Hardish landing = Stripped Servo
We need to find a replacement for nacelle servos! My Blitzworks V-22 arrived last week. As you owners already know, when transitioning from vertical to forward flight, a servo in each wing rotates the nacelles 90 degrees (as a pair). At each end position, the pair
should be either completely horizontal, or completely vertical. That is the best-case scenario, but the manufacturers took a guess as to where the endpoints of your radio will align those servos.
With my DX6i, the endpoints didn't align with completely horizontal and completely vertical and even after adding 120% endpoint adjustment, my nacelles pointed forward about 5 degrees. Of course, with me being driven by my ADD,
I flew it anyway, which resulted in my maiden VTOL "going south" ...err "north" as my V-22 wanted to move forward with relaxed sticks. Not optimal - but still flyable.
So, I looked to see how to fix it, and I have to tell you, it is a REAL pain. The manufacturers use a janky coupler from the servo to the nacelle shafts. At one end of the coupler, is a splined opening with a servo-screw hole down the center to attach to the servo. They also use 4 phillips-head screw to bite into the soft brass splines of the servo. The other end of the coupler has a smooth bore, and four set screws to bind the smooth nacelle shaft. This means that you need to unscrew 4 set screws to loosed the shaft to adjust it to vertical. In my case, they overtightened one of the setscrews on each coupler, so they stripped when I tried to loosen them. Get the drill. Drill out the setscrew. I was able to adjust the other 3 no problem. Ugg.
Everything is good. Perfectly aligned. Ready to fly. I test the nacelle rotation (bound to my Gear switch) and it works, but has a tendency to hiccup during rotation. Seems odd. Maybe the servos aren't up to task? Maybe a horn-and-control-arm would be better to drive the nacelle rotation? No matter. Let's fly.
It VTOLs great! 10 feet up and around and nose in, nose out, rotating, feeling good. Let's try a bit higher, wind is picking up (did I meantion a slight wind?), it starts to buck forward and backward - the "Osprey Yoyo" - as the gyros try to keep it level. I don't like it so I ease it to the ground and shut off the motor. Everything seems fine, but the right nacelle won't rotate now. Grounded. Back to the shop!
At the shop, I decouple the nacelle shaft from the servo, and dig out the servo from the foam wing. After removing the coupler from the servo, I take apart the servo case and see that the
teeth on the brass output gear are damaged.
I hit Bananahobby to find that they don't yet offer servo replacements in the spare parts! All I know is that they call it a "17G metal gear servo", but no specs are called out, and there are no marking on the servo.
http://www.bananahobby.com/17g-meta...2-osprey-rc-warbird-airplane-227487-prd1.html
Can I repair the servo myself? If the teeth are damaged on one side of the shaft and only 180 degrees is ever used, can I just spin it around and use the other side? Let's see. So, opened it up, removed the shaft gear, popped out the nylon retainer-with-stop-pins, rotated the retainer 180 degrees, and pressed it back in, rendering the servo usable. Too much McGyver, but I wanted to fly! It now rotates well under power, but cannot be rotated by hand which means either some other teeth on other gears are damaged, or I probably dorked something up during reassembly.
As I mentioned before, Bananahobby calls these "17G Metal Gear Servo", but shows no photos or specs on the spare parts page on the website. On the last page of the manual, it is listed as "15218 17g Servo for Rotating Axis", but a search of the BH site, and Google, yields no match for a "15218 servo". Perhaps ANY 17g servo would work? Bananahobby lists a 17g servo for a number of products, so maybe any of them would work. The one in the V-22 are unique, in that the top of the servo looks different when compared to other servos - as one edge of the top of the servo does not "stepdown".
A candidate:
http://www.bananahobby.com/17g-meta...mm-lead-lx-f18-04.html?pSearchQueryId=1960562
DM17G : 2.2kg or torque @ 4.8v, and 17g.
Looks like the FMS DM0170 servo, used in LOTS of Blitzworks planes.
A HITEC option:
HS-81mg: 2.6kg torque @ 4.8v, and 19g.
The Hitec servo's case is identical in length-width, but is narrower in depth (as pressed into the wing). The spline is identical in diameter (HS-81MG is on the left), but the output shaft does not align exactly with the nacelle shaft, when the servo is placed in the original wing slot. Not a "showstopper" by any means, but will require some foam carving if used.
Tower Hobbies 81mg is on the left - a cheap servo, with aluminum shaft, and small diameter splines. Not a candidate! Original (disassembled) servo is in the center, and Hitec HS-81MG is on the right.
I have an FMS servo coming in the mail tomorrow from an eBay seller, and I'll report back with the results.