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Brake Pressure Data Aquisition

 
Old 04-02-2009, 12:47 PM
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sundog
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Default Brake Pressure Data Aquisition

I was wondering if anybody uses inline pressure monitors to keep track of the pressure to all 4 calipers during events. During the last event It looks like my front brakes were doing the lions share of the work, and I was wondering if there was some air in the rear circuit.

We know what the brake bias valve should let the pressures be, but what are they actually. If there was a pressure sensor near each caliper then it would be possible to tell if the brake lines had air, or other issues.

Now to find sensors that are stable with temperature!
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Old 04-02-2009, 01:00 PM
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There are plenty of good motorsports-qualified pressure sensors out there. Most data acquisition vendors offer them. You might find that running two sensors - one in the front circuit and one in the rear circuit - would give you all the bias info you need.

What data logger are you using? The Racepak IQ3 can display brake pressure front and rear, or better still you can easily set a threshold that will set a warning light.

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Old 04-02-2009, 01:43 PM
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Pressure sensors tend to be quite expensive...

Here's a different thought - why not monitor pad temps instead? Might tell you more of what you really want to know... but cheaper (TC's being much cheaper). Plus, if you have a failure (our pressure taps - for work - have been known to fail) there's no loss of braking due to an open circuit...

Just a thought...
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Old 04-02-2009, 04:28 PM
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I will likely build my own DAS. We do lots of it for random vibration tests on satellites, and have boxes around that we can monitor graphically, or download after the fact. Part of the fun for me is building stuff and making it work.
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Old 04-02-2009, 05:01 PM
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Expensive yes but they can show driver input data that pad temps cannot. Two different things I would venture to say as temps are influenced by many outside variables.
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Old 04-02-2009, 05:13 PM
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If I could only have two data points from a DA they would be brake pressure and throttle position.
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Old 04-02-2009, 05:37 PM
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Do any ABS systems use brake pressure signals? I was just hooking up a DL1 in my wife's Elise and I thought I saw something about brake pressure in the workshop manuals.
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Old 04-02-2009, 05:52 PM
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I monitor/log both front and rear pressures with my MoTeC. On it's own, the f/r pressure isn't going to tell you much (it's just the bias). If your bias is off, then you can adjust it but knowing it's off doesn't come from pressure data.
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Old 04-02-2009, 09:04 PM
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Originally Posted by Tom W View Post
I monitor/log both front and rear pressures with my MoTeC. On it's own, the f/r pressure isn't going to tell you much (it's just the bias). If your bias is off, then you can adjust it but knowing it's off doesn't come from pressure data.
I was wondering though if there is air or another compressible gas/fluid in the system, then wouldn't the pressures not be what the Bias valve should be reading.

One of the issues that I'm having is that 2 track days ago, I had the rear right very hot, and melted off the balancing weights, in addition to spinning off the track twice. This last weekend, it seemed like the rears were not getting nearly as hot, and the fronts were working much harder than before.
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Old 04-03-2009, 04:51 AM
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You could have a sticky piston. Have you had your calipers checked lately?
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Old 04-03-2009, 08:46 AM
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Originally Posted by Tom W View Post
I monitor/log both front and rear pressures with my MoTeC. On it's own, the f/r pressure isn't going to tell you much (it's just the bias). If your bias is off, then you can adjust it but knowing it's off doesn't come from pressure data.
You can make your data more meaningful with some math channels. This is what I did on my MoTeC - using the diameter of master cyls, caliper piston diameter and number of pistons, compute the actual clamping force front and rear. Then calculate bias from that. It is far more meaningful. I also had my dash programed to display this bias value when under braking (When front pressure exceeds some small value, have one field display bias value - I used that same field for other stuff in different modes, such as min corner speed, etc).
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Old 04-03-2009, 09:07 AM
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Originally Posted by TheOtherEric View Post
Do any ABS systems use brake pressure signals? I was just hooking up a DL1 in my wife's Elise and I thought I saw something about brake pressure in the workshop manuals.
ESC systems do, yes, though not typically ABS-only systems. They monitor the pressure in the MC. You could very likely get the pressure from over the CAN bus, if you were tapped in to read such signals and were able to get the message ID. Wouldn't tell you proportioning, though.
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Old 04-03-2009, 09:40 AM
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Originally Posted by SundayDriver View Post
You can make your data more meaningful with some math channels. This is what I did on my MoTeC - using the diameter of master cyls, caliper piston diameter and number of pistons, compute the actual clamping force front and rear. Then calculate bias from that. It is far more meaningful. I also had my dash programed to display this bias value when under braking (When front pressure exceeds some small value, have one field display bias value - I used that same field for other stuff in different modes, such as min corner speed, etc).

Brake pressure traces are useful and valued by drivers and race engineers.

Other things brake pressures are good for is monitoring any bias migration and balance bar condition.
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Old 04-03-2009, 11:10 AM
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Originally Posted by sundog View Post
I was wondering though if there is air or another compressible gas/fluid in the system, then wouldn't the pressures not be what the Bias valve should be reading.
....
I don't think the presence of air affects brake pressure per se; it's the fact that you run out of pedal travel (since air is compressible) that will affect brake pressure.
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Old 04-04-2009, 02:44 AM
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Originally Posted by Tom W View Post
You could have a sticky piston. Have you had your calipers checked lately?
Rears are new, less than 1k miles. The fronts have about 180K, I'll check them when I take the front wheels off.
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