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Futaba 'G-501' Piezo Gyro

Written for 'MHW'.

Futaba 'G-501' - Setting up - Flying - Conclusions

Solid state gyros have been around for a few years now but, having waited for the demise of the early brave attempts, we are beginning to see a spate of them from all of the major manufacturers. History relates that the early ones were temperature sensitive and showed marked neutral drift with changes in temperature.

The first unit that I was aware of was the Wilson unit from the USA. This cost around $250 some eight or more years ago, although the price was later dropped.

This was followed more recently by the Sundance unit, also from the USA, which was aptly named according to some people.

The JR unit appeared at roughly the same time as the Sundance, but cost rather more in this country. It has its devotees, but the redoubtable Mr Youngblood only uses it after modifying it to his own requirements.

Currently, there are at least two units being worked on in this country, but both are long overdue. There is also a new unit from Sanwa (the SG-10), which we will tell you more about next month.

All of these units utilise a sensor which is produced by the Murata company and intended for the stabilisation of hand-held video cameras. According to Colin Mill, who has been investigating such things, it is only meant to work at room temperature!

Futaba 'G-501'

My first sight of the Futaba unit occurred when I was visiting Ripmax for other reasons and it came as a surprise, because I had heard nothing of it prior to this. In fact, it was used by the first and third placed finishers in the recent world championships.

First impressions were that it was very similar to existing Futaba units apart from having a much smaller, lighter, sensor. Apart from the sensor, there is the usual electronics package, a control box, a small screwdriver and a servo with the usual arms and grommets.

The inclusion of a servo is a new departure for Futaba, but this is a special type and we understand that the gyro can be obtained without the servo.

The sensor is only about a one inch cube and is connected to the electronics via a long screened multi-core cable terminating with a plug which is similar to a servo plug but not interchangeable.

The electronic package is roughly the size of a slim-line receiver and has two sockets at one end to receive the plug from the sensor and from the rudder servo. Two cables exit from the same end and terminate with servo plugs which connect to the receiver rudder output and an auxiliary channel. Also at this end is a fixed cable outlet which goes to the control box. Note that the electronics package and the control box are permanently connected.

At the other end of the electronics box is a small switch which sets the gyro connection. The label for this covers the whole end of the box - of which more anon.

The control box has two trimmers for setting the 'Hi' and 'Lo' gain. There are no other controls on this unit. The usual on/off switch is absent.

The servo is a special high-speed type (0.1 sec. transit time!) which is deemed to be necessary to obtain the best performance from the gyro.

Setting Up

The instructions tell you that you must switch on the transmitter and receiver (in that order) without moving the model and it should not be disturbed for at least 15 seconds. This is so that the electronics can decide where the rudder neutral is and establish this as a reference. You are also told that if the model is taken from a warm car to a cold flying field (or vice versa in some countries?) it should be left for 15 minutes for everything to stabilise. Otherwise, you are warned, there may be a neutral drift. Presumably, this is the Futaba solution to the problems experienced by other units.

Having been told to go ahead and fly the unit and report my findings, attempts to install the unit in a model produced some confusion. This was caused by the fact that the gyro electronics change the relationship between the movement of the rudder stick and the action of the servo. At first, this was thought to be due to the special servo, but using a standard servo and then a different transmitter, produced the same result.

What happened was that the normal amount of servo movement was obtained at about half stick movement, at which point the servo 'bottomed out' and further stick travel produced no more servo movement. The obvious 'cure' for this was to reduce the ATV on the transmitter until the stick movement matched the servo movement.

Subsequent tests with another gyro and conversation with other users confirmed that this was normal and it would appear to be a deliberate feature of the design. No doubt there are lots of you out there who are saying, "Well, of course!" OK, genius, it baffles me.

The next little hurdle was in setting the gain. According to the instructions (in somewhat quaint English), there are two ways of doing this. You can use a switched channel to select between the two controls on the gyro, or you can use a proportional channel to give you a linear control from the transmitter. In this later case, the two controls on the gyro act as upper and lower limits and the transmitter can vary the gain between these two settings. Interestingly, setting the 'Hi' control to a low setting and the 'Lo' control to a high setting actually reverses the gain function.

The use of this system can produce problems on some transmitters with getting two gain settings which are close to each other. In some cases, use of the ATV feature will give you one gain in the upper half of the range and one in the lower half - which may not be what you want. In this case, the easiest answer is to use a switch and adjust things at the gyro. Experience, and correspondence suggests that this is what most people will do anyway, since many seem to have difficulty in using linear gain controls.

Chatting to Nick Moss revealed that he had trouble in working out how to set the gain (to be fair, he was working from the Japanese instructions) and came up with the idea of using a programmable mixer and using 'offset mix' to set the gain. Here the percentage offset is the gain percentage. However, you have to remember that the 'offset' is from zero and that zero is actually 50% gain! If that isn't clear, Nick will explain it to you!

Flying

All my early flights were made by fitting the unit into the 'Concept 30SR-X' recently reviewed. The gain setting appeared to be very sensitive. Setting the gyro controls fairly close together to give a limited range of transmitter control did not really help and I am not convinced that it actually works in the manner described in the instructions.

In order to get a 'second opinion' as it were, the unit was next fitted into the review 'X-Cell 60'. I had been warned that the combination of the powerful gyro and the extra fast servo had been known to strip tail drive gears and this was exactly what happened!

At this point, two discoveries were made. One was that one of the rubber suspension members inside the sensor (rather like a bellows at each end) had been partly crushed. It should be pointed out that this was an early demonstrator unit and had been through many hands.

The other discovery was that there are two adjustment pots under that label at the end of the electronics case which set the throw of the rudder servo in each direction. If these are turned up to the maximum, it restores the normal stick/servo response (except that you now have a 180 servo!).

It seems clear that Futaba have produced a unit which has lots of adjustment so that the initiated can set things up to suit the expert flyer. It is also clear that they have had second thoughts about its use by the average flyer and have decided to make it a little more user friendly. It should be pointed out of course that removing the label and/or opening the case will void your guarantee.

Yes, it is now working fine and I enjoyed the learning experience.

Conclusions

If you really need it, then no doubt you will learn to get the best out of it. After all, it has just won the world championships (though I think Cliff Hiatt had something to do with it).

From the point of view of the average user the best part is the reduced battery consumption. The 'SR-X' has only an 800 mAh battery pack which is normally only good for a couple of tanks. With the solid state gyro I can safely forget about such things.

We must face up to the fact that mechanical gyros are a thing of the past and a time will come when you will have to buy a piezo gyro or nothing. Hopefully, the increase in demand will bring the price down. In the meantime, for the average flyer who may be thinking of buying one, the price alone should supply the answer for most people. If you can afford it, why are you asking?

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