Logging shock/strut travel

Discussion on Data Loggers, how to read your logs, what to improve, etc.

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96Mustang460cid
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Logging shock/strut travel

#1 Post by 96Mustang460cid » Tue Aug 28, 2007 1:21 pm

I am just starting to get some good suspension parts put on my car that have some decent adjustability. I have a Innovative LMA-3 datalogger.

I think it would be much quicker to properly tune the chassis if I datalogged exactly what the front and rear shocks/struts were doing at launch/shifts instead of 'eye-balling' it. Has anybody found some linear actuators that work well for this?

I think this would be better than a rubber band or zip tie because it would show exactly what the suspension is doing versus time, TPS, RPM, etc. The zip tie method only shows the extreme movements.

Have a good day!
Michael
96 Mustang 460 cid:
11.30 @ 121 mph

oilrag22
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#2 Post by oilrag22 » Tue Aug 28, 2007 1:29 pm

Racepak(now MSD brand), has some really good, precise liniar travel sensor in different strokes.

Also race-technology.co.uk sells real good tested and proven liniar sensors.

What is the framerate of your datalogger???
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96Mustang460cid
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#3 Post by 96Mustang460cid » Tue Aug 28, 2007 1:35 pm

oilrag22 wrote:Racepak(now MSD brand), has some really good, precise liniar travel sensor in different strokes.

Also race-technology.co.uk sells real good tested and proven liniar sensors.

What is the framerate of your datalogger???
Thanks for the suggestions, I will follow up on those. The LM-1 logs at a rate of 12 samples/second. While this isn't great...I think it'll be fast enough to generally see what the suspension is doing.

Have a good day!
Michael
96 Mustang 460 cid:
11.30 @ 121 mph

oilrag22
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#4 Post by oilrag22 » Tue Aug 28, 2007 1:43 pm

To seriously SEE anything concerning dragrace shocks, you need a data logger, capable of doing at least 100 samples/second...

I know the LM-1 is introduced as 44 minutes worth of data at 12 samples/second...
But can you crank it up to more samples per second and less data time??? Cause you really need to get to that 100 samples/second threshold...
Knowledge is power and with power comes responsibility...

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#5 Post by 96Mustang460cid » Tue Aug 28, 2007 1:57 pm

oilrag22 wrote:To seriously SEE anything concerning dragrace shocks, you need a data logger, capable of doing at least 100 samples/second...

I know the LM-1 is introduced as 44 minutes worth of data at 12 samples/second...
But can you crank it up to more samples per second and less data time??? Cause you really need to get to that 100 samples/second threshold...
I called and spoke with the Innovate Techline about this. They said, "There is no way to increase the sampling rate per se. It actually takes 1,000's of samples per second, but averages it together to come up with 12 datapoints per second."

With that being the case, I think it'll give a good enough picture to know if the car is bouncing, coming up/down too fast, ect.

Feel free to correct me if you disagree though :).

Have a good day!
Michael
96 Mustang 460 cid:
11.30 @ 121 mph

oilrag22
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#6 Post by oilrag22 » Tue Aug 28, 2007 2:13 pm

Okay, that being said, i gather he means that from all the input channels it puts together 12 datapoints per second. But can actually handle and show you 1000 samples/second on for instance one channel...

Let me put it this way... 12 samples per second, is 1 sample per 0.08 sec. So in actual fact you get one "picture" shot of your suspension only once every .08 of a second. During (pre)launch, you ONLY get 12 "pictures" during a second...,

Now keeping in mind how fast everything moves in dragracing, especially the ACCELERATION of the suspension, not so much the speed. You'd want as much "pictures" per second to get to the bottom of things.

For instance take your 11.92 run, taking a camera as example, you would get "only" 143 photo's of your whole 1320 feet(roughly 1 photo per 9 feet). Do you think that would give you enough "frames" to completely analise your run???
Knowledge is power and with power comes responsibility...

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#7 Post by 96Mustang460cid » Tue Aug 28, 2007 2:31 pm

oilrag22 wrote:Okay, that being said, i gather he means that from all the input channels it puts together 12 datapoints per second. But can actually handle and show you 1000 samples/second on for instance one channel...

Let me put it this way... 12 samples per second, is 1 sample per 0.08 sec. So in actual fact you get one "picture" shot of your suspension only once every .08 of a second. During (pre)launch, you ONLY get 12 "pictures" during a second...,

Now keeping in mind how fast everything moves in dragracing, especially the ACCELERATION of the suspension, not so much the speed. You'd want as much "pictures" per second to get to the bottom of things.

For instance take your 11.92 run, taking a camera as example, you would get "only" 143 photo's of your whole 1320 feet(roughly 1 photo per 9 feet). Do you think that would give you enough "frames" to completely analise your run???
I understand what you're saying. I will have to do some more research to see if my current data logger is capable of handling this task. I may decide to move to a different logger.

Linear Position Sensors
I called and spoke with this company about its products. This is what they supply the OEM to test its suspensions.

http://www.unimeasure.com/jx.htm

A linear position sensor from them is $156 (5 - 19 units) each.

This is a very interesting subject and I think it makes tuning the suspension a lot easier. Thanks for the input on this subject, guys!

Have a good day!
Michael
96 Mustang 460 cid:
11.30 @ 121 mph

oilrag22
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#8 Post by oilrag22 » Tue Aug 28, 2007 2:40 pm

Please steer clear of these kind of measuring devices and check-out the Racepak liniar sensor.

I'll tell you why..... the precision this sort of device is not good enough for dragracing. Since the spring in the sensor determines the maximum acceleration the sensor can "see". During the first extension stroke of the shock/spring this will be detected fairly okay. But think in terms of the shock compressing... and extending again...

In dragracing this goes so fast, that the spring in this device simply cannot roll back the measuring wire as fast as the shock travels. So actually, at high speeds during shock/spring compression, the measuring string will slacken...

Take a look at the liniar sensor Racepak sells, not saying you have to buy that one... but that being a shock-type liniar sensor. It actually travels at the speeds of drag shocks and springs...
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#9 Post by John_Heard » Tue Aug 28, 2007 3:06 pm

Those Race Pak 800-LN-TRV8 are LVDT's aren't they? Ouch..retail is $290 each, are they what you use Oilrag?

I've been using one of Randy's rotary position sensors on the rear of my car for a year, it's $47.00 and it's been a good investment. I can see bumps in the track with it. Course Randy also has a linear one too but it's $275 I don't know that I would learn that much more from it?

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#10 Post by oilrag22 » Tue Aug 28, 2007 3:24 pm

Yes, i use the liniar sensors even on our roadracing motorcycles to get more accuracy...

Have had experience with the wire ones, and they just don't seem to "see" the acceleration...

Especially as i explained, the wire ones seem to slacken on dragrace cars, just due to the speed in the extremely short amount of time when switching from stretch to compression...

There might be better wire ones now, which are able to take the slack out as fast as needed... But just giving the heads up...

Good and accurate data is invaluable, cheap inaccurate data is something i'd rather not have, let alone pay for it...
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#11 Post by John_Heard » Tue Aug 28, 2007 3:30 pm

The one's RPM sells don't use the spring loaded wires, they are rotary models that you make a linkage setup for so they don't suffer the take up speed issue you're talking about.

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#12 Post by RPM » Tue Aug 28, 2007 3:30 pm

Michael,

The guys are right, 100 samples per second is minimum for a rear shock travel sensor. The 12/sec will miss the information you need, mainly the initial extention, set and rebound. If you just want to know the final set extension/squat, it will show that.

The low cost sensors mentioned will do the job well if you be sure to have tight linkage, they just don't look as high tech.

The string type sensors have a bad reputation due to the return rate mentioned. If you know what travel rate you expect, check the specs on the string sensor before you buy one.

Randy

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#13 Post by oilrag22 » Tue Aug 28, 2007 3:35 pm

Then they would be able to do a good job...
The above mentioned link...

http://www.unimeasure.com/jx.htm

are the wire ones.
The ones i am warning for... Especially if you are orientating yourself in data acquisition, you should shop around, but certainly be on the look out to get the right sensors, datalogger for your specific application.
And the Unimeasure units will accomodate OEM vehicles, stock shocks and so on, but are not a good investment for dragracing...
Knowledge is power and with power comes responsibility...

Stickshifter 55
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Re: Logging shock/strut travel

#14 Post by Stickshifter 55 » Mon Oct 27, 2008 7:28 pm

This is an example of shock travel from my last run from 10-18.

-0.02 sec. 1.76 start
0.04 sec. 2.07 max ext.
0.18 sec. 1.41 max comp

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Re: Logging shock/strut travel

#15 Post by bracketracer » Wed Oct 29, 2008 9:18 pm

I just installed a sensor on the left rear shock. I have not got out to give it a try yet but here is what it looks like...I had to fabricate an upper and lower bracket..Hope it works :mrgreen:

Image

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