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TOPIC: Detecting Wheel Rotation - Reflective Tape or Paint - Ideas?

Detecting Wheel Rotation - Reflective Tape or Paint - Ideas? 3 years 2 months ago #17114

  • hop
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Hey guys! Long time no see! I have a question...

I have an exercise bike I want to add electronics to. Somewhat simple stuff really, but I need advice about detecting revolutions of the flywheel, with moderate resolution.

I have IR Emitter/Detector pairs in various forms and makes, and I want to use it to count ticks on the flywheel. I do not want to add any significant weight to the wheel, so I thought about reflective paint or thin tape so I can generate some kind of digital signal as the "ticks" pass by the sensor. If I use this technique, I thought about varying the length of a few "frame" points so the signal varies depending on what point is read. Not necessarily a complex encoding pattern, just a unique one to the wheel for knowing where the full revolution point is, and maybe at every quarter for timing/syncing correction. This presents a little coding problem overall because as the wheel varies in speed, so do the lengths of each point reading. I realize I cannot use static duration to my expectations. I thought about printing a simple bar code for each point with a start/stop bit, and encoded data that can be read at any speed. Not sure yet.

So that leaves me wondering what reflective surface to use. Paint? Adhesive reflective surface? Just paper with a black and white code printed on it and stuck on with light glue?

I thought about using tiny magnets with a hall effect transistor also. Each magnet will have a different magnetic signature but I'm not sure how that would change based on the speed it passes by.

Any thoughts? I would love to hear them!!!!

For the curious... the 'electronics' I am referring to is just display readouts for speed, duration, caloric burn, and maybe some memory function that tracks progress. I will be using over-kill hardware of course (hop style lol), using a BeagleBone Black (loaded with Debian Linux), a touch screen HDMI 5", the sensor package, and wifi to tie it into my home server for populating a database. I will simplify it with more scaled down processing and input/display hardware when I get the software tweaked the way I like it. I have been away from the PIC series for quite sometime, but my new BeagleBone Black supported test bed will allow me to write and use tools to make use of my favorite beloved PIC line again.

Thanks you listening, and your time!

Hop
Last Edit: 3 years 2 months ago by hop. Reason: That can't be right! Spell check passed? lol!

Detecting Wheel Rotation - Reflective Tape or Paint - Ideas? 3 years 2 months ago #17115

  • Baldor
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I dont understand why you want to know the position of the flywheel. Why not just a few strips evenly spaced, like the typical encoder, and just measure time between strips? Then you have RPM with a simple calculation.
Aprendiz de mucho, maestro de casi nada.

Detecting Wheel Rotation - Reflective Tape or Paint - Ideas? 3 years 2 months ago #17116

  • hop
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Hmm, actually, good point lol. I guess I was worried about missing a tick, thinking redundancy. Not sure why. Thank you. What about my reflective surface question? Strips of what?
Last Edit: 3 years 2 months ago by hop.

Detecting Wheel Rotation - Reflective Tape or Paint - Ideas? 3 years 2 months ago #17117

  • Jon Chandler
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Optical sensors like this one from Elecrow could work well in this application. They have a working range from a few centimeters to about half a meter. You can probably find similar sensors on eBay or maybe even Tayda.

The best target for these is reflective tape; a great source is the reflective tape used on bicycles. Use a single piece if you just want to know RPM. If you really need wheel position, you might put a strip of tape every 90°, with two pieces separated by a small gap at one of the positions.

These sensors have an open drain output. Connect a load resistor between output and V+. When the sensor sees the tape, the output will go low.

In a previous life, we used sensors like this when balancing rotating equipment. A single piece of tape on the shaft or coupling provides a phase indication between the "high spot" and a known shaft position. A problem there was always getting the reflective tape to stay attached on a shaft that might be oily, wet or have steam blowing on it. It was not a happy day when the tape went flying half way through the procedure!


Last Edit: 3 years 2 months ago by Jon Chandler.
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Detecting Wheel Rotation - Reflective Tape or Paint - Ideas? 3 years 2 months ago #17119

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That is awesome guys, thank you! Jon, I'll try what sensors I have first, then use this if I need something better. Thank you!

I finished my BeagleBone Black prototyping tray today. Here is what I have in that tray... (straight from my facebook)...
My BeagleBone Black Prototyping Station. Complete with wireless mini keyboard, WiFi, SSD drive support, 4gb on-board Debian Linux operating system, 8gb class 10 microSD database storage support, HDMI 5" screen (not touch yet), and a full-beefy 3a powered 7-port USB hub to support devices. She's beautiful, able to be hung off the side of my server rack, can connect via wireless or wired ethernet to my home network, and almost ready to help me build all the embedded wonders I want to introduce to the world. grin emoticon I can even run a virtual ANDROID machine on this device to test my mobile applications.
I should be able to program all my other embedded platforms from this station. I can also cross compile from any windows machine on my network and use this station as a hub for that purpose. This is a GIANT STEP for my research and development. WOOHOO!

the tray is a steel wire shelf-like unit that is designed to hang off my server rack on wheels. I just got wireless working with a static IP after having to compile an updated driver for the EW-7811Un 802.11n Wireless Adapter [Realtek RTL8188CUS]. Everything is working great! Now I can start work on writing code for sensors, etc, cross compiled in C++ and burned into more simpler devices. Big wins for me today! =)
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Detecting Wheel Rotation - Reflective Tape or Paint - Ideas? 6 months 2 weeks ago #18027

  • Jon Chandler
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Damnit. I missed clicking REPLY and hit DELETE instead and Hop's message was gone before I could blink. I am so sorry!

Reflective tape will work well with an optical sensor.. From personal experience, it will work reliably to 11,000 RPM, provided there are no steam leaks blowing directly against it and the shaft you're putting it on isn't covered in oil. It should be 100% reliable with no missed pulses.
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