GY-601 PRODUCT REVIEW

The amplifier features a full 8-character dot matrix LCD digital display screen, measures a rectangular 57 x 32 x 15 mm and weighs in at 34 g. The amplifier incorporates microcomputer high-speed arithmetic processing to enhance gyro response and high-resolution 12-bit A/D accurately converts the sensor output to a digital signal. The amp also utilises a super narrow pulse band of 760 us, that substantially improves the tail rotor servo response. The amplifier has a full interface facility and access is via rebated function plus and minus keys, whilst the values are adjusted via rebated data plus and minus keys. Of further interest is that the contrast of the screen can be adjusted and in normal use, the screen displays the actual gain sensitivity, the operating mode (normal or AVCS) and the voltage. However, if neutral offset is in place, this will be displayed and a very nice feature is that should the RX battery drop below 3.8 Volts, a flashing low battery warning will appear.

The actual GY-601 sensor utilises the latest Silicon Micro Machine (SMM) type of sensing and is mounted in a very compact low-back aerofoam case to improve vibration resistance and neutral characteristics. This dome shaped sensor measures 34 x 34 x 18 mm and weighs in at just 24.5 g. The quoted current drain for the combined Amplifier and sensor is 70 ma and the operating voltage is 3.8 to 6.0 volts. Included with the GY-601 gyro, is a specially developed S-9251 tail rotor servo. It is of the conventional 40 x 20 x 36.6 mm Futaba servo dimensions, weighs 57 g and to release a very high response rate, works at 0.07 sec over 60° of travel. The servo offers 3.7 kg of torque at 4.8 v and to keep all the internal components cool, it has an alumite heat sink built into the lower servo casing.

Installation and Initial Adjustment
Due to its compact nature, installing the GY-601 into any model helicopter would be very easy! Worthy of a mention is that you are advised to mount the sensor so that no metal or conductive objects can make contact and apply some caution to what is a suitable location? To ensure maximum performance, Futaba's advice is that the sensor should be located a minimum distance of 2 cm away from any servos, 10 cm from the engine and 5 cm from a GV-1 governor amplifier if being used. Once a suitable location is found, mounting the sensor simply involves sandwiching an anti-interference plate between two pieces of self-adhesive foam and sticking the sensor to the chosen location. With regard to the amplifier unit, it is relatively small in dimensions, so I easily mounted this next to my receiver, before connecting up the sensor, amp, servo and receiver as advised. This simply entails plugging the sensor and servo into the amp, before plugging the RX input lead and Aux. channel lead into the receiver as desired. Here, the RX 1-4 lead connects to your specific rudder channel and the Aux. connection that controls the gain and normal/AVCS types of sensing via ATV values, simply plugs into a spare channel of your choice.

Once connected up, the instruction manual carefully guides you through an initial set-up. This begins by selecting which of three possible gyro mode options you prefer. Here, you can have just normal sensing, just AVCS or a combined mode where either can be selected via your transmitter.

Next, you are guided through important mechanical tail rotor/servo setting up advice. This basically consists of ensuring the servo horn is at 90° to the linkage and a suitable size of horn has been selected. To achieve this, normal sensing mode is selected and with the rudder stick at neutral, the horn is adjusted on the servo splines so that it is as close to 90° to the linkage rod/wire as possible. Then the sensing direction of the servo can be tested and if incorrect, it is reversed in the gyro direction function.

With reference to the servo horn length, the manual advises you to rely on the advice given by your model helicopter manufacturer. However, I was pre-warned that the GY-601 Gyro system does not necessarily function at its best on a very long servo arm. So I was advised to fit a size of servo arm that ideally instigated a value of 110-120% in the Limit setting function whilst achieving the correct mechanical travel on the tail rotor linkage.

This method ensures that the servo response is quick enough to release a good performance, but is not over-sensitive to gyro gain. Of further benefit is that by making sure this level of overall throw is being used, it is said to ensure a long servo life. To achieve this, I did have to change the control ball position several times and check the correct values were achieved with no mechanical binding. However, this only took a few minutes and a final selection of 13 mm from centre of servo to control ball was settled upon, with about 110% Limit setting in each direction and no binding at left/right full tail rotor travel. Once the above has been achieved to full satisfaction, the AVCS neutral position is then set by switching between AVCS and normal, or by moving the rudder stick left to right very fast at least three times and then immediately returning to neutral. From here, I selected an initial low value of both gyro gain and tail rotor ATV in my transmitter and eagerly awaited the chance to test fly GY-601.

First Test Session
The very first time I used the GY 601, I had unknowingly put the gyros drift characteristics to the best test possible! I turned up at the flying field to become engrossed in conversation for about an hour whilst my model was left in the car and steadily cooked in bright sunlight with all the windows shut. So with a gas mark 7 1-hour pre-heated gyro, I removed my model from the car, instantly started up the engine and test flew the 601 gyro with no thought applied to temperature drift problems. Upon raising the model into the hover, I found the initial trim setting I had set on the bench was perfect and the tail end of the model was in perfect trim. From here, I cautiously increased the gyro gain in very small increments, until the tail showed a slight hint of wagging (over sensitivity) at 76% gain in Aux-2 ATV, before applying caution and turning the gain down to 68%. Once the gain was set, I slowly raised the rudder ATV in my transmitter until at a value of 120% in each direction, a fairly swift rotation rate was released.

Moving off into forward flight showed the tail trim was retained and my first test was to ensure that the gyro gain was not over sensitive in an unloaded situation. Thus I climbed to height and allowed the model to descend vertically nose down and then smoothly pulled out to safe horizontal flights before giving the rudder stick a flick to induce gyro wag. However, the GY-601 did not wag in this unloaded flight condition, so I now felt comfortable to explore just how well the tail held in AVCS (heading lock) mode.

Here I naturally started cautiously with a few gentle flips and rolls and was surprised at just how well the tail tracked throughout. It really was very locked in here and provided a very inspiringly solid feel to the model throughout. Next in line was the sideways flight test and for this I steadily increased the model airspeed until at full collective pitch, the engine was working very hard indeed but the model just rocketed along with the tail perfectly locked. So with a slower entry, the model was encouraged into progressively larger sideways loops. Here the model worked audibly hard in the larger sideways loops, but I was pleased to find that no real tail correction was required to hold a perfect line in what was an overly demanding scenario.

From here, I slowly built up to fast backward flight and the 601 locked remarkably well, not faltering once. So I steadily pushed the model into fast backward circuits and once confident progressed into fast backward inverted circuits. These ranged from slow but very tight, to very fast and wide and the GY-601 locked confidently throughout.

At this point, I backed off testing the ability to hold and began to slowly test the consistency of the pirouette rate and just how clean the stop rate was? This began with simple hovering pirouettes and here the consistency was superb and stops from a left-hand pirouette were awesome but a little soft from the right-hand direction. To further assess the rotation consistency, full pitch was banged in and out whilst pirouetting. Indeed, powering the model up and down in these conditions gave an audible loading of the engine, but the tail kept spinning at the same rate throughout.

From here, pirouetting flips were entered and from starting off slow and building up to 'chaos' speed, I expected some faltering of the tail. However, as I long as I managed to perform the correct cyclic/collective inputs, the tail held a very consistent rate of rotation. Even when slowing and speeding up the tail rotation, the change in rate was progressively smooth throughout.

With a sharp increase in confidence, I then entered a ripper scenario where the model was descended vertically as full tail rotor is applied. Now due to a steadily slippery increase in airspeed, the 3D NT has never been particularly outstanding at rippers and I really did not expect too much in the way of tail performance here. However, I did after a mild cautionary attempt, enter a full-blown ripper from an altitude of around 400-ft. Here the model descended swiftly with full right tail rotor applied and was totally consistent for the first 200-ft. Then some slight inconsistency began to show, but then held all the way down to the point where I ran out of bravery!

Overall, the GY-601 held the pirouette rate very amicably, until airspeed began to take over available tail-power and the scenario naturally faltered. However, even when this did eventually happen, I was surprised to find that the degrading situation came in very slowly and did not completely falter, thus giving plenty of warning that it may be time to exit the manoeuvre.

To carry on with the consistency theme, I then entered some of my legendary miss-shaped pirouetting loops and also found the tail consistency to be excellent throughout. Only when pushing the scenario to the very limits of overall size and as such involving large amounts of airspeed and collective pitch, with an overloaded engine, did the tail lose any consistency whatsoever. In average sized examples, the tail went round predictably throughout and a good improvement in the shape of my examples did actually take place.

My first test session with the GY-601 involved four steadily abusive 15-min flights and I went home feeling very inspired by the overall performance! It had locked in to all manoeuvres brilliantly and the tail was noticeably consistent throughout all but the most incredibly demanding scenarios, where the need for endless power would have helped. However of more interest to me, was that only when I had returned home, did I eventually realise that I had not changed the tail trim once since the very first adjustment on the bench!

Further Testing
Further testing of the GY-601 was much more generalised for the next session and I simply relaxed into my normal flying. Overall, I found the performance of the GY-601 to be extremely confidence inspiring and simply because the tail stayed in trim perfectly, I found many manoeuvres to be much easier to perform. The only areas where I found life with the GY-601 to be slightly more difficult, was in rolling and flipping circuit manoeuvres where I am admissibly not at my personal best. Here, I found the tail locked so well, that efforts to change line had to be much more pronounced and required a slight change in method. Here smaller and much more positive movements that were correctly timed had to be used, or the tail would happily sit outside the intended line and motion would come to an abrupt halt which is after-all better defined as a clear case of pilot error!

The only real defined flight-testing came when one club member visually noticed how well the tail appeared to be locked in and threw down a suitable test. Here it was suggested that I took off, adjusted my line and then flew a full series of linear manoeuvres, with zero assistance from tail rotor to see how long the tail held the correct line? So keen to satisfy his curiosity, the test schedule consisted of fore/aft flips, large inside/outside loops, backward loops and a host of other combinations. Now in zero wind conditions and with careful applications of accurate cyclic control, I actually managed to keep flying on the same line for at least 5-min with absolutely no correction of the tail. However, my forgetfulness finally took over and in a moment of weakness, I threw in a pirouette to the backdrop of the loud but friendly abuse that we subject each other to from time to time!

Advanced Functions
Within the GY-601 amplifier is the ability to interface many of the gyro's characteristics, allowing you to fine tune this gyro to your particular model or tail rotor set-up. Thus I did my very best to assess what effect each of these functions have, but with modern gyro technology being so good, I can assure you this can be quite difficult at times! However, I did manage to reach some firm conclusions on most of the functions and as such I have listed the function with a general description and what effect they have below

GYRO GAIN ADJUSTMENT: This simply sets the overall gyro gain value and is not to be confused with adjusting the percentage of heading lock to conventional gain. As such if you want to release more or less overall gain to raise or lower the ATV values in your transmitter, or do not have a remote adjustment facility on your transmitter, you can use this to adjust the actual value of overall gain released. This function allows you to set an independent value for Normal and AVCS mode and is adjusted by percentage.

RUDDER CONTROL GAIN: This function is used for adjusting out any differences in operation gain between normal and AVCS mode. So if you tend to change between Normal and AVCS mode in flight and recognise a different feel to tail rotor inputs for each mode, you can use this to achieve a similar feel. Adjustment is available for both directions of tail rotor in both AVCS and Normal gyro modes.

CONTROL DELAY 1: This is used to control the amount of delay when the rudder stick is operated in both left- and right-hand directions. Thus, if you feel that the initial application of tail rotor happens too fast, you can slow the initial start of tail rotor applications. The initial factory value is 0% and increasing this value slows the initial tail response proportionally all the way up to 100% where the reaction is noticeably slow.

CONTROL DELAY D: This function is used to control the amount of delay when the rudder stick is returned to neutral and can be adjusted for each direction. If you feel that the tail rotor stops too quickly for your liking or your model helicopters, you can adjust this to suit. The initial value is 0% where the stop is at its fastest and raising the value through to 100% will proportionally slow the stop from a tail rotor demand. Once again raising the value to its maximum produces a very slow stop rate.

GAIN TRACKING: This allows you to balance out left- and right-hand pirouette stops so that within mechanical limitations, they have an identical feel. The setting range is 0-20% for each direction of tail rotor. I mentioned earlier that I found a noticeable difference in the left and right stops from a pirouette on the 3-D NT. I initially tried to balance this out with mechanical tail rotor throw and whilst the situation did improve, the stops were still different in nature. So upon entering this function, I found that by steadily inducing a plus value, the stops began to balance out perfectly and upon reaching 15%, I could detect no difference between the two directions.

FLIGHT MODE: This function is designed to give you a choice of tail rotor operation characteristics which are better suited to 3-D or F3C style of flying. Thus the adjustment is a simple choice between the two. The F3C option is aimed at the very best tail suppression and stop, whilst the 3-D option is claimed to slightly sacrifice suppression and stop, but allow you a higher pirouette speed and more proportional control. When testing these options back to back, the pirouette rate is higher in 3-D mode and the tail response does feel different. However, I found it hard to notice a discernible difference in pirouette consistency and stop rate, so as I was quite happy with the F3C mode I retained this option.

AVS SENSE: This function adjusts the overall tail rotor feel whilst in the AVCS (heading lock) mode. The initial setting is 100% with the range of adjustment being 50-150%, with no adjustment for each direction of tail rotor. Thus it is an overall adjustment and appears to effect how much gyro gain is released whilst pirouetting. Going from one extreme to the other did not produce dramatic effects, but a notice in feel and consistency was found. I eventually settled on a value of 85%, which I thought gave a nicer feel to pirouetting manoeuvres.

Overall Verdict
The GY-601 is aimed at the serious model helicopter pilot and as such, has a price tag to match. However, the package includes a top quality servo and the unit can be instantly interfaced at the amplifier. So I feel that for those seeking this level of quality, the GY-601 actually represents excellent value for money. I was genuinely surprised at how well the gyro holds a given heading and by the total lack of drift throughout all testing. The consistency of the pirouette rate is excellent and with very little adjustment, the stop rate ended up being superb in both directions. The gyro simply did not drift at all throughout all testing and this certainly provides an added level of pilot confidence! I found the testing of the interface facilities to be surprisingly easy and even by going from one extreme to the other in each function, I came across no nasty surprises that could catch you out in the air. Thus the interface facility is designed to allow fine-tuning of the gyro to suit your preferences or your model needs. By following the advice I was given on choosing the servo arm length, the Gyro was incredibly good from the very first lift off and despite its incredibly high performance, it gave me the impression of a very easy-going and utterly reliable device at all times. To sum up the GY-601 is an extremely commendable package that works superbly and I could personally recommend this unit to anyone seeking a genuine top of the range gyro!

QUICK SPEC

Reprinted with permission.
January, 2003 Model Helicopter World