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I'm curious what the data rate on the suspension can bus is - and whether logging the ride height signal is possible there.
The reason I'm concerned is, when the car is moving quickly, will the suspension signals be sufficient to identify what the suspension is doing? (trying to avoid aliasing)
Digging around tonight I think I found that the CAN Chassis bus is 500kbps. (someone mentioned it here)
500,000 bits divided by 4 (4 struts) / divided by 2 (send and receive I assume is on the same CAN bus) If the value I want to log is 4 digits in length (10 bits), then the bus supports up to 1059 data frames a second (49 bit for overhead and 10 bit for data).
Thats 1,059 samples a second I could log per wheel which seems sufficient.
So my assumptions aside - does anyone know what values the suspension sends on the can bus? Are they suitable for data logging the suspension or do I need to measure this without the assistance of pasm?
The limit on CAN isn't the bus speed, it's the general architecture. It's often limited to 100 or 250 Hz. That is the bottom of what yo want to log suspension at.
I'm curious what the data rate on the suspension can bus is - and whether logging the ride height signal is possible there.
The reason I'm concerned is, when the car is moving quickly, will the suspension signals be sufficient to identify what the suspension is doing? (trying to avoid aliasing)
Digging around tonight I think I found that the CAN Chassis bus is 500kbps. (someone mentioned it here)
500,000 bits divided by 4 (4 struts) / divided by 2 (send and receive I assume is on the same CAN bus) If the value I want to log is 4 digits in length (10 bits), then the bus supports up to 1059 data frames a second (49 bit for overhead and 10 bit for data).
Thats 1,059 samples a second I could log per wheel which seems sufficient.
So my assumptions aside - does anyone know what values the suspension sends on the can bus? Are they suitable for data logging the suspension or do I need to measure this without the assistance of pasm?
Matt, I'm a bit new to this but how is the 100Hz/250Hz calculated relative to the bus speed? Bandwidth is bits over times, so is the effective Hz a result of the microprocessor clock speeds on the CAN bus?
And yep, I feel like 100-200Hz will be too low as well
Matt, I'm a bit new to this but how is the 100Hz/250Hz calculated relative to the bus speed? Bandwidth is bits over times, so is the effective Hz a result of the microprocessor clock speeds on the CAN bus?
And yep, I feel like 100-200Hz will be too low as well
@edub For the AiM on CAN on a 718 GT4 street car, there isn't any suspension displacement info coming through on the AiM driver that is effective and working on that car. So unless it's in there, which I don't think it is, you'll need to write something yourself.
Different channels have different sampling rates on the bus they're on or determined by the gateway. Here's the list (991_911, direct wired) for the protocol I use on the 718 GT4 street car. Some channels are available, some aren't. Some are limited to 10 Hz, some will allow 50 Hz or more. https://www.aim-sportline.com/downlo...11_109_eng.pdf
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But, you're limited not only to the default sampling rate for all channels in the VBOX unit itself and the standard, most useful analysis software has no other way to show it other than individual strip charts and/or dynamic on-screen elements on the video, rendered real-time with values.
To do this right, you'd need a dedicated AIM or MoTeC logger with linear, rotary (with an arm) or non-contact sensors and set up the software for chassis analysis, not only ride heights and damper compliance, but pitch, rake, roll (separated by front and rear on the latter).
John Block (auto-ware.co) is the best resource to help you set it up for usable, actionable information, IMO.
Haha, that's what inspired this research, that McLaren I just have tucked away in the back of my garage
I'm pretty surprised this information isn't already in the existing data buses on the car. I wonder what the DSC/PASM computer is reading and interpreting to make changes to the struts then?
There is a ride height sensor on the front suspension - are they suitable for sampling or are they also too crude?
If this post is accurate, then it suggests the ride height sensors will not be accurate enough to log strut position for tuning purposes using the OEM equipment.
If this post is accurate, then it suggests the ride height sensors will not be accurate enough to log strut position for tuning purposes using the OEM equipment.
With winter approaching I wanted to try and get a couple data logs in on the track to see what the viability of suspension data there is from the OEM sensors.
I added some traces to the suspension controller to pickup the raw voltage from suspension height sensors and the existing CAN high/low thats on the controller. Likely, I'll have to add another CAN hookup to get other interesting data, however I already have EXLAP and thats not terrible telemetry for amateur data logging.
I'll be able to log the suspension sensors to 12bit at 1Khz this way. Somewhere on rennlist I have a post about how much telemetry I estimate I can get from the OEM suspension sensors, but I'm guessing having not really logged them before or even opened one up.
06-10-2022, 04:46 AM
data sampling suspension on the can bus?
