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Spartan RC is committed to its customers and our pre-sales and after-sales service is second to none. If you have a question or problem with any of our products we will do out best to assist you in a timely fashion.

Please read the information below which deals with the most common issues. If you are still having any difficulty then please feel free to contact our support team.


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Frequently Asked Questions & Troubleshooting

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1. Can you please explain what is frame rate and pulse width?
    The servo position is controlled by an electrical pulse or variable duration which in electronic terms is called pulse width. The pulse repeats at constant intervals and this repetition frequency is also known as frame rate and is represented in Hertz (Hz). The majority of RC receivers will produce a frame rate of around 50Hz which means that they will instruct the servo where to go 50 times each second. The position of the servo horn is defined by the pulse duration. For a typical RC servo a pulse duration of 1520uSec means that the horn should be at the mid-point of the servo travel. If the pulse duration becomes shorter or longer the servo horn will move clockwise or counter-clockwise respectively.

    As gyros evolved it was apparent that 50Hz was not enough to achieve the desired performance as the time intervals between pulses were too long. So manufacturers starting pushing the frame rate up. JR gyros went to 250Hz and Futaba pushed as high as 333Hz. This allowed the gyro to talk to the servo more frequently but the position command remained the same (1520uSec still means mid-point).

    Then the GY601/611 gyros came along with the non standard 760uSec system. With this system the servo travel mid-point is at 760uSec as opposed to 1520uSec. In theory by shortening the pulse to half it can reach the servo faster and therefore the servo can react sooner. In reality the benefit is negligible as the savings are less than 1mSec. Considering the inertia of the motor windings and the helicopter as a whole 1mSec does not give any practical benefit and very likely this system was only implemented to tie specific servos to these gyros.

    So when buying a new tail servo the important things to look at are speed, torque and 333Hz frame rate. With the exception of the older JR servos (8700G etc) most new digital servos will work at 333Hz. This includes all Futaba digital servos and therefore the S9254 will work as good as the S9256 since they have the same torque and speed spec but perhaps a little hotter due to the lack of metal case.
2. Is it necessary to setup the tail with 8deg pitch in rate mode?
    You only need the 8deg adjustment if you want to run your Spartan gyro in rate mode. In AVCS mode Spartan gyros work equally well whether the "neutral" tail pitch is set to 8deg or 0deg. However, keep in mind that if rate mode is not setup correctly the helicopter may piro uncontrollably if you accidentally switch to it in flight.

    On a related topic; despite common misconception tail servos are not overworked if the "neutral" tail pitch is set to 0deg. For the servo holding any shaft position is pretty much the same.
3. Is the gain of my gyro too low?
    The optimal gain value is a function of several parameters including rotor speed, tail rotor diameter, tail blade efficiency, servo arm length, servo make/model and mechanical design of the aircraft. As such, it is not possible to make a general recommendation and the gain will need to be adjusted experimentally. Starting with a gain of 30% should provide enough stability to at least hover; however you should always proceed with care. If insufficient stabilisation or tail wag is seen the gain should be raised or lowered respectively. The optimal gain value is the highest value you can reach that does not cause tail wag at any time during flight.

    It is not uncommon to find that the optimal gain value for a helicopter may be a small number such as 35-45%. The small value does not mean that the gyro will be limited in performance. Any gain value performs well as long as it is the optimal gain value. However, a gain below 35% indicates that the mechanical gain of the tail is too high and it is therefore recommended moving the servo arm ball link further in. Similarly if 100% is reached and no tail wagging is seen the ball link needs to be moved further out and repeat the gain adjustment procedure. The previously indicated 35% is for guidance only. There are significant variations in the tail design of helicopters and in some cases it may be deemed essential to use a value below 35%.
4. Do I need to use the supplied metal plate?
    The supplied metal plate is used to increase the gyro mass in order to provide more effective vibration attenuation. Electric helicopters have much lower vibration levels and thus it is unlikely that you will need the metal plate on any electric helicopter. You should however use the thick adhesive foam pad. On nitro and gas helicopter it is more probable that the metal plate will be needed. In either case you can experiment mounting the gyro without the metal plate and if any tail drift is observed in hover use the plate and try again.
5. I fly with reverse tail. How should I setup gyro reversing?
    If you use reverse tail (meaning that with left rudder stick the helicopter yaws clockwise) while configuring your Spartan gyro reversing you need to push the stick in the opposite direction that you would do normally. Therefore if the gyro is mounted upright you will need to push the rudder to the right and if mountted invrted to the left. Always check that the gyro responds correctly before taking off.
6. When I spool up the helicopter pirouettes uncontrollably.
    Ensure that the transmitter reversing is correctly setup before proceeding with setting up the gyro direction reversing as explained in the gyro user guide.If the gyro is mounted in inverted orientation you will need to push the rudder stick to the right instead. Finally, If you use reverse tail (meaning that with left rudder stick the helicopter yaws clockwise) while configuring your Spartan gyro reversing you need to push the stick in the opposite direction that you would do normally. Always check that the gyro responds correctly before taking off.
7. I plugged my servo to the gyro with the wrong servo type selected. It is damaged?
    As a general rule 1520uSec/333Hz capable servos will also happily run at 1520uSec/250Hz but not the other way round. In certain cases use of the wrong uSec/Hz setting will cause the servo to travel to the end of its range and bind. If left unnoticed for several seconds the servo will very likely get damaged as a result of the binding and excessive current passing through the stalled motor. If the servo was left binding for more than a brief moment you should thoroughly test it and seek expert advice from the servo manufacturer before using it in flight. No damage is caused to the gyro if the wrong servo mode is used.
8. Which tail servo do you recommend for use with the Spartan gyros?
    To get the best performance from your Spartan gyro always use fast tail servos. Futaba S9254, S9256, BLS251 and JR 8900G work very well with our gyros. For smaller helicopters JR 3400G at 6V and Futaba S9257 work very well too. We list these servos for guidance only. There are many other servos on the market that offer similar speeds. Always choose a servo with enough torque for your application.
9. The helicopter pirouettes too slow.
    The ds760 is a sophisticated microcomputer system in charge of controlling the helicopter's tail. Unlike traditional rate gyros the rudder channel from the transmitter no longer controls the tail servo position directly. Instead the rudder stick is a command for the ds760 indicating how fast the pilot wishes the helicopter to yaw. The ds760 then decides on required amount of tail pitch to achieve the commanded yaw rate. As such adjusting the transmitter's rudder endpoints will not affect the tail servo limits, it will only affect the magnitude of the command to the ds760 thus resulting to slower or faster yaw rates when full rudder is applied. If you would like the helicopter to be more responsive to rudder stick movements increase your transmitter's rudder endpoints and dual rate.
10. The tail does a slight bounce when it stops.
    Let's imagine a car driving at high speed when suddenly the driver needs to do an emergency stop. From the moment such decision is made until the car has come to a stop, the car has continued to travel due to the reaction time required to hit the break and the time required for the car to decelerate. A similar effect happens to a helicopter that yaws fast when suddenly the pilot returns the rudder stick to neutral, thus command the gyro to stop the helicopter. Time is required for the servo to respond as well as to decelerate the tail. Depending on the servo speed and the mechanical capabilities of the heli the combined deceleration distance may vary from a few centimeters which is hardly perceivable by the human eye to several centimetres. However, unlike the car example, the gyro remembers where the tail was the moment that the stick was returned to neutral. Thus as soon as the helicopter stops the gyro will continue driving back to that point. This appears as a bouncy stop. Bouncy stops can very easily be fixed using the Deceleration Profile adjustment via the PC, PDA or detachable LCD. Effectively, this adjustment tells the ds760 how rapidly to decelerate the tail with the aim of keeping this task within the mechanical capabilities of your helicopter. You also also adjust the CW/CCW stop gains which control the responsiveness of the gyro during stops.
11. The tail stops too hard and I fear it may strip the tail gears.
    Lower the Deceleration Profile adjustment via the PC, PDA or detachable LCD to match the mechanical capabilities of your helicopter. You may also adjust the CW and CCW stop gains to fine tune the stops to your preference. Detailed information on these adjustments can be found in the help of the PC software.
12. My servo is not listed in the user guide. Which mode should I use?
    The most reliable way of determining the correct parameters is to seek advice from the servo manufacturer or their representatives. When Spartan RC has reliable information about a servo, either from the servo manufacturer or through extensive testing, the servo is included in our gyro user guide. Unfortunately with so many servos on the market it is impossible for us to characterise all of them but we do try to keep our list updated with the most popular tail servo choices. If you are unable to obtain accurate specification from the servo manufacturer you may wish to follow the general advice we list below, but please do so at your own risk and pay particular attention to the warning notes.

    • The servo control signal is defined by two parameters. The neutral pulse width which will be either 760uSec or 1520uSec and the frame rate which for digital servos is typically 250Hz or 333Hz.

    • With the exception of Futaba S9251 / S9256 / BLS251 and LogicTech 6100G (accurate at the time or writing) the great majority of modern digital servos follow the 1520uSec standard.

    • Servos that are capable of 333Hz will also happily run at 250Hz but not the other way round. If you are unsure about the frame rate capability of your digital servo you may choose to run it at 250Hz.

    • The older JR super-servos (example 2700G, 8700G, 810G) are only capable of 250Hz frame rate. However, the newer 8900G is capable of 333Hz and perhaps other modern JR servos ware capable of 333Hz too.

    • All Futaba digital servos that we tested were capable of accepting the 333Hz frame rate.

    • Even if the servo appears to be working on you should check that it continues to do so throughout its travel range.

    WARNING!

    In certain cases use of the wrong uSec/Hz setting will cause the servo to travel to the end of its range and bind. If left unnoticed for several seconds the servo will very likely get damaged as a result of the binding and excessive current passing through the stalled motor. If the servo was left binding for more than a brief moment you should thoroughly test it and seek expert advice from the servo manufacturer before using it in flight.
13. Do the servo endpoints need to be unequal?
    No, and this is why our gyros provide independent endpoint adjustment for each end. You should however try to avoid extreme difference between the two endpoints if possible.
14. I am unable to setup the endpoints and gain as the user guide suggests.
    The user guide provides general guidance on the preferred conditions for using our gyros. In practice design variations between helicopters may dictate the use of a different servo arm length, endpoints or gain than we suggest. Our gyros are designed to cope with such differences and this is not an issue of concern. You should however try to stay as close as possible to the advice provided in the user guide.
15. The tail kicks to the right when I suddenly increase the collective.
    This it typically the result of low gyro gain, slow tail servo or tail mechanics that are unable to provide enough thrust to compensate for main rotor toque.

    Try increasing the gyro gain as high as you can reach without and tail wag seen at any time during flight. A slow tail servo, stiff push-rod or faulty tail grip bearing may prevent you from reaching the optimal gain value for your helicopter. On these grounds it should also be noted that the S9650 servo that has been a popular tail servo choice in past in 450 size helicopters is not fast enough to bring out the best performance from your Spartan gyro.

    If the helicopter has been fitted with a significantly more powerful motor than the helicopter manufacturer's recommendation and the collective range gas been increased it is possible that the tail may not be able to provide enough thrust to compensate. If enough clearance is available between the main and tail rotor, try fitting longer tail blades.

    Finnally, it should be noted that some ESCs with build in governor create an irregular/delayed response resulting to such tail kick on sudden collective changes. Disable the governor function and observe in the problem persists.
16. I can't enter configuration mode.
    • Check that the rudder and gain inputs of the gyro are plugged to the correct receiver outputs.
    • Check that the LED responds when toggling the gain switch. On one side the LED should be lit (AVCS mode) and on the other side the LED should be off (Rate mode).
    • The gain value may be too low resulting to the switch toggling not being detected. Temporarily increase the gyro gain to 100% in both AVCS and Rate modes.
    • When using a Spektrum DX6/DX7 radio place the mode selection switch to Rate mode during pairing.
    • Ensure the correct servo type has been set.
17. I can't enter servo selection mode.
    • Check that the rudder and gain inputs of the gyro are plugged to the correct receiver outputs.
    • Check that the LED responds when toggling the gain switch. On one side the LED should be lit (AVCS mode) and on the other side the LED should be off (Rate mode).
    • The gain value may be too low resulting to the switch toggling not being detected. Temporarily increase the gyro gain to 100% in both AVCS and Rate modes.
18. The servo is not moving.
    • Check that the rudder and gain inputs of the gyro are plugged to the correct receiver outputs.
    • Make sure that the correct servo type has been selected.
19. The servo sometimes moves and sometimes does not.
    This is almost certainly the result of using incorrect servo type. Change the servo type to 760uSec or 1520uSec as needed for your servo.
20. The helicopter tail drifts.
    Spartan gyros offer exceptional tolerance to the vibration levels that are commonly found on model helicopters. However, there are many factors that can manifest as drift varying from incorrect transmitter configuration to incorrect mounting or a very rich engine. If you have tried all sensible measures and you are still having drift issues please contact the Spartan RC support team which will be able to guide you further. You may also consider the following:

    • Some radios offer different trim setting on each flight mode. Ensure that the trim setting for all modes is identical.
    • Never use trim to cancel drift in AVCS mode.
    • Use the supplied steel plate and two layers of the 3mm foam tape for mounting the gyro.
    • Do not fix the cable to the helicopter for the first 5cm (2 inches) from the gyro end to reduce transmission of vibrations through the cable.
    • Check you engine is not excessively rich.
    • Unclip the tail pitch control rod from the servo arm and check that it can move freely with minimal amount of force.
    • Ensure that there is not excessive backlash in the tail pitch control mechanics.
    • Check your servo runs smooth and does not have excessive backlash or a worn potentiometer which often results in a dead-band.
    • Check that your transmitter rudder stick centring operates correctly. Worn potentiometers affect the centring accuracy of the joystick which will manifest as drift.
    • Ensure that the gyro and the gyro wire harness are kept away from sources of electrical noise such as ESC, BEC, motor etc. If no doubt reposition the gyro and reroute the wiring.
21. Difficulties entering setup mode when using Spektrum and 2.4GHz JR radios.
    These receivers produce servo signals at power on and before the link with the transmitter is established. This initiates the gyro calibration process which is sometimes completed before the link is established. At this point it is no longer possible to enter the setup modes as this must be done during the calibration period.

    Starting from firmware version v1.02 the gyro will not start calibration until the rudder stick is seen at the centre. Spektrum users should bind their radios while holding the rudder stick off centre. This becomes the default rudder output when the receiver is powered on which will now prevent the gyro from starting calibration until the link with the transmitter is established.

    Starting from firmware version v1.07 the gyro will not start calibration until the gain is raised above 15% (either AVCS or Rate mode). Spektrum users should bind their radios while the gain is set to a value around 10% preferably in AVCS. This becomes the default gain output when the receiver is powered on which will now prevent the gyro from starting calibration until the link with the transmitter is established. This method of setting low gain is preferred over binding with the rudder stick off center which will become obsolete in future firmware revisions.
22. How do I setup my gyro for eye blurring piros?
    Whilst the gyro operates in AVCS mode the tail pitch is entirely controlled by the gyro. In this mode the pilot’s rudder inputs become a command for the gyro telling it how fast to yaw; the gyro then controls the tail pitch as needed to maintain the commanded yaw rate. It is also possible to command the gyro to open the tail pitch fully which – depending on the mechanical capability of the helicopter – can result to spectacular yaw rates well over 3 turns per second. To achieve this you should set the rudder endpoints of your radio to a very high value effectively commanding the gyro to yaw faster than its sensor’s measurement capability. For some radios you may also need to increase the gyro's rudder stick sensitivity via the PC, PDA or detachable LCD. You may also wish to set the deceleration adjustment to a slower setting to soften the stops from such fast yaw rates.
23. Using a voltage regulator or step-down.
    The ds760 feeds power the servo from the black rudder plug. The gyro itself gets powered from the red gain plug. If you want to use a voltage regulator or step-down for your servo you may fit it either before the rudder plug (between the receiver and the gyro) or at the servo plug (between the gyro and the servo). Either way works equally well and you can therefore choose the one that best fits the wire routing on your helicopter. The ds760 will happily work from unregulated voltage up to 8.4V and thus it can be powered directly from a 2S LiPo battery.
24. Can I see the actual gyro gain using the Flash-Link interface cable?
    • Download and run the latest version of the PC software.
    • Power on the helicopter/gyro and your transmitter.
    • Right click anywhere on the top bar of the PC software and from the drop down list click on "Start Diagnostics".
    • Over the large Spartan RC logo will appear a line of gray text which shows the sensor, rudder and gain signals read by the ds760's microcomputer. The actual operating gain is displayed as a % at the right hand side.
    • To exit diagnostics mode right click on the top window bar and select "Stop diagnostics".
25. I have misplaced my user guide.
    The latest version of the user guide and supporting software can be found on the right hand side of each product’s web page.
26. My computer can't find the Flash-Link cable.
    Ensure that the drivers for the FlashLink are correctly loaded. Then proceed carefully step by step exactly as described in your product’s user guide.
27. How do I return a product for service or repair?
    If you wish to return a product for service please contact us with a detailed description of the fault. We will evaluate the fault and issue a Return Merchandise Authorisation code if return of the item is required. Your should clearly write the RMA code on the package next to our address. Packets without and RMA will not be accepted.

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