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Author Topic: 'Interfacing' with a bicycle - sensing braking [solved]  (Read 2761 times)
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I made a bike brake counter using a linear potentiometer and had fun building it. My uno checks the pot and when triggered by position change, writes date-time and value out to a SD file. The potentiometer is mounted along the bike top tube and clamps the brake cable with a brass wire stop nut. Easy to put on - take off the bike frame and no problems with brake interference...but my uno-SD hardware needs a better case and battery mount. I've not analyzed my data yet - other than to check that the numbers seem valid. My intent was to gather data to predict "brake pad wear" - not likely to happen quite yet, but good fun just getting the data so far.


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* sensorOnBike.jpg (35.21 KB, 606x275 - viewed 18 times.)
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"The old Europe"
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That's NICE.

Was the case a custom milling job?
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A switch for brake sensing comes with this cheap brake light kit:
http://www.dealextreme.com/p/3-in-1-electronic-bike-horns-with-brake-light-and-turning-signals-3631

I was tempted to buy it just for the switch! I look forward to hearing how you do with the linear pots.
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custom milling? no, the case is just sheet styrene (.080 ") with gray primer. I glued together a basic box to hold the potentiometer plus longer tangs to attach the frame mounts. Used flexible bike light straps with extra long bolts to go around the larger frame tube. To mount and use, I have to undo each strap and thread it underneath the brake cable into position on the frame, then align the wire stop screw on the pot arm onto the brake cable and snug it down - easier than it sounds. But the whole rig is custom to my bike for sure.
 


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If you are using v-brakes, why not just put a flex sensor across the two arms (where the rubber boot is in the pic below):



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Most of those solutions measure movement, not force. If you really want to measure braking force, I'd go with:

Quote
* Direct measurement of the wire tension. Similar to this geometry.

but instead of a tactile switch, I'd use a strain gauge force sensor to measure the force on the middle wheel in that diagram. That way, the middle wheel hardly moves and the travel of the brake lever won't increase significantly.
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People! Surely the following should have been addressed before now!

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The goal is to trigger an 'action' as soon as the brakes are used, not when the effect of using them becomes apparent (or not).

It is worthy of a thread in its own right! A deep discussion of fundamental Heisenberg issues!!

===
But to turn to something useful...

Do you need to know how hard/ how much braking? Or merely that braking has been initiated??

If the latter will do....

A weatherproof (your environment IS challenging!) pushbutton switch kludged onto the thing you squeeze to apply the brakes, and held shut (pressed up against some part of frame) when you don't squeeze. When you squeeze, pressure on the button released, "braking" detected!
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"The old Europe"
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No, let's not stray from the topic please. Quantum mechanics gives me a severe migraine.

We're dealing with macroscopic observables here, no need for collapsing wave-functions / PDFs and CDFs to measure stuff on a bike.
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On the brake handle, between your hand and the grip, put something like this...
http://www.sparkfun.com/products/8712

The harder you squeeze, the more braking.

Or was something like that already suggested?
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"The old Europe"
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Sort of ;-)

And I have my doubts about how long this piece of plastic would last under my grip. Linear potentiometer it is for now.
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A little update.

I very crudely attached the sliding potentiometer to the bike and used one of my old LED projects to show how strongly I pull the lever. The principle seems sound.

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Looks good, minor remark, from esthetical point of view I would one LED array move clockwise and the other counterclockwise so it becomes symmetrical.

Another option is to make the pattern "logarithmic" -> 1 red -> 2 red -> 4 red -> 8 red   - would be nice symmetric too.

That said, Well done!!
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Rob Tillaart

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Commencing symmetrization!



Now I need to look into weather-proofing this thing. Last winter I used a plastic bag. That works, but it is not what I'm after. Ideally I'd make a permanent project and get some sort of transparent coating and a battery box under the saddle.
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looks better - more professional - imho.
You can also add a indication you want to go left or right by blinking the appropiate side.

PS, silly effects vid was good too ! 
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