T E A M
Hi,
I bought a Trex 700E DFC recently. I have been using the Skookum SK540 for a few months now and very happy with its performance and the confidence it gives me. I thought with the new Trex 700E, perhaps it is a good opportunity for me to try out the topnotch FBL, SK720 with the GPS module. I like to try out the self leveling and rescue features. So, I bought the SK720 + GPS as a combo from Zenm Tech. As combo, I got a free power bus (for power distribution), LCD terminal (this is useful for tuning the heli at the field without a PC), T-shirt, Tx neck strap, a small bag and a nice BE box, LOL. The SK720 can work without the GPS module, so you don’t have to buy the GPS if you don’t want to.
The setup for the SK-720 is almost the same as the SK540, using the same software but with some additional settings when software detects that it is a SK720. Setting of the GPS is also through the same software.
While SK540 is very “insensitive” to heli vibration (probably the best in all FBLs in term of vibration resistance), meaning mounting is never an issue. In fact, SK540 prefers hard mounting (i.e. mount it using a thin 3M tape). But for SK720 you cannot use hard mounting if you are going to use the self leveling feature as the SK720 uses the accelerometers which is sensitive to vibration. You need to mount the SK720 using the supplied metal plate (non-magnetic), thick foam tape, and the thin 3M tape. The SK720 comes with a very good vibration analysis feature which will help to check if the vibration is acceptable to the FBL for self leveling purpose. If the vibration is too high, the SL will not work. The vibration analysis can almost pinpoint where is the heli vibration come from. I like it very much.
The mounting of the GPS is a challenge. It needs to be mounted upright only, and the Trex 700E was not designed to cater for it. And it needs to stay away from motor, servos, ESC, BEC, including their cables; even the GPS cable has to be an inch apart from those cables. I first mounted it on the tail boom but found later that it interfered with the canopy. The only possible location is on the real ESC mount, but it is not horizontal, it is tilted. So, I need to make a simple structure using CF (see pictures) to provide the GPS a flat and vertical surface for mounting.
SK720 Recovery (Bailout) Features.
SK720 has two kinds of recovery feature, one is the Self Leveling (which is provided by the SK720 itself), the other is the Rescue feature (which is provided by the GPS).
By the way, I always thought the Self Leveling (SL) is only a bailout feature, but it is not just that. Besides being used as bailout, it is also a flying/training assistant especially for newbies.
Self Leveling Modes.
SL function has nothing to do with the GPS module. So, you do not need to have the GPS to use SL.
The SL has four modes:
A. Always On
B. Centre Stick
C. Always On & Inverted
D. Centre Stick and Inverted.
Of course you can turn off the SL feature completely. But if it is enabled, it needs to be set to one of these four modes. Mode A and Mode B will always try to level the swashplate for you, so effectively it makes the heli flies like a coaxial. Mode A will only self level the heli into the upright position while Mode B is cable of self level the heli in inverted position. Mode B and Mode D will only level the swashplate when you hand off the sticks (i.e. centre stick). So the heli will fly normal (almost!) until you hand off the sticks. In addition to the mode selection, you can also select the “rate of self leveling”, it is a percentage (0 to 200%) of the cyclic rate settings. So, if you want the self leveling effect to be responsive or quicker, set a higher value. For recovery purpose, set it to max (i.e. 200%), and for training purpose set it to 70% to 90% (just my one cent).
In summary, if you are going to use the SL as a recovery (bailout) feature, you need to set a switch that when flipped (when panic) it will enable the SL; set the SL control rate to max (200%) so that heli will be levelled in the fastest manner. SL is not auto hovering, so when SL set in, you still need to take control and hover the heli. Once you hover it, you need to switch the SL off and bring the heli to land safely.
For beginners and newbies, SL is a good feature (my view) for you to use it for training purpose. To use SL as training feature, it needs to be enabled throughout normal flying. For absolute beginners, select Mode A and set the SL rate to 100%. Anytime when you are panic, just let go the sticks, and your heli will be self levelled but you need to continue to hover it as it will drift. As you progress, you can reduce it to say 50% to 60%. At some point, when you can fly better and gain confidence, you will then select Mode B. Mode C and Mode D are inverted capable. If your heli is tilted more than 60 degree, the heli will be self levelled to inverted. Similarly, if the heli is tilted more than 60 degree at inverted, the SL will bring the heli to upright level. Eventually, when you are out of newbie status (from Ah Boy to Man), you can disable the SL feature and fly like a pro. LOL.
I tried Mode A and it really flies like a coaxial. I tried Mode B with 60% rate, I can fly the heli as normal but when the sticks are near to centre it will self level. One thing you cannot do is stall turn when the SL is on as it will self level the heli on the way down as the sticks are near to centre.
SK720 Rescue Features
This feature requires to have the GPS module installed. There are three modes for this feature.
A. Rescue Now
B. Rescue Hard Floor
C. Rescue Soft Floor
Mode A (Rescue Now) is the most common one. At the flip of a switch, the FBL will rescue the heli at any position by bringing it to upright, level it, turn the tail towards you (i.e. tail in), and hover it at that position. You can still turn the tail around if you want to. You need to flip back the switch to gain back the control of heli and land it manually. I tried this, the rescue was fast and everything happen within about a second or so. It levelled the heli first and then turn the tail.
Mode B. You enable this mode in your normal flying. But when the heli drop below a predefined minimum altitude (10m to 15m), the rescue function (as above) will kick in automatically without you doing anything. I think this mode is more suitable for sport flying.
Mode C. Same as Mode B except that the FBL (GPS) will calculate how much distance is needed to stop in time, and will activate rescue function if it thinks it is running out of room to recover before going below the set minimum altitude. This allows you to set a lower minimum altitude, however it gives less control to the pilot. I think this mode is more suitable for 3D flying. I dare not try this Mode C, waiting for the now big time Skookum’s Singapore pilot (aka Damien Tan) to try. LOL.
On top of the rescue modes, the SK720(GPS) has a “Go Home” function. At the flip of a switch, the FBL will take over the control of heli and fly the it to a predefined Home position, turn it to tail in, and hover the heli at the Home position. It will not auto land, pilot needs to deactivate the Home function and take control of the heli to land it manually. I find not much use for heli as we are unlikely to fly the heli to a position that we can’t even see it. Perhaps this function is more useful for quadcopters as SK720 (and SK540) is designed for quadcopter as well. I never try this function.
Overall, I am very happy with SK720+GPS although I still have some tuning to do for both cyclic and tail. Will post the settings here after I complete the tuning. For bailout, I think the rescue modes provided by the GPS is better than the SL modes. The rescue mode is faster and it auto hover the heli after the bailout whereas the SL is a little slow and it doesn’t auto hover the heli.
Unlike SK540, SK720 cannot work with USB3 port somehow. So, if you are connecting your PC to SK720, use USB2 ports.
Some pictures.
Pictures of the GPS mount.
I bought a Trex 700E DFC recently. I have been using the Skookum SK540 for a few months now and very happy with its performance and the confidence it gives me. I thought with the new Trex 700E, perhaps it is a good opportunity for me to try out the topnotch FBL, SK720 with the GPS module. I like to try out the self leveling and rescue features. So, I bought the SK720 + GPS as a combo from Zenm Tech. As combo, I got a free power bus (for power distribution), LCD terminal (this is useful for tuning the heli at the field without a PC), T-shirt, Tx neck strap, a small bag and a nice BE box, LOL. The SK720 can work without the GPS module, so you don’t have to buy the GPS if you don’t want to.
The setup for the SK-720 is almost the same as the SK540, using the same software but with some additional settings when software detects that it is a SK720. Setting of the GPS is also through the same software.
While SK540 is very “insensitive” to heli vibration (probably the best in all FBLs in term of vibration resistance), meaning mounting is never an issue. In fact, SK540 prefers hard mounting (i.e. mount it using a thin 3M tape). But for SK720 you cannot use hard mounting if you are going to use the self leveling feature as the SK720 uses the accelerometers which is sensitive to vibration. You need to mount the SK720 using the supplied metal plate (non-magnetic), thick foam tape, and the thin 3M tape. The SK720 comes with a very good vibration analysis feature which will help to check if the vibration is acceptable to the FBL for self leveling purpose. If the vibration is too high, the SL will not work. The vibration analysis can almost pinpoint where is the heli vibration come from. I like it very much.
The mounting of the GPS is a challenge. It needs to be mounted upright only, and the Trex 700E was not designed to cater for it. And it needs to stay away from motor, servos, ESC, BEC, including their cables; even the GPS cable has to be an inch apart from those cables. I first mounted it on the tail boom but found later that it interfered with the canopy. The only possible location is on the real ESC mount, but it is not horizontal, it is tilted. So, I need to make a simple structure using CF (see pictures) to provide the GPS a flat and vertical surface for mounting.
SK720 Recovery (Bailout) Features.
SK720 has two kinds of recovery feature, one is the Self Leveling (which is provided by the SK720 itself), the other is the Rescue feature (which is provided by the GPS).
By the way, I always thought the Self Leveling (SL) is only a bailout feature, but it is not just that. Besides being used as bailout, it is also a flying/training assistant especially for newbies.
Self Leveling Modes.
SL function has nothing to do with the GPS module. So, you do not need to have the GPS to use SL.
The SL has four modes:
A. Always On
B. Centre Stick
C. Always On & Inverted
D. Centre Stick and Inverted.
Of course you can turn off the SL feature completely. But if it is enabled, it needs to be set to one of these four modes. Mode A and Mode B will always try to level the swashplate for you, so effectively it makes the heli flies like a coaxial. Mode A will only self level the heli into the upright position while Mode B is cable of self level the heli in inverted position. Mode B and Mode D will only level the swashplate when you hand off the sticks (i.e. centre stick). So the heli will fly normal (almost!) until you hand off the sticks. In addition to the mode selection, you can also select the “rate of self leveling”, it is a percentage (0 to 200%) of the cyclic rate settings. So, if you want the self leveling effect to be responsive or quicker, set a higher value. For recovery purpose, set it to max (i.e. 200%), and for training purpose set it to 70% to 90% (just my one cent).
In summary, if you are going to use the SL as a recovery (bailout) feature, you need to set a switch that when flipped (when panic) it will enable the SL; set the SL control rate to max (200%) so that heli will be levelled in the fastest manner. SL is not auto hovering, so when SL set in, you still need to take control and hover the heli. Once you hover it, you need to switch the SL off and bring the heli to land safely.
For beginners and newbies, SL is a good feature (my view) for you to use it for training purpose. To use SL as training feature, it needs to be enabled throughout normal flying. For absolute beginners, select Mode A and set the SL rate to 100%. Anytime when you are panic, just let go the sticks, and your heli will be self levelled but you need to continue to hover it as it will drift. As you progress, you can reduce it to say 50% to 60%. At some point, when you can fly better and gain confidence, you will then select Mode B. Mode C and Mode D are inverted capable. If your heli is tilted more than 60 degree, the heli will be self levelled to inverted. Similarly, if the heli is tilted more than 60 degree at inverted, the SL will bring the heli to upright level. Eventually, when you are out of newbie status (from Ah Boy to Man), you can disable the SL feature and fly like a pro. LOL.
I tried Mode A and it really flies like a coaxial. I tried Mode B with 60% rate, I can fly the heli as normal but when the sticks are near to centre it will self level. One thing you cannot do is stall turn when the SL is on as it will self level the heli on the way down as the sticks are near to centre.
SK720 Rescue Features
This feature requires to have the GPS module installed. There are three modes for this feature.
A. Rescue Now
B. Rescue Hard Floor
C. Rescue Soft Floor
Mode A (Rescue Now) is the most common one. At the flip of a switch, the FBL will rescue the heli at any position by bringing it to upright, level it, turn the tail towards you (i.e. tail in), and hover it at that position. You can still turn the tail around if you want to. You need to flip back the switch to gain back the control of heli and land it manually. I tried this, the rescue was fast and everything happen within about a second or so. It levelled the heli first and then turn the tail.
Mode B. You enable this mode in your normal flying. But when the heli drop below a predefined minimum altitude (10m to 15m), the rescue function (as above) will kick in automatically without you doing anything. I think this mode is more suitable for sport flying.
Mode C. Same as Mode B except that the FBL (GPS) will calculate how much distance is needed to stop in time, and will activate rescue function if it thinks it is running out of room to recover before going below the set minimum altitude. This allows you to set a lower minimum altitude, however it gives less control to the pilot. I think this mode is more suitable for 3D flying. I dare not try this Mode C, waiting for the now big time Skookum’s Singapore pilot (aka Damien Tan) to try. LOL.
On top of the rescue modes, the SK720(GPS) has a “Go Home” function. At the flip of a switch, the FBL will take over the control of heli and fly the it to a predefined Home position, turn it to tail in, and hover the heli at the Home position. It will not auto land, pilot needs to deactivate the Home function and take control of the heli to land it manually. I find not much use for heli as we are unlikely to fly the heli to a position that we can’t even see it. Perhaps this function is more useful for quadcopters as SK720 (and SK540) is designed for quadcopter as well. I never try this function.
Overall, I am very happy with SK720+GPS although I still have some tuning to do for both cyclic and tail. Will post the settings here after I complete the tuning. For bailout, I think the rescue modes provided by the GPS is better than the SL modes. The rescue mode is faster and it auto hover the heli after the bailout whereas the SL is a little slow and it doesn’t auto hover the heli.
Unlike SK540, SK720 cannot work with USB3 port somehow. So, if you are connecting your PC to SK720, use USB2 ports.
Some pictures.
Pictures of the GPS mount.
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