Tom, great idea. The laser tachometers will usually work over much greater distances than a few inches. Mine worked easily at about 6 feet. They work by analyzing the pulses of the reflected laser light.
I also recommend laser thermometers (or more properly remote temperature sensors). They are not so precisely localized as the laser aiming spot would suggest. The infrared sensor just picks up whatever is obvious. To get the best temp readings, put a square inch of black tape on things that are not already black. Wait for the tape to acquire the objects temp. Measure within inches.
It is possible for a particular remote temp sensor to have a precise lensed IR sensor that differentiates a square centimeter from 2 meters away, AND that the aiming laser is installed so that it always indicates this highly localized target. Possible, though unlikely for anything less than several hundred dollars.
The cheap ones (US$30) are great. Just make sure they cover the desired RPM or Temp ranges.
Great tools!
Mark Stafford
--- In electricboats@yahoogroups.com, "Tom" <boat_works@...> wrote:
>
> I just had a chance to try out the laser tach I recently bought on Ebay.
> This item, but not this seller:
>
> http://cgi.ebay.com/Digital-Laser-Photo-Tachometer-Non-Contact-RPM-Tach-NEW-/300533163851?pt=LH_DefaultDomain_0&hash=item45f92c274b
>
> I paid a bit more.
>
> The good news is it works great. Just put a 1/2" long strip of reflective tape (provided) on the shaft or pulley or belt or whatever,
> hold the unit within a few inches of the tape, and push a button. In a couple seconds you have your reading.
>
> My Millipak controller needs either a fairly expensive handheld programmer, or some fairly expensive software to display RPM. Here's another solution.
>
> In my case, I found the motor was only turning 1610RPM when I was running 5.2kts at 25A. Looks like I could use a smaller gearbelt pulley on the motor to step up the RPM and get the motor's cooling fan turning faster. Not enough room to put a larger pulley on the prop shaft.
>
> I have never tried to run at max current the motor is capable of, since the max output voltage of my Hall effect throttle gets too high for the existing configuration of my controller. When the controller sees too much throttle voltage it shuts down until you cycle the throttle. Even as it is, I can easily exceed hull speed at 80A (for a while). I never knew I was operating at such low motor RPM.
>
> Until now.
> -Tom
>
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