally stiff 'corner' springs as the central spring handles that load. Thus suspension compliance can be increased and mechanical grip will improve.
Third springs can also be easily tuned to change the pitch of the car as speed changes, allowing drag to be reduced at speed.
For reasons of cost-control, third springs are outlawed in a lot of race series these days. This has meant that cars have had to resort to bump rubbers to mimic the effect. There's a lot I'd like to say about this, but seeing as most of my knowledge about this has been gleaned from the engineers who design race winning ADAC, DTM and GT3 dampers for KW, I think I'll hold off telling the world their secrets!
Active suspension
There are many types of active suspension system, all of which are outlawed in modern race series with no exceptions. One example would be a system which 'learns' a circuit as well as a car's aerodynamic attributes. Springs and dampers are replaced with linear electromagnetic motors which are programmed to hold the car at predefined ride heights in various situations or points on the circuit. Takes a huge amount of number crunching to get right, but the results are total optimisation, or if you're a 1992 Williams FW14B crushing domination.
What you can do about it
Let's be clear, a little bit of porposing at high speed in a straight may not have any detrimental effects. It might make your motion rig shake a lot or your buttkickers go crazy, but that is what it's supposed to do.
It becomes a real issue when it starts to happen in the middle of turns and it can send you straight to the scene of a huge high-speed accident before you even know what's happened. Now hopefully we've spent enough time setting up our cars so that doesn't happen on our default setups, but should you start to tinker it may well become a factor.
If you find a car is porposing so hard you loose control, here's what you should do:
Original Source: Sector3 Studios.
RaceRoom Racing Experience is available now, exclusively to PC.
Want to get the most from your installation? Start a thread and ask a question in the R3E Sub Forum right here at RaceDepartment!
Many of you will be aware of the world Alex has undertaken at RaceRoom Racing Experience since starting with the studio in recent years, having been one of the key individuals to bring a range of new and impressive physics and force feedback developments to the simulation, and it looks like a few more changes are on the way this month too... as Alex explains in his recent blog posting below:
...
Tyre Models
No version/empty cell
Pre-2017 development. Not really sure about the method here and didn't really dig too deeply in to it, so there's not much to say.
V1 (2017)
This was my first attempt at making a tyre generator tool for RaceRoom in excel. It's actually built on something I started for rFactor in around 2009, adapted to suit RaceRoom. It's quite basic truth be told as all tyres use the same core characteristics. Slip angles, slip reaction and grip curves are all exactly the same across the different tyre sizes. Different tyre weights are accounted for, and affect unsprung weight as well as the spinning inertia of each corner.
V2 (2018)
Built on the work above, this version takes into account a few more criteria in order to generate each tyre's character. The slip curves are updated to match some findings, which actually give a narrower operating window than previously. Cars are more responsive, but grip drops off more quickly.
V3 (2019)
With this update tyre construction becomes more of a factor. How much the optimum slip angle changes as the tyre loads up is now calculated per tyre size and according to tyre construction. In addition, each tyre's vertical stiffness (how much it compresses as downforce builds, for example) is particular to each individual tyre width, sidewall height, construction and weight.
We added flat spots at this point. Each tyre is divided into radial segments which can wear down at different rates depending on how they're treated during the tyre's life.
Also started to implement different compounds with differing characteristics other than the obvious grip and wear rates. Harder tread compounds tend to have softer construction as they operate under less load. If soft compounds had the same construction as hard compounds, they would feel mushy as they're under more load.
Different compounds also have differing grip drop off at different wear levels, an example of which is below:
V4 (2020)
Moving from V3 to V4 was the biggest step of all. Until now, optimum camber was a set value - tyre grip peaked at whatever that value was set at and dropped of either side. With V4.0, that code was re-written. Now the optimum camber changes according to how much load is on the tyre. The greater the load, the higher the optimal camber. So we can now take two different cars, one heavy and one light, fit the same sized tyres to them and simply due to the different loadings the camber requirements will be different. Nice stuff!
Slip angles are calculated per tyre, and are related to tread width, aspect ratio, sidewall height and construction. Now if we change tyre sizes on a car, the characterises change slightly.
The final big thing was a creation of a new slip curve generator. This now adjusts slip/grip curves slightly per tyre to account for different characteristics. As an example, for the same construction, a taller sidewall will tend to flex a bit more initially but then be more progressive as load increases. Lower profile tyres will flex less initially, so slip angles are lower, but then drop off is a bit steeper afterwards.
In other words, now we're getting really close to just punching in a tyre size to our calculator and getting something completely bespoke out.
V4.1 (2020)
This is really just a small tweak on the V4.0, as the .1 suggests. I had a re-think on how to calculate slip ratios and applied it. Gives the calculator tool a wider operating range which will allow a larger range of tyres to be generated without having to 'fudge' at any point.
The following cars will be updated with the new tyre model:
- GT2 (new)
- GT3
- GT4
- Audi TT Cup
- Audi TT VLN
- Touring Classics
- DTM 1992
- Group 2
- Group 4
- Group 5
- 2003 DTM Mercedes
- 2005 DTM Mercedes
- Formula RaceRoom 1990
- Formula RaceRoom Junior
- GTE
- Hillclimb Icons
- Volkswagen ID.R
- NSU TT
- Porsche GT3 Cup Sprint
- Porsche GT3 Cup Endurance
- Porsche 964 Cup
- Silhouettes
- WTCC 2014/15/16/17
- WTCR
- Cupra E-Racer
- DTM 2020
- Porsche Cayman Cup
Engine Maps, Throttle Maps, Turbo Updates & More
I'll start by going straight in; when the December update drops, your driveline tuning page will look like this:
With two new new additions:
Engine Braking Reduction:
This is something we always had to tinker with behind the scenes. The real power of this became apparent when we started to look at dialling out some tricky behaviours from some of our cars. Namely the off-throttle any-speed unrecoverable spins, also known as instabins. Some of us rarely had any trouble with such behaviour whereas others were very vocal. It turned out those who had little issue with it were naturally keeping a little bit of throttle applied at corner entry to keep the car stable. Those who regularly spun were completely off the accelerator pedal on entry.
This lead us to realise that some drivers would benefit from a little bit of throttle being applied in order to reduce the engine braking and keep the car stable, even when they were not pressing their actual pedal. We also realised that would not suit everybody as agility is sacrificed. Thus the answer was to make it adjustable and that's when this slider was conceived.
More clicks/higher values here will decrease the engine braking and make the car more stable when not pressing the accelerator pedal.
It's worth mentioning that the name engine braking reduction was decided on as the normal English idle adjustment doesn't translate well to other languages, as it intrinsically linked to when the engine is at tickover revs and thus easily confused.
Porpoising and How to Stop It Happening
Porpoising
Verb
To move through the water like a porpoise, alternately rising above it and submerging.
"the boat began to porpoise badly"
or in our case to drive along the road, alternately rising and diving.
This is a phenomena which is specific to cars which rely heavily on ground-effect to create downforce.
A ground effect car uses a sculpted lower surface in order to create an area of low pressure beneath it. This low pressure area causes the car to be 'sucked' down towards the ground:
The forces generated by ground effect are immense. At the peak of their development in the early 90s ground effect Group C cars were producing more than double the downforce of anything that's racing today.
However, ground effect development is far from plain sailing. This style of downforce generation can be hugely sensitive to the pitch, yaw and roll of a car's body. So much so that a Williams F1 engineer once admitted that if the ride height changed as much as a few mm, downforce generation could drop by as much as half. One of the biggest issues that GT, Prototype and Touring cars have with ground effects is when the front of the car gets too close to the ground. Air flow to the underbody is cut off, which quite literally switches off the downforce. This is less of an issue with single seaters as air can flow more freely around the front of the car given that the front wheels are not enclosed.
This sudden switching off of downforce causes the car to jump upwards as the springs are no longer being compressed by the huge downforce. Once the ride height has risen up and the airflow has re-attached, the downforce builds quickly again, forcing the car back towards the ground and the whole cycle starts over. To an onlooker, the car can be seen to be physically jumping up and down, like a Porpoise swimming in the sea. Pay particular attention to the high speed sections in the video below, especially this section to see what this looks like inside RaceRoom;
Aerodynamic solutions
So how do you solve it? For the first race teams to experience it, it was a real conundrum. Considering how much downforce the GTP cars of the late 80s and early 90s were making and how stiffly they were sprung to keep them from scraping the ground, the porpoising effect was incredibly violent.
Once they had worked out that the route cause was cars running too close to the ground, they increased spring rates and damper rebound settings. The stiffer springs would increase the ride height at speed, and the rebound would stop the car from springing up so violently should the underbody stall. That however was a less than ideal solution as it dramatically increased the load and also the load variation of the tyres, meaning mechanical grip reduced and tyre failures became more frequent. Some teams also used very small bump rubber gaps meaning the cars had effectively no suspension at speed.
Something better was needed.
One example is the Nissan NPTI team's solution of installing front diffuser vents, shown in the picture below above the car's headlights. Referred to as BASSholes, they syphoned off the airflow from inside the front wheel arches even when the splitter was running extremely close to the ground, thus reducing the possibility of total downforce loss. Louvres placed over front wheel arches are a more common solution which is still seen nowadays and which performs a similar task.
The most common solution applied to most flat-floored race cars since the mid/late 90s is to scallop out the centre section of the splitter, highlighted below in yellow. Air flow in though this scalloped out section will not be blocked off should the rest of the splitter touch the ground, so downforce production can continue.
Third Springs
I'm often asked what the third spring on a race car is for, and this is it's intended purpose; to hold the car at an optimal ride height so that the underbody downforce production can remain optimal and consistent.
Look at the picture above and you'll see that the third (central) spring is connected to both suspension pushrods as well as both left and right damper/spring assemblies. There's also a pivot on that connection which means the left and the right damper can move independently, but should a force act on both left and right damper the central spring is also compressed. So any force pushing the car down towards the ground equally on both corners of an axle needs to compress left spring, right spring and central spring.
This now means that there's no need to run exceptionally stiff 'corner' springs as the central spring handles that load. Thus suspension compliance can be increased and mechanical grip will improve.
Third springs can also be easily tuned to change the pitch of the car as speed changes, allowing drag to be reduced at speed.
For reasons of cost-control, third springs are outlawed in a lot of race series these days. This has meant that cars have had to resort to bump rubbers to mimic the effect. There's a lot I'd like to say about this, but seeing as most of my knowledge about this has been gleaned from the engineers who design race winning ADAC, DTM and GT3 dampers for KW, I think I'll hold off telling the world their secrets!
Active suspension
There are many types of active suspension system, all of which are outlawed in modern race series with no exceptions. One example would be a system which 'learns' a circuit as well as a car's aerodynamic attributes. Springs and dampers are replaced with linear electromagnetic motors which are programmed to hold the car at predefined ride heights in various situations or points on the circuit. Takes a huge amount of number crunching to get right, but the results are total optimisation, or if you're a 1992 Williams FW14B crushing domination.
What you can do about it
Let's be clear, a little bit of porposing at high speed in a straight may not have any detrimental effects. It might make your motion rig shake a lot or your buttkickers go crazy, but that is what it's supposed to do.
It becomes a real issue when it starts to happen in the middle of turns and it can send you straight to the scene of a huge high-speed accident before you even know what's happened. Now hopefully we've spent enough time setting up our cars so that doesn't happen on our default setups, but should you start to tinker it may well become a factor.
If you find a car is porposing so hard you loose control, here's what you should do:
- Raise the ride height, particularly at the front
- Increase spring rates of corner springs and/or third springs if the car has them
- Increase high-speed rebound damping
- Porposing is often triggered by hitting a bump at high-speed. See if it's possible to drive a different line which avoids it.
Original Source: Sector3 Studios.
RaceRoom Racing Experience is available now, exclusively to PC.
Want to get the most from your installation? Start a thread and ask a question in the R3E Sub Forum right here at RaceDepartment!
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