What kind of on-board tachometers are available for planes? Are they all optical, do any of them work on exhaust pressure pulses? Do they transmit a signal to the ground, store readings for later, or spit out information some other way?

Thanks,

banktoturn

[
SIZE=3]large[/SIZE] orange-red Hi Bank to turn I`m real glad I happen to see your ? I`ve wondered the same for a few years now. Would really be great to know just exactly where the engine winds-up to in flight...............Thanks much for asking the ?. If it turns out that you get an interesting/helpful answer, Would you mind sending a copy to bipeman_red I`d sure appreciate it.


May you (allways) land on the wheels/floats first!!!


Thanks much.........bmr

If you will go to i4cproducts.com they are testing an onboard digital readout tachometer. When I talked to them they hope to have it avaiable for sale by Jan. , they also have lots of neat products.

Here is one for ya...
http://www.sky-spy.bigstep.com/
Has lots of useful information including tach transmitted right back to ya!

Keith

flybynitro & snaught,

Thanks for the pointers. I didn't find any mention of tachs at i4cproducts, maybe they got out of that business?? The sky-spy gizmo looks like it has everything I had in mind, for a lot more money.
Good handles, by the way.

Thanks again,

banktoturn

banktoturn,

We are currently testing our new onboard tach. Here is a little info about it. Will be shown and for sale at the IMS show in Calif. mid January.
The meter will be the size of our C-Volt, which you will mount in the dash or cockpit floor. Hold your plane for run-up, look at the tach to see RPM. When you turn on your receiver, the meter will display your receiver battery voltage to the hundreth of a volt. As you start the engine(20 rpm or better) the meter automatically changes to RPM readings. After landing, when you turn the engine off, the meter will display(for 10 seconds) the highest RPM from that flight. (unloaded rpm of flight) After 10 seconds, the meter reverts back to voltage. The RAM memory of the meter will keep this highest RPM reading untill the receiver switch is turned off/on again. This will aid in tuning for max power in flight.
The prototype works very well with NO glitches or bugs so far. Will read to 20,000 rpm. No switch is necessary because the microprocessor senses when the receiver is turned on, which then turns on the meter, and visa versa on turning off. Total weight will be approx. 1 to 1 1/2 oz. Hall effect sensor used which gives best wave (square) without the electronics involved as in optical tachs. Very accurate even at higher rpms. This tach can be used on most any type of engine(not just r/c). Works well on helis also. Our target price is $60 to $80 retail.
One more new product for us will be an onboard amp meter. The prototype is being tested now. Follows the same meter size as our voltmeter and tach. Target price around $45. Should have display for this product at the IMS show also.

Rod Johnson
www.i4cproducts.com

i4c,

Thanks for the info.

banktoturn

I'm assuming the user needs to mount a magnet in the spinner backplate for the hall effect sensor?

DMcQuinn,

You are correct. The Hall effect uses a small(3/16") magnet mounted on the spinner backplate. We tested optical, infrared, inductive, and Hall effect sensors. Without a doubt, the Hall effect is the most accurate with the least amount of electronics. Also the small magnets have been tested at 1/4" gap and still perform well. Our goal is to sell a premium instrument that is accurate and easy to mount/use. I think we have it.

i4c Products
Rod Johnson

How hard would it be to get a higher max RPM reading..say 30K?? TIA

i4c,

Have you considered using pressure pulses from the tap on the muffler? This seems as though it would be fairly non-invasive.

Thanks,

banktoturn

Hey Rod, HOW YA DOIN'?

Wouldn't this be a heck of a time of year to have the dog lock me out of the car.

Guys, I stop at i4C's booth at every show that I see him, just because I think he puts out good products and I want to see what's new. He always has a small demo board set up so you can try his equipment out. I will say some of the stuff has a bit of a heafty price tag on it, but I think it is well worth it. The gear that I have bought from him has never failed.

Jeff

Chuck,

Talked to our engineer about this and he said it can be done with a few changes and programing of the microprossor. If there is some interest in wanting a 30,000rpm model of this tach, we are listening. We are guessing that your need is for ducted fan?

Rod

banktoturn,

Please explain.

Rod

Hey Jeff,

Thanks for the plug. We are modelers ourselves and strive to sell quality products. As you know we attend both indoor and outdoor R/C shows across America and face to face with our customers lets us know how we are doing and also what the customer wants. Thanks for your support and RCO rules for sure. Keep up the good work, and get a hide-a-key cause you never know.

Rod

Jeff,
Sorry for the typo. Of course I meant RC Universe. There is no other.
Rod

Rod,

Sorry, I didn't mean to be too brief. It seems that instead of picking up the engine speed optically or magnetically, one could use some kind of pressure transducer to pick up the frequency of the pressure pulses in the exhaust system, or even the crankcase, if it is tapped. I am assuming here, but it seems that there would be an obvious pressure peak that would occur once per revolution. Since the muffler is almost certain to have pressure tap, and the tubing could be routed to the transducer, you could avoid the need to mount an optical pickup behind the spinner, or mount a magnet on the spinner.

Also, for the purpose I have in mind, it would be nice to get readings up to around 30,000 RPM. There seem to be a fair number of people out there getting more than 25,000 RPM on their pylon planes and Whiplashes, so there should be quite a bit of interest.

Thanks,

banktoturn

banktoturn,

Interesting concept for tach readings that I have never heard before, but could probably be done just as you state. The pressure wave is there on every stroke and could be counted. To be pondered. That is what I like about modelers. ALWAYS thinking. Many times out of the known box. Defying gravity for sport.
As for the higher rpm tach, let me ask you. Would readings to the 100rpm be adequate? If it is then 30,000rpm we can do. If it is not , then we would need to use another meter which has more digits. That can be done also, just more cost.

Rod

APC get in-flight rpm using a sound recording:

http://www.apcprop.com/Engineering/engineering.html

Quote:

Engine in-flight RPM

from ground based video audio recording

Engine in-flight RPM is determined using a video camera to record engine audio, and, spectral analysis software to determine dominant harmonic content from the signal. Audio data are collected with the model flying both toward and away from the pilot. Differences in apparent frequency are used to determine and remove Doppler shift effects.

End Quote

Rod,

I think +/- 100 RPM is fine, for the use I have in mind.

Thanks,

banktoturn

That would be plenty close enough.

i have an on board tach hour meter for my sig and it shows rpm's when running and mins.\hrs. when off. it looks great mounted in the cockpit i only gave 27.99 for it when they first came out. at our store. for gas engines only.

Chuck and banktoturn,

Thanks to your replies we have now tested the unit and found that a 40,000rpm model of this tach WILL BE MADE and sold at the same price as the 20,000rpm model. Very accurate to the 100rpm. Our test have shown easy-to-mount sensor and relatively wide tollerence on sensor/to/magnet gap. On planes that already have electronic ignitions(C&H types), the sensor can read from that Hall Effect magnet that is in place already. Mounting the tach in a model was very easy. Pre production models of these tachs are being sent to various RC testors this week for our final evaluations. Syd Clement (200mph group) will be testing the 40K tach on one of his missiles. I am sure he will post his findings in RCU. We will try have pics of the tach on our website in the next week or so.

i4c Products
Rod

Hey to all,

The tachs are being tested, but the weather is making it slow go. Syd has the 40,000 rpm version. He lives upthere where snow gets in the way. We are also going to have a heli model of the tach which reads the rotor blades accurately to 2000rpm. Most sport helis like the 1800 to 1850 rpm range. Mounted on the heli, one can read the rpm at hover at 10-12'. Also stores the highest rpm during the flight. Voltmeter when engine is not runing. The one we are testing on our show display, and on airplanes, are working perfect. On it goes.

Rod

Hi Rod,

Thanks for the heads up on your new tachs. I was looking to build an optical tach but it looks like you've saved me a lot of work.

I do have a couple of questions. I'm pretty new to RC planes so if I ask something dumb, please don't hesitate to let me know!

First, how is the magnet mounted to the back of the spinner? I'm assuming it's not strong enough to hold itself in place.

Second, it would seem to me that the magnet would through off the balance of the propeller/crank/etc and might effect the low speed idle. Any problems? Are two magnets mounted to maintain "prop shaft" balance?

Third, ... and you had to know this would be coming, although maybe not before full production started ... how do I read the tach with my onboard microprocessor/data logger? Does the LCD display have a standard serial interface such as TTL, RS232, RS485, or SPI that I could monitor (receive only) or is it a parallel interface that wouldn't be so easy?

Thanks for any additional information you could provide!

Cheers!

Cub