Hi folks.
There's a major new series coming for the Race Engineer blog. We'll be covering setup sheets in quite a bit of detail.
And, we're going to offer content for download in the Setup Sheet series, as well as in future ones. I'll be using http://www.scribd.com/. If you're not familiar with the site, it's sort of analogous to iTunes, only for documents instead of music and video.
Every document will be available free as a PDF, either to print or download. Not free beer, not free lunch, but the best I can do in a blog.
Many will also be available for purchase in the native format, which will typically be XLS. For forms with a lot of formatting and information, like setup sheets, this will save quite a bit of time compared to creating your own version from scratch. For real engineering tools, you get all the calcs behind the visible input and results.
I puzzled some over pricing. Some of this stuff is pretty simple, but some of it represents literally days, if not weeks, of work. Radiohead's pricing strategy of letting the user decide how much to pay was intriguing, but Scribd doesn't work that way. I do need to get something for my effort, but on the other hand I want to make this stuff widely available. In the end, I decided to make the forms $10 each, unless they are really simple. You're already paying that for an album download on iTunes or Amazon. And it's waaaaay cheap compared to the time you'd spend duplicating it. Real engineering tools will be priced according to their content.
The imbedded PDFs will display a frame from Scribd. Preceding each will be two links, one to the PDF, one to the native format.
Click the PDF link to print or get the free download.
Click the native format link to purchase. There will be a big yellow button "Buy Now" on the right side of the screen which takes you to the typical online purchase dialog to enter your credit card info.
The Scribd site asks you to register to get the free download or print. Wish they didn't do that, but at least it's free. Oh well...
As a sample, here's a setup sheet for an IRL car in 1998. Left or right click on the Scribd window to activate the various controls, zoom, and so on.
PDF - Print or Free Download
XLS - Purchase Download
Please drop me a comment if all this doesn't work correctly for you.
Friday, December 25, 2009
Thursday, October 29, 2009
Vehicle Dynamics, Vol. 1 - Thinking in 3 Dimensions
At the outset, I promised that this blog wouldn't be a vehicle dynamics tutorial. Still true. Get out your Milliken, Gillespie, and even Carroll Smith's timeless "Tune to Win".
But, here's an observation.
When many race engineers and chassis tuners think about handling, they focus heavily on roll moment and roll stiffness. That's a vital topic, but it's only part of the total handling equation.
The car operates in 3-dimensional space, with forces and moments acting on it along the X, Y, and Z axes (longitudinal, lateral, and vertical to regular mortals). At any point in time, its handling is dependent on how it reacts to ALL SIX of those forces and moments. Limiting your thinking to roll only addresses lateral forces and longitudinal moments.
For example:
1-Savvy oval track engineers have long been focused on the vertical forces from both banking and aerodynamics.
2-When a car is cornering, it is rotating around its Z (vertical) axis. The are a number of very significant sources of moments around that axis, some of which are under the control of the engineer.
There is much to be learned from data acquisition. Install a steering travel potentiometer calibrated in spindle degrees. Install a 3-axis accelerometer and a yaw rate sensor. Just in the Z-axis, you can calculate understeer gradient (see Gillespie), yaw gain (yaw rate divided by steering), and stability index (see Danny Nowlan's excellent recent series in Race Car Engineering magazine). Use your imagination. There's more.
Apologies for the lack of illustrating diagrams. I'm still too busy with real work to explore the tools that Blogspot offers. Eventually.
The proverbial word to the proverbial wise should be sufficient. Go for it!
But, here's an observation.
When many race engineers and chassis tuners think about handling, they focus heavily on roll moment and roll stiffness. That's a vital topic, but it's only part of the total handling equation.
The car operates in 3-dimensional space, with forces and moments acting on it along the X, Y, and Z axes (longitudinal, lateral, and vertical to regular mortals). At any point in time, its handling is dependent on how it reacts to ALL SIX of those forces and moments. Limiting your thinking to roll only addresses lateral forces and longitudinal moments.
For example:
1-Savvy oval track engineers have long been focused on the vertical forces from both banking and aerodynamics.
2-When a car is cornering, it is rotating around its Z (vertical) axis. The are a number of very significant sources of moments around that axis, some of which are under the control of the engineer.
There is much to be learned from data acquisition. Install a steering travel potentiometer calibrated in spindle degrees. Install a 3-axis accelerometer and a yaw rate sensor. Just in the Z-axis, you can calculate understeer gradient (see Gillespie), yaw gain (yaw rate divided by steering), and stability index (see Danny Nowlan's excellent recent series in Race Car Engineering magazine). Use your imagination. There's more.
Apologies for the lack of illustrating diagrams. I'm still too busy with real work to explore the tools that Blogspot offers. Eventually.
The proverbial word to the proverbial wise should be sufficient. Go for it!
Thursday, October 22, 2009
Modifying Production Suspension Geometry
Well, after literally weeks of not having the time to do a new blog post, I was looking forward to a new post on testing. I'd even spent two whole airline flights outlining it.
But then, today, I had a rush job to prepare some modifications to the geometry of a production-based race car. And, surprisingly, that project generated the theme for a new blog entry. So, here we go...
We'll conveniently assume that you have already measured the car (probably a whole blog post of its own) and that you are already up and running with kinematics software. Bill Mitchell is an old friend, and I've used his programs for years.
The starting point to the whole process is learning what changes the race series rules will allow.
If the rules allow modifying or replacing the spindle/upright, you are most of the way to a from-scratch design. The steering geometry will be yours to invent, as well as most of the instant center-related items like camber gain and static roll center location. The series rules on inner pickup points will mainly handicap the ability to design the desired anti-squat or anti-dive, and will likely effect roll center migration.
If you're stuck with using the original upright geometry (with or without a usually tight spec on allowed modifications), then the freedom to improve the goemetry is much more constrained.
So, here's the basic situation:
-You will never be able to get a geometry with optimized roll center location and movement, camber gain, anti- geometry, steering geometry, and spring/shock motion ratio. Give up on that notion.
-The series rules and the car's original geometry will limit your options.
-It's pretty common that a geometry modification that helps you reach one of your targets will hurt your ability to reach another.
So, it follows that the MOST important job is NOT necessarily the design itself. It is, instead, successfully figuring out what change is most important for your car. For example, is it more important to lower the roll center, increase the anti-dive, or reduce the camber gain? Having decided what change is most important for your car, then it's time to review whether the almost-unavoidable tag-along changes will hurt the car, and understand how and how much they will hurt it. Finally, consistent with the theme of many of my posts, you will now hear me say that experience and education will only improve your chances of identifying what the car needs, not guarantee it.
Be prepared to be surprised. Design more than one option and test them all. This also guards against two common foibles:
-Believing that you know more about suspension goemetry than the car's designer. Maybe so, maybe not...
-Believing that you know what the car needs. Surprises abound...
Keep your mind open. Spacers, offset bushings, parts swapping, machining, moving inner pickup points, allowed tolerances, and fabrication may be among the options for revising the production geometry. Study the rules carefully.
Keep in mind that your changes should ideally be either high-confidence or reversible. It's a big plus to be able to A-B-A test them, too. If the changes require major fabrication or machining, or are irreversible, then they must be high-confidence as well.
Consider a simplified or partial version of the expected direction. For example, maybe it's an easy job to move the roll center 0.50", but a hard one to move it 1.00". But you want to move it 1.00", don't you? So, move it 0.50" and test that. If the car and driver like it, now there' s ample justification to try the more difficult second step. If not, much work and money was likely saved.
As always, geometry is just part of a total package. Be prepared to tune bars, springs, and shocks to optimize the car for the new geometry.
Good luck!
But then, today, I had a rush job to prepare some modifications to the geometry of a production-based race car. And, surprisingly, that project generated the theme for a new blog entry. So, here we go...
We'll conveniently assume that you have already measured the car (probably a whole blog post of its own) and that you are already up and running with kinematics software. Bill Mitchell is an old friend, and I've used his programs for years.
The starting point to the whole process is learning what changes the race series rules will allow.
If the rules allow modifying or replacing the spindle/upright, you are most of the way to a from-scratch design. The steering geometry will be yours to invent, as well as most of the instant center-related items like camber gain and static roll center location. The series rules on inner pickup points will mainly handicap the ability to design the desired anti-squat or anti-dive, and will likely effect roll center migration.
If you're stuck with using the original upright geometry (with or without a usually tight spec on allowed modifications), then the freedom to improve the goemetry is much more constrained.
So, here's the basic situation:
-You will never be able to get a geometry with optimized roll center location and movement, camber gain, anti- geometry, steering geometry, and spring/shock motion ratio. Give up on that notion.
-The series rules and the car's original geometry will limit your options.
-It's pretty common that a geometry modification that helps you reach one of your targets will hurt your ability to reach another.
So, it follows that the MOST important job is NOT necessarily the design itself. It is, instead, successfully figuring out what change is most important for your car. For example, is it more important to lower the roll center, increase the anti-dive, or reduce the camber gain? Having decided what change is most important for your car, then it's time to review whether the almost-unavoidable tag-along changes will hurt the car, and understand how and how much they will hurt it. Finally, consistent with the theme of many of my posts, you will now hear me say that experience and education will only improve your chances of identifying what the car needs, not guarantee it.
Be prepared to be surprised. Design more than one option and test them all. This also guards against two common foibles:
-Believing that you know more about suspension goemetry than the car's designer. Maybe so, maybe not...
-Believing that you know what the car needs. Surprises abound...
Keep your mind open. Spacers, offset bushings, parts swapping, machining, moving inner pickup points, allowed tolerances, and fabrication may be among the options for revising the production geometry. Study the rules carefully.
Keep in mind that your changes should ideally be either high-confidence or reversible. It's a big plus to be able to A-B-A test them, too. If the changes require major fabrication or machining, or are irreversible, then they must be high-confidence as well.
Consider a simplified or partial version of the expected direction. For example, maybe it's an easy job to move the roll center 0.50", but a hard one to move it 1.00". But you want to move it 1.00", don't you? So, move it 0.50" and test that. If the car and driver like it, now there' s ample justification to try the more difficult second step. If not, much work and money was likely saved.
As always, geometry is just part of a total package. Be prepared to tune bars, springs, and shocks to optimize the car for the new geometry.
Good luck!
Sunday, September 13, 2009
I haven't forgotten you
Yes, I know the last new post was July 29. No, I absolutely HAVE NOT given up on the Race Engineer blog.
I have simply been covered up, in a major way, since late July. In today's business climate, that means, for me, multiple small jobs instead of one or two big ones. And, there's overhead associated with that. And, for you, an eventual blog post or two about how to get work, the new-job startup process, and juggling multiple clients.
There are also a number of new posts that are jelling in concept. Shortly, we'll commence two series, one on testing and one on setup sheets.
Hang in there, folks. Thanks for your understanding.
I have simply been covered up, in a major way, since late July. In today's business climate, that means, for me, multiple small jobs instead of one or two big ones. And, there's overhead associated with that. And, for you, an eventual blog post or two about how to get work, the new-job startup process, and juggling multiple clients.
There are also a number of new posts that are jelling in concept. Shortly, we'll commence two series, one on testing and one on setup sheets.
Hang in there, folks. Thanks for your understanding.
Wednesday, July 29, 2009
Philosophy, Vol. 1 Revisited
I'll touch on this subject one more time and then let it rest.
Just to show that our preconceived notions of what the racecar needs are often wrong, and that slavish devotion to simplistic notions of vehicle dynamics are equally wrong, it happened again this weekend at Autobahn.
One car I engineered felt like it needed a crisper turn-in with more support. But, it was worse with a slightly stiffer front bar, not better - as is often the case. Turns out it needed more low-speed bump damping and less front bar.
Another car I engineered lost front grip with a lower nose on the bump damping curve, despite expectations that it would gain front grip from that change. After all, the rear had just gained grip from a similar change.
At the next event, I may have to abandon these seemingly solid conclusions, too, if they prove to have been track-specific.
On my soapbox for the last time on this subject, for at least the next week:
-Listen to the car and the driver. They are reality. Your preconceived notions are not.
-The solution to a question may go contrary to common theory or your experience.
Just to show that our preconceived notions of what the racecar needs are often wrong, and that slavish devotion to simplistic notions of vehicle dynamics are equally wrong, it happened again this weekend at Autobahn.
One car I engineered felt like it needed a crisper turn-in with more support. But, it was worse with a slightly stiffer front bar, not better - as is often the case. Turns out it needed more low-speed bump damping and less front bar.
Another car I engineered lost front grip with a lower nose on the bump damping curve, despite expectations that it would gain front grip from that change. After all, the rear had just gained grip from a similar change.
At the next event, I may have to abandon these seemingly solid conclusions, too, if they prove to have been track-specific.
On my soapbox for the last time on this subject, for at least the next week:
-Listen to the car and the driver. They are reality. Your preconceived notions are not.
-The solution to a question may go contrary to common theory or your experience.
Thursday, July 9, 2009
Springs, Part 2
Tuning with springs
If there were any question that springs are a powerful tuning tool, we'd only have to look at the extensive spring inventory in the typical race trailer and at the amount of time the typical race car spends on the setup pad getting springs changed. A complete treatment of spring tuning would probably be a whole chapter of a book. Today, we'll just offer some fundamentals to stimulate thought.
There are two major influences that springs always have:
-Dynamic ride height changes from longitudinal load transfer,banking loads, and aero loads.
-Roll stiffness and the resulting front-to-rear distribution of roll couple
Tackling these first...
Softer springs allow more ride height and pitch change from braking and acceleration, stiffer less. For example, allowing the nose to drop more on braking should increase front downforce percentage and maybe total downforce amount, lower the height of the mass at the front of the car, and lower the front roll center. IF these work, the result is a sharper turn-in response, which in turn can lead to less mid-turn understeer (even after the nose rises) by the simple virtue of getting the turning done earlier in the corner. But, too much drop can destabilize response, shut off the front aero, move the suspension into the bump stops, cause adverse camber changes, blah, blah. A similar but different set of concerns exists for stiffer springs. And, a similar but different set of concerns exists for the rear springs. As always, the key is finding how much is just enough and how much is too much.
In roll, the springs affect both the roll stiffness and the feeling of support perceived by the driver. With front AR bars creating a fairly significant portion of front roll stiffness on most rear-drive cars, the effect of springs on roll stiffness on the front of the car is relatively subtle compared to their effect at the rear, where the AR bar is relatively soft or even disconnected. But subtle may be all you need, if the front-to-rear bar balance (a whole 'nother blog) is already good.
Of course, one reason springs are so powerful for tuning is that you get both ride height and roll stiffness changes in one tuning change. If you choose to run the same static ride height with a stiffer spring, you get more roll stiffness, less vertical movement, and higher dynamic ride height under aero/banking loads. If you choose to run a lower static ride height with a stiffer spring, you still get more roll stiffness and less vertical movement, but the dynamic ride height will depend on where you set the static. You have to choose.
But wait, there's more. We haven't gotten the full $29.95 worth yet.
Springs have to be matched to the tire. I've seen a change in rubber compound and carcass construction require as much as a 20% change in spring rate to retune a car. With serious sim work and full tire test data, we might be able to reduce the "cut and try". Outside of F1 and NASCAR, the average race team simply doesn't have the money or information, though. The tire might have different vertical or lateral stiffness, different contact patch shape, different internal damping, a compound that requires "working" the tire to generate sufficient heat, etc. There's also the issue of the extent that tire performance falls off over the tire's life.
Springs have to be matched to the track. In broad generalities, lower-grip venues require softer springs, within reason. At higher-grip venues, the car may feel sloppy and unresponsive if not supported by some combination of stiffer springs, stiffer bump damping, and/or stiffer bars. Bumpier venues may require softer springs and higher static ride heights, if a solution doesn't exist in damping. Tracks that put a premium on corner-exit traction or tracks with a persistent reputation for understeer may require a different front-to-rear spring proportion.
Springs have to be matched to the driver. Some drivers like softer, some stiffer. Engineering doesn't completely win out. If the driver isn't happy, you aren't fast. I once saw a team make a nearly 100% stiffer spring change to accomodate a new driver. He won the same number of races as the preceding driver, and was equally or more competitive in general. Same car, same tire, same tracks...
The holy grail of 7-post rig testing, the RMS variation of contact patch loads, is generally better as the springs get softer. But, we can't chase this in isolation either, as should be clear by now.
So, how do we choose spring rates and then tune them?
-Thoughtful consideration of the driver's comments
-Detailed review of the the logged data
-Careful analysis of the available tire data
-In-depth review of all the vehicle dynamics and aero data for your car
-Testing, either stand-alone or in the context of a race event
-Assessment of the track's needs
I can't over-emphasize the need to break free from dogmatic thinking. On two different cars in the last 12 months, I've improved front grip by going stiffer on front springs. Both cars were simply moving too much. On one of these, I saw too much front roll in the logged data. Fairly easy call. But, on the other, it came to a "gut level" call. Nothing in the data or the driver's comments pointed the way. On that car, I had to buck the skepticism of the drivers and the car owner. Luckily, one of the drivers was open-minded enough to go "Hey, it worked even though I thought it wouldn't".
And one detail - street car thinking says don't have the same natural frequency front and rear. See Gillespie. While many factors may well lead you away from this on a race car, I personally haven't found it to be a sin when it did happen.
Have fun!
If there were any question that springs are a powerful tuning tool, we'd only have to look at the extensive spring inventory in the typical race trailer and at the amount of time the typical race car spends on the setup pad getting springs changed. A complete treatment of spring tuning would probably be a whole chapter of a book. Today, we'll just offer some fundamentals to stimulate thought.
There are two major influences that springs always have:
-Dynamic ride height changes from longitudinal load transfer,banking loads, and aero loads.
-Roll stiffness and the resulting front-to-rear distribution of roll couple
Tackling these first...
Softer springs allow more ride height and pitch change from braking and acceleration, stiffer less. For example, allowing the nose to drop more on braking should increase front downforce percentage and maybe total downforce amount, lower the height of the mass at the front of the car, and lower the front roll center. IF these work, the result is a sharper turn-in response, which in turn can lead to less mid-turn understeer (even after the nose rises) by the simple virtue of getting the turning done earlier in the corner. But, too much drop can destabilize response, shut off the front aero, move the suspension into the bump stops, cause adverse camber changes, blah, blah. A similar but different set of concerns exists for stiffer springs. And, a similar but different set of concerns exists for the rear springs. As always, the key is finding how much is just enough and how much is too much.
In roll, the springs affect both the roll stiffness and the feeling of support perceived by the driver. With front AR bars creating a fairly significant portion of front roll stiffness on most rear-drive cars, the effect of springs on roll stiffness on the front of the car is relatively subtle compared to their effect at the rear, where the AR bar is relatively soft or even disconnected. But subtle may be all you need, if the front-to-rear bar balance (a whole 'nother blog) is already good.
Of course, one reason springs are so powerful for tuning is that you get both ride height and roll stiffness changes in one tuning change. If you choose to run the same static ride height with a stiffer spring, you get more roll stiffness, less vertical movement, and higher dynamic ride height under aero/banking loads. If you choose to run a lower static ride height with a stiffer spring, you still get more roll stiffness and less vertical movement, but the dynamic ride height will depend on where you set the static. You have to choose.
But wait, there's more. We haven't gotten the full $29.95 worth yet.
Springs have to be matched to the tire. I've seen a change in rubber compound and carcass construction require as much as a 20% change in spring rate to retune a car. With serious sim work and full tire test data, we might be able to reduce the "cut and try". Outside of F1 and NASCAR, the average race team simply doesn't have the money or information, though. The tire might have different vertical or lateral stiffness, different contact patch shape, different internal damping, a compound that requires "working" the tire to generate sufficient heat, etc. There's also the issue of the extent that tire performance falls off over the tire's life.
Springs have to be matched to the track. In broad generalities, lower-grip venues require softer springs, within reason. At higher-grip venues, the car may feel sloppy and unresponsive if not supported by some combination of stiffer springs, stiffer bump damping, and/or stiffer bars. Bumpier venues may require softer springs and higher static ride heights, if a solution doesn't exist in damping. Tracks that put a premium on corner-exit traction or tracks with a persistent reputation for understeer may require a different front-to-rear spring proportion.
Springs have to be matched to the driver. Some drivers like softer, some stiffer. Engineering doesn't completely win out. If the driver isn't happy, you aren't fast. I once saw a team make a nearly 100% stiffer spring change to accomodate a new driver. He won the same number of races as the preceding driver, and was equally or more competitive in general. Same car, same tire, same tracks...
The holy grail of 7-post rig testing, the RMS variation of contact patch loads, is generally better as the springs get softer. But, we can't chase this in isolation either, as should be clear by now.
So, how do we choose spring rates and then tune them?
-Thoughtful consideration of the driver's comments
-Detailed review of the the logged data
-Careful analysis of the available tire data
-In-depth review of all the vehicle dynamics and aero data for your car
-Testing, either stand-alone or in the context of a race event
-Assessment of the track's needs
I can't over-emphasize the need to break free from dogmatic thinking. On two different cars in the last 12 months, I've improved front grip by going stiffer on front springs. Both cars were simply moving too much. On one of these, I saw too much front roll in the logged data. Fairly easy call. But, on the other, it came to a "gut level" call. Nothing in the data or the driver's comments pointed the way. On that car, I had to buck the skepticism of the drivers and the car owner. Luckily, one of the drivers was open-minded enough to go "Hey, it worked even though I thought it wouldn't".
And one detail - street car thinking says don't have the same natural frequency front and rear. See Gillespie. While many factors may well lead you away from this on a race car, I personally haven't found it to be a sin when it did happen.
Have fun!
Monday, July 6, 2009
Travel to Watkins Glen
This is as close as I'll get to personal blather on The Race Engineer. I did warn you that I'd write about life as a race engineer, and that includes travel. So, here are a few random notes about this weekend's trip to the Finger Lakes region of NY for a race at Watkins Glen.
-The dining scene in Corning has lost the old standby, London Underground.
-Tony R's, Corning's excellent new chop house, more than makes up for losing LU. Our group enjoyed steaks, seafood, and some of their Italian specialties. We also had the largest baked Alaska known to man. Not cheap, but well worth the trip.
-Ithaca/Tompkins Regional Airport is a nice alternative to Elmira.
-I finally got to tour the Corning Museum of Glass. Well worth the time.
-If you connect through DTW, the "trippy tunnel" connecting Terminal A to B and C is, well, pretty trippy.
-There is nothing in racing quite like the view from the paddock down the valley to Seneca Lake.
-Does it always rain at Watkins Glen? I've never had a totally dry weekend there.
Back again soon with another "real" post. See you then.
-The dining scene in Corning has lost the old standby, London Underground.
-Tony R's, Corning's excellent new chop house, more than makes up for losing LU. Our group enjoyed steaks, seafood, and some of their Italian specialties. We also had the largest baked Alaska known to man. Not cheap, but well worth the trip.
-Ithaca/Tompkins Regional Airport is a nice alternative to Elmira.
-I finally got to tour the Corning Museum of Glass. Well worth the time.
-If you connect through DTW, the "trippy tunnel" connecting Terminal A to B and C is, well, pretty trippy.
-There is nothing in racing quite like the view from the paddock down the valley to Seneca Lake.
-Does it always rain at Watkins Glen? I've never had a totally dry weekend there.
Back again soon with another "real" post. See you then.
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