Tachometer

[Ross Clarkson]

Hi,

 

I tried to use my Tachometer the other day with no result!

 

I applied one reflective little square of tape (as per the recommended size) to the front of one prop blade, about an inch in from the tip. (14 x 10 wooden prop)

I then started the engine and tried the Tach but no readings!

 

I could see the red laser was in line with the bit of tape going around but nothing!

 

Am i doing something wrong, or is it my Tach?

[flytilbroke]

Could be the Tacho. My understanding is that they "read" both props, or three on a three blader.

 

I use mine from Behind the prop. So do most of the other guys I know who use them, including one very well known article writer.

[Simon Chaddock]

Ross

I tested mine by putting a tape square on the chuck of my drill.

This gave me an idea of the range and angle that the tacho would successfully 'see' the reflection from the tape, much safer than experimenting round a prop.

The tacho has to be pretty much at right angles to the tape so as flytilbroke says better to be behind.

 

 

One further point the back of the blade is almost flat so you will get a stronger refection as well.

 

Hope this helps.

[001]

I thought that the sensor reads the interruption of the light by the dark propeller.

 

So by putting white tape on the rotating bit the sensor is 'seeing' a uniform whiteness.

Usually done by reading off the black bits rotating against the bright sky.

 

I don't think it has ever been normal to use white tape on a propeller, but for checking the speed of a black disc or drill chuck.?

Edited By Richard Bond on 13/03/2011 17:14:14

[Klippy]

Try pointing it at a flourescent light, it should show 3000rpm, or 1500 if it's a dividing tacho.

[Biggles' Elder Brother - Moderator]

I think Richard may have a point. My tacho definitely works by the prop blade effectively "reducing" the ambient light as it goes past. If you put retro-reflective tape there then there would be no "dark bit" and my type of tacho may well not work under those circumstances.

 

But having said that my tacho has no laser - just a light detector.

 

BEB

[PatMc]

I take readings from behind the prop, if the background is dark or the light weak I put a section of white melamine in front of the prop or shine a flashlamp on it.

[John Privett]

Ross mentions a red laser and reflective tape. This sounds like quite a different type of tacho to the one that I have - or that Pat, Tony, Richard, BEB etc. are also familiar with.

 

Ross - have you got a model number for your tacho? It would be interesting to find out more about it!

Edited By John Privett on 13/03/2011 22:39:42

[Ross Clarkson]

Hmmmm, maybe i have a rubbish Tach! I can't seem to find it online anywhere now and i can't remember where i bought it from!

I know it has worked before, and when i wiggle it fast over the supplied reflective tape not attached to a prop, it seems to be reading and working.

 

Maybe i should buy a new one. Do the ones you have guys have a laser and tape?

Can anybody recommend a good one that i can replace mine with?

[John Privett]

This is the one I have.

 

Actually, I'm quite surprised to see it's still (apparently) available, as I must have bought mine a good 10 years ago! There do seem to be other much smaller equivalent ones around now.

 

It works very simply by detecting the changing light level as each prop blade briefly obscures the bright sky (or Pat's flashlight or white melamine!) and determines the rpm from that. No lasers, reflective tape or anything like that!

[Biggles' Elder Brother - Moderator]

My tacho is the same sort of thing - no tape, no laser. You just point it at the prop - from behind if you are smart! It deals with two, three and four bladed props. Very light, easy to use.

 

You can see it here. Available in most model shops - or something similar.

 

BEB

Edited By Biggles' Elder Brother - Moderator on 14/03/2011 00:34:23

[Ross Clarkson]

Think i will be purchasing a new one!!!!!!! Cheers guys.

[Simon Chaddock]

Here is the non contact laser tacho just like I have!

 

[Erfolg]

Could you be having a similar problem I had, where I attempted to use it under artificial light?

 

Used in daylight there was no problem, nothing reflective used, a translucent white prop.

Also as recommended by someone on the forum, when using under artificial light, I placed a torch in front, again a good reading was obtained.

 

As also suggested bt flytilbroke, I use it whilst positioned behind the model. I feel safer there.

 

My tacho cost only about £7 incl p&p or so and it works really well, when I do things correctly.

Edited By Erfolg on 21/03/2011 16:35:00

Edited By Erfolg on 21/03/2011 16:39:58