rotational energy scavenger and sensor

Think about a Hall effect rotation sensor.

You might need to put a couple of aligned Samarium/Cobalt or Neodynium/Iron magnets onto your pulley (around the shaft) to get a reasonably constant magnetic field at your static sensor. The relationship between the shaft angle and the magnetic field angle is never going to be perfect due to odd bits of iron in the vicinity, but it should be at least monotonic for all but the most pathological of cases.

A pancake motor/generator might be what you want, but it probably wouldn't qualify as inexpensive.

You do not say what that pully mounted monitor is for or what it is supposed to do, or... If you want something extremely sensitive, get one of those baseball-sized (partial) vacuum globes that has vanes balances on a long pin; light makes it spin...

Thanks for the replies everyone. What I'm trying to come up with is an inexpensive way to monitor an automotive pully. Basically, all I care about is rotating vs. not rotating. The ideal device would be easily mounted to the pully or to a fixed point near the pully. The pully diameter is about four inches, and the maximum rpms would be in the tens of thousands. As for power requirements, I envision a simple circuit consisting of the sensor, the necessary signal conditioning/conversion, power generation, and a low power transmitter. I'm not sure about the power requirement yet.

Obviously a non-rotating sensor would be much simpler to read and power, but a wireless sensor would be easier to mount.

Thanks again for your ideas!

-Gary

"Brass Rat", 1962? You're an MIT alumnus?

That would be simple, but I want to monitor the pully not the belt.

-Gary

ps: I'm an MIT grad also, class of '96

Paint a white stripe on the belt?

(I've done that :-)

...Jim Thompson

"Are you now, or have you ever been, a member of any association who members have expressed the opinion that the U.S.A. isn't already perfect in every way?"

Should do wonders for MIT's academic standing.

Yep. And member of the MIT Educational Council, interviewing high school seniors for admission.

...Jim Thompson

You're a child ;-)

What course? VI?

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

Me, 2001, UC Davis (University of California) If he's a child, I'm a baby... waah! :)

Yup, course VI.

-Gary

Rich, I think that this is probably the solution that I'll go with. So far, the integrated optical transmitters/receiver pairs that I've found don't have a long enough focal length.

-Gary

At those RPMs, if you mount something physical to the pulley it better be centered and balanced pretty well!

Would an optical sensor pointed at the side of the pulley work (with a retroreflective sticker- or paint as JimT suggests)? Optical tachos can work from a fair distance (feet), depending on the optics and whether they use a laser or not.

Or maybe you could attach a fan to the end and measure differential temperature from a self-heated sensor vs. an ambient sensor.

Best regards, Spehro Pefhany

Why not an "electric eye", like they use to keep garage doors from closing on the car or the dog. They work all the way across the garage door. You could put a strip of retroreflective tape on the pulley and mount the "eye" anywhere you want to so it can see the tape once per rev.

Good Luck! Rich

It sounds like you need the "rotating/not-rotating" signal on the rotating part, not the stationary part, and you would also like to generate power on the rotating part. A fixed magnet, rotating coil arrangement with diode and capacitor could generate power on the rotating part and perhaps also be the "rotating" signal. Do you need to measure speed, or just detect rotation? What is your pulley diameter and maximum RPM expected, and what kind of signal do you need for whatever the presumably also rotating device that needs the rotation signal? Do you need to supply power to the device recieving the rotation signal, and if so, how much?

Retro-reflective tape helps a lot. The reflectors in the tape seem to be corner-cube reflectors, so if your receiver is close to the source-tape optical axis you do get a lot of reflection.

As someone else mentioned, at 10,000 RPM gwgjr10 might want to use two pieces of tape diametrically opposed - I got in trouble once for putting a floppy disk label on a CD, and it made the boss's computer vibrate.

Good Luck! Rich