SK540/SK720 basic setup overview
By Alvin Chai. Last updated Dec 2012.
– The SK540 likes to be hard mounted, even on nitros. I know the earlier SK540 came with the black foam tape, it will work but not as good. I like using the 3M Exterior Mounting Tape. All new SK540 now comes with thin white tape, those work really good as well.
– The SK720 can be mounted on thin tape too if you are not using the Self-Level feature. Please note that the gyro sensors in the SK720 is very vibration resistance, it is the accelerometers that does not like high vibration. I’ve seen people saying the SK720 is very sensitive to vibration, however this is only the case if you want to use the self-levelling.
– I use 10 degrees of cyclic pitch on my helis. Some team pilots are using 8-9 degrees as they feel it suit their flying style and setup better. I would say 10 degrees is a good number to use.
– Some people may find the cyclic pitch values may not be equal on both sides (e.g. left and right aileron cyclic, front and back elevator cyclic) but it doesn’t matter as long as each side is at least 10 degrees.
– Please note that cyclic pitch values does not determine your heli’s roll and flip rate, it is just to tell the SK540/SK720 what the cyclic range it has to work with.
Swash Servos Tab
– Trim each servos so they are centered and swashplate is level with zero pitch at center stick
– Before adjusting the Travel (%), check to make sure the swashplate is level throughout the pitch range. If one servo is moving more (or less) than the others at max or min pitch, adjust the Travel (either + or -) for that servo so the swashplate is level at max, mid, and min collective stick.
– Once this is done, use the Swash Mixing to set the pitch range you want, and adjust the Travel (%) to get equal positive and negative pitch if necessary. Make sure you increase or decrease the same % amount on all Center, Right, and Left so the swashplate stays level.
– Don’t worry if the final Travel (%) is all over the place, it all depends on the servos you use, but as long as the swashplate remains level, it will be fine. However take care in not to overdrive the servo by having too high Travel (%). I limit mine to around max 130%. I shoot for overall Endpoints in the 100-125% range – Nick
– If you are maxing out your swash mix and travel, and still not getting enough collective or cyclic pitch, then increase the distance of the servo horns.
– Control Rates are basically flip and roll rate. The higher the control rates, the faster the heli flips and rolls. Do some FULL flips and rolls, and adjust the control rates to suit your liking.
– Bell Gains are basically how fast the heli response to your stick movements. High bell gain will make the heli “react” faster to your sticks, and low bell gain will slow it down. However high bell gain may cause the heli to rebound at stops.
Self Tune Bell Gain
– Self-tune Bell Gain is a good start to tune the bell gain. The self-tune value will work for the majority of pilots. Just enable self-tune bell gain and allow 2-3 flights for the 540 to auto tune to your flying style. After that you can turn it off if you wish.
– I think the manual suggest to adjust the control rates to achieve around 85% of bell gain. That is a good starting point, but I will discuss later on how we tune it.
– Hiller Gain is the “locked-in power” of your heli, basically it works like your normal tail gyro gain. The higher the gain, the more locked-in your heli feels. However too high hiller gain will cause the heli to shake or wobble in hover or in 3D (just like how the tail will hunt if gain is too high) I always keep the default value of 50,50 for the hiller gain, and run an overall gain of around 50-60%. You can adjust this thru your transmitter or use the Lock Cyclic Gain function.
– For smaller heli, I like to run around 30-40% overall hiller gain, as too high will cause the heli to wobble in aggressive 3D.
– Damping Gain. I find that the default value of 18,16 for the damping gain seems to work well for most helis. However if you have some cyclic rebound at stops, try reducing the damping gain. One thing to note is that the damping gain is propositional to the hiller gain i.e. if you increase hiller, damping increases as well. I’ve personally started to automatically set my Damping Gains to 10,16 on all my helis to start. This seems to eliminate the inherent elevator bobble that some have complained about. – Nick
Tail Drag Comp
– Tail Drag Comp basically help keep the heli level throughout the pitch range. This is more for elevator than for aileron. Since helis have big heavy bodies and long light tail booms, there may be drag in the tail when you give full positive or negative pitch. For example if there is no Tail Drag Comp, when you give full pitch and climb, the tail will dip down and lag behind the body, and vise-versa.
– Do a full pitch climb out and full pitch descend, and adjust tail drag comp so the entire heli remains level throughout.
– Hiller Decay. The lower the hiller decay, the more “heading hold” the swashplate has and helps keep the heli stable in high winds. Just as an example of how hiller decay works, if you set it to 0%, the swashplate will hold the last position/heading in flight and will stay there until you move it back. At max 200%, the swash will always move to level slowly.
– However low hiller decay can cause some oscillation during 3D. I like higher hiller decay because it makes the heli feels more smoother in manoeuvres. For 600-700 size helis, I prefer around 150-165%. For smaller helis, I like using 185-200%. For you VBar users this is similar to the flying style slider. A lower Hiller Decay will give you a more rigid feel while a higher number will give you a more vivid feeling. – Nick
– Cyclic Accel is the acceleration of your cyclic. It does not affect the sensitivity or range of the cyclic. Imagine the Control Rate is the top speed of a car, and Cyclic Acceleration is how fast the car can accelerate to that speed.
– So the higher the Cyclic Accel, the faster the cyclic moves.
– Control Rates controls how fast you want your tail to spin. The higher the rate, the faster the tail spins.
– Rate Gain makes the tail stable, without it the tail will go crazy
– Hold Gain makes the tail locked-in into a heading. This is more or less like the Hiller Gain for cyclic. – I hardly adjust the Rate and Hold gain, and the default values works well in all my helis.
– Collec Mix helps keep the tail straight during full climb and descend. Almost all helis today have powerful motors, and the instant torque created by these motors can caused the tail to kick or not keep up when pitch is applied. Adjust Collec Mix so the tail stays straight.
– Start Accel controls how fast/powerful the tail starts moving when you move the rudder sticks. If you tail feels soft to start, increase Start Accel.
– Stop Accel controls how fast/powerful the tail stops when you let go of your rudder sticks. If your tail rebounds after a stop, reduce the Stop Accel.
– Check all pitch, cyclic, and rudder direction is correct, and make sure the gyro is compensating in the right direction when you tilt the heli.
– Find a nice calm day, set the Hiller Decay to 200% and hover.
– If the heli drifts to one side, adjust the swash linkage to counter the drift. For example, if the heli drifts to the right, either lengthen the right servo linkage or shorten the left servo linkage. Do one turn at a time.
– Don’t worry if the swash level is slightly off after doing this. However if it is too much, then something else needs to be checked on the heli.
– Once the heli remains stable in hover, adjust the Hiller Decay to your liking.
SK540/SK720 Advance Setup
I will concentrate on how I set up my Cyclic as I get asked that a lot. Some of the values may not work for the type of flying you do, but it will give you an idea on how I tune it.
For all helis, big or small, I usually start with the following values for the first flight,
Control Rates 280, 280
Bell Gain 55, 55
Hiller Gain 50, 50
Damping Gain 18, 16
Tail Drag Comp -6, 0
Overall cyclic gain 50% (in transmitter or using Lock Cyclic Gain) Self-Tune Bell Gain – Off
Hiller Decay 165% Cyclic Accel 30%
– I will get the heli in the air and start doing some full flips and rolls. I will then increase or decrease the control rates to get the final rate I like.
– What you are doing here is finding the maximum roll and flip rate you want. That’s basically what Control Rate is.
– I hardly use the self-tune bell gain as I find the auto tune values are a bit too high for my liking. But I’m not saying Self-Tune Bell Gain does not work, it works pretty well for many pilots, but for my flying style, I prefer a lower bell gain.
– I think the manual says to give sharp jabs on the cyclic sticks and see if the heli rebounds. That method kinda works in a way but I feel it is not the best indicator for tuning the bell gain.
– There’s no “magic number” for Bell Gain, I’ve seen people referencing setting the Control Rates to achieve around 85% of self-tune Bell Gain. That may work for some beginners and sport flyers, but for
3D that method does not work well.
– I usually start with 55, 55 as I feel it gives a neutral feel for most helis. I will then proceed to fly my routine and see how the heli “reacts” to my cyclic sticks. What I’m looking for is a balance “reaction” feel, not too fast, not too slow. Then I will check if the there is any rebound during hard stops and tic-tocs, mostly with elevator. If there is some rebound, I will decrease bell gain.
– When I adjust Bell Gain, I usually use the same value for both elevator and aileron, just to make things simple.
– I find my Bell Gain usually end up around 50-65%.
– A lower bell gain will slow down the “reaction feel” of the heli to your cyclic stick, but it will make the heli fly better in hard maneuver (less bobbing/overshoot)
– To counteract the “slow” feel, you can increase the Cyclic Accel to speed up the cyclic.
– So Hiller Gain is the “locked-in” power of your heli. The higher it is, the more locked-in the heli feels in the air. However too high Hiller Gain will cause the heli to shake /wobble in hover and/or during 3D.
– I always leave the default value of 50, 50 and only adjust the overall Hiller Gain with my radio through my GEAR channel, or you can use the Lock Cyclic Gain function.
– For most sports flying, Hiller Gain is pretty easy to tune, just increase the Hiller Gain and if you see the heli wobble or bobble during your flight, then just back it down a bit.
– To fine tune it for 3D, I usually do fast continuous elevator and aileron tic-tocs, or pirouetting tic-toc, if the heli wobbles during the maneuver, decrease Hiller Gain until you get a smooth transition throughout the maneuver. I find fast continuous maneuver is the easiest way to fine tune Hiller Gain for 3D.
– I usually end up about 50-60% Hiller Gain on my big helis (600-700) and about 30-50% on small helis (250-500)
– I always start with the default value of 18, 16 for Damping Gain. I start with 10/16 on mine – Nick
– The only time I tune the Damping Gain is when I get slight bobbing/rebound during elevator hard stops that I could not get rid of with Bell Gain and Hiller Gain.
– So if you experience some slight elevator rebound, reduce elevator Damping Gain. Aileron hardly needs adjusting.
– Do note that damping gain is propositional to the hiller gain i.e. if you increase hiller, damping increases as well.
Tail Drag Comp
– As explained in the basic tuning, Tail Drag Comp helps keep the heli level throughout the pitch range. – Tuning is pretty easy, just do a full pitch climb out and full pitch descend, and adjust tail drag comp so the entire heli remains level throughout.
– The explanation in the basic tuning basically covers how I tune the Hiller Decay.
– To recap, the lower the hiller decay, the more “heading hold” the swashplate has and helps keep the heli stable in high winds.
– However low hiller decay can cause some oscillation during 3D.
– I like higher hiller decay because it makes the heli feel smoother in maneuver and transitions. For 600- 700 size helis, I prefer around 140-165%. For smaller helis, I like using 165-200%.
– As mentioned above in the Bell Gain tuning, low Bell Gain slows down the “reaction feel” of your heli to your cyclic sticks. So to counteract the slow feel, I increase the Cyclic Accel to help speed up the cyclic. – I’m using 35-45% in my helis.
Just some notes with regards to TX settings, the only things I adjust on my TX are (I’m using a JR9303)
– GEAR channel for overall cyclic gain (gain value adjusted thru end points) and switching between Cyclic 1 and Cyclic 2
– AUX 2 channel for overall tail gain (thru end points) and switching between Tail 1 and 2
– Aileron and elevator expo (if needed to smooth my cyclics out)
– Throttle curve
– Pitch curve
– Throttle hold
– And if using Skookum governor, throttle end points to set up the esc or throttle servo
The rest of the values are set as default and all other tuning are done in the setup software.
Relationship Between Expo, Cyclic Accel, Stick Deadband
– So the Expo in the TX basically lets us adjust how sensitive or non-sensitive we want the center sticks to be.
– You can use the expo in your TX if you like, on some models I’m using 15%-20% expo just to smooth things out a bit.
– Cyclic Accel on the other hand is the acceleration of your cyclic. It does not affect the sensitivity or range of the cyclic. Imagine the Control Rate is the top speed of a car, and Cyclic Acceleration is how fast the car can accelerate to that speed.
– So the higher the Cyclic Accel, the faster the cyclic moves.
– Stick Deadband does not affect the cyclic sensitivity and range as well. Basically it creates a dead zone in the center of the stick. So if you move your sticks within the deadband (let’s say 2%) the servo will not move.
– Deadband helps remove any unwanted small movement in your sticks when you fly and also make sure the heli stays stills when you leave the sticks center. This is because the stick pods in our radio can drift with temperature and it can sometime make the servos jittery in the center, which can affect the heli, so setting deadband will help.
– Also some digital servos really buzz when left in neutral, deadband will help remove it. – I usually set my deadband from 0% – 2%, and leave it as is.