S.A.S.C.
Solo => Technical Talk => Topic started by: MurrayPeterson on March 20, 2017, 10:30:46 PM
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As most of you know, I have quite a technical "bent", and like to apply science to most things.
I just finished reading Neal Tovsen's blog article http://www.conecoach.com/2017/03/17/when-to-put-on-the-cape/, and it brings to mind some deficiencies in the current data logging and analysis tools. In particular, how close to the limit are you really driving? Or in other words, are you under-driving or over-driving? GPS and OBDII sensors just don't come close to answering this question, and I think it is possible (although very difficult) to do better.
So, what I am proposing is to mount an accelerometer and gyroscope on the front or rear of a car, and log some high speed measurements (perhaps 1000 samples per second?).
That's the easy part. The hard part is going to be doing the math to deal with all of the sensor's readings and then decide what constitutes "at the limit" on any given run. If I am very lucky, I can discover patterns that indicate tire break-away. At worst, I guess I will know a lot more about matrix math and Euler angles than I do now :)
Does this sound like a worthwhile endeavour? Or do the current GPS logging and analysis tools give you everything you need?
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Murray, I would agree it is very difficult to do better. I would state that there are so many variables that go into maximum available grip/contact patch that you could chase those variables to insanity.
The goal may be to start with simple data logging techniques and analysis and intimately understand them before seeking more data. In my experience managing large amounts of data sometimes it has to be approached simply first to draw more straight forward conclusions, which then drives in the right direction of what you should be collecting more detailed data on. If you start to the level you may be thinking you will be so overwhelmed with information that it may be hard to achieve what you are after. Call the starting portion of your project a bit of a gap analysis on existing techniques.
I think the project would be fascinating, and enjoyable, but I don't know how much more you will achieve outside of existing tools that currently exist.
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Murray, I would agree it is very difficult to do better. I would state that there are so many variables that go into maximum available grip/contact patch that you could chase those variables to insanity.
I really don't plan on chasing those variables -- many of them are almost impossible to measure in-situ anyway.
I think the project would be fascinating, and enjoyable, but I don't know how much more you will achieve outside of existing tools that currently exist.
I think that I can get/use data that just isn't available via existing loggers. Almost all of them use GPS to infer acceleration and speed, and even then, they miss the "little stuff". I want to capture that moment when your front wheels start slipping sideways, while existing loggers capture the moment when the entire car is sliding.
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You mention patterns that indicate tire break-away, I bet that to an accelerometer (and probably even to a gyroscope) tire break-away looks a heck of a lot like the driver backing off in certain drive configurations (mainly FWD or understeerey AWD) - perhaps a steering angle sensor would be useful as well? When I toyed with this idea I wanted access to individual wheel speed sensors as well, and trying to poll these at the necessary frequency necessitates dedicated monitoring hardware - even on cars where you can read this on the CAN bus I don't feel like you can get updates fast enough.
I also dislike the use of GPS to infer acceleration, even the best commercially available GPS is vastly inadequate for measuring the detail required on an autocross course.
On the up side, there's well over 20 events this year in the Calgary area for data collection!
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I would *love* to have access to the raw data stream from the car's sensors, but that just isn't feasible :( I'll be going the route suggested by Cagare -- collect the data first and then see what might be interesting out of all that noise.
This project isn't likely to go very far this year, since I have a brand new car that will need some serious attention to get it set up and tuned for racing. I am spoiled from driving the same car for many years, and never had to spend any effort on setup.
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I've got a canbadger that isn't getting any use ;)
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I've got a canbadger that isn't getting any use ;)
LOL ;D
How complete is the info you get out using it? And perhaps more important, how fast can it feed you data?
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As for how complete the info is, the device is basically a raw bridge onto the CAN bus and since part of the challenge is building your own cable (or just buying one) you can pick which CAN bus you want to place it on. The device is supposed to be very flexible when it comes to data rates and CAN bus parameters. Javier said that it would grab everything on the bus and it supports both USB and ethernet capture so I'll venture a guess it's capable. Unfortunately the internet is very... light... on documentation so I've been a bit shy of doing anything with it.
I think I have the right cable to plug it into my van - I should try that at some point and see what I can get. I wanted to plug it into somebody else's van with EVIC and use the EVIC to disable the horn honk on remote lock so I could capture the message for that and replay it on my non-EVIC van :D The lengths I go to for such stupid things....
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Sadly, the signals I really want are the raw feeds into the ECU, long before they make it to the bus. I don't think all of the sensor signals even make it onto the bus (wheel speed data?).
I did find a cool little board that will save me a boat load of effort: https://www.sparkfun.com/products/14001
It even comes with a micro SD card socket for logging the data.
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Sadly, the signals I really want are the raw feeds into the ECU, long before they make it to the bus. I don't think all of the sensor signals even make it onto the bus (wheel speed data?).
I might be wrong. Found this reverse engineered info about the high speed bus on a Mazda 3:
https://docs.google.com/spreadsheets/d/1SKfXAyo6fbAfMUENw1KR3w4Fvx_Ihj6sTPSVXBdOXKk/edit#gid=0
Looks like individual wheel speeds are sent out every 15ms. And a bunch of other good info is there too.
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Does this sound like a worthwhile endeavour? Or do the current GPS logging and analysis tools give you everything you need?
I don't have a definitive answer to your questions but in my opinion the hardest two things to do are: 1. Remember just what the heck you did on that last run, and 2: was it faster or slower? Data aquisition should help with both those especially if it incorporates video. The system I am considering is the VBox lite because it allows comparisons between laps based on GPS position so its easy to see how you drove the section differently and what the consequenses were. However the VBox does not allow you to input the position of gates so it is a little limited for autocross. I would expect that between video, a friction circle and words spoken into a mike and recorded you could gather a lot of useful data about how the car and driver are behaving.
But since you like techy stuff you might want to take a look at this: https://www.youtube.com/watch?v=uUyvyUthHIc
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So, I got the sensor board and tried it out this week. I said that I wanted to capture the "little stuff", but that turns out to be a deluge of data. The accelerometer is so sensitive that it captures road and engine vibrations, enough to pretty well swamp out any actual driving data.
Here is an example of 20 seconds of idling and then letting out the clutch and driving forward:
https://drive.google.com/open?id=0ByeFbiNdvLbGS1hlSDV0WlN5S28
I'll be playing with data smoothing and data acquisition rates, since this is not usable as it stands :(
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Maybe even a better, more vibration-free mount? There are some special materials we have used to mount MRI's to prevent vibration interference from the building's vibrations (mechanical equipment, people walking, etc.).
R
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I am not sure one would help enough. Those mounts act as a low pass filter, but I can do that with software as well. The problem is that road and engine vibrations are too close to the frequencies that I wish to capture. I am beginning to see why most data collection systems for racing top out at 10-20 Hz.
Of course, the GPS-based systems are immune, since they don't even see those low level movements. Which makes them genius or very crude -- take your pick :)
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I wonder what DSL cameras and lens use for vibration reduction? Might be software as well?
R
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Cameras usually use software to move the captured frame around inside the raw pixel sensor, but there are some lenses that have mechanical anti-vibration mechanisms.
Drones have a huge selection of anti-vibration systems as well. e.g.
https://hobbyking.com/en_us/vibration-and-shock-absorbing-mounts-400g-a4plus4-100g.html
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So a bit of smoothing and low pass filtering does wonders for the results:
https://drive.google.com/open?id=0ByeFbiNdvLbGWnAzQkVxMEtEVTQ
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Interesting.
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Murray, I've done some work on a lap timer app (iOS/Android). My use case is for endurance racing but I've dealt with some of the same issues with sensor and GPS data. If you haven't already, take a look at the Kalman data smoothing filter for time-series data. I found it useful and incorporated it into my app. There are well-tested implementations of the algorithm freely available for many different languages.
https://en.wikipedia.org/wiki/Kalman_filter
My experience with GPS data is that it's quite good for calculating speed and acceleration as that relies on calculations requiring only changes in relative co-ordinates over time. Where it starts to fail is when doing driving line analysis as that requires comparison of absolute position co-ordinates. Then you have to start worrying about all kinds of other issues like drift, sat signal strength, sat count, etc.
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Thanks Jim -- I'll look into that filter. My biggest issue so far has been the sheer sensitivity of the sensors, especially acceleration. That sucker will actually show the effect of me turning up the bass on my stereo, so road and engine vibrations can drive it crazy. Thankfully, the unit has a pretty good DMP processor on board, so I can do some nice stuff before I even see the data.
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So here is some fairly readable data from one of my runs on Sunday:
https://drive.google.com/open?id=0ByeFbiNdvLbGaGpUbDNtcHJVVm8
I was amazed that I was hitting a bit more than 1G on the sweepers -- those tires sure handle the cold.
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So here is some fairly readable data from one of my runs on Sunday:
https://drive.google.com/open?id=0ByeFbiNdvLbGaGpUbDNtcHJVVm8
I was amazed that I was hitting a bit more than 1G on the sweepers -- those tires sure handle the cold.
Which tires were you on?
Also, interesting to see the slalom migrate, the first right hander was 0.8g, then 0.72g then 0.7g, while the lefts went higher. Is that the tires rolling under the rim and the car starting to hop I see at 17-20s?
Looks like there really wasn't a lot of room to brake in a straight line, but it's neat to see how consistent you are getting hard on the brakes then easing off as you dial in the steering.
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I was on new, unscrubbed RE-71Rs.
The slalom acceleration shows a driving error -- I have other runs that look like perfect sine waves, including the throttle and car rotation rate (gryo).
There were no scuff marks that even came close to going off the tread blocks, so I don't think the tires were rolling over all that far. However, that rough plateau was definitely where the car had transitioned into understeer. I need to sort out tire pressures and sway bar settings to eliminate that problem, since it is costing me some serious time.
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that rough plateau was definitely where the car had transitioned into understeer. I need to sort out tire pressures and sway bar settings to eliminate that problem, since it is costing me some serious time.
Somewhat off-topic, but I wonder if what's happening there is that you're hitting your front bump stops, which is in turn "shocking" your tires and causing them to break loose.
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Somewhat off-topic, but I wonder if what's happening there is that you're hitting your front bump stops, which is in turn "shocking" your tires and causing them to break loose.
So that would suggest that a stiffer sway bar setting would work? I am soooo confused :)
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I was getting understeer (as well as some other spots) there also but I felt that was more because of the changing off-camber of the pavement that seemed to induce it. For me it was more that the front winters were more worn than the rears ... both of which were old ... Just thinking that your front tires hit that first and then your rear ... sort of like going off a jump.
How was the car elsewhere? e.g. understeer-wise?
R
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Car was perfect except for that understeer. However, it happened on every sweeper, independent of camber. It might have been due to cold pavement and tires, but it did seem to be consistent.
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Somewhat off-topic, but I wonder if what's happening there is that you're hitting your front bump stops, which is in turn "shocking" your tires and causing them to break loose.
So that would suggest that a stiffer sway bar setting would work? I am soooo confused :)
Maybe? Normally a stiffer bar would induce more push, but if it kept the front off of the bump stops, and hitting the stops is really what's inducing the death push currently, then the stiffer setting might still result in a net improvement in front-end grip.
Only one way to know for sure: test.
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Car was perfect except for that understeer. However, it happened on every sweeper, independent of camber. It might have been due to cold pavement and tires, but it did seem to be consistent.
As I mentioned Murray back when you got the car, fitting a big front sway bay on the Miata is a backwards step, you give away all the front end grip and as you've experienced the car washes out. I would suggest you refit the stock front bar and fit a 17.5mm rear bar, run the rear dampers as little softer and then get a trick alignment that compensates for the rear being a little loose. My NC is almost totally neutral, all most zero understear. Did you uprate the bump stops, very important on a Miata. The car has a huge amount of body role, trying to eliminate the body with the shocks will only take away grip, the car needs to role and lean on the bumpstops as it creates massif weight transfer to the weighted side. As you have discovered this isn't an S2000. No need to reinvent the wheel here lots of stuff on line.
Conventional wisdom says FWD Big Front, AWD Big rear bar. The Miata is none conventional due to its weight distribution and its softly sprung. Stiff dampers and a big bar in most cases are a backward step in a softly sprung car. Once you go down the road of fitting stiffer springs everything changes and stiff shocks, are needed to control the springs, the Koni set is ok but in reality its only a compromises as the dampers at full stiff overpower the springs, which is why the need to be run 1/2 hard. tire pressure needs depending on temperatures 30F - 32R, soften the rear if the rotation is to aggressive. The alignment is one of the most important mods on the Miata.
Base line: Front camber 2.3, rear 2. rear tow, zero, front tow, just a tad out to sharpen up the turn in. Mild rotation is always better as you can keep your foot in it, and it usually points you in the right direction. I played around with my car for over a year, its now just right for my driving style.
Good luck Murray, I'm sure once you got it sorted you'll be kicking our arse.
This advice was given to me by Chris Harvey. US National winner.
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Somewhat off-topic, but I wonder if what's happening there is that you're hitting your front bump stops, which is in turn "shocking" your tires and causing them to break loose.
So that would suggest that a stiffer sway bar setting would work? I am soooo confused :)
Sorry Stephen with all respect that's nonsense LOL
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https://forum.miata.net/vb/showthread.php?t=549409
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That link is for the NC. The ND is quite a bit different (100 kg lighter for one thing).
Ron Bauer has worked with Mazda from the beginning getting a CS setup done and then the STR setup so I would pay attention to what he did but also use his setup info as a starting point since this is still early in setup. Andy Hollis has an ND as well and is very good at setup so he would be another fellow to follow for setup advice.
Here's the ND autox thread and I notice Ron and Andy are both commenting in there:
https://forum.miata.net/vb/showthread.php?t=590076&page=28
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I'm quite confused Terry, first you say that bumpstops are very important then you tell Stephen that his idea about bumpstops is nonsense. What he said about the bumpstops is the exact reason they are important as you go from a relatively softly sprung car to an extremely stiffly sprung one in an instant (and in many cases will break the tires loose)
On a side note, when did Chris Harvey win nationals?
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My comments were related to a stiffer sway bar, not the bump stops
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Somewhat off-topic, but I wonder if what's happening there is that you're hitting your front bump stops, which is in turn "shocking" your tires and causing them to break loose.
Sorry Stephen with all respect that's nonsense LOL
My comments were related to a stiffer sway bar, not the bump stops
Terry, I have two thought exercises for you:
- From first principles: Please think about what the effect is on a loaded tire when the suspension on one corner of a lightly sprung / lightly damped car "slams" into its bump stop. Explain what effect this will have on the car's behavior if it happens to the car's outside front tire at corner entry. Then think about how this behavior would change if the suspension's transition into the bump stop was more gradual. Which behavior will be preferable, and why?
- Specific to your refutation of my recommendation: Consider that most, if not all, of the fast guys in ND Miatas are following my nonsensical recommendation to run a stiffer front bar:
- Julian Garfield, 2nd at 2016 Nationals in CS: Runs a stiffer Karcepts front bar (posted on a "secret" forum, but if you know what I'm talking about, paste the forum URL followed by /showthread.php?56587-ND-Miata-prepped-for-C-Street&p=1845160&viewfull=1#post1845160). Note also the comment at the end of this post: "Julian went almost a second faster than Chris' NC at Wilmington so the Karcepts bar must worked pretty well. :)"
- Tyler Kvetko, 3rd at 2016 Nationals in CS: Runs a stiffer Karcepts front bar (https://forum.miata.net/vb/showpost.php?p=8181316&postcount=462)
- Andy Hollis, multitime national champion: Runs and recommends a stiffer Karcepts front bar (https://forum.miata.net/vb/showpost.php?p=8387729&postcount=550)
- Ron Bauer, multitime national champion: Ran and recommends a stiffer front bar (https://forum.miata.net/vb/showpost.php?p=8084689&postcount=363)
(I can't find a post by 2016 CS national champion Daniel McCelvey describing his setup, but I'd bet money he's also running a stiffer Karcepts front bar.)
Given all that, apply Occam's Razor while considering which is more likely:
- They're all wrong, and the advice that you read on the internet for a different car is coincidentally also the best way to set up an ND Miata, or
- The advice that you read on the internet for a different car is not also the correct way to set up an ND Miata.
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Just a quick note here on why you may want to run a stiffer front anti-sway bar even in the front of a FWD car: As opposed to the track, in autox you want the stiffer and faster reacting front end so you get quicker turn-in response at corner entry which is more helpful (sometimes) than even a balanced car.
One of the odd-ball characteristics of autox vs. track setup. :)
Reijo
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Hmmmm......interesting thoughts on a large FSB and driving style. It just occurred to me that if you have slight understeer due to a stiff FSB, you might have to alter your driving style to keep weight/traction on the front tires by trail braking until you are ready to exit .... e.g. balance the car with the brake. That may also mean a slightly (very small) different line to account for the handling characteristics ... or some variation ...
Interesting.
r
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Normally a stiffer bar would induce more push, but if it kept the front off of the bump stops, and hitting the stops is really what's inducing the death push currently, then the stiffer setting might still result in a net improvement in front-end grip.
I'm procrastinating here, so let me elaborate on my thinking:
Picture a graph showing the effective spring rate of your springs and sway bar at the wheel:
(http://i.imgur.com/0wZl3wE.png)
(This is of course an idealized representation.)
Now picture the equivalent graph for the bump stop:
(http://i.imgur.com/5PEgH5p.png)
The bump stop only affects the last part of your suspension travel.
Now add the two:
(http://i.imgur.com/Xmp2uTI.png)
Note the step function spring rate increase when you hit the bump stop. In reality, the increase would be a little more progressive, but the spring rate would also asymptotically approach infinity as the bump stop reached full compression.
My theory is that, if you're hitting the bump stop while already at the limit of your tires' traction, the resulting step function in wheel rate is causing the tires to break loose. This theory's consistent with the behavior that we observed, where the car would turn in and transition great, but halfway through steady-state corners it would settle into an unrecoverable death push.
If you add a stiffer sway bar, the step will become smaller, and thus the transition into the bump stop would be less likely to shock the tires into breaking traction:
(http://i.imgur.com/FchNTRM.png)
The greater roll stiffness would also decrease the chance that you'd hit the bump stop in the first place.
Of course, by stiffening the bar you'd be increasing the wheel rate before you hit the bump stop, which, all else being equal, would increase push in that condition.
To get around that, perhaps you could leave the front bar as-is and instead use a softer bump stop:
(http://i.imgur.com/G4KpN4U.png)
This would reduce the magnitude of the step without increasing the wheel rate when you're not riding the stop.
Please note this is all a theory based on two runs in your car. It ignores, among other things, camber gain or loss in roll. I'm not offering a prescriptive solution like Terry is; I'm just suggesting that you try adjusting your bar and/or your bump stops at an event to see if that helps.
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Two more thoughts:
Stiffening your front shocks would also reduce the rate (but not the ultimate amount) of roll, thus potentially decreasing the magnitude of any "shock" resulting from hitting the stops.
...but stiffening your front shocks could also cause your car to jack down and ride its bump stops.
Confused yet? If not, I can keep going. :D
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Thanks guys!
I'll be trying a stiffer FSB setting at the next event(s). The turn in response is superb, so a stiffer bar setting won't hurt too much, even if it forces me to be gentler on initial turn in. Bump stops aren't something I am willing (or able) to play with right now.
I hadn't though about shock settings with respect to roll rate and hitting bump stops. I do know that Andy Hollis runs his front shocks at full stiff, which I never did try on Sunday. Something else to test :)
I am also going to try playing with tire pressures, especially in the front. I know that RE-71Rs were quite insensitive to pressure on the S2000, but that doesn't mean it will be the same on the Miata.
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Personally I like setting the tires pressures at the optimum all around and then use shocks, alignments etc. to "tune" the handling .... Why wear the tires unnaturally.
I know some people ran really high pressures in some stock FWD's some years ago as a desperation measure to get them to rotate but I think that was the exception ... but then again I haven't played with the setup on a FWD in a very long time. Or not much.
R
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I agree with you Reijo, and have no intention of using tire pressures to reduce grip anywhere. Instead, I was thinking that if my tire pressures were "off", then I could be losing grip in mid-corner.
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I agree with you Reijo, and have no intention of using tire pressures to reduce grip anywhere. Instead, I was thinking that if my tire pressures were "off", then I could be losing grip in mid-corner.
Yes, good point. Of course, as we discussed before, this weekend is not "really" ideal for setting up a car anyway due to the cold temps and consequent lack of grip. However, you still need a setup for cold temps that we get but then also for the concrete and heat of Lincoln.
Who said setting up a stock/street car was easy, eh? hahahaha
R
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I got spoiled by driving the same car for 10 years -- all of the setup work had been long done.
Next event, I'll probably just boost the FSB up to full stiff (no small changes here), and then twiddle the shocks to see if I can find a good balance. Fort Macleod has only the single sweeper, so I'll probably have to run that set up for the next YYC event as well.
BTW, Sunday's course was superb for setting up a new car!
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Did some more research.
Sorry Stephen with all respect that's nonsense LOL
My comments were related to a stiffer sway bar, not the bump stops
I can't find a post by 2016 CS national champion Daniel McCelvey describing his setup, but I'd bet money he's also running a stiffer Karcepts front bar.
McKelvey doesn't post much, but from another forum:
I would not run the car without some kind of front swaybar upgrade. The shocks will help but reducing the amount of terminal roll is very important in getting this chassis working.
Unfortunately he doesn't elaborate on why he feels that's the case.
/showthread.php?56587-ND-Miata-prepped-for-C-Street&p=1832142&viewfull=1#post1832142
Note also that, in the link above, Kvetko (3rd at Nationals) mentions that he's running his bar at a setting that's more than four times stiffer than the stock bar per http://www.karcepts.com/shop/product.php?id_product=125.
Last but not least,
Chris Harvey. US National winner.
Harvey is undeniably a great driver, but for the record I searched the SCCA rule book (which lists all past championship winners in the back), and his name isn't there.
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Maybe Harvey won a Tour or a Pro out east? I recognize the name but don't know him nor have met him.
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You guys are all nuts.
Murray - stock front bar and giant rear bar. Do it! Not only does it work on an NC, but it worked great on my STS Civic :o
Disclaimer - I might be saying this for selfish reasons because I fully support anything that slows you down :P
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Chris Harvey is Tire Rack's brand manager for Brakes & Suspension. Great guy. Chatted him up last summer prior to my Koni's purchase from Tire Rack for the FRS.
Duo of Fenter / Harvey placed...
2nd / 4th in CS at '14 Nationals
2nd / 3rd in CS at '15 Nationals
This was with Fenter's $$$ Penske's personally revalved, set up for Harvey's NC Miata
In 2016 Harvey alone placed 11th in CS. Behind 6 ND Miata's & 4 Twins
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Maybe Harvey won a Tour or a Pro out east? I recognize the name but don't know him nor have met him.
He seems to be a fairly consistent top 10 runner at nationals in BS, CS and STR over the last 15 years (that's as far back as the online SCCA results go)
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You guys are all nuts.
Murray - stock front bar and giant rear bar. Do it! Not only does it work on an NC, but it worked great on my STS Civic :o
Disclaimer - I might be saying this for selfish reasons because I fully support anything that slows you down :P
Now, don't start being nice to me Brian, I wouldn't know how to handle it :P
I changed the sway bar setting from hole #2 to hole #5 (stiffest) today. Damn, but that Karcepts FSB is one beautiful piece of work. No need to jack up the front, I just turned the wheels enough to get easy access with one hand and a small ratcheting box end wrench. Total time for change, perhaps 7 minutes.
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This should be interesting, my best guess is it will increase the understear, but I've been wrong before. 8)
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I also expect it to increase understeer, but if the severe mid-corner understeer is caused by bumpstop "shock", then the mid-corner understeer should be lesser and predictable, at the cost of more understeer in other parts of a corner. If so, I have hopes that shock settings can ameliorate those areas, but they are unable to do anything about mid-corner issues.
At this point, all I/we have are conjectures, with no proof one way or the other. Testing at a different setting should help clarify matters.
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I hope it works for you. All I can say that when I had the big from bar on my car the understear was dreadful, and the worse it got the stiffer I made it. Probably has sometime to do with my driving style. All I can say is the re fitting of the stock front bar, and fitting the 17,5 RB the problem has gone away
Hope you find the results your looking for. Dont you just love R&D
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The stiff sway bar setting turned out to be a mixed bag. On Saturday, it handled well, without much understeer at all. However, on Sunday, I had a waiting list for people wanting a ride in the car, and as soon as I had a passenger, it under-steered like a pig. Run solo, and it was fine. Go figure...
I have also developed a loud clunk when the suspension hits full travel. I am taking it into the shop for analysis this Thursday.
I stopped on the scales on the way home, and the car weighs 1160 kg (2552 lbs) with 1/4 tank of fuel, me sitting in the car, and all the (heavy) timing gear in the trunk.
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So nothing looked out of place in the suspension. I got them to tighten up the sway bar clamps to prevent any sideways motion. And now it squeaks when I drive it on the street :(
Getting a much more aggressive alignment this Friday -- toe out, here we come!