XRB SR Lama Sky Robo

Helicopter flying is very different and looks like a lot of fun. I am far from the only RC airplane driver who thinks so; there are thousands. However, flying a model Helicopter is far different than flying an RC aircraft. Therefore, many fixed-wing pilots think of a helicopter as a victory of lubrication oil and horsepower over common sense.

So much is different between the two disciplines. The pilot’s perspective is different, especially from the rear. Unlike aircraft, the helicopter requires continuous pilot input to remain airborne and this particularly applies to the left, or “rudder”, hand. Every time I try to fly a helicopter on any RC Flight Simulator, I learned that I would only be buying some owner of a helicopter parts store a new Mercedes every year.

While helicopter parts are easy to obtain, they are not cheap and most beginning helicopter pilots would need a lot of them: Probably a whole lot of them. This single fact limits the number of new model helicopter pilots. That is until now. A recent advance in helicopter design has opened up the realm of vertical indoor flight to everyone with some fixed wing RC piloting experience.

Photo 1

The development of indoor, twin-rotor electric helicopters (photo 1) has made it possible to transition from fixed wing flying to whirly wings. These helicopters are extremely stable and easy to fly. Most any experienced RC pilot can keep one airborne without scaring everyone else in the same room. Well, without terrifying them anyway.

Despite being easy to fly and not needing a tail rotor for direction, a twin-rotor helicopter does keep that left hand busy. In fact, the XRB helicopter teaches the same skills that will be required to fly the more advanced single-rotor designs that might lay in the new helicopter pilot’s future. It also teaches that helicopters require a very gentle hand on the transmitter sticks. Helicopters respond quickly and decisively to every control input. This is another difference from fixed wing piloting.

Photo 2

Hirobo’s XRB SR Lama Sky Robo is marketed in the United States by Model Rectifier Corporation (MRC) in Edison, New Jersey. MRC did a very good job packaging the helicopter both for protection and for sales appeal. Nothing was damaged in shipment and everything arrived safely.

The XRB SR Lama Sky Robo meets all the aircraft requirements of the Academy of Model Aeronautics’ (AMA) Park Pilot Program. The aircraft weighs less than 2 pounds (the Program’s upper weight limit) and has a level top speed under 60 mph (the Program’s upper speed limit). For complete Park Pilot aircraft details, follow this link.

The AMA Park Pilot Program offers non-AMA members the opportunity to become AMA members at a much reduced cost. Park Pilot membership includes a great magazine “Park Pilot”, $500,000 personal liability insurance, $2.5 million liability insurance for the indoor flying site owner (see insurance details) and membership in the world’s largest sport aviation association – the AMA. For complete information and details about Park Pilot membership, just click here.

Photo 3

When I say everything, I do mean everything. Photo 3 shows that attractive box’s contents. There are twelve, yes twelve, extra rotor blades. Counting the blades factory mounted on the helicopter, four complete sets of the foam blades are included just in case the new helicopter pilot has a few misunderstandings with hard objects while learning to fly. Of course, the expected 7.4-volt, 720 mAh Lithium Polymer (Li-Poly) battery and its 120-volt wall charger are inside as are all the tools necessary to assemble and tune the helicopter.

 
Photo 4       Photo 5

But there are some extras that are unexpected. While the regular landing skids are fine for flying, new pilots sometimes land harder than they should. The XRB has special landing skid braces that are easy to install (photo 4). There is even a “trainer” landing gear (photo 5) in the package. Another unexpected item, but a welcome one, is the small black balancing stand used to confirm, or adjust, the balance of each rotor blade.

 

Photo 6    Photo 7

One more unexpected item is a set of lighter weight “fly bar” weights. The fly bar, stabilizer bar, is the metal rod with the two weights attached in photo 7. Its function is to stabilize and adjust the angle of the top rotor blade‘s disk, thereby keeping the helicopter stable. Using the lighter weights on the fly bar makes the helicopter more maneuverable but also more sensitive and difficult to fly. For now, it might be a good idea to keep to the factory installed heavier weights.

Photo 8

The transmitter is the Hirobo model CHO3-F four-channel analog transmitter. The transmitter broadcasts on the standard RC aircraft frequencies, in this case 72.630, and is useable in any aircraft. The transmitter features servo reversing and trim on all four channels. It is powered by 8 “AA” Alkaline (non-rechargeable) batteries. The batteries are not included.

Even though there is far more in this “kit” then would ever be expected, there is one notable exception. The battery charger included for the Lithium Polymer (Li-Poly) can only be used with 120 VAC current. There is no 12-volt DC powered charger included. But since this is not an outdoor machine, that isn’t a real problem.

Assembly

 
Photo 9          Photo 10

Although the XRB is supplied ready to fly, it is a good idea to install the landing skid braces and the trainer landing gear. Photo 9 shows both these systems. The gray plastic legs reinforce the landing skid while the white pieces comprise the training gear. Install the braces first to help protect the landing skid during installation of the training gear.

The shorter braces go on the rear of the helicopter as shown in photo 10. Snap the brace onto the skid cross bar above the rear vertical strut as shown. The top piece is held in place by the same screw that holds the tail boom in position (photo 10). Remove one screw at a time to keep the boom in place, position the brace end and install the screw. Do not over tighten the screws as they are very tiny and are seated into plastic. You do not want to strip the treads in the plastic mounts. Use the small screwdriver provided.

 
Photo 11     Photo 12

The longer, front braces attach on the top to the small top screws just outboard of the front coreless motor as shown in photo 11. Again, be careful not to strip the screw threads. The front braces clip to the front vertical strut just above the landing skid. Photo 12 shows the completed landing skid braces on one side. This side also shows the receiver crystal, in this case on Channel 42. If necessary, you can change the Channel just by changing both this and the transmitter crystal.

 

Photo 13            Photo 14

Photo 13 shows the mounting “hardware” for the training gear. Using this gear helps to prevent the XRB SR from falling over on its side during a “sideways” landing. We new helicopter pilots have a difficult time landing while the helicopter is in a true, motionless hover. The machine always seems to be moving one way or the other when it finally touches down. If it is moving fast enough when it lands, it can fall over on its side, wiping out one or more blades. The training gear ends this hassle and keeps the helicopter upright during “dynamic” landings.

 
Photo 15   Photo 16

Photo 14 shows the training gear itself. The four “legs” of the gear and the ball ends are cut from the white plastic “tree.” The ball ends are just slid on the rod to the stop on the far end. There are two types of soft skid mounts (photo 13). Align them as shown in photo 15 and slide a rod into each with the ball end outwards. But do not mount the rods into the center 4-cornered hub yet. Position each rod towards the center as shown in photo 16. Once they all meet, then install the center hub.

Photo 17

After about 20 minutes of assembly time, the XRB SR looked like photo 17. The braced landing skid system is very strong and the light-weight training gear keeps the machine upright even during a rather harsh landing; and I had plenty of those at the start but there was never even a hint of damage. When fully assembled, the XRB SR Sky Robo is a very attractive looking helicopter.

In photos 13 and 15, you can see a few of the many illustrated directions that are included with this aircraft. The instruction book is very detailed and complete. It includes three pages with fourteen illustrations just on pre-flighting the helicopter. There is a six page flight instruction manual and six pages with 36 illustrations on making post-flight adjustments.

Another four pages show how to adapt the XRB helicopter and its receiver to a different transmitter than the one supplied. As they gain experience, some helicopter pilots may wish to use a computer transmitter instead of the analog one supplied. This is done to increase mixing options such as rudder trim to throttle to adjust trim as the motors heat up during operation. The receiver and its integral gyroscope, used to stabilize the helicopter, are compatible with all brands of transmitters.

Battery Charging

Before flying, charge the battery using the included wall charging unit. It is important to always use this charger when flying the XRB. Li-Poly batteries are a great technological advance over older Nickel Metal Hydride or Nickel Cadmium batteries. In fact, small electric powered helicopters like the XRB SR would not be possible without Li-Poly batteries. But with increased capacity and light weight, Li-Poly batteries also have increased risk factors.

Using a non-Lithium charger will cause the batteries to explode. Burning or damaging them will also cause the battery to burn. Lithium Polymer batteries burn with a temperature around 2,000 degrees F. That is very hot and will certainly ignite any burnable items, including aluminum cans, within reach. Lithium is an extremely reactive metal and combines explosively with the oxygen in the air. No other ignition source is required. If the battery pack is ever physically damaged or shows any signs of expansion or swelling, do not use it. Discard it at an approved recycling center.

The battery charger puts out 0.65 Amps. That means that it will fully charge the .72 Ah (720 mAh) battery in about one hour. In practice, the battery is never fully discharged so plan on about 40 minutes to recharge after each flight. An extra battery, Hirobo part number 0301-032, would be a good idea for more flying time. Just be sure to allow a ten minute cooling period for the motors between flights.

The charger appears to be a “balancing” charger. This means that the charger individually senses each of the two 3.2 volt cells in the pack. As one cell reaches full charge, current to it is reduced while the other cell completes its charging cycle. This is an important safety feature and is fast becoming the norm with Li-Poly chargers. Without balancing during the charge cycle, one cell may reach capacity before the other. The non-balanced charger would continue supplying full current to the fully-charged cell and it could rupture or explode.

Never charge the battery inside the helicopter; always remove it. It would be safest to place the battery and charger on a non-flammable surface such as a concrete block or steel, not aluminum, plate. Make sure nothing is within five feet of the area above the battery or within two feet on any side.

These safety precautions apply to ALL Lithium Polymer batteries, not just the one supplied with this helicopter.

First Flights

Photo 18

The entire assembly process took about 30 minutes. All the control movements were checked and they all wiggled in the right directions. The battery was inserted with the connector under the front cross member as shown in the instructions. This makes it easy to snap the cockpit on and off. Connect the battery to the receiver and everything is ready to go.

Remember this is an indoor helicopter. So the first flights were done in a school cafeteria with ten foot high ceilings. The XRB SR has a convenient on-off switch so it is possible to safely connect the battery before turning on the transmitter. For flight however, the transmitter must be turned on first.

Then hold the helicopter still with one finger on the landing skid and gently turn the receiver on. Do not let the helicopter move until the LED on the side is lit. The short, about three seconds, startup period sets the gyro for straight flight so it is important to make sure the helicopter is motionless during this period.

Then just lower the throttle switch all the way to arm the motors. There is an extra safety that prevents the motors from turning until the transmitter throttle is reduced all the way. Once the safety is disarmed, the red and green LEDs should be lit, warning that the gyro is initialized and the motors are ready to be armed. Carefully press the motor arming switch, called the start switch, and the XRB SR is ready to fly.

I like it that this helicopter has three separate safeties to protect my fingers from the blades. But in reality, these safeties actually protect the foam blades from my fingers. While the coreless motors are powerful for their “180” size, these are not four-horsepower units from a 30% Extra and cannot cause much physical damage to people or furniture. The foam blades resist scratching tables or skin, but it is always good to be on the safe side.

Photo 19

Photo 18 shows the XRB SR Sky Robo just before its first liftoff. Remember that I do not fly helicopters, only fixed-wing models, and that this was a new experience for me. The helicopter lifted off and hovered with a slight backwards motion (photo 19). I held the right transmitter stick forward just a small amount and added some “down” trim.

Photo 20

The machine moved forward during this process and rotated its nose to the right. One thing a new RC helicopter pilot learns quickly is to watch the nose direction, not the tail motion. With the helicopter pointed away from the pilot, moving the left-hand “rudder stick” to the right moves the helicopter’s nose to the right while the tail boom swings leftwards. However, when the helicopter is pointed at the pilot, moving the transmitter stick to the right swings the tail boom to the right while the nose seems to travel to the left. This is similar to the aileron control reversal a fixed-wing pilot experiences when the airplane heads back to the pilot.

 
Photo 21       Photo 22

I was very surprised by just how easy this helicopter is to fly. It is extremely stable and goes just where it is pointed. There is plenty of reserve power; liftoff needed only about half throttle. After about 5 minutes of hover and landing practice, I was getting to feel just a little bit of confidence that “hey, I can do this!” and brought the helicopter up to eye level and hovered around. This is a very easy machine to fly.

I tried left and right side movements using the “aileron stick” and these also were predicable and stable. Intentional backward flight, not the accidental one on liftoff, proved possible but needed some more pilot orientation to keep the tail boom pointed “straight ahead”. Still, there were no stability problems but the rearward motion was very slow.

 
Photo 23      Photo 24

Now over-confident by just how easy this machine is to fly, and fun too, I lifted off and went to “high altitude” to set out on a cross country flight (photo 23). After flying about five minutes and now recklessly over-confident, I decided to land at the far away “Table Top Mesa” airport as shown in photo 24. You know, the darn thing landed like it was being guided in by a Tractor Beam.”

 
Photo 25    Photo 26

Liftoff from Table Top airport was uneventful as was the return trip (photo 25). However, remember that the XRB SR is designed primarily for indoor flight. As such it does not cover ground quickly. Maximum controllable forward motion is 3-5 mph. Trying to fly faster than 5 mph causes some instability and rocking motion. But 5 mph indoors is 7.5 ft. / second and that seems pretty fast when the wall and ceiling start to approach the helicopter. While attempting some high altitude flights, I bounced the XRB SR off the ten-foot high ceiling (photo 26). The rugged construction survived with no damage and the foam blades never scratched the fragile ceiling tiles.

 
Photo 27       Photo 28

Returning from the cross country flight, and after having determined the aircraft’s service ceiling, it was time to land. Still not quite believing how easy this helicopter is to fly, I made the landing approach (photo 27), hovered a bit and landed (photo 28) with just the slightest side motion. Not bad for a first helicopter flight.

How It Works

Photo 29

Twin rotor helicopters simplify rotary flight because they sacrifice, up to a certain point, forward motion for stability and easy control. The twin rotors shown in photo 29 rotate in opposite directions to eliminate the torque effects caused by a single large rotor blade. This means that a tail rotor is not required.

Photo 30

Having the twin rotor blades counter-rotate around a single shaft reduces the mechanical complexity usually found in twin rotor systems. The upper blade and moveable head are not connected to a servo. Instead, the stabilizer bar, fly bar, senses the helicopter’s body movements and automatically adjusts the cyclic operation of the top blade to control “rudder” direction opposite to body motion. This stabilizes the machine in directional flight.

Photo 31

The angle between the stabilizer bar and the top rotor blade is important and should be about 90 degrees. However it is adjustable should that be required for trim. Our XRB SR did not need adjustment.

The lower rotor blades and head are not stabilized. Instead they are controlled by the servos. The servos control the rotor through a swash plate for “aileron” and “elevator” control. By angling the lower rotor disk downwards or upwards, an elevator effect is induced. By pitching the disk angle left or right, there is an aileron effect.

Photo 32

“Rudder” control is determined by the twin coreless “180 series” motors. Depending on the transmitter inputs, one rotor is made to turn faster than the other and creates a torque that controls the yaw axis.

How is forward flight limited? Inputting “down” elevator tilts the bottom rotor disk downwards toward the front. Pointed in this direction, the bottom rotor disk provides some forward thrust. But the top rotor is stabilized by the fly bar and remains rotating in a plane horizontal to the air. Its disk is not pointed downwards at the front as is the bottom rotor disk. Increasing the angle between the top and bottom rotor disks too much, by asking the helicopter to fly forward quickly, begins to result in an instability caused by the widely divergent disk thrust angles.

But the twin rotors sure make the XRB SR easy to fly for a novice helicopter pilot! And indoor flight is measured in feet, not miles, so fast forward speeds are not useful nor desired. This is a very sophisticated machine. Tiny control inputs have big results. While not overly sensitive, the XRB SR responds quickly to inputs. You will find that stick movements are almost imperceptible, even to the pilot. Fortunately, the helicopter flies itself, right from the start.

Everything needed for a beginning helicopter pilot is included and then some. The list price for a painless introduction to rotary flight is $350.00. But the street price is usually $300 or less. For more information about this very complete package, please go to:

http://www.modelrectifier.com/products/rcHelicopters/xrb_Sky_Robo.asp

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