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HeliHobby Super CNC CCPM Hummingbird Conversion

Steve McBride converts the Century Hummingbird, using the HeliHobby.com's CNC-produced CCPM kit to make this great little micro helicopter collective pitch. Includes detailed instructions of how to make the modification on your own Hummingbird and more than 2 minutes of flight video!

Splash

Introduction


Helicopter:Century Hummingbird
Battery:Bishop Power Products 680 SHC
Motor:Astro 010 brushless from CC
ESC:Phoenix 10/Pixie 7
Available From:HeliHobby

The introduction of collective pitch to the micro helicopter lineup has brought about a whole new experience to a segment of the hobby that has seen tremendous growth over the past decade. The earliest micro helicopters, such as Ikarusí Piccolo and MS Composit Hornet, feature a fixed pitch rotor where the blades are set at a specific pitch and ascending and descending was accomplished by variations in the motor throttle. You give more throttle, the helicopter goes up; conversely, lower the throttle and the helicopter goes down. There are both positives and negatives about this type of main rotor system. On the positive side is simplicity. There simply are not as many pieces on a fixed pitch (FP) helicopter to fiddle with, to break, etc. And one of the biggest downsides is the fact that stability and cyclic response is directly affected by rotor speed. Reducing the main rotor RPM when descending or when in forward flight will result in a reduction in gyroscopic stability and cyclic control. I have had several occasions where my fixed pitch micro helicopter has encountered a thermal and the only way to reduce altitude was to keep lowering the throttle and rotor RPM until it would descend through the lift. This effectively turned the cyclic control into mush and maked for a very interesting flight to say the least.

Enter collective pitch (CP) control. What CP consists of is a method to vary the pitch of the main blades during flight which allows the main rotor RPM to stay fairly constant and allows the helicopter pilot to apply more pitch to ascend and less pitch to descend. The cyclic response is retained as is the gyroscopic stability the rotor disk provides. Of course, there is a downside to CP in the form of more components, complexity, longer setup time and generally higher expense. But you simply canít get that instant response that CP offers with a FP machine, or the stability in hovering and forward flight. Of course there is the 3D aspect, but weíll leave that for the experts.

The Kit

The HeliHobby.com kit consists of a CCPM head similar in function and design to the MS Composit CP head offered as an upgrade to their FP Hornet micro helicopter or as standard fare on their CP kit. HeliHobby.com offers the Super CNC CCPM head as a complete package or individual components. I chose the complete package. One could mix and match parts with the MS Composit upgrade kit, choosing only those pieces you wish to upgrade of the plastic kit parts. As the majority of the Super CNC CCPM head is constructed of aluminum using CNC processes, you can argue that the complete kit would be both stronger and more precise than the MS Composit components. One thing is for sure, they certainly look nicely constructed.

The head will fit without modification onto the collective Hornet, but as I had a bit of experience with a Century Hummingbird micro helicopter, I chose to go that route. When using a Hummingbird for the conversion project, a new, taller mast, or main shaft, will be a necessity. This shaft can be built by the hobbyist or can be purchased from HeliHobby.com. The HeliHobby.com version is constructed of titanium and seems to be a fairly nice affair and a good deal at about $16.00.

The complete kit consists of the following pieces:

  • 120 degree CCPM swashplate
  • CNC Collective Horn
  • CNC Stabilizer Dome
  • CNC Rotor Head
  • CNC Pivot Support
  • CNC Blade Grips
  • CNC Stabilizer Arm
  • Shaft Collar
  • CNC Connecting Rods
  • Bearings and Hardware Kit
  • Loctite

You will need to supply the following materials to complete the conversion process:

  • 120 degree servo mounting plate
  • Longer mast (shaft)
  • Hornet flybar
  • Hornet paddles
  • Links and threaded link connectors
  • Main Blades

Helihobby.com also offers the links, link connectors, and main blades in a kit for little more than the cost of the main blades. It is certainly worth looking at when making the initial purchase.

There are a couple of differences in the design of this kit and the MS Composit kit. The most obvious is the Super CNC kit is constructed of aluminum that has been anodized red. What may not be so obvious is that the pins, both the rotor head securing pin and the stabilizer arm pins, are threaded. This makes replacement as easy as unscrewing a bent pin (hey - it happens) and replacing with new. The replacement pins are available from HeliHobby.com, but for the adventurous modeler, I will detail how to make your own later in the article.

Overall I was impressed with the quality of the kit. My only problem with the kit parts were with the connecting rods. The links on each end of the connecting rods were plastic and seemingly cut from a longer link. On one of mine, the link was not cut straight which placed the link at somewhat of an angle. I replaced this with a link that I cut to length. Also the screws on the connecting rods were not countersunk screws, but the connecting rod aluminum is countersunk for them. Using CS screws will help to squeeze out a few extra degrees of pitch, so it may be worth replacing them. I also replaced the links with longer links to achieve a bit more pitch range. This is not necessary though. Considering this was a relatively new kit, I was not surprised to see this small issue and am quite pleased with the other pieces of the kit.

Disassembly

I will assume you have a functioning, flight ready Hummingbird that you want to convert. If you are starting with a new kit, skip the servo removal steps.

First, remove the canopy and set it somewhere safe, as you wonít need it until after you have performed some flight trimming on the converted helicopter. Remove the servo arm screws and the servo arms from the output shafts on the servos. If the servos were attached using the stock double sided foam tape or similar, they can be removed by twisting the servo gently back and forth until the bond is broken. Clean the servos of adhesive residue if you are planning to reuse them.

The rotor head is removed by first releasing the ball links from the head. Gently twist them until they release. Donít force them or you may break one or the rotor head ball. Once the links are removed, the head can be popped off of the bearings by lifting the head from at the end of one of the blade roots. Repeat on the opposite side of the rotor head.

The skids and tail boom supports need to be removed next. This is accomplished by removing the single screw from under the horizontal stabilizer. Remove the silicone tubing from the back ends of the battery supports at the back of the chassis. The horizontal stabilizer then snaps off of the boom and the boom support struts will slide back off of the battery supports. Pull the remaining silicone tubes from the battery supports along with the battery holders. The two battery supports then can be removed and the landing gear and struts simply pull free from the main chassis.

The rotor hub, timing yoke, swash, etc. are released from the main shaft by pulling a pin that secures the hub. Use fine needle nose pliers to pull the pin. Once the pin is removed, the whole works simply slides up and off of the shaft. The shaft and spur gear can then be removed from the bottom of the chassis. The top and bottom bearings should also be removed and set aside for use during re-assembly.

Take a break and clean up your work area, get a cold drink and congratulate yourself as you have just completed the disassembly phase of the project!

Modifications

There are a few key modifications that need to take place on the chassis and the main gear.

  • Remove the stock anti-rotation link at the top of the main shaft support tube.
  • Cut the electronics box down to size.
  • Install a 120 degree servo mounting plate.
  • Remove the stock shaft and install the new, longer one.
  • Add the aluminum anti-rotation link to the main shaft support tube.

The stock anti-rotation link is cut from the top of the main shaft support tube using a sharp single edge razor blade, #11 X-Acto blade, razor saw or rotary cutoff wheel. Once the link is removed, the lip/ring needs to be removed. I started by using a sanding drum in a rotary tool, but I eventually settled on using a single edge razor blade and shaving the ring off. Just take care not to remove too much material as it is important to have a snug fit with the new anti-rotation link. After you have shaved the ring down to approximately the diameter of the support tube, switch to sandpaper to finish and blend your work. I started with 180 grit and worked slowly, switching to 220 and then to 400 to give it a nice finish. Stop frequently and check the fit of the new anti-rotation link. Remember, you want a snug fit.

The electronics box needs to be cut to allow the servo mounting plate to fit. One option is to remove the entire box. I first chose to remove just enough material to fit the servo mount while leaving the canopy mount in place. The illustration above shows the approximate cutting line I followed. Again, go slowly and take your time. A mistake here can cost you. I used a single edged razor blade here. After you are satisfied that you have removed enough material, use some sandpaper to achieve a somewhat finished appearance. It should be noted that I later cut the entire box off and simply glued the canopy mount to the top of a servo.

The 120 degree CCPM servo mounting plate is available from HeliHobby.com but I elected to make my own. I used some .032Ē Plexiglas and a pattern that I found on the internet. It is a simple process and works very well. I like the idea of using a thick material like this as it gives a better bond line than a thin material. Drill the center hole of the plate so that it is a snug fit over the shaft support tube. I suggest waiting until you have the shaft installed....

A new, longer shaft must be installed into the stock Hummingbird gear. My first attempts were unsuccessful until I determined how the main gear was held in place. At the bottom of the main shaft is a pin that is set into the plastic hub of the main gear. On most of the shaft/gear assemblies out there, this pin is not visible. I understand that on the "Hummingbird IIĒ this pin is visible and removable, allowing the main gear to be removed from the shaft. If your pin is not visible, the best method I found to remove the shaft is to use a single edge razor blade or #11 blade to cut the plastic away from the bottom of the hub. If you turn the gear/shaft assembly upside-down, you will see a small hole at the center. Shine a light into this hole and you can see the end of the shaft. You will need to cut this material until the end of the shaft and the retaining pin are exposed. Then you can place the hub of the gear onto a nut or socket of appropriate size to allow the shaft to pass, and tap the shaft out through the bottom. Resist the urge to press it out from the bottom up...you will break the main gear. Once the main shaft is out, clean up the hub, squaring the cut. I used the equivalent of 30 minute epoxy on my first one, but found that 5 minute epoxy works well. Clean the inside of the hub and the shaft, mix your adhesive and apply a thin layer inside the hub. Insert the shaft from the top of the gear, making sure that the end of the new shaft is approximately in the same position as the old one. You have some tolerance here as you will adjust the servo mounting plate later, based on the position of the main shaft. After inserting the new shaft, roll the assembly along a table edge to make sure the main gear runs true. You donít want any wobble. I apologize that I didnít take any photos of this step as I performed it at work where I had a better selection of tools but forgot my camera.

Assembly

Now that you have the modifications complete, we can start the assembly. The first step is to install the chassis bearings and the new shaft/main gear assembly. Install the shaft collar and make sure the assembly runs smoothly. Make sure there is no vertical movement in the shaft.

Next, re-install the landing gear, battery supports, tail boom braces and horizontal stabilizer. The front of the battery support rods extend from the front of the chassis. These make an excellent support for a gyro mounting tray. I constructed one from the discarded electronic box cover that was removed from the chassis. Simply clip the plastic pins and CA in into place. At this point, I suggest you install the motor of choice so that you can properly adjust your servo mounting plate for proper motor clearance. I initially chose an Astro 010 10T heli motor and the folks at Castle Creations were gracious enough to supply one for use in this review. Donít worry about the pinion or ESC at this point - you just want to use the motor as a gauge.

If you did a good job drilling the servo mounting plate, it will be a snug fit. Slide it over the main shaft support tube. Install the new anti-rotation (A/R) link onto the support tube. Again, it should be a press fit. You can install the A/R link forward or, like the original Hornet CP, to the rear, which is how I chose. I cannot think of any particular advantage one direction has over the other except perhaps the placement of the servos. I fit mine on both ways and never really gained any extra motor clearance. However I did have to remove the rest of the material from the chassis electronics box as it was interfering with my servo placement.

Assembly of the head is pretty much per the Hornet instructions which are available on the internet. I wonít go into detail on the head assembly as simply looking at the pictures should be enough. One unique difference between this head and the stock Hornet CP head is that the pins, both on the head and the stabilizer arm, are threaded instead of pressed into place. This allows them to be removed easily in the event one or more gets bent with an unintentional meeting with terra firma. Assemble everything except the main blades and paddles to get an idea of where the servo mounting plate needs to be positioned. I installed mine 18mm from the top of the support tube. Use this as a general guide to adjust your links. With the servo arms horizontal, you will want the blade grips to be at zero degrees pitch with the pivot support halfway to the top of the stabilizer arm pins. Donít use the supplied Loctite yet as you will be disassembling the head so that you can glue the A/R link and servo plate.

The servos are mounted on their sides and I elected to use double sided foam tape as I have had great luck with it on small servo applications like this. Your servo selection is quite extensive as about any sub-micro (HS-55 or smaller) servo will work. I have used both HS55s as well as GWS Pico BB servos and they both work well. Others have used HS50 servos which work as well and are smaller than the HS55s and perhaps a bit less power hungry than the GWS Pico servos. Install the servo arms and links and attach them to the swash balls. Adjust the servo links so that there is not any potential binding and so that the servo plate clears the top of the motor or any potential motor you may use. After you have the servo plate positioned, use a drop of CA to hold it in place. Disassemble the head and remove the main shaft and bearings. Now use epoxy to secure the servo plate in place. Again, I used 5 minute epoxy here and it has been working very well. Now remove the A/R link and roughen the inside of it with some 400 grit sandpaper. Apply a very thin coat of epoxy and reinstall. Be very careful that you do not get any epoxy into the bearing mating surface of the support tube. A little bit goes a long way.

After the epoxy cures, reassemble the head, making sure to use Loctite on any threaded fasteners. Be sure the blade grips rotate freely and all the links operate freely. Install the servo arms and secure them with screws.

Now you are ready to install the speed controls and gyro. I am a fan of Castle Creations speed controls and again, they came through by supplying both a Phoenix 10 for the main motor and a Pixie 7P for the tail. The P10 that was supplied included the latest Ďsoft startí mode for governor spool-up. I was eager to give that feature a try. I originally chose to use a CSM HLG200 lightened gyro and installed it in the proper orientation on the front of the chassis. The speed controls need to have their battery wires connected together so they receive power from the same battery. The tail speed control should have its red wire removed from the receiver plug. Donít worry, the receiver and servos get their power from the main motor ESC. The Astro 010 heli motor included a set of reversible connectors which I used. These work great, and if you manage to wire it so that it runs in reverse, it is a simple matter of disconnecting the mating plug, and rotating it 180 degrees and plugging it back in. It also comes in handy for maintenance as both speed controls can be removed if you use the proper connector on the tail motor wires. I simply taped the speed controls together and secured them to the right rear side of the chassis just under the servo mounting plate. I used a JR 610M receiver to control everything. I first removed it from the case and covered it with some shrink tubing I had on hand. I also installed a Deans micro receiver antenna and zip-tied it to the landing gear struts. Note that I elected to use the stock tail motor as I had some success with it on a moderately powered fixed pitch version of this helicopter.

The canopy was fitted to the heli and the canopy mounting rod was positioned and glued to the top of the rear servo using a single drop of thin CA. This seems to work well enough. An optional method would be to glue the mounting rod to the main shaft support tube and relocate the canopy grommets forward.

At this point I was ready to supply some power and begin adjusting my pitch curves. As I was going to use the Phoenix 10ís governor mode, I didnít really need to worry about a throttle curve - just set the low point so that it arms and the rest are set equal. Pitch curves are set to suite the individual's flying style and desired responsiveness. I basically set up a conservative pitch curve with a slight negative pitch at the low end and a high pitch at the top end. This would hopefully give the smoothest curve. Besides, I didnít plan on any 3D with it.

Flying Time!

The first flights were with a 3 cell pack of 1200mah E-Tecs. I installed a 10 tooth pinion on the Astro 010 and made sure the lash was acceptable. The first test flights were a bit of a disappointment in that the CP Hummingbird would just barely get off the ground with full collective. I eventually changed my upper pitch curve to allow for maximum positive pitch and set the throttle to 100% but it was still a bit sluggish. At this point, I decided to swap in a Razormotors.com RZ350. I have used this motor in my fixed pitch hummingbird with decent results and knew that itís constant (RPM/V) was similar to the Micro Heli V2 from Razor Motors. Because the Hummingbird comes with a 120 tooth spur gear, the ratio was a bit high even with an 8 tooth pinion so I started with a 50% throttle curve. The first flights with this motor were a bit better after I dialed the throttle up to around 75%, but still not what I wanted.

I began to examine the blade grip linkages and decided to adjust them for more positive pitch at maximum collective. Just a couple of degrees made a huge difference. Now it would leap off the ground and was much more responsive, but the tail motor struggled to keep up. In fact, with a decent stab at the collective, the tail would swing a full 180 degrees even while holding full left rudder. There simply was not enough power there. So off came the old motor and on went a high authority motor with the stock tail motor pinion. The motor actually came from a GWS EDF50 fan, but you can buy them directly from Helihobby.com. It is a mod that I consider necessary as now the tail held much better. But now I had a bit of a problem with the CSM HLG200 gyro in that the gain seemed impossible to set properly. I either had too much gain and the tail would wag severely, or the tail didnít have enough authority and would swing wildly with changes in collective.

After fooling with it for some time and talking with others about it, I decided to give my JR G410T HH gyro a shot. I removed the case, shortened the wires and shrink wrapped it. This time I had a winner! The tail was very solid and would hold even without inputs from me, swinging about 45 degrees with a sharp stab on the collective unless I input a left rudder command; then it would hold very steady. But now I was getting some Ďpoppingí where the heli would be in a stable hover and suddenly jump straight up or drop. I was also getting glitches and decided to swap out the receiver for a JR 700 that I had. I didnít shorten the antenna, just wrapped it around a skid and left it dangling. I know itís not a good idea to do this with a heli, but I needed to get it into the air so I could trim it for flight. Again, I had the popping problem and after reading on the subject, I decided to swap all the servos. This time everything worked as it should have, no glitches and very good power.

At this time, I received a Kokam 680SHC battery (340HD 3S2P) from Bishop-Power-Products.com. From the first flight with this battery I was amazed! It made my ageing E-Tec battery look like AAA NiMH cells. Now this was more like it! A stab at the collective would send the little heli to 25 feet in a second. My tachometer decided to quit me so I never got any good head speed readings, but I can say that the calculated speed is up around 3000 RPM! But with the CNC Head, I was not worried. Even at these speeds there would be no distortion of the components which would perhaps fail on the stock head assembly. I flew the heli in this state for many test flights, each one trimming and adjusting the throttle and pitch curves. The only other change I made was turning off the governor mode and setting up a throttle curve. The governor mode worked very well to maintain the head speed I wanted, but if you were not loading the rotor disk, the motor was constantly speeding up and down to try and maintain the speed. I am confident that if I had a one way clutch/bearing on the main gear, this constant pulsing would go away. But as I didnít, I elected to switch it off and it all runs smooth as can be.

Downloads

Conclusion

No kit is perfect and the Super CNC CCPM head is no exception. I had a problem where the connecting rod ball links were a bit too short and seemingly crooked. I had some extras on hand and simply replaced them. This let me have a larger collective range than the stock ones would have allowed. Additionally, the pivots for the assembly where the flybar teeters would press the bearings into the flybar if tightened too much. Using loctite and being careful not to tighten them too much solved the problem, but I feel a machined shoulder would be a better idea. The various locating pins are an item that will need replacement after a crash of moderate severity. They can be purchased from Helihobby.com or built from 2-56 x .5Ē setscrews. I made a replacement set by chucking a setscrew into a 3 jaw chuck on a rotary tool and then turning it down to the proper diameter with a fine tooth needle file. It takes about 10 minutes per pin and there are three necessary. Just be sure to get the stainless steel setscrews. They are available from McMaster-Carr.com for about $4.00 for 50. Not a bad deal for several replacement sets and a few minutes.

After quite a few flights, I had a pre-installed ball come loose from the swash in flight. In looking back at the video of this flight, I realize that the heli was making a bit of a different sound prior to its failure and I should have landed at that time, but instead I kept flying until it failed. Even after a fall from about 25 feet up, the only damage was a broken flybar. I suggest that you check each ball link on the swash before use. Remove any that are loose, clean with acetone and replace, adding loctite to make sure it does not happen again.

Those issues are all I can complain about. I am very happy with the smoothness in the headís operation and its obvious sturdiness and ability to handle very high head speeds. Itís doubtful that I will manage to ruin any piece of the assembly and as such I am not so worried about pushing the heli to the limits of my ability. The cost seems a bit much up front, but considering the cost of a replacement swash plate and other pieces, the Super CNC head is really a decent value in my opinion. The modifications to the Hummingbird may seem daunting, but are really quite simple to do. Just take your time and double check before cutting or gluing. It becomes even more of a value when you are considering moving up to a CP heli from your fixed pitch hummingbird. The cost of a collective micro will run close to $200.00 before you make any modifications or additions. In all actuality, I probably saved a bit of money by upgrading my FP heli that I already had.

Overall I had a lot of fun doing the modifications and learned quite a bit along the way. I now have a very responsive heli that looks great with all the red pieces. The addition of the Super CNC head is one that I would recommend to anyone seriously into the micro heli segment of the hobby and who plans on staying there for some time.

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