RCU Review: Forgues Research Fiber Optic Servo Extensions

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    Contributed by: Roger Phillips | Published: September 2004 | Views: 16438 | email icon Email this Article | PDFpdf icon
    Forgues Research Product Announcement


    Reviewed by Roger Phillips, RCVA8OR

    Product Name
    Fiber Optic Servo Extensions
    $35 for a 4-foot extension, complete with connectors
    Available online at:

    Forgues Research Fiber Optic Servo Extensions


    As our model airplanes get larger and larger, certain aspects come into play. Power sources have moved from glow fuel thirsty motors to bigger more powerful gas engines. Most gas engines on the market today have electronic ignitions, but there are still some available with magnetos to provide spark for a spark plug. In addition, the longevity of gas engines is such that there are an amazing number of older magneto engines that have been flying for many years.

    Radio interference has been with us since the very first R/C airplanes took flight. Through the AMA and radio manufacturers, many steps have been taken to ensure that we have a safe environment to fly our models. Often a major source of radio failure is ourselves, the modelers, and the model itself.

    The major source of radio interference today is RF, or radio frequencies, put off by our models themselves. Ignition "noise" is a major contributor as well as metal to metal vibration. It is not my purpose to have a tutorial on Radio Frequency, but suffice it to say that RF can be generated by many things, such as metal to metal contact and ignition noise. Some may recall in the early days of radios and automobiles - your favorite song was often accompanied by a buzz that coincided with the speed of your motor. That was radio interference, generated by the spark of your ignition.

    Our receivers are subject to the same interferences. Metal to metal vibration can be easily remedied, by making sure all control rods do not have metal touching metal that can vibrate. However, ignition noise can be a very troublesome problem to find and/or correct. Very often searching out interference can result in moving equipment around to avoid unwanted signals. With gas engines it is often desirable to install our servos close to the carb allowing for shorter, more secure linkages. This places the servo and it's associated signal wire in close proximity to the major source of RF noise in our models, the ignition. There are three leads to a servo, two for power and one for signal to the servo. Sometimes these leads can serve as an antenna picking up noise and letting it feed back into the receiver, resulting in interference as well.

    Another major cause of RF interference is the longer servo leads used in some of today's larger models. It's not uncommon to have 3 or 4 feet of wire for servo leads serving to try to feed back noise to the receiver.

    Roger Forgues, of Forgues Research, formerly Aerografixs, has developed a product that helps to greatly resist blocking RF interference caused by ignition noise as well as long servo leads from making it back to the receiver.

    Fiber Optic Extensions

    Fiber Optics have many applications in use today. Basically it is a clear glass flexible rod that allows light to pass through with very little losses. Because of the inherent losses in traditional wire, many telephone and communications are using fiber optic transmission. A phone line using fiber optics has a lot less signal loss and sounds clearer. And since there is very little loss, there is less equipment necessary to "boost" the signal over long distances. Basically what goes into the fiber optic cable comes out the other side with little if any loss. Since there is not metal to serve as an antenna, fiber optic cable are impervious to outside "noise". This is the key to fiber optics being used in our airplanes...

    Fiber Optic Extension



    Forgues Research Fiber Optic Extensions are comprised of basically 3 components. The first is a solid state encoder board. This board takes the signal from the receiver and transforms it into a digital light signal. The second component is the fiber optic cable which passes the digital light signal to the third component, the decoder board. Forgues Research supplies the cable with connectors in a 4 foot length, but it can be easily cut to any length to suit your needs, as well as longer lengths available through Forgues Research. The last component, the decoder board then decodes the digital light signal and passes on the original signal to the servo itself.

    Whereas a standard wire-type servo extensions gets its signal voltage directly from the receiver itself, it is limited by what the receiver voltage is internally regulated to. In the photos below are scope traces of the signal generated over standard 22 gauge 24 inch extensions. The first is a 4 cell pack, at 5 volts. The second is with a 5 cell pack, slightly over 6 volts. The trace on the left shows that even with 5 volts available at the receiver only 3.7 volts is present on the signal. On the right, the 6 volts available on show a 4 volt signal. This is important, especially in larger planes that may have 3, 4 or possibly more servos driven off the same channel. The signal is reduced as more servos are added.

    Signal trace using a 4 cell NiCad pack with standard wire extension

    Signal trace using 5 cell NiCad pack with standard wire extension

    The Forgues Research Fiber Optic Extensions only use the receivers power to power the encoder itself. The actual signal voltage is provided by a separate battery, normally 6 volts. The photo below is a trace of the signal with a 3 foot Fiber Optic Extension, with the 4 cell 5 volt pack on the receiver, and a 6 volt battery at the decoder. Voltage on the signal is the full 6 volts of the battery powering the decoder and servo. The advantage of this is fairly obvious - not only do the servos respond faster with more torque, but the signal itself can drive more servos.

    Signal trace with 5 volts on receiver, 6 volts on decoder on Fiber Optic Extension

    Forgues Research has run as many as 7 servos y-cabled from a single channel through a Fiber Optic Extension. This would be nearly impossible with a standard wire extension, without the signal degrading to the point of being unusable. In addition, since the signal does not degrade regardless of the length of the fiber optics, the signal will be just as strong with a 5 foot Fiber Optic Extension as with a one foot extension. Very handy with larger planes.

    In addition to the signal strength, signal interference from noise is very important. I tried several different things to create noise, which usually appears as spikes in the signal trace, without much luck. Since noise is undesirable, efforts are made to combat it, not to induce it. However, no matter what I did try, the signal didn't vary whatsoever between the standard wire extensions, and the Fiber Optics. However, I did manage to get a very sloppy signal when I put a very noisy small electric motor in close proximity to the wire extensions. This was a small 3 - 6 volt DC brushed motor, that has been in my shop forever. I ran it on a 6 volt battery. When it was about 12 to 15 inches from the wire extension, the trace became very fuzzy. Although I didn't see any change in the servo status, such a signal could mean trouble. This should be of special interest to the electric flyers. With the same motor, I actually laid it directly on the Fiber optics, with no signal distortion whatsoever, as evidenced in the photos below.

    Signal distortion on standard wire extension from electric motor, with 6 volt NiCad on receiver
    Signal from Fiber Optic Extension with motor laid directly on extension itself. No apparent distortion


    During testing I subjected both the encoders and decoders to severe vibration, going so far as to slam them both against the table. Both encoder and decoder are well constructed and all components are securely soldered, and potted with a flexible yet strong resin-like material, and wrapped in a heavy heatshrink jacket. No damage occurred whatsoever. I exposed them to much worse treatment than any hard landing could, short of a crash.


    Some flyers never have any problems with ignition noise induced radio interference or problems with long extensions and/or multiple servos driven off the extensions. However, as planes are getting larger and more complex, with a greater number of servos and chances for interference. The Forgues Research Fiber Optic Extensions are a welcome addition to the modelling community.

    Although I was aware of the ability of the Fiber Optic Extensions to remove the ignition noise from large gas engines and the ability to ensure greater signal strength to multiple servo setups in larger planes, it hadn't occurred to me how useful the Fiber Optic Extensions would be in electric plane setups. And with advance in electric powered flight, Forgues Research Fiber Optic Extensions are worth looking into.

    Other accessories available at Forgues Research

    Forgues Research has developed the Fiber Optic Extensions even further, and has developed a True Redundancy System. With this system, two receivers are used with any number of batteries desired to power the servos through a 14 port power bar. The signal comes from both receivers to the modified decoder. Should a receiver fail for any reason, signal is uninterrupted. Although I have not tested this system, Forgues Research has extensively tested it. This will be a big advantage to 33% and bigger planes, providing redundancy, protecting a large investment. Details are available at www.aerographixs.com. Click on the orange Forgues Research banner, and check out the True Redundancy link.

    In addition to the Fiber Optic Extensions, Forgues Research also supplies many other useful items for the modeler. Also available are his Motor Standoffs and Throttle Extensions. Roger has some of the strongest Kevlar cord out there, with 200 pounds strength. I have used fishing lead, wire, and just about everything, but I will be using his Kevlar from now on. And he shows an easy way of attaching it, with a bit of CA, and heatshrink. That is the setup I am using on my 35% Giles from Wild Hare R/C, and it will be more than substantial, even with the huge rudder area.


    In this age when our planes are becoming bigger and much more complex, any affordable product that aids in making our planes safer is a welcome product. I found the Forgues Fiber Optic Extensions to be very well constructed, perform even better than expected, and a worthwhile addition to my planes.
    There is a wealth of knowledge available on the Forgues web site, and worth the time spent carousing the site. Just click on the orange logo, and enjoy!

    Manufacturer & Distributor Information

    Forgues Research, formerly Aerografixs.
    168 Heritage Place

    Cornwall, Ontario K6J 5V6
    Phone: 613-933-7296
    Web site: www.aerografixs.com
    email: aerografixs@hotmail.com

    Comments on RCU Review: Forgues Research Fiber Optic Servo Extensions

    Posted by: Mr. Mugen on 04/20/2008
    Just how do I get one of these? I click the links here and get nowhere. I get a site that gives me more site and so on. I would like to order 2 of these.
    Page: 1
    The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in products like the one featured in the review.

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