Fun with my tach...

[Scott Richlen]

Seems like my tachometer works better sometimes but not so good at other times and I'm beginning to think it has to do with the lighting conditions.  And yes, I've replaced the battery.  Often in the morning light and under other similar conditions it gives a very steady reading.  At other times it can't seem to zero in on an RPM but bounces all over the place.  I am actually wondering if I need to paint the backs of my propellers so it will better see them.

Anyone else have this experience?  What did you do about it?  Did you paint the back of your propellers white, black, or silver?  And why?

[Dan McEntee]

   Depending on the lighting conditions, as you say, you may try pointing it from behind or from in front. If I were to paint the prop back side, I would think a lighter color would be best, but have never had to do that.
   Type at you later,
    Dan McEntee

[John Leidle]

  What brand, model is it?  What battery is in it ?
  John L.

[Reptoid]

Most optical tachs have the sensor mounted on the suface of the case with no shielding. Too wide a view causes the sensor to pick up unwanted reflections, movement, light variation, etc. 99% of the time if you add a short 1/4"-5/16" ID tube (1/4"-3/8" long) over the lens it will improve consistency 100%. Use a piece of arrow shaft or plastic opaque tubing. Dark ID is best. Stick the tube to the case with silicone or glue with the lens centered.

[Bill Adair]

I always read from in front of the prop so the sensor does not get coated with oil and engine exhaust. Best to have a light or reflective item behind the engine for the sensor to see the prop blades against. This can be open sky or any white or light color surfaced item. I usually set my white flight box behind and to one side of the engine and point my tach through the prop arc at the box.

You should probably clean your tach sensor if you have been holding it behind the running engine. Any window spray cleaner should work to cut the oil spray. I use Windex and wipe the sensor lens with a clean paper towel.

Bill

[BillP]

What brand tach do you have? Did you check it on a light bulb? My old tower hobby tach worked ok on models but was sensitive to distance. On the flip side it worked in my full scale plane pointing it through the windshield 4'-5' away from the wood prop without a problem.

[Scott Richlen]

Thanks for all of the input guys!

It is an LCD Digital Mini Tach by Hobbico.

I'll clean the lens, but also will add the tube as recommended to shield the lens.

It gives me a reading of 3600 on a light bulb at the 2-blade setting.

I hold the tach behind the prop as a safety measure while I am adjusting the needle valve.  I am reluctant to have my hands on either side of the prop at the same time.  If I have a momentary burst of "duh" I might move one of them in the direction that the other should have moved in.  I can't just ask myself: "is this safe?"  I have to ask myself "is this safe if I do something dumb".

[John Leidle]

  Scott,
  What batteries does it use ? ( voltage )
    John L.

[Scott Richlen]

What batteries does it use ? ( voltage )

CR 2032

3V

[John Leidle]

  Long time ago Gary Nelson had me clean the battery contacts to a tach that was acting up. The tach used low voltage batteries maybe 3 volt I don't remember. Told me if I lose a fraction of a volt from dirty contacts the tach may not work properly or at all. After cleaning the battery terminals with alcohol all was fine seemed like I had to reclean every 6 weeks or so. All was a lot better when I went to a 9 volt tach...
   John L.

[Dave Harmon]

  Long time ago Gary Nelson had me clean the battery contacts to a tach that was acting up. The tach used low voltage batteries maybe 3 volt I don't remember. Told me if I lose a fraction of a volt from dirty contacts the tach may not work properly or at all. After cleaning the battery terminals with alcohol all was fine seemed like I had to reclean every 6 weeks or so. All was a lot better when I went to a 9 volt tach...
   John L.

If anyone else is having this problem....just clean the contacts and battery with alcohol as above but then add a little Vaseline to the contacts to delay or eliminate any further slight corrosion.
Also, the contact pressure could be increased by slightly bending the contacts.

[Brett Buck]

Thanks for all of the input guys!

It is an LCD Digital Mini Tach by Hobbico.

I'll clean the lens, but also will add the tube as recommended to shield the lens.

It gives me a reading of 3600 on a light bulb at the 2-blade setting.

    They always do that. This tach had an older brother, even worse, that you could calibrate any time on a light bulb, but never actually worked reliably in real life. It is not a problem with the calibration per se.  It is a problem with detecting the light changing as the prop blade goes by. A baffle should help, but don't expect miracles.

     Brett

[Scott Richlen]

but don't expect miracles.

Why not?  In free-flight they pray to Hung, god of thermals.  I suppose that wouldn't help in this case.  Do you think I'm being punished by Saint Duracell because I "won't go electric"?  You know, a little jab to remind me that I still have to rely on electricity, like it or not....?