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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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SL720 GYRO (& SL630)

"The best gyro I have tried" Fred Annecke
Model Helicopter Technique Magazine, March/April 2006.

Downloads:
SL720 Manual - pdf format......................... SL720 Quick Reference card - pdf format
SL720 PC Interface Manual - pdf format.....SL720 PC Software - zipped file

SL630 Manual - pdf format ........ ................SL630 Quick Reference card - pdf format

Compatibility

RC System: These gyros are usable with  PPM, PCM  and  2.4GHz with 7 channels or more. The wiring is compatible with all current transmitters. If you are uncertain about the compatibility please email CSM's technical support on tech@csm-ltd.co.uk

Servo: These gyros will only work with digital servos. Please do not use with an analogue type servo. We recommend fast, coreless-motor servos, with speeds better than 0.1 seconds for 60 degrees. We do not recommend using this gyro with the JR 810G or the Volz Speed-Maxx - although digital their initial acceleration is slower than is required.

SL720 only: This gyro can be set up to drive servos with standard 1520ms or short 760ms pulsewidths  The default is 1520ms - this can be changed using the PC interface. To use the Futaba 9251, 9256 or BLS251 and other 760ms pulse width servos: please change the gyro settings to 760ms and 333 frames/sec using the PC interface before connecting your servo. The Logictech 6100T (as sold with the Logictech 6100G gyro) and the Hitec 5083MG servos are quoted as having a 960ms pulse width but our pilots have found they can be used with the SL720 gyro set at 760ms pulsewidth .

Frames per second: The default frame rate of these gyros is 250 frames per second,  but they can also transmit at 333fps by using the frame link on the SL630, and the PC interface on the SL720.

Batteries, power consumption and wiring: Due to their  three stage power supply regulation, they will accept a voltage of 3.3v to 8.4v, a greater range than any of our previous gyros. For best servo performance, we recommend using the highest voltage that your servo and RC system will accept (please note that this may be more restrictive than the gyro). We supply voltages droppers to go between the gyro and servo if you wish to run the gyro at a higher voltage than the servo will stand - see Spares and Accessories.

Although the power consumption of the gyro unit itself is very modest, high performance gyros work the tail rotor servos harder and the power consumption may be high. We recommend that you use a good quality battery state monitor and check it carefully before each flight. You may wish to consider maintaining the charge in your receiver battery between flights by the use of a quality Delta Peak type field charger. The latest SL720 and SL630 gyros have the added feature that if they see a static electric discharge, or a power dip or spike, during flight, the SET LED will be flashing when the model is landed.

Computer: To use the PC interface, you will need a PC with a USB or an LPT (printer/parallel) port. Unfortunately, the PC software cannot be run on a Mac. Please note: most people find that they get very good performance with the default settings, however, you will not be able to use 760ms pulsewidth servos without using the PC interface.

Features

If you have not previously used a CSM SmartLock gyro, you may not be familiar with the following features:

Quick Setup: Quick Setup is a simple routine which gets the gyro up and ready to fly. You enter it by toggling the gain switch back and forth whilst the model is on the ground. You then set the Gyro Sense, Vibration Filter and Servo Travel Limits using your transmitter sticks. The gyro will also automatically pick up your stick centre and information about your radio gear.

Quick Trim: Quick Trim is a simple method of correcting for any small linkage errors. Toggle the gain switch five times whilst in flight, and the gyro will correct the trim. Please do not use stick trim when flying the SL720 gyro as it may cause the stick centre information to become inaccurate.

Dual Mode switching: Two modes are available. Default setting has one as Standard and the other as Heading Lock, but you may alter these using the PC interface. The gyro gain channel is used to control these modes - the gain switch switches between the two modes, and the travel adjust (ATV) of the gain channel is used to adjust the gain in each mode. The gain in each mode can also be altered using the PC interface.

Vibration Filter: Again, this can be turned on and off either through the PC interface or from the transmitter (in Quick Setup). This filter should only be necessary in large petrol (gas) driven models or highly-tuned 90-size glow models. We recommend that you do everything possible to eliminate the vibration without using this option, as it slightly reduces the gain.

PC Interface: This feature is only available on CSM SL560 and SL720 gyros! See the screenshot for all the parameters that you can customise. Most importantly, the PC Interface on the SL720 allows you to use all commonly used digital servos by setting the correct pulsewidth and frame rate. Note: now available for USB ports.
720 software screen

Only once you have achieved the best possible performance from a stock CSM SL 720 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 SL720 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.

4-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.

5-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.
In Conversation with Colin

Dr Colin Mill explains how he developed the SL720 and why he's confident it's the best gyro out there today.

What made you choose the new Micro-Machined Silicon sensor from Analog Devices?

I was very excited when I heard that Analog Devices had finally brought out a gyro sensor. I've been using them for other components for nearly thirty years, and I know they can be relied upon for high quality.

What are the advantages of using a silicon sensor over ceramic?

Stability. A silicon sensor has inherently low temperature drift. Unlike earlier designs of SMM sensor, the Analog Devices sensor also has all the sensor support electronics integrated on the same silicon as the sensor element itself, and includes a temperature sensor. This allows for the accurate tracking and compensation of temperature drift.

To exploit this, each SL720 gyro goes through a temperature calibration procedure followed by a test for residual temperature drift. The result is a gyro with a drift of less than 5 degrees per minute over the temperature range minus 10 C to plus 50 C (14 F to 122 F)

Speed is another advantage. The sensor has a rapid response to rotation rate changes. This is important in minimising the delays in the tail rotor system, which in turn maximises the gain, hold and stop performance.

CSM has never used a silicon sensor in the past. What made you change?

The AD sensor is capable of measuring to high rotation rates, in excess of 750 degrees per second, which previous SMM sensors were not capable of doing. This is a feature we consider vital for the extreme 3D pilot, as it gives full control in high-speed travelling piro manoeuvres. Sensors with lower sensing limits under-correct for the whip, simply because they underestimate the rotation rate. Now we are able to offer this performance along with the stability of a silicon sensor.

The AD sensor is also extremely small - about 5% of the weight and volume of previous generation SMM sensors. This has allowed the SL720 to be much smaller lighter than other fully featured SMM gyros, bringing it comfortably within the carrying capacity of the smallest electric helicopters. (The SL720 weighs 16g and measures 37 x 26 x 19mm)

You've described the SL720 as having 'servo optimisation'. What do you mean by that?

New in the SL720 is the ability to adapt the output characteristics to get the maximum from a wide range of digital servos. There are three aspects to this:

1. Adjustable frame rate
All digital servos are capable of 250 frames per second. However, some are capable of higher rates and, to allow the maximum performance with these, the SL720 can be set to 285 or 333 frames per second.

2. 1520/760 microsecond pulse centre support
Some servos (e.g. 9251 and 9256) only accept reduced width position pulses, 760ms. To allow you to use these servos, the SL720 can be switched into 760ms support mode.

3. Wide voltage range capability
Coreless motors wound to run off higher voltages generally accelerate better than those wound for lower voltages, so there is an increasing trend for high performance servos to operate at 6v or even 7.2v. Although they can be run at lower voltages, they give significantly better performance when run at their highest permitted voltage. The SL720's three-stage power supply regulation allows gyros to be operated on supplies up to a nominal 8.4v, in anticipation that even higher voltage servos will become available.

Is there anything else that you've changed for the SL720?

We've been working continuously on the control algorithms used in heading lock gyros. The SL720 is the result of nine years of experience with heading lock - more than any other manufacturer.

Several areas of handling have been improved in the heading lock, for example the accuracy and speed of small heading adjustments in high tail load situations, and the smoothness of acceleration into pirouettes. An adjustable 'deadband' at stick centre has been added, since we found that many pilots introduce minor, unwanted deflections of the rudder during rapid collective movements.

Overall, we are always driving towards more consistent and predictable handling at the extremes.

To find out more about the features of the SL720 and how to use it, please take a look at the manual (pdf format)

PC Interface Manual - pdf format

If you have any problems or questions, please contact CSM on +44(0)1457 854680 or email tech@csm-ltd.co.uk


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