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Loser
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Discussion Starter · #1 · (Edited)
Working on an experiment and was hoping to hook up a pressure transducer to my shock to record some behavior while I'm riding. I want to size the transducer/hoses to make sure they can handle the maximum pressure that could be seen during operation. Fox publishes maximum static pressure and compression ratios w/ various spacers for their shocks. Is that enough to calculate a maximum internal pressure at full compression? Are there other factors that must be taken into account?

Here's my calcs so far for my 200mm x 57mm shock (both are overkill for my 150 lb weight but I'd rather err on the side of caution so the transducer doesn't pop off) :
Max static pressure: 350 psi (SHOCK- 2018 FLOAT DPS and DPX2 | Bike Help Center | FOX)
Max compression ratio: 3.47 (red volume spacer) (2002-2020 Air Volume Reduction (FLOAT, FLOAT X, FLOAT DPX2 and DHX Air Rear Shocks) | Bike Help Center | FOX)
Heat capacity ratio of air: 1.4 (Heat capacity ratio - Wikipedia)
1943487

Maximum pressure at full compression with all values maxed: ~2000 psi (yikes)
Max pressure at full compression using my current shock settings (135psi, 2.52 compression): ~500 psi (seems more reasonable but I'm a fairly light rider)

Anything else I'm missing? I think sizing to the 2000 psi is unrealistic so maybe I'll target 1000 psi so I can test on my friends as well.
 

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Pressure realistic. Padding it up 1.5x to 3000 is safer than assuming your math is wrong and saturating the channel.

Is your data rate sufficient for pressure rate of landing from several feet up without aliasing and can your transducer's response keep up with it? Is your plumbing sufficiently sized to take the flow in and out sufficiently faster than shock events?

Volume spacer in the shock to take up the volume of your plumbing.

What are you going to do about the negative side?

It's only nearly adiabatic.

There was a guy a few months ago who was using software on GoPro footage of two dots on the crown and lowers to measure travel.
 

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Thicc Member
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All my experience with transducers and filters always led to the irritating process of trial and error. I'd order twice as many components as you think you'll need. What software are you using, Labview? something better? It's been a while since I've done this.
 

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Loser
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Discussion Starter · #5 ·
Pressure realistic. Padding it up 1.5x to 3000 is safer than assuming your math is wrong and saturating the channel.

Is your data rate sufficient for pressure rate of landing from several feet up without aliasing and can your transducer's response keep up with it? Is your plumbing sufficiently sized to take the flow in and out sufficiently faster than shock events?

Volume spacer in the shock to take up the volume of your plumbing.

What are you going to do about the negative side?

It's only nearly adiabatic.

There was a guy a few months ago who was using software on GoPro footage of two dots on the crown and lowers to measure travel.
All good questions, this is going to be alot of trial and error. I'm hoping to get at least 50 Hz sampling but everything is subject to change.

All my experience with transducers and filters always led to the irritating process of trial and error. I'd order twice as many components as you think you'll need. What software are you using, Labview? something better? It's been a while since I've done this.
For now I'm just going to store the data on a memory card and process with Python or Octave. If the sensors/circuit/data collection work I'll likely develop a little application with bluetooth streaming to a phone.
 

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All good questions, this is going to be alot of trial and error. I'm hoping to get at least 50 Hz sampling but everything is subject to change.
Doing math first works really well. This is the second number you've posted that doesn't look good enough. Look up some plots that people have posted here before and figure out the data rate that must have been needed for them
 
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