The GV-1 sensors are reliable but the plastic case is not the best. Often the sensor case will crack or break off. Great Planes offer replacement sensor cases but I have been and still am waiting over a year for some. The Futaba GV-1 sensor costs 60 dollars so it is a little expensive to replace as a full sensor unit for the sake of a cheap plastic part.
Someone has invented an optical sensor circuit design which anyone having basic soldering skills might assemble for about 5 bucks. From what I have researched it appears the original design came from Yoram Shalev. I have tested the device and it works fine. It relies on a single shiny reflective stripe on something rotating at engine speed to receive a signal. Silver paint on a fan or silver tape on a black fan will do. The device supplies its own IR light source which is reflected back to cause a pulse that the GV-1 recognises as one engine rotation. Best of all it functions with a relatively large gap between the optical sensor and the reflective stripe. The sensor screen on the GV-1 works normally for air gap setting.
For guys with buried engine cooling fans then several equally spaced stripes might be installed upon a main gear for a higher sampling rate. Some counter gears could be used also. Remember though the engine fan is the best point to sample engine rpm since the GV-1 is after all an engine governor.
By manufacturing the sensors they can be economically installed on several machines sharing the same GV-1 controller. The cost is about 6 or 7 dollars Canadian. You end up with a fleet of plug, program and play helicopters. This is also called beating the system. The money you save on GV-1 controllers can be used for fuel……or good food!!
The OPTEK703 sensor is a little large for my liking. Several sensors are available in different dimensions and all work well with the resistors shown. The smallest sensor I could procure is a bit difficult to solder due to the size. I choose the OMRON EE-SF5 as a best selection since it fits the Futaba type mount nicely and easily clears obstructions. The OMRON has proven itself over time compared to the OPTEC since it has been around successfully for a decade with the Throttle Master governor. I expect the OPTEC should be just as good while the other is time honoured in a governor atmosphere. On the smaller OS32 one can still have access to the carb retention screw without having to remove the sensor. For the best results I paint the fan bottom with flat black urethane paint which is fuel proof after sanding the surface for good adhesion. I then glue aluminium duct tape to the fan with CA. I clean the tape with acetone first to remove the sticky gum prior to applying the CA.
We have been installing the sensors on different helicopters and came across what might be an issue. The sensors are supposed to be all the same with the same basic focal point but we found some that were different. The focal point is the air gap which gives the highest reading over the shiny tape. The sensor in question operated with a much larger than normal air gap between it and the reflective surface for this reason. This allowed direct sunlight to swamp the sensor and not let it turn off after the reflective strip passed over it. We found the problem during a bright sunny day while doing some flips. The GV-1 as expected turned off resorting to the normal stunt throttle curves. Not a big deal if you have a fair backup throttle curve ingaged but this potential problem needs to be addressed in a preventative manner. The GV-1 will not turn back on unless you cycle it. I have spoke to other people who have had problems with both optical sensor types when flying inverted at high noon.
It is my advice that people be made aware of a need to check the sen display in the sunlight by positioning the helicopter in a manner that might expose the installed sensor to direct and reflected sunlight. If the display low value (non-reflected) goes over 40 based upon futaba documentation it may become a problem. I’ve added a big safety factor as you can see below.
With the addition of a sun shade shown below (which is made from black shrink tubing) we were able to keep the lower reading typically under 10 with a large focal distance at all helicopter attitudes. Attached is a picture to clarify. The shrink tubing should be c/a glued, it needs not be a perfect job and can over lap the sensor eyes more than a tad. From the look of the OPTEC unit the wedge shape is not ideal for shrink tubing retention. One other alternative which may help out is to move the sensor closer to the crankshaft center away from the edge of the fan parameter. A third factor for consideration is to make sure the sensing side of the unit is closest to the engine crankshaft. All you have to do is tape one window and shine a flashlight, the window that gives a reading on the GV-1 display should go inboard towards the crankshaft.
It is a good idea to keep the reflective tape the same width and length as the sensor face. A large reflective area may deflect sunlight when not over the sensor and confuse the governor. To remove this potential it is best to use the sun deflector with the fore mentioned smaller reflective surface keeping the gap between the deflector and fan to 1mm. What I am trying to do is make this installation as “murphy proof” as possible, make you aware of a potential quirk even though many have not come across this issue. Again, both the OPTEC and OMRON may be subject to these conditions. Remember to use back up throttle curves with all governors. Any setup problems, send them my way by e-mail and I shall try to help out.