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Motion Control Specialists
with special interest in R/C model helicopter control
PO Box 101, Glossop SK13 5ZW, England.
email: tech@csm-ltd.co.uk       Tel: +44 (0)1457 854680
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Getting the most from your SmartLock Micro gyro
The SL range of gyros is now on Revision 4 internal software. If you wish to have your gyro upgraded, the cost is 12 including postage. Send your gyro to PO Box 101, Glossop, SK13 5ZW, with a cheque or credit card details. If you are outside the UK, or need further details, please contact us at tech@csm-ltd.co.uk.

Please note that the new default settings are more appropriate for 30 size helicopters and up. Flyers of small electric models may not find a great advantage with Revision 4 software, and if you have a SL420 we would not recommend that you upgrade. If you have Revision 4 software and wish to fly a small electric model, with the SL560 you can use the PC interface to put the Heading Lock gain down to  26 and the acceleration gain up to 180. With the SL420, you will need the 'e' version - your normal version can be changed to 'e' for 7 - see details above about upgrading. We do not recommend the SL310 for small electrics.
Optimizing setup

The CSM Smart Lock gyros incorporate the latest technology to remove most of the burden of interfacing your gyro to achieve superb results. So they perform superbly out of the box, but the ultimate tail rotor performance can only be obtained when all of the tail rotor components are fully harmonised. Achieving this is usually very easy, but it does help to have a good understanding of the following components and the effects they can have on the tail rotor system before attempting the process.

The gyro must be mounted with the supplied gyro pads and in a suitable location as far away from the engine as possible. This ensures that the gyro is not subjected to vibration and sudden temperature changes. In addition to this, the leads that exit from the gyro must not be taut or flapping against the gyro / frames.

The model helicopter mechanics must be running as smooth as possible and in perfect balance. All components must be tightened correctly and the tail boom must be well supported to obtain good gyro gain levels.
Raptor 50 boom supportsOn a Raptor 50 we have done the following alterations to improve rigidity:

Left: Lowering the boom supports improves the rigidity of the tail boom and enabled an increase of gyro gain by 3-4 points. To achieve this, move the fuel tank out of the way and carefully drill 2mm pilot holes and then use the existing screws to re-fix the boom supports.

Right: Another trick to improve frame rigidity is to file two notches in the lower carbon plate. Then drill and tap into the engine mount and use spacers to lock the mount to the lower carbon plate. This alone gained an extra 2-3 points of gyro gain.
Raptor50 side frames

The engine is the main source of vibration, so unless the engine is running correctly, you will never realise the full potential of your gyro. The signs of an incorrectly adjusted engine include frothing fuel in the tank, harsh / lean sounding, rich spluttering, over-revving or shaking of the mechanics. You will never achieve good gyro performance until you obtain a smooth consistent engine run, so it is worth spending as much time as is required to achieve this.

Gyro Gain
All tail rotor gyros work on the basis of sensing a movement and installing an opposing movement. We adjust the amount of opposing movement by adjusting the percentage of gyro gain. Too low and we are missing out on potential holding power, whilst too high and the gyro will over-compensate, which is indicated by a visible wag on the tail. The problem is that whilst our model helicopters are capable of having a higher gyro-gain in the hover, the gyro sensitivity increases in certain manoeuvres and modes of flight. So our aim is to run as high a gyro gain as possible without inducing a gyro wag whilst flying. However, the sensitivity of the gyro in certain modes of flight is depicted by many factors. So achieving the best overall gyro performance can only be obtained when the best compromise of all components has been obtained.

Tail rotor blade length
Model helicopters use fixed gear ratios for both the main and tail rotor blades. As such, a change in rpm on the main rotor blades will translate to a change in tail rotor rpm. If we raise the main rotor rpm, the tail rotor rpm will also be raised and vice-versa. For a fixed length of tail rotor blade, a change in rotor rpm translates to the potential tail rotor thrust being increased / decreased as the main rotor rpm is raised and lowered. Tail rotor thrust is usually referred to as ‘tail rotor efficiency’ and this has an effect on the value of transmitter gyro gain you will achieve. The lower the tail rotor thrust, the higher the achievable level of gain, whilst a high amount of tail rotor thrust will dictate a reduction in gyro gain for an identical mechanical set-up.

Smart Lock gyros have been designed to be at their most efficient when in the 75-80% transmitter gyro gain region. So if the tail rotor blades are too short, this will permit a very high gyro gain value, but the available tail power will be low. In flight, this will feel like the gyro is very locked in whilst in the hover and the tail will be insensitive to wagging (over-compensating), but it will fail to hold in aggressive 3-D manoeuvres. Conversely, a tail blade that is too long will give you plenty of power to hold the most aggressive manoeuvre, but will be very sensitive to gyro gain. In flight, this means that you will have to lower the gyro gain to avoid constant wagging through manoeuvres. In doing this, the tail rotor will feel much less locked in and the reaction time of the gyro to small deviancies will be greater. As a general rule; the correct size of tail blade is achieved by ensuring the tail has just enough power to hold the most demanding 3-D manoeuvre.

Main Rotor Speed Consistency
If the main rotor speed is deviating then the tail rotor rpm will be changing and the tail rotor power will vary. The result of this is that you will have to set the TX gyro gain to the highest average main rotor speed and you will be losing out on potential holding power at lower main rotor speeds. The more consistent the main rotor speed, the more overall gyro gain you will be able to realise for a given mechanical tail set-up and the more effective your gyro will be! Of course the easiest way of maintaining a steady rotor speed is to use a governor.

Servo Arm length
The faster the tail rotor can react, the better the potential reaction time of the tail rotor system. We are blessed with the fact that tail rotor servos have a rotary arm output. Whilst the actual operating speed of the servo is identical regardless of the length of the servo arm, we can change the effective reaction speed of the servo. The reason for this is that we can enhance the speed by fitting a longer servo arm and reducing the servo travel. So while the operating speed of the servo is identical, it does not have to travel so far to obtain full tail linkage travel. The disadvantage of a longer arm is that you reduce the torque it produces - this is usually less of a problem, but be wary of  low torque mini servos - small electric helis often need more torque than you'd think,  and a shorter servo arm (ie higher torque) may solve poorholding problems.

Using a tail rotor servo that operates at 0.10 of a second for 60 degrees of motion, with a 10-mm servo arm to achieve 20-mm of linkage travel for 60 degrees of servo throw in each direction. This gives an actual servo response of 0.10 for the 60 degrees of motion required to obtain the correct amount of tail linkage travel. However, if a 20-mm horn is used, the servo would only have to travel for 30 degrees to obtain the same 20-mm of linkage travel. So the servo is now moving half the distance and will in effect be twice as fast!
However, whilst a longer servo arm will increase the gyro reaction speed, the resolution (accuracy) of the servo will reduce and the gain sensitivity will increase as the servo arm length increases. So adjust the length of the servo arm to match the overall tail rotor / gyro set-up.

Servo Arm Neutral Position
Very few model helicopters have truly corrected tail rotor geometry and this creates a natural flaw in the tail rotor’s ability to stop at equal speeds from left and right hand pirouettes. When hovering a right-hand rotation model helicopter, we need about 8 degrees of tail rotor pitch to hold the tail stationary.

This is a very easy way of setting up the initial 8-degrees of tail rotor throw at neutral. Simply set the pitch gauge to
 8-degrees of right tail and then adjust the linkage until the outer section of the gauge is parallel with the tail boom.
pitch gauge
If we then make a demand for full right tail rotor, the tail pitch changes from 8 to about 40 degrees. This equates to a change of 32 degrees of tail pitch from neutral to full right tail rotor. If we now return the tail linkage to neutral and then apply full left tail rotor, the ideal change in tail rotor pitch would be from 8 degrees of right tail to 40 degrees of left tail rotor, which equates to an overall change of 48 degrees of tail rotor pitch. So the tail rotor linkage will obviously take longer to move from neutral to full left in comparison to neutral to full right. So when stopping from a right hand pirouette, the servo will reach full left tail linkage travel slower than when stopping from a left-hand pirouette where right tail is activated. In real terms, this means that the gyro gain is in effect higher for the right hand direction and lower for the left direction. This has the effect of producing a slower stop from a right-hand pirouette and a swifter stop from a left pirouette.
It  helps to introduce a mechanical differential on the servo arm to assist the gyro in this respect. This is best thought of as a mechanical offset and in the case of a right-hand rotation machine, the servo arm is offset in the right direction of tail rotor. This has the desired effect of reducing the servos mechanical effectiveness for the right direction of travel and enhancing it for the left. On the SL560 the PC interface has a ‘dual gain-tracking feature’ making it  very easy to achieve an equal speed to the stops for each direction.
offsetting the servo armTo help overcome poor tail rotor geometry and balance out the left / tight stops,
offset the servo arm in the right tail rotor direction. This is the position of the
servo arm at neutral in a standard Raptor 50 tail rotor servo installation.

And this is what it looks like when using a rear servo mount:
rear mounted servo
pitch sliderFor those looking for the ultimate right hand pirouette stop performance, try relieving the tail pitch slider as shown with a round file to increase the left tail rotor throw. This modification provides 40 degrees of tail pitch in both directions and enhances the gyro performance.
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Interfacing the SL560

Only once you have achieved the best possible performance from a stock CSM SL 560 gyro, can you then look towards the interface function to fine tune the gyro to your model and flying style. Whilst there are many interface functions, I have found that unless the gyro is being used for an unusual specialist application, just the following five functions require fine-tuning. I strongly recommend that you adjust just one function at a time and carefully assess each change before re-adjusting or moving on to the next function.

1-Acceleration Gain:
Amongst other in-built functions, this controls how quickly the tail rotor can start and stop a pirouette. The lower the value, the quicker the gyro will start / stop a pirouette, whilst a higher value will slow the start / stop of a pirouette. However, the gyro can only start / stop pirouettes at a speed the model helicopter mechanics will allow. Smaller less efficient models tend to be less capable of starting / stopping fast, whilst larger models tend to be more capable. As such, the CSM SL 560 comes pre-set with a value of 90% to cater for average model helicopters with an average set-up. To enable the helicopter to start / stop faster from pirouettes, lower this value in 5-10% steps and assess the tail rotor performance. If you find a slight decline in general handling and a slight bounce has developed when stopping from pirouettes, then raise the value back up in 5-10% increments until the best compromise has been achieved.

2-Heading Lock Decay:
This function is designed to allow the tail rotor to slowly drift back to neutral after being carried out to the flying field. The pre-set value of 60% is generally small enough to be unnoticeable in flight. However, you may experience a slight change in tail rotor trim when operating your model at different rotor speeds for separate flight conditions. If this is noted, try reducing the value in 10% steps all the way down to 0% where required, until you feel the effect is eliminated.

3-Dual-Independent Stop Tracking Controls:
This function allows you to adjust the gyro gain for the left and right travel independently to balance out left / right stops from pirouettes. If the model helicopter stops slower from a right-hand pirouette, then increase the value. If regardless of the amount of right stop control, the helicopter still stops quicker from a left-hand pirouette, then reduce the left value until the stops are equally balanced.

Linear Stick Sensitivity:
This function adjusts the feel of the tail rotor response around centre stick. If you feel that the tail rotor is too responsive to small inputs, then reduce the value until you obtain the feel you like. If however, the tail rotor feels too unresponsive to small tail rotor inputs, then raise the value until you obtain the feel you like.

Exponential Stick Sensitivity:
This function controls the tail rotor response towards full stick deflections. Lowering the value softens the response just prior to full stick deflection, whilst lowering it enhances the response close to full stick deflection. Once again, experiment to find the best feel of tail response to suit your flying style.

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Optimizing your Revision 4 gyro

Revision 4 was developed to respond to new developments in 30+ size models. Users of small electric models may find the default settings in the SL560 inappropriate; we recommend you use the PC interface to put the Heading Lock gain down to approx. 26, and the acceleration gain up to 180:  please note that as part of the revised code many of the internal parameters have been rescaled so it is not possible to make direct comparison of internal parameter values between Revision 4 and earlier versions.

Stop equalisation
This is the aspect of gyro/tail rotor set-up that requires the most attention if optimum performance is to be obtained and the techncique for equalising left and right stops has been changed. The available tail rotor authority dominates stop times from fast pirouettes and most stop equalisation problems arise from a lack of tail-rotor authority one way, usually in the leftward (anticlockwise) direction. This lack shows up in slower entry into left pirouettes and slower stops
from right pirouettes. This is especially noticeable with governed systems in low-g manoeuvres (e.g. stall turns) where the amount of assistance from torque is much reduced.

We find that good tail performance is obtained with 45 degrees of right tail pitch and 35 degrees of left tail pitch. During the initial installation of the gyro you should make sure that the travel limits of the servo are set such that the pitch throw is limited only by the mechanical limits of the pitch linkage. To assist in this we have increased the available servo travel in Revision 4. Ideally aim for a servo arm length that gives throw limits between 90% and 120%. You can measure the required throw limits by temporarily connecting the tail servo directly to the receiver and adjusting the rudder ATV values until the mechanical limits are reached. (Remember to return the rudder ATVs to 100% after you have finished this check). We find it’s a common problem to have the tail servo arm too short; we rarely find one that’s too long. For the SL560, use the PC interface to check the throw limits and if these exceed 120% we recommend you fit a longer arm to the tail servo and reduce the throw limits correspondingly. Ideally aim for a servo arm length that gives throw limits between 90% and 120%.

During the initial flight carry out the Quick-trim procedure, adjust the gyro gain to the maximum that gives no wagging and assess the quality of the left and right stops from fast pirouettes (i.e. full stick). If there is a marked difference note which stop is the softer. After the flight, switch the gyro into Mode 0 (conventional, non-heading lock mode) and compare the left and right pitch throws at full stick from the hover pitch (stick centred). Generally, if you have noticed a difference in the fast pirouette stops there will be a corresponding imbalance in the left and right throws.

If the softer of the two stops is acceptable for your style of flying then it will be satisfactory to simply reduce the throw to soften the harder stop. To soften the stop from right hand pirouettes reduce the available left pitch and to soften the stops from left-hand pirouettes reduce the available right pitch. If you do this via the Quick-setup remember to repeat the Quick trim procedure on the following flight. (On the SL560, if you adjust the throw via the PC interface the Quick-trim value will be preserved.)

If the softer stop is unacceptable you will need to increase the available tail thrust. Check if more pitch throw is available in the appropriate direction. If there is, change the throw limit to make it available. If no more pitch is available the simplest way to increase the tail thrust is by fitting longer tail blades. This increases the tail rotor disk area, the tail blade area, and the tip speed so a 10% increase in blade length will raise the available tail thrust by about 30%. Please remember to check that the longer tail blades do not touch the main blades. If you cannot increase the length of the tail blades, try increasing their chord.

Once the softer of the two stops is satisfactory the equalising of the two stops can be done by adjustment of the throw limits as described above. Generally this will be all that is required to obtain matched stops from all speeds. However if stops from more modest speeds of about 180 deg./s show some left-right imbalance then on the SL560 these can be matched by use of the stop tracking controls via the PC interface.

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If, having read the info in the manual and this page, you still have questions/problems in your setup, or would like further advice on improving the performance of your gyro and helicopter, please contact us on  +44 (0) 1457 854680 or email tech@csm-ltd.co.uk

All our helicopter products are distributed worldwide through RC Models Distribution Ltd, and should be available from your local model shop or mail order company. To find your nearest stockist see the RC Models shops page

phone +44 (0)1457 860001 or email sales@rcmodels.org
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