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Sanwa 'SG-10' Piezo Gyro

Written for 'MHW'.

Sanwa 'SG-10' - Setting up - Other controls - Flying - Conclusions

Following on from last months potted history of piezo gyros and a look at the Futaba unit, we recently had the chance to sample the unit on offer from the remaining member of the 'big three' - Sanwa.. The early Sanwa mechanical gyros were highly regarded by many, and it can be no coincidence that this company has bided its time before bringing out a piezo unit. It does have one or two new ideas, some of which should - and probably will - be copied by other manufacturers.

Sanwa 'SG-10'

This consists of just two units; an electronics package and the sensor, both of which are of similar size to its competitors. The electronics pack is about the size of a slimline receiver and has three controls:

a) A reversing switch on one side.
b) An 'exponential' trimmer in the opposite end to the connections.
c) An 'AGC' on/off switch next to the above trimmer.

The sensor is about a one inch cube and has silvered external finish - presumably to increase temperature stability. Its cable is detachable from the electronics.

Apart from that, there are two cables which go to the receiver and a socket for the rudder servo cable. If you are not using Sanwa radio equipment, beware of the fact that their plug connections are of a different polarity to the other manufacturers.

There is no mechanical gain adjustment. This is done entirely from the transmitter and gives a linear proportional control over the entire range.

Comprehensive instructions are included which have the now usual warnings about letting the temperature of the unit stabilise before use. Also supplied is a small jewellers screwdriver to adjust the trimmer.

Setting up

This was simplicity itself because, in essence, the unit is a straight swop for any other gyro. A couple of adaptor leads were made up to connect the Sanwa plugs to my other equipment and the unit was installed in the same 'Concept 30SR-X' that was used for the Futaba unit. Adaptor leads were necessary because the unit had to go back to Irvine Engines. Apparently, there is another model heli magazine in this country and they were due to test it too (thoughts of sabotage never entered my mind!).

Many people have problems setting up their radio equipment when using linear gyros. In some cases this is caused by the equipment. Sanwa have come up with an ingeneous answer to this one. The channel which you use to control the gain can be switched or proportional and the centre (1.5 mS to the initiated) of the channel travel is zero gain. Movement away from centre in either direction (1 or 2 mS) increases the gain. Thus you can use the ATV on a switched channel to give two independant gain setting, each of which can be anywhere between 0 and 100%. The beauty of this is that it will work with any radio and the ATV percentage is the gain percentage!

Other controls

The exponential adjustment can be set to either a negative, or positive, value so that the gyro has more, or lass, gain around neutral. Unfortunately, the recent spell of continuous bad weather meant that there was no time to explore this. My brain doesn't seem to like anything that is not linear so that was no great loss to me.

The AGC function is an 'anti-wag' circuit, which reduces the gain when the tail oscillates. The on-board processor then memorises this new setting and holds it until you next change the gain from the transmitter. The instructions do warn that this can result in the gyro turning itself right down in some circumstances. This is another thing that there was no time to explore, although there did seem to be some degree of anti-wag present even with this feature turned off.

Flying

I know Bob Johnston is waiting for this bit, so here goes.

I started off with a gain setting of 50% and was delighted to find that the tail was so solid that I could barely turn the helicopter. There was a slight tendency to wag in some circumstances, but this rapidly damped itself out.

This soon became uncomfortable to fly!

I reduced the gain to 40% and found that this was about as much gyro effect as I could use without seriously limiting what could be done with the model. On this setting, stall turns were just possible, but took ages.

When I tried to perform a 540 stall turn, I found that it was necessary to reduce the gain to 25%, or less. All of this with a wire tail drive and a front-mounted tail rotor servo!

It would have been interesting to try the unit with a large machine with a tube drive, etc. In this situation, in conjunction with the anti-wag and AGC functions, it should be possible to acheive an absolutely solid tail.

Conclusions

On the basis of a very limited amount of flying, the Sanwa unit appears to have a very impressive performance. The fact that it is also the cheapest of the 'big three' is something that cannot be ignored.

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