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-   -   Shock Pot Calibration (https://rennlist.com/forums/data-acquisition-and-analysis-for-racing-and-de/1133795-shock-pot-calibration.html)

38D 03-15-2019 09:18 AM

Shock Pot Calibration
 
Questions for the collective wisdom. Should I calibrate my shock pots 0-100% or in millimeters of travel? I’ve read some that advocate for % so you apparently don’t need to recalibrate when doing setup/alignment changes, and then use maths to calculate actual shock/wheel travel using suspension measurements.

Also is it possible to calibrate without having to remove the springs? That will just be a huge pain to do.

Matt Romanowski 03-15-2019 09:44 AM

Short answer for now is distance in caveman units . You can always convert to metric and your shock guy probably works in imperial. You can also do math for percentage but I've never used shock pots that way (directly).

Don't know your car, but probably have to remove the springs. You need sensor length and motion ratio to the shock and tire. You probably want it to other places as well.

ProCoach 03-15-2019 12:13 PM


Originally Posted by 38D (Post 15705253)
Questions for the collective wisdom. Should I calibrate my shock pots 0-100% or in millimeters of travel? I’ve read some that advocate for % so you apparently don’t need to recalibrate when doing setup/alignment changes, and then use maths to calculate actual shock/wheel travel using suspension measurements.

Also is it possible to calibrate without having to remove the springs? That will just be a huge pain to do.

I and most folks I know use mm/travel through total potential range when using MoTeC because that is the default unit of measure. So easy to zero in Dash Manager on the pad.

Maths for shock travel (if not mounted linearly with the shocks) and wheel travel (using motion ratios) are separate, and do require removal of the springs and bars to calculate those measures. You would want to do accurate measures of ride height, rake, track and wheelbase to begin to fully exploit all the good things you can now do with this great information. Pitch, roll (f+r), front splitter height, rear wing height, aero and downforce measures are now possible.

I don't know anyone who takes things apart to calibrate, just to get the initial measurements for all the maths.

Matt Romanowski 03-15-2019 03:38 PM

So I saw go by imperial units since most shock guys work in that (I haven't seen anyone using mm/s but I'm sure there are some that do). if you set your car up in mm, then consider keeping the units the same. Doesn't really matter what unit you pic, though parsec would be a bit large and cumbersome :)

I've never seen anyone use percent for the calibration. Part of the use of shock pots is to look at the shock speeds in various areas of the track and overall. For that, you need it calibrated in speed. Since you know the stroke of the sensor, it's easy to then calibrate that to a percent of travel, but I'm not sure why you would use that? You can see full extension and compression by the travel numbers and the characteristics of the movement of the shock. Also, you'll want to look at speed histograms to get an idea of the symmetry of the shock speeds and tuning the suspension, and to do that you need speeds (low and high speed bump/compression).

In my experience, it's worth taking the time to really measure everything. Like Peter said, you can measure shock ratios, wheel ratios, etc to you know those speeds and positions. Then you can measure for hard points on the car if they matter (dynamic ride heights). splutter if you have one, etc. You'll also use the measurements on the shock movement to calculate down force if you want it as well.

But, if you are mounting your linear pots on the shocks or parallel to them, then it's much easier. Then all you need is a motion ratio and a couple of measurements and Bob's your Uncle!

ProCoach 03-15-2019 05:19 PM

Porsche uses metric measures for ride height... AiM and MoTeC use metric by default. That's why I do metric measures on the shocks. ;) Color me easy! :)

In the end, it doesn't really matter which you use, because shock histograms aren't in a distance measure, only the strip charts are. And the strip charts "look" the same using either measure.

Fun to talk about, though.

Matt Romanowski 03-15-2019 05:58 PM

I've found the units are only important for the user and the shock guy. I don't know any shock guys who work in metric and I've never got a dyno sheet that was in mm/s, so I go with inches and ips. But, you're mileage may vary!

Yes the graphs look the same, but shocks the numbers become really important. I'm good at both systems, but not everyone is. That's why it's a choice for the user!

ProCoach 03-15-2019 07:32 PM

You ever talk to a Sachs factory guy? They only speak metric! ;)

Frank 993 C4S 03-15-2019 07:35 PM


Originally Posted by ProCoach
Maths for shock travel (if not mounted linearly with the shocks) and wheel travel (using motion ratios) are separate, and do require removal of the springs and bars to calculate those measures. You would want to do accurate measures of ride height, rake, track and wheelbase to begin to fully exploit all the good things you can now do with this great information. Pitch, roll (f+r), front splitter height, rear wing height, aero and downforce measures are now possible.

I use mm travel as it allows you to do things like calculate front/rear body roll. Plus my "chassis guru" is a Brit ;)

Ideally, as Peter says, you want to calibrate them with ride height so you calculate lift/downforce. You will need a math channel for that.

Matt Romanowski 03-15-2019 08:43 PM


Originally Posted by ProCoach (Post 15706730)
You ever talk to a Sachs factory guy? They only speak metric! ;)

Penske, Ohlin, Bilstein (US Guys), JRi. If we are going to talk preferred units, I like smoots!

Matt Romanowski 03-15-2019 08:46 PM


Originally Posted by Frank 993 C4S (Post 15706746)
I use mm travel as it allows you to do things like calculate front/rear body roll. Plus my "chassis guru" is a Brit ;)

Ideally, as Peter says, you want to calibrate them with ride height so you calculate lift/downforce. You will need a math channel for that.

An important point I think we all glossed over a little - you want to do it in a way that you can easily reset the 0. In AiM, I've done this with math channels (when needed) to change the the sensor movement to match the shock motion ration and the wheel motion ratio. This makes it much easier to account for ride height, rake, and other chassis changes. If you do it as a custom sensor from the start, you have to do more work to get ride height, etc. But, it seems that everyone who gets this deep has their own methods.

ProCoach 03-15-2019 09:11 PM

Iíll go with the way Frankís engineer does it. John Block, Chris Brown and others, too. But I agree, just like driving, there are many ways to skin a cat (sorry Coochas Dave).

aryork 03-19-2019 11:52 AM


Originally Posted by ProCoach (Post 15706730)
You ever talk to a Sachs factory guy? They only speak metric! ;)

Both you guys have it all wrong - use the best features of each system. You use integer inch measurements and then add some mms. Like 2 in 4 mm. That's way better than 2 5/32 in. When you get good, you can use, say, 2 1/8 in 1 mm. :D

Matt Romanowski 03-19-2019 12:58 PM


Originally Posted by aryork (Post 15713993)
Both you guys have it all wrong - use the best features of each system. You use integer inch measurements and then add some mms. Like 2 in 4 mm. That's way better than 2 5/32 in. When you get good, you can use, say, 2 1/8 in 1 mm. :D

I like the cut of your jib!


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