It seems these days that electronics are becoming better and better with a larger variety of products available world wide. When a good idea hits the market many manufacturers and distributers jump on the band wagon. This is to our enjoyment as the end users. I have a personal interest in rotor speed control devices and am very grateful to have the opportunity to test but another unit. Besides informing you about this unit I shall also attempt to have you think a bit like myself…scary isn’t it!
For those unfamiliar with the term governor a brief description is in order. It is a device that senses rpm or the speed of a rotating shaft. This information is compared to a desired rpm and if the difference is large enough the throttle will be opened or closed the proper value to meet the criteria. In other words, it maintains the rotor rpm to that which is programmed into it and deliberately compensates for changes in engine torque loading requirements from the varying rotor demands. Think of it like cruise control on a car, when you climb a hill the throttle is automatically opened to the point where the speed is maintained. With the helicopter as collective is added so is throttle. With the automobile gas mileage improves since small changes are adjusted for in exacting amounts. The important thing is that it looks at rotor rpm and automatically makes fine or large adjustments to the throttle position as required.
Some may wonder why do we need a governor with all the available programing included in today’s high end computer radios. Pitch and throttle curves offer multi point selection on the curves and sometimes even include an acceleration mix. Certainly all this requires good programming skills to set up for the best performance. Even with the best person on the key pad more than one set of curves are required to cover different flight modes. While one can expect very good results in the hands of the capable when using curves they cannot compensate for all flight conditions since the rotors thrust and engine loading will vary depending on G-loadings, airspeed etc., at similar collective and cyclic stick positions. I almost forgot to mention that in the search for perfection a cyclic to throttle mix is sometimes used to maintain the rotor speed within acceptable limits. Changing weather conditions and engine setup can require an adjustment to these curves. By using a governor someone with a lower grade radio can now more fully explore aerobatics without having to replace their radio transmitter. In any case the use of complicated electronic mixes are not required by a governed system. I think by now you may see some advantages to having a governor since perfecting these curves are no longer important for a constant rotor rpm.
The next question is why do we need a stable rpm? Simply put for consistency of cyclic, collective and tail rotor control response. A higher rotor speed will give a higher cyclic response and to a lesser degree collective. If the rpm varies substantially throughout flight so will the control feel, and your observed performance as a skilled model aviator! If the tail rotor rpm is more constant the job of the gyro becomes easier as it has one less thing to chase around. Some rotors and engines have undesirable rpm bands where vibration and poor handling are present, so it is in our favor to avoid these areas.
Up until recently it was rather hard to control the models rpm with electronics due to the unpredictable nature of the reciprocating engine power flow at different intake pressures (throttle openings) and rotor loadings. Tiny computers can now think faster and in more directions, thus making a mockery of previous conceptions. Some can anticipate an upcoming demand by making reference to the throttle/collective stick position and movement including the rate of change.
The Heli-Max governor came in a compact no business, practical servo like packaging which reflects its niche…the average modeler with average financial resources. The HMXM-1500 governor is made in Germany under the CE logo or standard. The basic governor features are as good as any but without the bells and whistles. This keeps the cost down while offering competitive operational performance. This is a meat and potatoes product which requires a free 6th switched channel with ATV adjustment capabilities as a minimum system requirement. There are older analog radios out there without such features and in this unfortunate case one would have to choose a different product.
The governor is smaller and lighter than most receivers with a 7ma current draw and the ability to work within 3-9V. The standard bandwidth is 900 to 2200 rotor rpm using three magnets mounted at 120 degrees spacing on the main gear or mast. Sensing is by a hall effect semiconductor using the three polarized magnets.
The governor has four male electrical sockets as follows, a sensor input, test jumper, servo reverse jumper and the throttle servo output. In addition to these are three wire harnesses. One for the receiver throttle channel, another for the aux speed or governor switching and a third blank one which appears to be for a JR/Hitec/Graupner from the color coding. The third harness has the connector cut off and looks of out of place. The instructions speak of only two. These two are supplied with Futaba connectors as understandably there are more of this particular brand in the world. These can be replaced or modified to fit most all radios. Personally I prefer to replace the connectors and retain the plug indexing for polarization safety. With this unit one specific plug can be installed either way so reverse polarity is possible. Even the indexed Futaba plugs can be installed backwards into the non-indexed throttle output. My recommendation in the interest of “Murphy’s Law” would be to make a short harness and bond the throttle connector exterior to the plastic governor case with goop or silicone rubber. Why tempt fate. I used “Custom Electronics” PN Cel1173 Airtronics connectors to ensure the most professional wiring job possible. The gold connector pins installed very easily but I decided to use a dab of solder to increase integrity after crimping before insertion into the plastic portion. The sensor is very tiny so I would advocate bonding it to a custom mounting bracket including potting the wires to increase the mechanical durability. The part number for the tiny device is on one side, so record it in case it is ever damaged.
Like most modern governors, the system can be checked for proper setup and operation before flying. This is a very wise feature to adhere to in my opinion. Basically the checks are carried out with the jumper in the test mode and pulsing the sensor with one of the magnets. The number of pulses decides the feature being checked. When the governor LED glows, flashes or goes out will confirm system integrity. Throttle servo position is also referenced to a specific number of testing pulses as this will test the mechanical endpoints and the governor off position. If you can read instructions and count to eight you should have no real difficulty! This is much like the trouble logic codes sometimes used in the automotive industry for engine management computers and peripherals. The instructions come typed on six pages of no frills plain paper stapled together. They are very well written, simple, basic and to the point, more so than some glossy booklets I have read that were included with a competitor’s product. All I can say is I like the written instructions and description, since it gave me a very good idea of exactly what I was dealing with, why and how.
Here is a question you might want answered…what am I not getting in features? Well you have an LED instead of an LCD screen to aid in setup. You won’t get a mixture curve or battery fail safe, both of which are not necessary since this is a governor after all. If you have a 6 channel radio using the aux channel for controlling a CSM HH gyro (as an example) you are going to feel pretty limited, even if you use a Y harness. The HH mode could be disabled though and remove the limitation, but with the additional creation of another. Another product will however operate with bottom grade radios since rpm data can be stored independently in the governor non-volatile memory. Mounting the unit will require some thought including minor sensor bracket fabrication, but so do most all governors in many situations. Some main gears with a top/bottom gear track for the tailrotor output quill will be difficult to fit the magnets to and to get the sensor within an operational distance. Hopefully this will help you make a sound happy purchasing decision based on your specific situation. You will get the ability to remotely turn the unit on and off, alter pre-programmed rpms in flight with a two position switch, or use a variable knob to adjust governed rpm to your personal taste. Throttle hold can be set to turn the governor off automatically. It should be noted that two programmed switched rpms cannot be both on the same side of the center 1478 rpm if your radio program allows ATV settings down to zero and not positive/negative values. A gyro sensitivity switching mode might not have this centered ATV restriction. With the three position switch configuration two speeds and governor off can be selected. To expand on the use of the rotary radio transmitter knob, it will have infinite adjustment possible within the operational band width, and will also have the possibility of governor off at one extreme. You should also have some change left in your pocket considering the alternatives.
Like most governors it likes a linear throttle curve with 100% ATV, so the throttle linkage will have to be mechanically adjusted to suite this requirement. We still remember how to do this do we not?!! This is because the governor electronics are designed to deal (output) with a standard unmodified specific throttle servo pulse width when controlling the throttle servo.
Consideration has to be given to the top collective since any governor cannot be expected to maintain the rotor rpm if the engine overloaded. So top collective should be set so that it just starts to pull the rotor speed down and then be reduced slightly. Advanced flyers might adjust the collective slightly lower because extreme cyclic and tail rotor commands will extract extra power from the engine.
So now that you know a little about the basic physical and theoretical nature I shall take you through a typical installation including some choices I made. Just for a change I will use a glow machine since my gassers are set up and working fine presently. I’d like to have put it in my scale BK-117 but feel that something like the pod and boom Raptor 30 might be better able to demonstrate the unit benefits, operation and any short comings if present…..read extreme service. It is also an easy installation!
The first thing on the agenda was to seek the most reliable method to mount the rotating magnets to the main gear. The gap between the sensor and the magnets can be as large as 2mm so consideration was made to recessing the magnets in the gear and using a thin round plastic or aluminum cover to sandwich them in position. This would be in addition to bonding and probably totally unnecessary, but it was an alternative we thought about. We choose not to do so. What we did do was drill the three holes partially through the Raptor main gear using a number 10 drill. We then cut off the dimples left from the end of the drill apex on the gear back side. The magnets being a press fit into the holes were carefully tapped into place until they became flush with the gear top surface. The magnets have a correct side that must face the sensor which can be located using the status LED, then marked prior to installation in the main gear. From the back side where the dimples were cut off, thin CA was wicked in and then the thick CA version added. We left a little glob bigger than the dimple hole as an extra restraint.
There should be deliberation given to the main gear vertical free play (end chuck) due to the design of the Raptor auto hub with respect to the auto clutch fit on its inner race. The free play is about .22mm or more and if your air gap is too small contact may occur, so set it with the main gear assembly pushed upwards on the mast.
The sensor bracket is made from plastic shimmed to meet the gap specifications by having no adjustment slots. It makes use of RTV attachment and thus requires no drilling of the side frames. We decided to use the forward side of the gear for sensing to avoid making a sharp bend in the wiring harness since the controller is installed forward in the radio tray. The sideframe web can be used just above the main gear for a mounting spot.
A mid grade throttle servo of average speed was used since I felt anything more to be a waste of resources. This servo is lightly loaded as compared to the collective. The rotor has stored inertia which must be bleed off in order to alter the rotor speed. This will take a fraction of a second and the governor relies on a small rpm change so it can make corrections. Basically the rotor inertia acts as an accumulator by exhibiting a delaying action and besides a minor change in rotor rpm is nothing we will feel in the controls.
The throttle servo should not be considered in the same light as the tail rotor since the collective controls are moved much slower, command a larger mass of air and rotor inertia. If you moved the sticks with two different servos connected by a Y harness at a speed less than that (rated) of the slowest servo they should both more closely follow the stick or changing pulse position. I’ll probably take some flack on this one, but sometimes common sense never enters into the equation when servo specs are considered. If you are really worried about a mismatch you can use a shorter servo arm on the collective servo and increase its end points past 100 percent which effectively slows the linear control rod travel down due to the bigger angle/smaller arc. People never worry about the ATV differences between the throttle and collective, yet some are very insistent about a fraction of a second difference in rated servo transit time!
Alternatively it also takes time for the air velocity to change through the rotor and a stable of attack to develop at the blades. This initially causes an increased but temporary drag /lift situation over the disk which tends to slow the rotor at a higher rate. Tic-tocs come to mind here. I have run .11sec on the swashplate/ collective and .20 on the throttle successfully with several modern governors and noticed no change in rotor droop as compared to identical servos. There will always be a tiny delay of the engine response in specific situations. One might compare this establishment to that of a car traveling rapidly over the steep crest of a hill with cruse control. In the case of the helicopter rotor, suddenly the rotor is off loaded and still accelerating as the engine waits for the rpm to drop to the desired speed. Under this condition the engine will not wait at exactly the governed rpm since the designers did not want engine instability, but instead it will be producing a minimal torque and minor overspeed. It is still trying to govern the main gear though.
The nice thing about the installation is that we did not have to pull the engine and exhaust or dial indicate the fan again. Since the main gear turns much slower than the engine the magnets should stay attached better. This fashion is also subjected to lower vibration levels compared to the engine fan mounted magnet and sensor mount. The disadvantage I see is if any slippage becomes evident at the clutch it may pose a problem at lower rotor speeds. The sampling rate will be lower at 6600 pulses per minute compared to more than double this figure for a single fan mounted magnet. If this makes any difference it should certainly show up in testing. By adding an extra magnet the standard band width of the Heli-Max governor can be shifted to allow operation at lower speeds simply because it thinks it is running at a faster speed.
The unit was setup after some discussion as to which method we would use. The instructions mention several but we decided to deviate and have a single switched speed setup on the landing gear channel allowing on/off operation. We used a basic older 7 channel computer radio to control the machine. This still left a backup governor switching mode using the throttle position to turn off the unit, so two speeds could be setup if desired. Most all governors can be turned off using the lower throttle servo signal position and this is considered a safety feature. This is why an idle up is used to keep the throttle signal above this point ensuring the governor will remain on at low collective settings during flight. Since the throttle hold can be set lower than this point it will automatically turn the governor off when activated. All I can say is that we were a little cautious of this technology at first in that a secondary method of on/off switching was initially desired. After some flight tests we went to the dual speed setup by adjusting the lower ATV on the gyro channel. You can certainly do quite a lot with this governor by indulging in a little creative transmitter programming. It should be noted that all the setup adjustments except governor servo reversal are done at the transmitter, with most being electronically fixed only to be verified at the governor status light and by noting the throttle servo travel in the specific procedural steps. This is a secondary reason why the ATVs of the throttle have to be set at 100 percent including the corresponding correct mechanical rigging requirement. This ensures that the governor cut out safety feature is located near the proper throttle opening.
An area of concern to me with this governor is that of the fixed engagement position on the throttle curve, which in other words is non adjustable. It is located at about 35% travel which is fine for a glow engine that normally hovers at about 50% throttle. A gasoline engine hovers at about 30%. Since the idle up must be set above this approximate 35% fixed value for the governor to be operational, the rotor could encounter an overspeed or engine torque spike before the machine leaves the ground, until the governor takes over throttle command. I would suggest that the governor be engaged before the idle up is selected should this become an issue. Conversely turn the idle up off before disengaging the governor> with a switch. Just make sure both pitch curves are at the same point to avoid a collective jump if using flight modes. It’s a minor thing but it is one you should be aware of none the less.
The system has soft engagement when turning on or switching speeds which may be perceived as a small delay. This is intentional in the design and prevents torsional spikes occurring from a sudden a throttle opening. The minimum engagement point is built in for this same reason.
The moment of truth arrived and after a complete check out, the controller was sandwiched in foam then strapped to the receiver. The rpm ATV was set to a low value of 20 percent for the first run to prevent a rotor overspeed.
On the first run it might be necessary to adjust the normal throttle curve to ensure adequate rpm for flight should the governor ever fail or be turned off. Personally I’d recommend a basic flight circuit with the servo plugged directly into the receiver even though this has no effect on governor performance. I normally like to cover all the bases so as not to get caught with my pants down. Just remember that the low and high points should be left alone and not to be too fussy since it is really only a backup for an emergency situation when flying. We must remember the “normal” throttle curve lower portion is also used as a governor off switching mode. The sensor was unplugged to see just what such a failure would do to engine control. As expected the normal commands are fed to the servo allowing continued safe operation. If you had a failure (or thrown magnet) inverted close to the ground and the throttle curve did not allow the proper carb opening to sustain rotor speed you are going to crash. The low point on an idle up curve would certainly cure this to a degree. This applies to all governors. Once again, lets think redundantly and safely by planning ahead.
We started the helicopter and checked out how the ATV adjustment worked. It was not overly sensitive allowing easy and accurate adjustments using the MA optical tach for a reference. We made rapid collective changes in flight and found little lag in the throttle. We did find a very, very tiny deceleration of rotor speed when nailing the collective from a hover to the maximum position. Without the tach it could not be noticed and it does help governor accuracy. Descending quickly during the hover in a vertical manner indicated no hunting or overshoot. The collective was cycled, bounced and the governor kept up pretty well to the carefully set pitch/throttle curves. The gyro also follows better in the “governor torture mode”. At this time all the governor safety features were checked including off switching using low stick/idle up off, aux channel switching and throttle hold activation. It worked exactly as advertised and we were able to have two speeds on one side of the centered speed using the gyro ATV points if we liked. This was not mentioned in the manual and is certainly a benefit if a single rate gyro is used, or the gyro is moved to a seventh channel.
Like all governors it will speed up when going through zero pitch on the ground if it is left engaged. Not to worry because you don’t fly with the skids on the ground.
Since it works so well close in and we were not able to make it hick-up we thought some steep fast descents were on order. Descents of this nature are very hard for any governor especially if the shaft speeds are split or close to this separation point. By that I mean if the main shaft/mast rpm exceeds that of the maingear, or more broadly if minimal engine torque is demanded by the rotor, the governor tolerance cannot be expected to be held as tightly as usual. We encountered about 150-200 rpm increase on steep descents. This is the only thing I didn’t find acceptable but the governor could be turned off for this flight configuration.
During circuits and sharp turns the rotor rpm remained within 80 rpm of the hover rpm. We did notice during one of the initial flights that the governor is sensitive to mixture settings or carb problems. It tended to overspeed and hunt if things got too lean or the engine hung on the pipe. Once we realized this and made appropriate mixture adjustments it worked just fine. Tests up to this point in time revealed a substantial improvement to the helicopters handling as compared to its previous non governed configuration. You should again keep in mind that the machine was set up well by an average, competent, experienced person before the governor was even installed.
Stall turns were performed with the application of zero pitch and the rotor speed remained within +100rpm. We couldn’t hear or feel the difference from the ground. The machine did feel smoother in response with application of collective and tail rotor. The 540s were fast, nice, smooth and ratchet free on recovery with the machine sounding very comfortable. Pirouettes at maximum T/R stick deflection while hovering or climbing out posed no problems for this governor.
Multiple rolls with application of negative collective were improved and did not drag the rpm down too much. This added confidence in flying the machine but equally important no throttle to cyclic mixing was required.
All I can say this is a neat little unit, especially as I watch many sport flyers spend so much leisure time tapping the programming buttons on their expensive radio transmitters. I had loaned this unit to a budding modeler and had a hard time getting it back as he enjoyed the ease of setup so much. The more guys that see these devices in action the more impressed they are with someone’s setup skills! Why tell them what’s under the hood?
At no point in time did we experience a harmful reduction in rotor speed from that set into the device. This included all flight envelopes since the collective was never over pitched in adjustment. This fact is very important with a model helicopter performing aerobatics especially if you want to punch out of a situation you made for yourself!
The device can be found at Tower Hobbies or other Heli-Max retailers for about $130US. I have no problem in recommending this device to the average and advancing sport modeler where cost is not a factor since it is a little over priced by todays standards. A person starting to hover has no need for such a device and should be concentrating on the basics. For guys in the leagues of Bob Johnson, Curtis Youngblood etc. I cannot comment on any product for its suitability, but they after all are the minority in this noble hobby. To put the whole thing into perspective, this device can help those without the time to perfect the pitch/throttle relationship required for 3-D and advanced aerobatics. There are better performing governors on the market even though this one does the trick.You may find this governor type marketed under the Vario name “Vario control” P/N3290 although Vario USA has discontinued it. I encourage you to investigate other governor products on this web site such as the Futaba GV-1 and Throttle Jockey.