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Old 07-02-2020, 09:36 PM   #1 (permalink)
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Join Date: Apr 2020
Location: Birmingham, AL
Default align 300x swashplate fix

Jayrat and I have been discussing this issue. For those unaware, the swashplate-servo links have an issue. The back servo (elevator) is mounted lower than the other two, yet all 3 have the same sized linkage. You basically can't level the swashplate with servos at 90 degrees.

Here's what I did last night.

1. Removed the head/blades/DFC links...

2. Removed two front swashplate links from both the servo and swash. If you look, you can see that the link rods are threaded far enough that if you thread them all the way into a ball socket, it will punch into the interior or bulge the interior so that the link will pop off. Yet we need these two links to be as short as possible since the rear link is already 4-5mm too short.

3. Took dremel and ground 1-1.5mm off of each end of those two links. Which will shorten them by 2-3mm. Re-install and level the swash with the servos at exactly 90 degrees. Now it works.

4. Next problem is trying to get zero degrees pitch at the same point (servos at 90 degrees). Could never get there. Always had a +2 to +3 pitch at the zero point. So, I removed the DFC links and cut about 2mm off the end of each one (I measured the depth and it was about 3.8-3.9mm so I took one half of that.)

5. I then threaded the linkage rod into the DFC link and measured how far it was from burying the threads all the way inside. I ground off the link rod on the end this much. I think this was about 1-1.5mm. I then ground the same amount off the other end. Screwed the links into the DFC with some align locktite, and then threaded on a ball link for both.

6. Reassembled everything and checked pitch. woah. -4.5 to -5 at the neutral point. So I actually had to thread some of the DFC linkage out of the ball joint to get it up to zero (think it was 2-3 turns.

I now have servos centered, swash level, and zero (+/- 0.2) pitch.

Had to spend a few minutes playing with the pitch curve after all of this, but really like the way it behaves now. At 50% throttle heli sits on the skids. Used to almost fly.

This all took maybe an hour or so to do.

One other note. We had talked about the 200 skids from amazon. They offer a wider stance and a slightly better skid shape for flying off grass. But it is pretty hard to keep the tail rotor clear unless your grass is cut to " high.

They provide some spacers and I took two of the shortest ones and put them on the screws on the back of the lg (between the cross mount and mounting point on heli). Gave it a little of that align "forward cant" which helps. Thing still does not like any taller grass, and Bermuda gives it fits since any skid will snag the way Bermuda runners grow. But landings and takeoffs are uneventful other than for the occasional cleaning grass particles off the damned tail rotor.

Other notes. You could probably reduce the amount you cut off of the DFC arm to 1mm, and trim the link rod to bottom out. If you feel a little antsy about going too far. What Align should do fits into two categories.

(1) provide a longer elevator link, enough to exactly offset its lower mounting point.

(2) very slightly raise the Jesus screw hole. Then you would not need to fiddle with cutting the DFC linkage at all. I came within an inch of doing this with my drill press. Drill a new hole at 90 degrees to the existing hole, maybe 2-3mm higher. Chamfer to make it easier to get the screw back in and the DFC linkage part of the heli would then be ok. Only question would be if the second hole would significantly weaken the shaft. I don't think so since that part of the shaft would still be inside the head.

More on this later as it is not a hard fix to try.
AMA #118235
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