(Click on Photos to Enlarge)

Introduction

The quest for a truly 3D capable electric helicopter led me to the Mikado LOGO 20.  While the ECO 8 can supposedly be powered and upgraded to be a capable 3D machine, I had reservations about investing that much in such a relatively small and light duty helicopter.  And while the LOGO 20 appears expensive ($549 US) compared to an ECO 8 ($199), the basic kit really doesn't require any upgrades (unlike the ECO). The .30 size LOGO is a very substantial design with high quality parts, much like a lightweight version of a Robbe helicopter. 

If you want to buy a LOGO, you may have to want it bad. After sitting on a waiting list at RC-Direct for several weeks, the kits arrived, but I was told unless I had actually placed the order, I wasn't in line for a kit (apparently there's a little failure to communicate over there).  As it turned out, they had one left over after they filled their backorders, so I grabbed it.  Unfortunately they had no motors or controllers to go with it, and no immediate prospects of getting any.  After searching around I did find a seller with a Plettenberg motor and Schulze controller combo that was close to what I wanted.

Early on in the process of fondling all of the parts bags in the kit I spotted several parts missing, namely the entire thrust bearing sets for the main rotor and one of the guides for the tail pitch push rod.  Although I had been assured that RC-Direct carried a complete line of parts, I found out that thrust bearings are not considered necessary replacement parts.  On top of that, they had no other kits in stock from which to rob the parts, and no specific date on when they could get them.

As a hedge, I emailed Mikado directly and I received a courteous (and apologetic) reply that same evening.  They indicated that the parts would be mailed directly to me.  I expected about a three week wait, but they arrived in a week.  I'd have to give Mikado a top rating for service in this instance.  A few weeks later the same parts came straggling in from RC-Direct, so I now have a set of spares.

The design and kit quality are excellent, putting weight where it needs to be and trimming it where it's not necessary.  This is, at least on first impression, a design truly optimized for electric power.  The all metal swashplate is very well made with very little slop.  The 10mm main rotor mast is surface ground and hollow, with a much thinner wall than a Raptor mast.  The main and tail rotor gears have massive teeth compared to the 48 pitch ECO gears, which makes the gear lash setup much less critical.  All the usual points are ballraced, and nearly all ball links are metal.  The plastic links fit the balls without doing the plier squeeze, a small but much appreciated feature.  Push rods are a massive 2.5mm diameter, larger than on a .60 Xcell.  The canopy and windshield are preassembled carefully and neatly.  This was a blessing for me, because if the windshield had not been glued in place I probably would have chosen to turn the project into a two week painting ordeal.  Instead, I opted for a self adhesive trim design that hopefully looks a little better than the patchwork-quilt trim supplied with the kit. 

The rotorhead has a head button large enough to rest the palm of your hand on.  Note the metal swashplate and the large diameter push rods.

The molded frame sides are very rigid, leaving wide open space for the motor and controller to be placed well away from the rest of the electronics.  The tail rotor is belt driven, and the forward pulley is an integral part of the tailboom assembly, allowing easy removal of the tailboom without touching the belt.  There is no adjustment between the main gear and the tail rotor gear, and the gear lash is a little excessive.  This has been noticed by some others also, but I have seen no reports of any problems, probably because of the hefty gear teeth.

Assembly goes quickly, although, like the Robbe Nova kit, the parts are not necessarily bagged in the sequence that they need to be opened.  Sometimes a few bags need to be open at one time.  I do believe that I needed to borrow some screws from my stock in some places, although I ended up with some spares also.  I think there were a few discrepancies on small parts, but nothing serious.

I opted for the Plettenburg  HP300/25/A3 motor because it has an integral squirrel-cage cooling blower and cooling fins machined into the motor case.   This avoids the added task of having to figure out how to mount a small DC fan (and  duct the airflow) to provide cooling that is usually needed unless you want to cook the motor.  This is an 8 pole sensorless motor with unusually fine wire on the exposed stator windings. The matching controller is a  Schulze Future 35 HO. This is a sensorless, optocoupled controller that can be operated both in a normal throttled mode as well as a speed governed mode.  The arming sequence determines the operating mode.   

The Plettenberg HP300/25/A3 motor is sensorless and has only the three leads for the main windings.  The Schulze controller has onboard sockets (instead of leads) connecting to the motor, allowing easy removal.  With all the fins, this is a cool running combination.

The large gear teeth make clearances much easier to set than with the 48 pitch gears used on the ECO helicopter. The Futaba GY401 heading hold gyro was mounted on a small aluminum plate mounted on the tailboom clamp.

For example, to operate in speed governed mode, it is recommended that the speed controller be plugged into a slider or dial channel, not the throttle channel.  The slider or dial is set to full speed position (for 8/10 pole motors; the procedure is different for 2/4/6 pole motors), and then the main battery is connected. After three beeps are heard (the motor is the loudspeaker), the slider is brought to full off, and another single beep announces that the controller is armed.  The slider is set to the desired RPM/headspeed, and you fly.  No throttle curves are needed, although if you do set them up you will be able to operate in both governed and non-governed modes.  As with a conventional governor, the RPM will remain constant with pitch, as long as you don't run out of torque.

Having to fiddle with a dial or slider for the arming sequence would be a recipe for disaster for me sooner or later, so I set up the 9Z transmitter to allow a more conventional start up sequence.  Since I am used to starting glow helicopters with the idle switch in normal position, I assigned the throttle to the stick for normal mode only.  The throttle channel is assigned to one of the dials for all other flight modes.  This way the stick is active for performing the proper arming sequence.  

The Schulze helicopter controller has a very smooth soft start feature that can supposedly be overridden to allow sudden restarts during autorotations.  The soft start only occurs if the throttle is brought back to almost a full idle.  If the pulse width stays above 1.18 mS (slightly above idle), the motor will restart immediately when throttle is reapplied.  So far this feature does not appear to work in governed mode, and conventional mode has not been tried. Another nice feature is the built-in finned heatsink on the top of the controller.  Again, this is a simple addition that is too often overlooked.

Despite the optocoupled controller input, it is recommended that the signal cable be wrapped several times around a ferrite toroid to minimize glitching.  This is apparently intended to attenuate common mode RF switching noise from being conducted into the receiver.  Glitching appears to be a fairly common problem on the LOGO, with some reports of pretty ominous and visible static discharges (ala Van de Graaf generation) at the tail hub.  Antistatic treatment of the drive belt may help this problem.

The LOGO 20 can use mini servos (an adapter plate is supplied) or full size.  Since becoming a little skeptical of CCPM and unwanted swashplate inputs caused by the servos not tracking correctly, I decided to stick with decent quality full-size (9202) servos.  Another reason for this is that even if small servos have the required torque and precision, the supplied arms are sometimes too short to give a reasonably linear swashplate movement over the full collective range.  Short servo arms have to operate over a wide angle, and this also results in some unwanted conversions of elevator-to-collective or aileron-to-collective near the extremes of collective pitch.  The 9Z transmitter can compensate for this by linearizing rotary motion, but that’s another thing to mess with, and in fact it does not appear applicable to the pitch channel (?!?).  

Full size Futaba 9202 servos were chosen for this installation.  The servo tray is mounted on ball bearings and can rock for non-CCPM control. An "X" brace prevents the tray from rocking when used with CCPM.

Installation of the electronics was less of an effort that it is on some other, larger machines.  As stated before, the motor and controller are located in a spacious area well away from the receiver.  For the receiver battery, I used an 800 mAh JR pack inserted into the area under the servo tray.  The gyro was located above the tail boom on a little shelf made from .040 aluminum plate.  The receiver mounts vertically on the front of the main frame.  A slide switch/charging jack was installed in the unused tail rotor servo cutout at the rear of the frame.  A forward-facing Dean's antenna will be tried, although I expect to have some interference to deal with.

Items not supplied with the kit include main rotor blades and the motor pinion.  Plastic tail rotor blades are supplied, but I chose to use a set of ModelSport carbon blades instead. 

Interestingly, my fully loaded LOGO with twenty 2400 mAh cells came in at about the same weight as a fueled Raptor.

Flying Characteristics

The first couple runs on the LOGO consisted of bench (actually sawhorse) testing of the motor and controller with the main blades removed and the landing gear clamped down.  Unanticipated overspeeding would be controlled by yanking the battery leads (against the controller manufacturer's recommendations), although this fortunately proved unnecessary.  The arming procedure was tested many times to gain some confidence in the reliability of the system, and the governor control was set up using an optical tachometer.

First flight.

A set of Raptor wood blades were used for the first hover tests.  The first hops using twenty cells and a 9 tooth motor pinion showed that the top-end collective pitch was set too high.  During full stick climb the headspeed would sag if the governed speed was set much above 1500 rpm, even on freshly charged cells.  The pitch was reduced, which stabilized the headspeed, but resulted in lackluster climb for 3D performance.  An 8 tooth pinion was tried, with some improvement.  Performance improved considerably when 24 cells were used on the next flight.  The climb rate was very good, and the headspeed could now be run in the 1650 to 1750 rpm range without sagging . My benchmark is the climb rate of the OS32 powered Raptor, and I think the LOGO is already there, at least in the first minutes of a fresh charge.

In flight the LOGO has the feel of a .30 size machine, although it doesn't have the stability or the powerful rotorhead design of the Raptor.  Stock flip and roll rates are slow compare to a Raptor.  The motor/controller operating in governed mode does tend to bounce around the target RPM a bit when hit with sudden loads, such as when performing an abrupt full-stick pirouette.  I suspect that there will be some optimization of the headspeed, gyro gain, and gearing needed to get rid of this.  Normal throttle mixing cannot be used, since this would not be adding more power--it would be changing the target headspeed.  The governor is really a closed loop to which the user has no access, except to set the static speed.  There's always the non-governed mode to fall back on, if all else fails, but I'm confident that with some experimentation that the governor will work well.

Hovering flight times have been running 7 to 8 minutes with some short full power climbs mixed in.  Immediately after flight, the Plettenberg motor and Schulze controller are actually cooler than the battery packs, a welcome change from my experiences with Aveox and Astroflight motors in the ECO helis.

UPDATE:  3D flight with the governor has proven to be enough of a problem that I have created a new model setup with conventional throttle curves and mixes.  I suspect that the governor related problems are really more related to the gyro/tail response, and even though they could probably be resolve I decided not to mess with it for now.  Operation in conventional throttle mode is working well, and the rpm "ringing" that occurs when punching the throttle/collective is no longer a problem.  A little throttle delay has been added to slow the throttle response for sudden throttle changes, since the motor torque comes up so quickly that the gyro can't quite keep up with it, resulting in a quick tail wag.  

Another benefit of getting off the governor is that I now have at least a little warning when the batteries are going down.  The governor does everything it can to maintain headspeed, and when the speed drops, the batteries are really gone.  Operating in conventional throttle mode allows the motor torque to gradually soften as battery voltage drops.

Cyclic response has been improved somewhat by changing the flybar and paddles, although I am still working on this (see below under modifications).

Tips and Modifications

Blade Grip Bolts

The 3mm bolts for the main rotor blades have been bending at higher head speeds.  Since the LOGO 20 uses 580mm to 600mm blades, these bolts appear too small.  Drilling the blade holders for 4mm bolts will work, if you don't mind the fact that the larger nuts will no longer fit in the molded hex cavity in the bottom of the blade holder. 

Carve the Head Button

The instructions tell you that using the head button will limit the extremes of pitch.  That's true, but it won't limit it by much.  The button is thick enough that a couple small depressions can be carved in the bottom to clear the links that just bump into it. 

Battery Connectors

 Hard mounting the main battery connectors to the heli frame (instead of letting the wires dangle) allows one-handed insertion of the battery connector.  This leaves the other hand free to hang on to the rotorhead or to talk on your cell phone, whichever you are more comfortable with when arming a one kilowatt powerplant.

If If things go berserk you'll only need one hand to pull the battery wires if you hard-mount the mating connectors to the frame.  

Elevator Link Mod

The link connecting the center servo to the elevator bellcrank interfered with the motor pinion gear as installed according to the plans.  I reversed the servo arm position and made a double offset bend in the rod to clear the frame.  This results in a better geometry for the link and bellcrank, and eliminates any chance of metal-to-metal contact with the pinion.

TheThe elevator pushrod (going to the center servo) was modified to jog around the frame.

Radio Switch

Mounting the radio switch under the canopy near the access hole is probably preferable to rear location that I used.  This reduces the possibility of controller noise coupling to the battery leads.  That said, there have not been any apparent problems with the setup as shown.  I just like using the combined switch and charging jack whenever possible.

RF Noise Suppression

The instructions call for the use of a ferrite ring on the speed controller signal line.  Wind the three conductor cable around the toroid ring neatly and evenly spaced, keeping even separation between the turns and some separation between the wires entering and exiting the ring.  Some CA or Goop will hold the windings in place.  Do not bundle the two free ends of the wire together, since this would negate the benefit of the ferrite.

Keep the motor, controller, and battery leads separated from the receiver and antenna.  The controller connection to the receiver is the only essential link between the "dirty" and "clean" electronics, and that line is hopefully filtered through the ferrite.  The high current conductors are extremely noisy, and source/return conductors should be twisted together whenever space allows to minimize the loop area that can radiate noise.  The battery itself should be treated like a high current noise loop, so keep your antenna and receiver well away from the cells themselves as well as the leads.  Noise coupling is worse between lines running parallel to each other; perpendicular crossings are preferred if separation is not possible.  The use of ferrites on individual battery or motor leads is ineffective.  The high currents magnetically saturate the ferrite, rendering it useless except for ballast.  In some cases a ferrite encircling the both the forward and return current leads (both battery leads, for example) can help.  In the case of a brushless motor, the ferrite would have to encircle all three leads.  Since ferrites are heavy, rearrange the components if possible to eliminate interference problems.

Headspeed Setup for Futaba 9Z Transmitter

There have been numerous comments about the headspeed increments in governed mode being excessively coarse.  This can happen if the headspeed dial range is not set up properly.  One way to allow smooth rpm adjustments is to start off by setting a flat line for the throttle curve.  This level is set by trial and error to give the lowest required headspeed.  Now add a mixed slider or dial input to the throttle channel that takes the headspeed up to the maximum you want at the full dial setting.  This way the entire dial range is used to control headspeed from min to max, and the speed increments between dial/slider detents are small.  Some transmitters will allow the dial to have the min and max set without having to mix with a fixed level. There are no doubt many different ways to accomplish this same goal on different transmitters.

Increasing Cyclic Response

As stated earlier, the flip rate was slower than I am currently comfortable with, so I tried a couple things.  First, I tried some KSJ flybar paddles, which resulted in excessively pitchy forward flight.  I then changed to a slightly longer Raptor flybar, and fitted some 60-size black Xcell paddles with bushings to work with the 3mm flybar.  The Xcell paddles are only 1.5 grams heavier than the Mikado paddles, but have considerably more area.  This paddle/flybar combination gives a much more agile response with good forward flight characteristics, and I am sticking with this setup for now.

The Bell/Hiller ratio on the mixers appears to be in the ballpark (greater than 1:1), but the actual amount of Hiller input (with flybar deflection) to the rotor blades is considerably less than on the Raptor.  This is still being studied, but there will probably be some homemade mixers tested in the near future.  

Rotorhead Phasing

For whatever reason. there seems to been a distinct cross coupling between pitch and roll (and vice versa).  Back flips drift left, and forward flips veer right.  Without too much analysis (time is short at the moment), about 10 degrees of swashplate phase correction has improved the situation (I hope it's not just my flying).

Related Links

Mikado Homepage

Risto Kõiva's RC Page
Has ECO and LOGO information and pictures, including extremely detailed bag-by-bag parts inventory for LOGO 20.

www.e-helis.com
Contains information on LOGO, ECO, and MS Hornet.

Adam's RC Helicopter Website
Primarily LOGO 20, with equipment list and pictures, including some with Curtis Youngblood at the controls.

www.logo-club.de/
In German.  Run it through Babelfish or one of the other translators.  Has lots of info, including videos.

Where to Buy

www.homestead.com/ehelicopters/
Carries LOGOs, Schulze controllers, and Plettenberg and Kontronic motors.  Package deals look pretty good.  Don't be shocked by the prices--those are Australian dollars.

www.rc-direct.com
U.S. distributor for Mikado.  They don't carry all parts, but still offer a good selection.