SundayDriver

Sorry for the extra wide format, but if I take it down, then it is hard to read the text.

Got my first data from the MoTeC system. There is a ton of info and I
thought this group might get a kick out of seeing some of it and trying to
make sense of it. I only collected data for one session and it was a
reasonably quick lap but with a fair amount of traffic (and I was being very
conservative with passes). Absolute numbers are close, but there are
areas that I have not verified calibration so things like oversteer angle
probably has an offset.

First chart - this is one of the most fun - downforce. The
shock position is measured, then filtered then run through calculations and
by knowing suspension ratios and spring rates, the downforce required to
move the car is calculated. Note that bumps and hills appear as changes
in downforce.




Next is a basic handling graph. G's, throttle, steering input and oversteer angle.




Finally, so no one thinks I don't know what I am really doing, the all
important g-g graph. Unfortunately, MoTeC is not as knowledgable as
some on this board, so the default logging rate for g's was set to 20hz so
the chart is choppy. But you can see how much there is to learn from
the FC. LOL



Have fun

Robert Henriksen

But... but... what's your g-sum?

M758

Sunday... You forgot the "WOW" on FC chart

I bet Z-man could help interpret the FC chart. Whada think?

DJ

Well, from looking at your fc chart, I can tell you that you definitely need more motor. It would make you faster.

bob_dallas

All I can say is - you really need to learn how to trail brake....

Got a source for Motec? DAS is next on my list to look into and I've heard great things about Motec but haven't dug much.

924RACR

Neato! Out of professional interest, the "oversteer" value - do you know how it calculates this, and what it represents? Is it another way of expressing vehicle slip angle (angle between body's centerline and the velocity vector)? We measure and evalutate this (slip angle) in my line of work, and I wonder if this is what we're looking at. Also, what's the "speed-weighting" it refers to? Very interesting to see the numbers...

SundayDriver

Do I really need to trail brake, or can I just learn how to make the pictures prettier? LOL

The folks I use for data are Dave and Ellen Ferguson in Silicon Valley
Veracity

They do lots of brands and are very good - focued on club racers. Dave is extemely helpful in setting up the systems and even provided me with his full math package.

SundayDriver

Oversteer is an internal calculation in the Motec. What was explained to me is that by looking at g's and speed, a corner radius is calculated and from that, the ideal steering angle is derived. From that, oversteer is calculated. That should be the angle of the car vs. the cornering arc. The system has all sorts of constants that may or may not be correct, at this point, as I have not checked them. Things like Ackerman. The oversteer is probably correct on a relative basis, but I don't think the absolute numbers are currently right.

924RACR

Hmmm... very interesting, yes, that's quite correct, and yes, there is a lot of estimation going on in there. Personally, I would rather see a yaw rate estimation (deg/sec) based on steering angle (via ackerman and speed), compared to a yaw rate based on Ay (lat accel), and compared to an actual yaw rate... and then you've got the beginnings of a vehicle dynamics controller! But enough about work! LOL

The numbers (magnitude) you're getting are plausible for decent control (if I'm reading the chart correctly), up to 7 deg - that'd be a pretty substantial slip angle, perhaps more than what the car'd really want at speed... kinda hard to say without more investigation of this. Very nice to see that you've got a steering angle sensor (correct?) and TPS in there... kind of a waste of DAQ capabilities without those, IMO - how else can you tune the driver?

I would definitely want to compare with race lap data... Makes me lust after my own DAQ so much more! (I'm going for a MyChron3 Auto Gold system)

SundayDriver

Yes, there is a steering angle sensor and TPS. Also, brake pressure (F & R) and pots on all the shocks, air box pressure and all the usual stuff.

The new, low cost systems, are absolutely amazing in what you get for a couple of $k. I have been through a Stack and Pi, now Motec as I decided that anything worth doing was worth doing to excess.

Robert Henriksen

Proud to be an American...

bob_dallas

Good point, I think if you increase the sample rate on your DAS then you'll be able to enter turns 1 & 3 7mph faster and turn 6 11.5mph faster...

Thanks for the tip - I'll look them up - I'm out in Silicon Valley on business fairly regularly.

924RACR

Stack, Pi, and Motec! A couple K! Dayum! Now I remember why I'm getting the MyChron (under 1k)...

SundayDriver

For some perspective, A stack system is generally going to be $3-$6k (more if you want shock data), Pi can be as low as a couple of $k but they make pro systems that go well over $30k. Motec is generally around $5-$7k, but more if you want shock data. A lot of the expense in any system is trasducers. Shock pots alone will run about $1100 for a set of 4. Brake pressure sensors are a few hundred each.

But the stuff we can do today for $3k cost $30k just a few years ago. Your sub $1k system probably does as much as the $6k sytems of 3 years ago.

SundayDriver

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