Fitting a brake pressure sensor for data logging

[Toilet Duck]

Seasons greetings all,

I've just ordered one of these data loggers from the UK distributor for an Ariel Atom 300. One of the things I would like to monitor is brake pressure, which means I have to fit a suitable pressure sensor.

I've found one sold here from Race Technology which looks to be suitable but it is £180 once you add VAT. I've found another that looks very similar for about £106 but its here on ebay. Is there any other suppliers that any of you guys on here could recommend? If I have to pay £180 for a sensor then so be it, but it seems ridiculous when I'm only paying £330 for the actual data logger with all the GPS gadetry etc.

Assuming that I go with one of the above sensors (unless I get a better option from PH), I need to work out where to fit it.

The Atom uses what appears to be three seperate Tilton master cylinders, one for the clutch, one for the front brakes and one for the rear brakes. It has an adjustable brake balance dial.

The following is what I have come up with, I would be grateful if anyone could confirm whether this is the best way to go or not.

Below is a pic from my car:




As you can see, the first master cylinder has a brake switch fitted. On the second master cylinder in the same place, I am thinking of removing the existing standard length bolt which retains the banjo fitting for the brake line, and fitting a double banjo bolt, which would allow me to fit a banjo male adapter. Onto this, I could fit a female to female adapter, which would allow me to then screw in one of the aforementioned brake pressure sensors. From my understanding, they are all available in 3/8 x 24 fitting. I would angle the second banjo male adapter downwards towards the pressure sensor, thereby hopefully avoiding created a "trap" for any air to accumulate during bleeding etc.

I would be grateful for any advice on whether my idea is "safe," or whether there is a better method using different parts. Any advice on brake pressure sensor suppliers or specific sensors would be much appreciate.

Many thanks in advance and Happy Christmas

Edited by Toilet Duck on Tuesday 24th December 21:03

[Steve_D]

I see no problem with your mounting point or method however your ebay find is way off the mark. Your brake pressure is going to be up in the 1200psi (83 bar) range so the ebay item will be useless at 10 bar max.

Steve

[stevieturbo]

Something in here ?

http://www.omega.co.uk/subsection/voltage-output-p...

[Steve_D]

stevieturbo said:

Something in here ?

http://www.omega.co.uk/subsection/voltage-output-p...

Yes my quick Google search landed me there.

Steve

[Pumaracing]

Toilet Duck said:

I've found another that looks very similar for about £106 but its here on ebay.

Looks great other than the fact it's not a brake pressure sensor.

"Typical applications include: Oil, Fuel and Shift Pressure."

0-10 Bar!!! That's only 145 psi.

[Web13]

In an ideal world you would have one on each brake line.

I have seen some people using a linear potentiometer or even a string potentiometer to mesure peddle movement. They units are cheaper, It's not the perfect solution but it gives you an idea of what the driver is doing.

[anonymous-user]

You need a 100 bar range sensor, preferably with a 200% safe working over pressure

My suggestion is buy an oem sensor off eBay as fitted to various cars. Often comes cheap £ on a s/h master cylinder

I paid less than £20 for an Audi a2 mc with 100bar sensor!

[Toilet Duck]

Thanks for all the replies, very much appreciated.

Steve D, I had no idea that the pressure measured in this application would be up around 1200 psi, I didn't appreciate that so thanks for that rather important fact!!

Stevieturbo, cheers for posting that link to the Omega sensor page. I've had a look through and the sheer number of choices/options has left me a somewhat confused, also it doesn't appear to show prices. I think I might email them and see what they suggest.

Web13, I get your point about having one sensor on each brake line in an ideal world, but the cost would be prohibitive for what I'm looking to do. I just want to use the data to get an idea of how hard the brakes are being used and at what point on track, and then overlay the data onto GoPro video footage. I'm not competing or anything like that, so it doesn't have to be "ideal" You mention "string potentiometers", I'd also like to monitor steering angle and have seen that those type of sensors are used for that, so I need to research those as well.

Max Torque, is there any chance you could link me to a suitable OEM sensor off of ebay like the type that you mention? I find the different working pressures, different thread type on the connector, different output voltage/current types all a bit confusing, especially when I'm trying to integrate it with an existing master cylinder etc.

I know that the pressure sensor should output 0-5v to work with my data logger input specs, from the info posted here it needs to have a minimum working range of 100 bar, the thread should ideally be 3/8 UNF to be compatible with the Tilton master cylinder unless I use additional adapters etc. I don't know if it makes a difference to the brake pressure, but on my car there is no servo assistance or ABS etc.

Thanks again for all your help guys, really appreciated

[Pumaracing]

I suggest your first step is to contact Ariel and find out what the maximum brake fluid pressures are in your system. Then you'll know if you need a 100 bar sensor or a 200 bar one. Then you can Google "100 bar pressure transducer" or whatever pressure and finds lots of options which you can then check prices for and connection thread dimensions.

Edited by Pumaracing on Wednesday 25th December 13:14

[anonymous-user]

Without a brake servo and with any sensible pedal ratio you will be below 100bar pmax
Most sensors are linearly ratiometric ie they return a voltage as a proportion of the supply voltage

[andybracing]

why would you want to know brake pressure unless you have one on both masters and used for adjusting bias, if you just need to know if on or off then use the switch already there

[poppopbangbang]

andybracing said:

why would you want to know brake pressure unless you have one on both masters and used for adjusting bias, if you just need to know if on or off then use the switch already there

Exactly. Either use the brake light switch with a pull up resistor if needs be to give you a driver braking/not braking flag or get two sensors (one on each master) so you can actually see what is going on with brake pressures vs wheel speeds, bias etc. Just logging rear brake pressure isn't really going to tell you anything useful.

A couple of UK Companies do 160bar sensors specifcally for brake pressure for £109 + VAT.

[Toilet Duck]

poppopbangbang said:

andybracing said:

why would you want to know brake pressure unless you have one on both masters and used for adjusting bias, if you just need to know if on or off then use the switch already there

Exactly. Either use the brake light switch with a pull up resistor if needs be to give you a driver braking/not braking flag or get two sensors (one on each master) so you can actually see what is going on with brake pressures vs wheel speeds, bias etc. Just logging rear brake pressure isn't really going to tell you anything useful.

Because it should be easy enough to get the throttle position from the TPS, I would like to get the brake pressure to compare. Not just when the brake is on or off, but how hard its being used. Sometimes on Moto GP/F1 etc, the onboard footage is overlaid with graphics showing how wide the throttle is open (not just on/off), and how hard the brakes are being applied (not just on/off). I'd like to do the same with my GoPro video footage.

I know that I should really have two sensors fro the front/rear braking circuit, but because I'm not a racer or competing or anything like that, I was hoping that one sensor on the front brake circuit would suit my needs, but I stand to be corrected if I've missed something?

I have a brake bias adjuster, but so far I've just adjusted it by "feel" when I get the brakes locking.

poppopbangbang said:

A couple of UK Companies do 160bar sensors specifcally for brake pressure for £109 + VAT.

Link please?

[poppopbangbang]

So is what you actually want to achieve an overlay on the video? If so then assuming you have longi G on your logger can you not just log decel off throttle in each gear, create a math channel which subtracts this decel curve from the current longi G and as such you have braking force which you can use for your video overlay? Actually you could probably just stick Longi G straight in there and it'd do the trick!

Brake pressure logging is really used for much more complicated things than just rate of vehicle decel.

Toilet Duck said:

Link please?

Would love to but I work for one of them and I don't think that's allowed.....

[mtrehy]

TPS and Brake pressure should be available through CAN (I don't know anything about your car though). The hardware supplier should be able to provide the dbc reference files to enable you to read the signals.

[Toilet Duck]

poppopbangbang said:

So is what you actually want to achieve an overlay on the video?

Yes, that is one of my primary aims regarding brake pressure. Having said that, I think it will be useful to see how hard I'm pressing the brakes and at what point on track, even if its just to compare between days out to see if I'm making any improvements.

poppopbangbang said:

If so then assuming you have longi G on your logger can you not just log decel off throttle in each gear, create a math channel which subtracts this decel curve from the current longi G and as such you have braking force which you can use for your video overlay? Actually you could probably just stick Longi G straight in there and it'd do the trick!

Showing my ignorance here I know, but I don't really understand this. What is "longi G"?

My data logger turned up today and its the first time I've seen one, so I'm on a steep learning curve

poppopbangbang said:

Toilet Duck said:

Link please?

Would love to but I work for one of them and I don't think that's allowed.....

Would it break the rules by mentioning your company website? Its not as if you are doing a sales pitch . Perhaps a PH moderator could confirm? If its going to cause "trouble," would you mind sending me a message through PH with your company detail etc?

If I can source a suitable pressure sensor at a sensible price, then once everything is up and running I may just bite the bullet and buy a second one so I can measure both the front and rear braking circuits.

anonymous said:

[redacted]

Yeah, thats my thinking. I want to see how/when the brakes are being applied and to what degree, not just if they are "on" or "off"


Going off topic a bit, but I'm also looking for a steering angle sensor and have been considering going for this one, its £90 from here

However, my data logger outputs 5v as a reference voltage, the steering angle sensor above needs 4.5v reference. Does anyone know if I can just "calibrate" the sensor to the 5v by making changes to the table map in the data logger software for this parameter? Or can I only use sensors that are made to work with 5v reference signals?

Thanks again everyone for the continued input and help, much appreciated

[Toilet Duck]

mtrehy said:

TPS and Brake pressure should be available through CAN (I don't know anything about your car though). The hardware supplier should be able to provide the dbc reference files to enable you to read the signals.

I don't think brake pressure is available through the OBD2 port as there isn't a brake pressure sensor on the car. The Atom uses some sort of Hondadata ECU. I did have one of those blue tooth OBD readers (now dead) that "talked" to my mobile phone. There wasn't a great deal of information available from it. I've bought the data logger now anyway, so I don't have the option of OBD/CAN interface, I need to use the cars existing sensors (e.g. for the throttle position sensor signal) and fit additional ones where required.

[Steve H]

Toilet Duck said:

Showing my ignorance here I know, but I don't really understand this. What is "longi G"?

TD, I think this is the main thing you need to look at.

Your logger will measure position via GPS so you can overlay the data onto a circuit map but it also measures G force. This means you can see at a glance if and how hard you are accelerating, braking and cornering and to a large extent it means you don't need to use steering, throttle or brake sensors to see what's going on.

The measurement will usually be displayed as a circle with a dot in the middle which moves according to how the car is experiencing G force, think of it like a clock face and when you are accelerating the dot would move towards the 12, braking towards the 6, left turn towards the 9 etc.

By looking at it this way you can see how hard you are braking but also how well you are transferring the grip of the tyres from braking to steering into the corner and then to acceleration on the way out. If you released the brakes and then turned, the dot would return to the centre and then move across but if you overlapped steering as you were progressively releasing the brake pedal the dot would move round the outer diameter of the circle from 6 to 9 (or 3), showing that you had maximised your use of the grip available. This is called the traction circle and visualising it as a driver or on data helps to ensure you are using as much of the grip as possible at all times.

None of this is to say that you can't learn from individual inputs but it takes a lot more analysis and would generally be a way of ironing out any last glitches rather than as a main tool, I'd suggest you start off with the basics!

HTH

Steve H

[stevieturbo]

Steve H said:

This means you can see at a glance if and how hard you are accelerating, braking and cornering and to a large extent it means you don't need to use steering, throttle or brake sensors to see what's going on.

And none of things tell you how hard the driver is working. How much steering input is required to make the corner, how hard he needs to press the brakes, how much throttle he is having to modulate.

ie all very useful information in the basic setup of the entire vehicle as a package.

You may not need the inputs above, but they hold a lot more information than you think.

[anonymous-user]

Toilet Duck said:

Going off topic a bit, but I'm also looking for a steering angle sensor and have been considering going for this one, its £90 from here

However, my data logger outputs 5v as a reference voltage, the steering angle sensor above needs 4.5v reference. Does anyone know if I can just "calibrate" the sensor to the 5v by making changes to the table map in the data logger software for this parameter? Or can I only use sensors that are made to work with 5v reference signals?

That SAS is just a multi turn(10), linear 10Kohm poteniometer. As such it's output is totally ratiometric with input voltage. You can use 5v fine (total current flow is 5/10,000 amps only!).
You can buy such a pot for less than a tenner:
10turn pot

Although that kit obviously comes with some nice pullies etc to make mounting easier

You need to set the SAS up so that the mid position of the pot wiper (i.e 5 turns from one end) is "straight ahead" on the column/rack and check that the pot doesn't hit it's end stops before the rack does (depends on the drive ratio between pot and column obviously)


On the orginal question, here's an A2 master cylinder for £24 that comes with a couple of pressure sensors:
A2 master cylinder