adding a sensor to CDS: Which one to add?
I've got an open port on the D+CDS. I had thought about adding brake pressure, but it has been suggested that unless you add front AND rear, it isn't much better than the Long G tracing. If you had only one port to work with, and you had the standard five [GPS speed, LongG, LatG, Oil pressure and water temp] what would you add, and why?
Jim
Swift DB-1
Talent usually ends up in front, but fun goes from the front of the grid all the way to the back.
Steering and throttle position are top priorities. I am surprised that you did not mention either of these in you list of haves.
Brain-fade on my part, Steve. I do have those
Jim
Swift DB-1
Talent usually ends up in front, but fun goes from the front of the grid all the way to the back.
Your unused port is analog or digital?
RPM
Steve, I would think its digital. I need to go back and look at the system. I need to take my Remidyl too, as I have RPM also, and forgot that in the list.
I think I have
LongG
LatG
ConbinedG
RPM
GPS Speed [and lap time]
Throttle Position
Steering
Temp
Oil Pressure
Jim
Swift DB-1
Talent usually ends up in front, but fun goes from the front of the grid all the way to the back.
If it's digital, you can't add brake pressure.
I'd remove the long G and add F&R brake pressure.
Unfortunately that means you can't do G-G plots.
Combined G is a math channel.
I was trying to calculate down force and found that GPS speed is not good enough to produce good data. For that calculation I really needed air speed indicator.
If the spare channel is digital, it is probably intended for wheel speed in the absence of GPS speed. In that case brake pressures are out as that requires a analog channel.
If the spare channel is analog, you can free up a second analog channel with the longitudinal Gs and use a math channel to calculate longitudinal Gs. I have often had more sensors on a car than I have channels and switch the sensors depending on what is important to be looking at that moment.
I would vote for front brake pressure. The rear brake pressure sensor is gravy and will allow you to compute things like brake bias and see if there are problems in the rear brake system - but that's basically all it does. 80% of the useful data will come from the front sensor alone.Originally Posted by swiftdrivr
Doppler-based GPS speed claims to achieve 0.1m/s accuracy.
At the end of the day, what you really want to see is how fast and where the car is decelerating. I think the longitudinal G sensor is the indicator of that.
I would opt for 2 brake pressures or forget it. But that is only my opinion and is a reflection of what I am looking for in data.
The PI systems I have worked with did not have longitudinal G sensors. The longitudinal Gs were calculated from speed changes.
My problem was I was matching other sensors that were logging at 150 Hz to speed that was logged at 10 Hz. A wheel speed indicator would have been way more useful. The accuracy of what I was looking at was severely degraded. On a race track some of the calculations were not even possible. I was looking at speed changes against load changes. Over a long enough distance, this is not a serious problem.
If you have the ancient commander2 system, you most likely have three digital inputs, to which you would have GPS speed, wheel speed, and engine rpm connected to.
I'd ditch the temperature sensor to have two brake pressure sensors.
Even though I call them ancient, I've got two 38 channel boxes in my two p2/DSR cars driving copilot displays that work great. If you too have a commander2 box and want additional channels I might be able to dig up a four port commander that would give you a few more channels.
Sorry guys, but my DSL went out last night. Thanks for the feedback. I had the body off, and noticed the un-used port that I had forgaotten about, and was wondering if it might be useful for something. Seems I need to do some research before pursuing this further. I have my old gauges still in place, so I could do without the water temp. Maybe two brake pressure sensors are posible, if the input is correct. Or maybe EGT? A second Gyro for better Yaw analysis?
Thanks,
Jim
Swift DB-1
Talent usually ends up in front, but fun goes from the front of the grid all the way to the back.
Just because you have a fourth port doesn't mean that there are more channels available. The most basic com2 probably had five analog channels. You obviously have more than that. If you don't know how many are available, contact CDS with your serial number and they can tell you how many are enabled.
I have gyro sensors if you want some.
Yes, some of the modern GPS's are quite accurate for speed. The unit I bought (but have yet to install) claims 0.03 meters / second accuracy, which translates to 0.067 miles per hour accuracy. It also updates at 100 hertz. In other words, it's wildly more accurate than a wheel speed sensor.
The modern GPS engines are quite accurate for speed.
You want LongG and I would recommend front brake pressure.
The reason to add rear pressure is to calculate and KNOW an accurate bias setting.
-Peter Krause
1984 Tiga SC
www.peterkrause.net
"The Driver is the Greatest Performance Variable in the Racing Equation"
Brake Pressure
Agree with Peter in regards to having brake pressure. One of the best uses for it is to see how you are applying the brakes -- or more importantly how you are getting off of the brakes. It is also useful to see if and how much you are trail braking and whether or not that is helping you in that particular corner.
Ray
The only difference between front brake press and Long G.. is the off throttle influence on the G signal, ie, the compression of the motor slowing the car. Outside of that , the Long G will follow the brake pressure signal. A FFord engine for instance, depending on speed, will show engine braking somewhere around .2 to .3 g for a lift. Top Speed, and aero drag add little more, not much though. You can record data in a test to find out the amount, just lift at top speed or at some other speed. Winged cars, and larger motors add more influence of engine braking. Obviously aero and the speed are important factors in this number. For instance a current trans am car can pull engine brake numbers as high as .5 g..
Once you have a grasp on these numbers.. then you know the "add" of engine brake.
Having both front and rear brake , are great for brake bias percentages to start with and balance in handling with a lot of trailbrake involved, for instance. So you can tune the car for a rotation with a bit of history in the data. Need more rotation at entry? Dial some rear in to the percentage of bias you know works.
George Main
SpeedSense consulting
There are currently 1 users browsing this thread. (0 members and 1 guests)
Posting Permissions
Reply With Quote