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Heli-Log 4:1:14

Posted 04-01-2014 at 11:28 AM by rcnut

Happy April Fools Day!...Saying good-bye to my Trex 700N!



Setting the stage…

I made the decision to convert my Trex 700N to gas, a Trex 700G! I picked the HeliXheli conversion kit as the gas conversion platform. I have the Hanson RC300 3D Max motor with the Century V2 pipe. I will be using the Futaba GV-1 governor and RC stator Gator. Running the “show”, is the AR7200BX driving 3 MKS HBLS950 cyclics, HBLS980 tail servo, and a Savox SC-1268sg servo for the throttle…all high voltage servos. I was looking for a less torque throttle servo, but couldn’t find anything in stock, so I went with what I could find available. I will be using Fromeco’s Relion 5200mAh LiIon battery and the Jewel generator to keep it charged.


My, now donor heli is a version 1 Trex 700 nitro heli. It has the Quick UK control link set, replacing all the links, balls, and rods. I bought the metal clutch stack, metal main bearing blocks, and tail control lever…as the plastic one keeps breaking in a crash and it became hard to find replacements, constantly out of stock. In time, I replaced all the frame shouldered screws for the aluminum inserts (forgot what they are actually called), then using regular cap screws. The frame shouldered screws worked for the first couple of times, then the allen head stripped out making it interesting to remove. I had to use my dremel with a cutoff wheel to make a screwdriver slot to remove the frame shouldered screws. The reason for these screws stripping is the hole for the allen head wasn’t punched deep enough. The Trex 600 kit uses the same frame screws, and those are fine, but also had the fate of running out of stock…constantly, so they were replaced.


The transformation begins…

I decided to follow Carey Shurley’s build thread (https://www.helifreak.com/showthread.php?t=506726) instead of “re-inventing the wheel”. It starts with setting up the motor. I took the air breather and stock muffler off so it would be easier to work on. I installed the motor mount, the clutch stack, and the ball link to the throttle arm. I have ordered a Trail Tech Temperature Meter (14mm) to use on the spark plug. Next is the clutch bell, bearing blocks, and pinion gear. This was straight forward, paying attention to the orientation of the bearing block. You install the first bearing block, then the pinion gear, and loctiting the screw through the clutch bell holding the pinion on. And add the top bearing block to the top of the pinion.

On to the fuel tank…per Carey, you use the same nitro fuel tank for gas. You don’t need to change the rubber stoppers. Just remove the fuel line and clunk, and then replace it with gas line and felt filter…like Viton tubing. Carey mentions to use 6 inches of fuel line, I opted to use 4-1/2”, I might shorten that some. The Whiplash gasser had had similar issues with the clunk line being too long. Sometimes the line would fold over on itself cutting off the fuel, and sometimes it would hold the clunk out of the fuel. So the fix was to shorten the fuel line to 4-1/2”...for the Whiplash gasser.

Carey used a Stens #610-014 fuel filter, but I used the filter that came with the motor, the Zenoah filter. This posed a problem. The Stens filter is a smaller diameter, but longer filter that will fit in the existing hole. The Zenoah filter is a bigger in diameter and shorter in length. So opted to open the hole to accommodate the filter…by doing this, I needed a bigger stopper to plug the hole. I used an extra fuel tank stopper I have for my Whiplash gasser. Now the plastic fuel fitting won’t fit in the smaller hole. I didn’t have an extra fuel fitting for my Whippy, but I did have and extra fitting for my Rave nitro heli…so I used that.

You need to add a vent line to the tank as most gas systems have one line for the fuel feeding to the carb, an overflow line, and a vent line. The carburetor has its own pump to draw fuel, so a pressurized system is not needed. To properly plumb the vent line, you need to make 3 coils of tubing (loops) close to the tank. This prevents the fuel from leaking out when flying inverted…then finish plumbing to the bottom of the heli. I used 3 wire ties to hold the loops to the tank close to the top. This will keep it from rubbing against the main gear and resting on the motor.

Now for the fun part…the frame. I began sanding all the edges of the frames and other carbon fiber pieces, getting that out of the way first! I built up the receiver tray and installed it up front, and then started installing the canopy stand off and canopy mount, or the Booya quick release, and the metal frame supports. I installed the clutch stack, main bearing blocks, and the mainshaft and main gear assembly. The gear mesh is perfect! No slop what’s so ever! I decided to look ahead of the build thread to see how the servos are laid out and to do a trial fit. According to Carey’s build thread, he says to mount the cyclic servos from the inside of the frame.

As I stated earlier, I am using MKS HV servos…and of course, they are too tall to fit back to back inside the frame. So I will have to mount them from the outside of the frame. This information was needed for the placement of the “PEM” nuts. I opted to use these as a better [IMO] method for mounting the servos vs. those dumb plastic screw holders. Not that the plastic holders don’t work, but trying to replace a servo in close quarters makes it very interesting getting to.

Note: A PEM® nut is an internally threaded fastener, that when pressed into ductile metal, displaces the host material around the mounting hole, causing it to cold flow into a specially designed annular recess in the shank of the fastener. A serrated clinching ring prevents the fastener from rotating in the host material once it has been properly inserted. Thus a PEM nut becomes a permanent part of the host material offering strong, load bearing threads in relatively thin sheets of metal. "PEM" is a brand name and registered trademark of Penn Engineering & Manufacturing Corp.[1] The generic term for this type of fastener is "self-clinching nut".
Reference from Wikipedia.org/wiki/PEM_nut


The holes in the frame had to be drilled to accept the PEM nuts. Once drilled, it’s a simple matter of tapping them in with a block of metal and small hammer. Now that all 5 servos have their own PEM nuts installed, it was time to mount the fuel tank and bolt on the other frame half.

To be continued…
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