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General control line discussion => Open Forum => Topic started by: Dick Pacini on March 30, 2013, 09:31:31 PM
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Who makes the best, most accurate tach? Cost isn't an issue.
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The Fromeco TNC ($90) http://www.rcaircraftcomponents.com/Details.asp?ProdID=44 (http://www.rcaircraftcomponents.com/Details.asp?ProdID=44) is generally considered the best generally available. I have one of the original TNC tachos...it's fine, but the Hanger 9 Mini tacho is the one I actually use ($28). http://www.horizonhobby.com/products/micro-digital-tachometer-HAN156 It's just as accurate, IMO, and just as good, but not hecho en USA. n~ Steve
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I don't know if it's just a matter of being accurate, but it's just as important to be consistent. I don't care that that my engine is really running at 10,750 RPM, it could be 500 RPM more or less. I just want it to read the same every time. You are just using it as a reference so that you can consistently set your needle at the same point every flight. Since they are relatively inexpensive, I have two in my flight box, but only use one for that reason. The other is just a spare or loaner. And they are of the cheaper variety but are pretty dog gone consistent.
And this reminds me, I haven't ever noticed and have been meaning to ask, do you guys that fly electric tack your motor runs to check for consistency? Or when change size and pitch of prop?
Type at you later,
Dan McEntee
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To check the accuracy of the point and shoot tachometer point it at an electric light bulb. (turned on) It should read 3600 if not it's not accurate. If it reads the same number every time it's OK for use as a reference. If it reads different every time it's no good.
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HI:
I think that only fluorescent lamps can be used for calibrating a tach.
I think that I was taught that they pulse at 60 cps where as an incandescent lamp will stay glowing when it is energized.
Good luck,
Frank
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The little tachs that I have used thru the years have said to use a normal light bulb. Flourescent doesn't have the same cycles.
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My tachs have always read 3600 when pointed at fluorescent lights.
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Dick, I have two of the original TNC tachs - it wasn't cheap - $200.00 when I got it but it is brand new (only tried it once to check calibration with my other one)...if you are looking to get one, let me know.
Geno
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Yes. If your eyes were fast enough, you would see a flourescent bulb going on and off 120 times per second. But "persistence of vision" integrates the light pulses to look continuous.
The incandescent bulb, on the other hand, has high thermal inertia, so the filament does not cool appreciably during the A.C. input.
Floyd
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I got one of those hot rod $200 TNC tachs long ago and it read the lights just fine but that's all it did. When I got around to trying to contact the seller they were history. I've been tuning by ear mostly since but, while reasonable most times, definitely not perfection.
Dave
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Lemme see if I can fix the TNC. They work dandy when they work, but the old ones in the black case were kinda crudely packaged and stuff broke. I left mine, alas, at the McMinnville circle long ago.
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I read somewhere that the old ones needed a retrofit, ,as I recalled they needed a shroud over the eye, I saw something somewhere describing it,,
I have one of the new ones, I love it,, except I have this tendency to inadvertently switch it to three blade mode,, other than that it is a jewel..
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I read somewhere that the old ones needed a retrofit, ,as I recalled they needed a shroud over the eye, I saw something somewhere describing it,,
This was/is the Fromeco model. David had one, and it was very inconsistent. It had the detector behind a window. I theorized that it was getting multiple reflections, so David cut a hole in the window, and added a short ~1/2" diameter baffle around it, so the detector was exposed and couldn't get reflections from the side. It worked good then. We relayed these observations to the people who make it and they changed it - *to have the detector at the bottom of a long, skinny, highly reflective* tube, about 3/16" in diameter and about 4" long. This was silly on two scores - first, the last thing you want is to put it at the bottom of a shiny tube, which guarantees you get lots of reflections, and second, the fact that the sensor is now buried deep inside the box, it's very difficult to move it to the front of the box, where it should be. It seems to work OK if you get it the right distance, but is nowhere near as consistent at getting readings, particularly at a long distance, as the original TNC or Skyborne.
The original TNC and Skyborne tachs had it right as far as the design goes. The weak point, to which Howard refers, is in the mechanics of the enclosure, switches, and display. The most common issue is that the display works its way out of the socket after too many drops and tosses across the circle. The symptom is that some or all of the letters fail to display, or the display is inconsistent. The solution is to push it back into the socket. To keep it from happening again you can make a spacer out of plywood and weatherstripping attached to the case that keeps it pushed into place.
Another common issue is that it fails to turn on, or it fails to switch from 2 blade to 3 blade. This is because the switches are soldered directly to pins sticking up from the circuit board. This puts all the load of moving the switch on the pins. Eventually, one or more of the solder joints breaks and the switch is ineffective. Quick fix is to solder it back. A longer-term fix would be to mount the switches directly to the case with screws, and then use flexible wire or a ribbon cable (with a lot of slack) to connect it electrically. Howard told me that the switches are failure prone, but I haven't seen a switch failure, just switch attachment breaking the solder joint. They get dirty so when I replace the battery every 5 years, I squirt some contact cleaner it there.
The last very common problem is that the plastic screw head pockets on the battery end of the bottom plate cracks from screw pressure. You can glue it back a few times, but eventually everybody ends up using longer screws with big washers on the outside. The same thing does not tend to happen at the sensor end, because the the thing that breaks off on the bottom is clamped solid to the circuit board.
I had one of the Skyborn versions that apparently used RoHS lead-free solder, and had a tin whisker that made it not work. I cleaned it up and no problems for the last 10 years or so. That's the only example of that I have found.
Oh, yeah, as everyone has found the plastic case is easily melted with Lacquer thinner or acetone, so all of the ones around here have ugly melted spots or bits of paper towel glued to the outside.
This all sounds like a lot of problems but it should be noted that I am using my very first tach that was acquired very early on from Tony directly, and it's about 20 years old and works as well as the day I got it. I think Ted is still using his, as well. I also have two Skyborn units that are essentially the same thing and also worked perfectly the last time I needed it. The biggest on-going issue I have had is not with the tach but with the battery failing or blowing up from the high temperatures you get in the back of a black van that sits out in the Sun for 12 hours.
If this is one of the originals or Skyborn types, I would be willing to be it can be made to work by checking the known trouble points.
Brett
p.s. btw, the battery lasts forever if it *doesn't* explode. I had a switch connection fail and after fiddling around with it as the field, I ended up taking some copper line-wrapping wire and shorted it across it by wrapping around it. I forgot about it, left it that way, put it in the box, and went home. About 3 weeks later I went to start my engine and sure enough it was still on, and worked fine.
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Vibratach, I think was what it was called. :)
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Howard, if you're coming to Portland for the Walker Memorial meet you can have a look at it then if you want.
Dave
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HI All:
I still am using a Heathkit Thumb Tac that I got in 1973. Have they made better ones since then? Lol
Stay well,
Frank
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I got one of those hot rod $200 TNC tachs long ago and it read the lights just fine but that's all it did. When I got around to trying to contact the seller they were history. I've been tuning by ear mostly since but, while reasonable most times, definitely not perfection.
Dave
Tony made the best tachs available at the time. He sold the company when his sight (then his health) failed. The tach was originally for his personal use until fellow flyers started asking him to make them. TNC was his initials.
Technology does not sit still...Fromeco updated the electronics and made further improvements.
Tony was a retired IBM electrical engineer.
George
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The real beauty of the tach, at least the original, is that the tach will pick up a prop at about 5 ft away.
I put a momentary "on" button to operate so that if the little off/on switch got left on it won't run the bat down. (also an old TI SR-51 case makes a perfect case for the tach.)
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Hi Dick,
I really like my Glo Bee tach. It appears to be very consistent which is the important part to me. The display has large, easy to see numbers. So far, so good.
BIG Bear
RNMM/AMM
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The real beauty of the tach, at least the original, is that the tach will pick up a prop at about 5 ft away.
I put a momentary "on" button to operate so that if the little off/on switch got left on it won't run the bat down. (also an old TI SR-51 case makes a perfect case for the tach.)
That's funny, one of the several improvements that David and I suggested was to *get rid* of the microswitch on the Fromeco, and replace it with an SPST slide switch so it would stay on!
I know for certain the the original TNC type will run for several months on the supplied *ultra-cheap* 9V. The battery that came with it was like something from the 60s. So far I have never worn out a modern alkaline battery in mine despite a few incidents of leaving it on for several weeks. The batteries have physically failed, presumably from heat cycling, before the wore out. I don't worry too much about leaving it on.
Brett
p.s. The original battery supplied with mine was one step up from this:
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Technology does not sit still...Fromeco updated the electronics and made further improvements.
I sincerely doubt that the Fromeco changes were improvements to the circuit, but they did have to deal with parts obsolescence. You can't get all the parts that were used in the original TNC any more, so they had to do something. The Fromeco types seem to be much more sound mechanically (no switches suspended on pins) and the original first version works dandy once you get rid of the front window (like this: http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=194150&mesg_id=194150 - note also that Kurt from Fromeco was posting in some of the threads on the debugging). I am less convinced that the second Fromeco version is a step forward as mentioned above. The two examples I have seen are perfectly serviceable but have nothing like the performance at very long distances of the very first originals. David uses the second version, so I suppose if it's OK for him, the rest of us will get by!
Brett
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I've been using this little miracle:
http://www.horizonhobby.com/products/micro-digital-tachometer-HAN156
It's consistent and doesn't cost as much as the new motor it is used to measure. Turns on every time, doesn't care if you drop it(it's just so light, it bounces.)
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Well when I was in Cleveland a couple of weeks ago my original TNC tach quite working. All it would read was all zero's. I replaced the battery and yup the same thing. I opened it up and checked things out....nothing. After I got back to Texas I opened it up again. Still no joy. I did a Google search on TNC tachs and there was a thread on RCGroups. After reading about the guy having the same problem and he fixed it using a different new 9 volt battery....Hmmmm. I changed out the new battery with another one from the same package and tada it works. So if your having problems replace the battery even with another new one!
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I don't know if it's just a matter of being accurate, but it's just as important to be consistent. I don't care that that my engine is really running at 10,750 RPM, it could be 500 RPM more or less. I just want it to read the same every time. You are just using it as a reference so that you can consistently set your needle at the same point every flight. Since they are relatively inexpensive, I have two in my flight box, but only use one for that reason. The other is just a spare or loaner. And they are of the cheaper variety but are pretty dog gone consistent.
And this reminds me, I haven't ever noticed and have been meaning to ask, do you guys that fly electric tack your motor runs to check for consistency? Or when change size and pitch of prop?
Type at you later,
Dan McEntee
i use a tack on my electrics ,.last week i swapped everything from one plane to another and needed to change the RPM, but it didnt seem to make a diff ,checked it with a tack and the motor wasnt following the timer, it just happened to be the right RPM for the first plane ,now need to find out why i cant change the RPM
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I had a neat one back in 1970. No battery, just pull out a long wire and set the case against the engine, and the wire would vibrate and a marking on the wire toldyou the rpms, that is until it got in the prop and bent all to he!! and the prop broke. Ah yes ,dem were da daze.. H^^ LL~
that is the Fowler vibra-tak. they are still made today. vibra-tak.com
i still use them. it's about 40$