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      09-06-2020, 05:48 PM   #1
fe1rx
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fe1x Adds Ride Height Sensors

My goal is to install ride height sensors at all four corners that can be used to log ride heights. This data can be used for estimating aero loads, and to generate shock speed histograms for the purpose of damper tuning. Step 1 is choosing an economical sensor.

The motorsport go-to for measuring real-time suspension travel is a linear shock potentiometer. Typical examples are available from AiM and others:

https://www.pegasusautoracing.com/pr...Product=MC-206

Isa-Racing in Germany sells a “clubman” line of lower cost linear potentiometers at about half the cost of the premium motorsport versions. Reportedly these are environmentally protected to IP60 (dust) vs. the higher IP65 rating (dust and water) of the motorsport versions.

http://www.dsmt.com/resources/ip-rating-chart/

Other linear sensors can be repurposed from other automotive application – notably Mercedes uses linear pots to measure lift gate position on some of their vehicles. These are expensive new, and using parts from the scrapyard sounds like a make-work project.

The other possibility is to use automotive rotary ride height sensors. Living in the wheel well, these will be designed to survive in that environment. Sensors designed for 4-wheel control of magnetorheological damper control are ideal, as they are designed to provide exactly the data we are looking for (with respect to accuracy and frequency response).

Motec has a lower priced rotary sensor as an example of this re-purposing.

https://www.motec.com.au/ac-sn-position/sn-position-rp/

They kindly publish some mechanical and electrical data for this sensor:

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A better solution is to search out other sources of these sensors. Some leg-work has revealed that they are used in a variety of GM vehicles with mag-ride suspensions. The basic rotary sensor appears to be common, with a variety of mounting bracket and lever arm configurations differentiating the various part numbers. Delphi sensors are OE in many cases, so limiting a search to that manufacturer will make things easier. A search for Delphi “ER100**” on Rock Auto finds variants from $25 USD to $130 USD for the same basic sensor.

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I purchased 4 of ER10031 for $25 each. This sensor is left rear on the Cadillac CTS and for some reason it is less than half the cost of any other ER10xx variant. Standard Motor Products has a mating connector with pigtail leads for this part – their part number S577. A search for GM 12085538 will find other sources for compatible connectors.

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With 4 of these sensors in hand, I set about confirming their physical and electrical characteristics. They are Hall effect devices, not resistive potentiometers, so it is necessary to provide them with a reference voltage and to measure output voltage, rather than simply measure resistance. I used three AA batteries in series to provide a stable reference voltage and measured the output voltage at a variety of rotation angles.

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The Motec document conveniently identified the pin functions for the sensor. Rotation angles were measured by applying a calibrated scale to the sensor as a reference.

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I measured the following ranges from the lever arm supplied with this sensor. Motec uses a different arm configuration, so their datum is different.

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The electrical range and useful range have been extracted from the output data as shown in the following graph. The output is distinctly non-linear with respect to rotation angle (more on that later). I have defined the useful range as 15° - 105° because the output for all 4 sensors is reasonably consistent for all sensors over that range. The output values follow an S curve that I have approximated by a third order polynomial by using Excel to fit a trend line to the data over the range from 15° - 110°.

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To minimize the installational non-linearity and to maximize the output range, it makes sense to orient the sensor arm useful range to operate at ±45° from horizontal. Referring to the output voltage as a percentage of usable over that range also simplifies the discussion. I have rescaled the output of the ER10031 accordingly below:

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One of the perceived shortcomings of a rotary sensor is the inherent non-linear relationship between the vertical height of the sensor arm and the rotation angle. Assuming the sensor is a linear rotary potentiometer, the sensor output will be linear with respect to rotation angle but non-linear with respect to sensor arm (and ride) height.

So here is where things get interesting. Assume we have a sensor that has a linear output with respect to ride height over a range of heights of ±0.5 (units). We can map that output against the rotation of an arm that rotates ±45°. That arm has a length of 0.5 x SIN 45° = 0.7071 to make that work out. At any given height, the arm angle is ASIN(h/0.7071). Tabulating a few values:

Height Angle
0.5 45.0
0.4 34.5
0.3 25.1
0.2 16.4
0.1 8.1
0 0.0
-0.1 -8.1
-0.2 -16.4
-0.3 -25.1
-0.4 -34.5
-0.5 -45.0

Plotting these against the ER10031 output with respect to arm rotation angle, we see a very good match.

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In other words, the non-linearity built into the ER100xx sensors has been designed to compensate for the inherently non-linear relationship between rotation angle and height change when using a rotary sensor. Very clever design.

Next task – figure out how to mount the sensors.
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      09-06-2020, 08:35 PM   #2
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Nice. Subscribed for further updates.
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      09-11-2020, 11:16 PM   #3
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This looks fascinating but I am literally lost...

Still subbed though

How are you recording the data that comes in?

And how often is each point or value recorded?


I swear the 1 series forum is filled with some mad experimental scientists
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      09-14-2020, 03:50 AM   #4
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found a low cost data logging solution?
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      09-14-2020, 11:47 AM   #5
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Quote:
Originally Posted by rac View Post
found a low cost data logging solution?
I don't have a solution in hand yet. It will be an AiM logger of some type, so "low cost" is unlikely.
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      09-14-2020, 07:38 PM   #6
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Quote:
Originally Posted by fe1rx View Post
I don't have a solution in hand yet. It will be an AiM logger of some type, so "low cost" is unlikely.
You can Arduino something if you're into that, I think they have CAN shields that would happily sit on the PT-CAN . Just pick an ARBID that's not on the PT-CAN already, read in four ADC channels and broadcast the data on the PT-CAN and add the channel to the AiM SOLO. Should be able to accomplish this with an afternoon of messing around and $50.

Edit, actually looks like the SOLO II DL has two CAN inputs so you probably don't even have to hang the Arduino on the PT-CAN if you don't want to.
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      09-14-2020, 09:10 PM   #7
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Quote:
Originally Posted by amg6975 View Post
You can Arduino something if you're into that, I think they have CAN shields that would happily sit on the PT-CAN . Just pick an ARBID that's not on the PT-CAN already, read in four ADC channels and broadcast the data on the PT-CAN and add the channel to the AiM SOLO. Should be able to accomplish this with an afternoon of messing around and $50.

Edit, actually looks like the SOLO II DL has two CAN inputs so you probably don't even have to hang the Arduino on the PT-CAN if you don't want to.
there is definitely DIY options. i think there is a market for low cost data logging that is not obviously filled after multiple google searches... if i knew where to start looking to find a developer/production company i'd consider funding a basic CAN & multiple analogue channel logger with removable flash memory (SD card, USB stick), with up to 1000Hz sampling rate, enough for any hobbyist's motor sport application.
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      09-15-2020, 08:31 AM   #8
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Quote:
Originally Posted by rac View Post
there is definitely DIY options. i think there is a market for low cost data logging that is not obviously filled after multiple google searches... if i knew where to start looking to find a developer/production company i'd consider funding a basic CAN & multiple analogue channel logger with removable flash memory (SD card, USB stick), with up to 1000Hz sampling rate, enough for any hobbyist's motor sport application.
I own a company that makes such things and have been thinking about this for a while. The hard part is the analysis/configuration software, all the good packages have proprietary data formats so you can't just use their software unless you're using their hardware. The hardware/firmware is fairly trivial.

A simple DIY thing to get analog data onto the CAN so an AiM can record it is a good stop-gap for a project like this.

Last edited by amg6975; 09-15-2020 at 03:42 PM..
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      09-15-2020, 08:01 PM   #9
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Quote:
Originally Posted by amg6975 View Post
I own a company that makes such things and have been thinking about this for a while. The hard part is the analysis/configuration software, all the good packages have proprietary data formats so you can't just use their software unless you're using their hardware. The hardware/firmware is fairly trivial.

A simple DIY thing to get analog data onto the CAN so an AiM can record it is a good stop-gap for a project like this.
your the right man to speak to then!

what fe1x is doing and what he could do further down the track imo only requires raw data dumped into a .csv that is timestamped and labelled CH1, CH2, CH3.... etc. most generic data loggers i've found do not have high sampling rates, enough inputs, or outrageously expensive.

then it is excel, a graphics package or fit for purpose analyses software. at some point excel is too slow with a lot of data that you might get with high data frequency, if you were logging multiple channels at 200Hz around a race track. but that's where the graphics packages (particularly ones with math functions) come in.

i'm not familiar with the compatibility issues on other brands - but as an example syvecs "SView" (which is freely downloaded) will graph both the ECU data logged file and import anything from a .csv. so both ECU data and imported generic data can be assessed together. i've imported my old jb4 and mhd data straight into SView no problem. you can also create your own math functions using imported data, that could be as simple as conversions for voltages to more complex analyses.

although it would be nice if you could directly program the analogue voltages to actual units of interest within the data logger, its not really required as it can be done post logging.

third party specialist chassis software should also import .csv raw data since they would generally not be tied to one of the hardware manufactures.

if the end user needs compatibility then that is not the market i am thinking of. realistically no analyses is done in the drivers seat so getting this data into a dash logger isn't required. the basics for chassis work;

-Steering angle
-Throttle input
-Damper pots
-Accurate accelerometer.
-Speed

8x channels.

but someone like fe1x could fill up another dozen thermocouple inputs just 'cause....

while i have your attention, what would be the best currently available solution to program inputs to generate an output?

so the situation is I have a standalone ecu, but i dont have many inputs left. in the future i'd like to add 6 EGT thermocouples, ideally i would like to write code that would assess the EGT data for abnormalities. i'm thinking like using a rolling averages per cylinder, and for all 6 to establish what is normal in real time then monitoring individual cylinders against the established "normal". If one cylinder spikes in either direction (rate of change and amplitude comparison), then code an output channel to 5v instead of 0v - feedback that single input into my ecu and use it as a limp mode trigger.

too complex? googling i found this, general purpose input / output board: http://megasquirt.info/products/diy-kits/gpio/
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      09-15-2020, 08:55 PM   #10
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Quote:
Originally Posted by rac View Post
your the right man to speak to then!

what fe1x is doing and what he could do further down the track imo only requires raw data dumped into a .csv that is timestamped and labelled CH1, CH2, CH3.... etc. most generic data loggers i've found do not have high sampling rates, enough inputs, or outrageously expensive.

then it is excel, a graphics package or fit for purpose analyses software. at some point excel is too slow with a lot of data that you might get with high data frequency, if you were logging multiple channels at 200Hz around a race track. but that's where the graphics packages (particularly ones with math functions) come in.

i'm not familiar with the compatibility issues on other brands - but as an example syvecs "SView" (which is freely downloaded) will graph both the ECU data logged file and import anything from a .csv. so both ECU data and imported generic data can be assessed together. i've imported my old jb4 and mhd data straight into SView no problem. you can also create your own math functions using imported data, that could be as simple as conversions for voltages to more complex analyses.

although it would be nice if you could directly program the analogue voltages to actual units of interest within the data logger, its not really required as it can be done post logging.

third party specialist chassis software should also import .csv raw data since they would generally not be tied to one of the hardware manufactures.

if the end user needs compatibility then that is not the market i am thinking of. realistically no analyses is done in the drivers seat so getting this data into a dash logger isn't required. the basics for chassis work;

-Steering angle
-Throttle input
-Damper pots
-Accurate accelerometer.
-Speed

8x channels.

but someone like fe1x could fill up another dozen thermocouple inputs just 'cause....

while i have your attention, what would be the best currently available solution to program inputs to generate an output?

so the situation is I have a standalone ecu, but i dont have many inputs left. in the future i'd like to add 6 EGT thermocouples, ideally i would like to write code that would assess the EGT data for abnormalities. i'm thinking like using a rolling averages per cylinder, and for all 6 to establish what is normal in real time then monitoring individual cylinders against the established "normal". If one cylinder spikes in either direction (rate of change and amplitude comparison), then code an output channel to 5v instead of 0v - feedback that single input into my ecu and use it as a limp mode trigger.

too complex? googling i found this, general purpose input / output board: http://megasquirt.info/products/diy-kits/gpio/
A simple analog to SD Card or USB drive logger is a dead simple thing to make. Even adding in CAN functionality is super easy. Steering Angle, TPS, all four wheel speeds, brake pressures, etc etc etc are already broadcast on the PT-CAN. Thermocouples are a bit harder but not bad. Accelerometer is also dead simple to implement and log. Even GPS is pretty easy. 200Hz is actually quite slow, I'm doing an instrumentation level analog capture device right now that samples up to 250k samples a second.

The logger could do some math, but yeah the analog would probably just have to be in volts. The configuration could be put in a text file on the SD card and loaded when it was inserted I guess.

Your EGT project is a very specialized situation. Adding inputs to your ECU will totally depend on your ECU.
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      09-15-2020, 09:17 PM   #11
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Quote:
Originally Posted by amg6975 View Post
A simple analog to SD Card or USB drive logger is a dead simple thing to make.
even if i have no formal background in any of the current programming languages? any recommended "diy kits"? i did C+ 20 years ago... not something i'd lean on now.

Quote:
Originally Posted by amg6975 View Post
Your EGT project is a very specialized situation. Adding inputs to your ECU will totally depend on your ECU.
the ecu side of it i've got covered. its the taking of multiple data inputs, applying customized math functions and generating an output in a separate "black box" that i'd need.
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      09-15-2020, 10:15 PM   #12
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I guess I meant this stuff is dead simple for someone like me who does it every day. You could definitely Arduino something and do a bunch of googling and get something working though.

You got me thinking though...
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      09-16-2020, 01:30 AM   #13
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https://www.instrumentchoice.com.au/...hannel-loggers

something usable here?
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      09-16-2020, 01:30 PM   #14
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Quote:
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I have no idea.
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      09-22-2020, 08:33 PM   #15
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there is very good free or low cost software for analytics as long as you stick with the same log format as something like a racecapture

I use this https://trackattack.io/
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      09-22-2020, 08:39 PM   #16
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also analog to can devices exist and they are not terribly expensive, autosports labs sells one, called analogX
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