Is the Fromeco Tach worth the extra money

[frank mccune]

     Anybody have an experience with the Fromeco Tach?  Impressions, opinions etc.?


                                                                                                 Tia,

                                                                                                 Frank

[Larry Renger]

My brother, the Electrical Engineer from Caltech, made me a Tach tester that goes up to 60K rpm. Every tach I have tested is within a few percent of correct at all rpm. The only ones that were off were a Heathkit tach and a very expensive one. All the regular ones from Tower, Hobby People etc were just fine.

On the other hand, I "hopped up" a tach by making a little tube that extends in front of the detector. It is black inside, and has a lens that focuses the incoming light on the detector, making it both more sensitive and directional. The lens has about double the area of the detector, so it gathers about twice the light, and the tube excludes external light.

[Fredvon4]

Larry can you post about the lens, size, and source and the distance out of the tube new lens?

[Motorman]

I tune racing engines to the Nth degree with a Hobbico mini tach if that answers the question.


MM

[tom brightbill]

My $.02 worth, the answer is yes. After using a series of the commonly named brands and having them fail to varying degrees (3 in 4 years) I bought the Fromeco. No need to cram it in close to the prop, it will read from as far back as I can hold it. If anything, too close seems to make it want to be too precise.
Here's more including Brett's earlier comments (as usual, spot on):
http://stunthanger.com/smf/open-forum/what-is-a-good-tachometer-to-purchase/

[Brett Buck]

     Anybody have an experience with the Fromeco Tach?  Impressions, opinions etc.?

   Probably. It's a much better performer than any of the others, and works reliably under a wide array of conditions. There's a thread on SSW where David and I diagnosed and corrected the problems with the first version of it which were then partially implemented for production. The people at Fromeco really listened to us and the resulting production unit seems to work well - even though it would probably work better if they had done it the way we did. The Fromeco is the distant descendent of the best tach ever made, the TNC, which went through a bunch of parts obselescene issue and 3 different companies to become the Fromeco.

    The biggest advantages are that you can measure from at least a foot or two away, rather than having to jam the thing into the prop disk, and that it is very stable over a wide range of conditions. I think this is because of the pulse-shaping circuit, where it takes the raw photocell output and "cleans it up" much like we do with scanning Earth sensors for space applications. That makes it more-or-less immune to light level variations. The majority of the cheapies have a very crude detector circuit, and while you can play around with calibrating them all day long with fluorescent lights, they sometimes give random numbers in practice

     At the time the TNC came out, the alternative was an ancient Heathkit tach (which worked OK but was big and fragile, and had a analog meter for output, which was readable to maybe 200 rpm) and the dismal Tower/Hobbico black square one, which was really compact, cost $40, used $15 batteries that died quickly, and gave absolutely random numbers. You had to use *your* tach and only yours, if you tried to use someone else's , it might be different by 2000 RPM.

    Whether it is worth it or not is up to you. If you want a tach that works and gives accurate readings, it's the only option. Many people misuse tachs, trying to screw the needle in and out for 30 seconds trying to hit a particular number and ignoring the fact that they are moving 1/2  turn from flight to flight.

    Brett

[Larry Renger]

The lens is about 5/8" in diameter and was out of an old jewler's loupe, I think. I got the distance by finding where the lens focused and then putting it that far from the surface of the sensor. It will read the prop from at least a foot away now.  The tach had the usual need to be almost touching the prop before. I suspect that just the black tube alone would help most tachs.

[Fredvon4]

Well dang I was hoping you had speced a specific lens my two loups use 1.25 inch lenses...

OH well off to google...

Thanks though

[Brett Buck]

The lens is about 5/8" in diameter and was out of an old jewler's loupe, I think. I got the distance by finding where the lens focused and then putting it that far from the surface of the sensor. It will read the prop from at least a foot away now.  The tach had the usual need to be almost touching the prop before. I suspect that just the black tube alone would help most tachs.

  That was the most essential fix that David and I made to his Fromeco. The issue in that case was that the sensor was behind a supposedly transparent (to IR) window. It was very prone to miscounting, etc, just like the cheapies. I theorized that there was glint/reflections from the window, and he cut a hole in it, exposing the bare sensor, and putting a tubular baffle to exclude light from the side. Just like we do with Earth sensors. Not coincidentally, this is also just exactly like the original TNC. I don't think the collimation was important, it was just removing the stray reflections and glint.

   These changes got flowed to Fromeco (along with putting a slide switch instead of a microswitch to allow you to turn it on before the start), and they implemented a version of it. The production version has a hole in the window but the sensor is moved inside the box and looks through a very small (~3/16") tube about 2-3" long. And shiny on the inside. This one appears to work pretty well, but not as well as the modified original and not as well as the original TNC. The reason is probably that there are still stray reflections and glint causing occasional miscounts, but that is overcome by the collimating effect of a long skinny tube. *If it was me*, I would disassemble the tach, remove the sensor and tube, remove the tube, and move the sensor to the edge of the box, and leave it bare with a baffle. There's some chance that the sensor will get damaged or contaminated, but that hasn't happened to my 20+ year old TNC despite the abuse I have put it to.

  All that said, the current version Fromeco is perfectly acceptable and performs far better than the junky cheap ones. To my mind, either get the Fromeco, or go without and go by ear (which is perfectly practical).

    Brett

[Robert Dible]

I always preferred expanded scale analog meter tachs.  It is easier to see trends.

[BillP]

My take is $100 is a lot of money for a model tach. I don't see the accuracy as an issue on model engines either...but I tested my cheap Tower tach against my full scale plane's tach while sitting in the cockpit and found it was accurate. Pointed it though the windshield and it read the same as the high $$$ tach. The Tower tach was purchased around 1990 (the one with watch type batts) just started acting up after all these years. It has been banged around, has scars from glow fuel and never a problem until now.  I would like to replace it for $30 or so...but they don't make them anymore. Tower doesn't even sell a tach now. I'll have to see what the $100 looks like before deciding whether it will do for just checking props but being compact is one of the reasons I like the little cheap ones.