Logo XXtreme Maintenance Report and MKS X8 Servo installation

[nebuchadnezza]

Hello fellow XXtreme Owners!

(Skip to post 2/3 for the pictures if you get bored of reading :-) )

I did some routine maintenance and some tuning on my heli these days and wanted to share my experiences. First of all I would like to inform you I'm not a native speaker; so please excuse any strange grammar etc.

The reason for my maintenance action was an "sat data out of sync" in my vbar log file. It appeared after switching from Jeti PPM to Jeti UDI. The error was probably there before, but went unnoticed due to PPM's shortcomings regarding error detection. Anyway, my problems are still here regarding the log file errors, but that is not the reason for this post. So let's get straight to the bottom of my finds!

The Heli is about 2 years old, born august 2012 to be exact. :-) It has somewhere between 300 and 600 flights on it. Yes, that's pretty inaccurate, but I don't keep track of my flights since I discharge my batteries using the chargers ability to monitor resistance of each cell. And you always see then go fat after 1-2 years...

First I thought it had to do with some motor insulation problems, and therefore I to my scorpion 5035 rewind by the awesome Bert, aka Power Dekker! It has gotten a 1,7mm2 single wire wind and new bearings; resulting in 411KV (vs 383KV before) and 9,2 mOhm. Due to the increase in KV I also went from the stock 18 tooth pinion down to a 17 tooth. That motor is a beast. Almost 20 degrees Celsius cooler than the stock. 58 C after the flight with 3500mAh in 4-5mins used and peaks up to 140A standard and 180A max. No regrets on this one!

Than I thought it could be back current from the servos. I went ahead and bought a Linus R2 Prototyping PowerBusMini and as a backup power supply a buffer-capacitor with 3x50F also made by Linus. http://www.demonaero.com/category_s/...show=20&page=1 . This system provides the power from the BEC, in my case Linus R2 Prototyping HV2Bec rated at 40 Amps, straight to the servos and on a second circuit it supplies the vbar and the receiver with 6 Volts. This prevents any back current interference; as an example check out http://www.vstabi.info/en/node/1422
For the buffer pack: it needs about 4,5 mins to be fully charged on the first flight; after that, if you switch it off after disconnecting the main battery, it just needs a couple of seconds. It supplies about 25-45sec of up-down movement of the servos on a bench test, so it should last long enough for an emergency auto. The only thing that still worries me is, that I can't "see" a BEC failure through my telemetry since it is supplied by the powerbus with a steady voltage until 6 volts out of the buffer and then switched off immediately. I can only recognize a main battery failure/esc failure leading to battery failure. Maybe i will by a second voltage monitoring sensor for the BEC output in winter...thanks to Jeti's Telemetry it's just easy to expand.

Well, since my errors kept showing up sporadically in the log I went ahead and decided to change ALL the bearings in my Logo. Luckily I was also able to sell my servos and went ahead with a servo upgrade; more on that later. So as a little reminder, the heli has 300-600 flights on it with no crash and no maintenance except cleaning and external oiling of easy access parts. The only things I changed right after 3 weeks were the swash and servo links and balls due to some damage I produced during the initial build. My heli is pretty heavy, about 5,2kg w/o battery and around 7-7,2kg RTF. And now let's get down and dirty...yes it was really dirty at some parts.

The Tail:
All 4 bearings in the tail shaft and umbrella gears were bad. Also took the opportunity to shim the umbrella gears for better mesh. Had some play, but nothing to worry about, although no shimming for the last 2 years. The thrust bearings were ok, changed them anyway. I think one of the 4 bearings in the tail blade holders was bad as well.

The torque tube:
1 out of the 4 bearings was bad, but I didn't bother to spend 40€ on a new torque tube set just because of 1 bearing :-). So kept it installed.

Motor counter bearing:
Since I couldn't find the measurements of the bearing I had to buy the hole counter bearing holder for 15€. Kind of sucks...anyway, the bearing was really bad.

Main shaft bearings:
Long story short. Pain to get out and in. Pain to install the 3 metal parts in the CF frame without disassembling all. 2 out of 3 were bad. Only middle one was OK. The one way bearing was ok, cleaned it and greased it.

Main rotor hub and blade shaft:
Oh man...that was hell. It took me 2-3 hrs to get it done. I wasn't able to unscrew one of the 2 big screws that hold the blade grips on the shaft; using some tools I scratched the shaft. Had to Polish it using my nail file and some sanding paper to get it through the bearings again. Here the parts that were bad: 2 of 4 bearings, 1 of 2 thrust bearings, dampers were completely dry. Messy with all the grease and so on, but this will become a definitive winter maintenance item...

The gearbox:
It was a little hard to get out of the heli, but not as bad as I feared. About 1 hr of work required if the main shaft and the main gear are removed already. The gear mesh seamed fined, the umbrella gears looked as on their first day and 2 of 4 bearings were like new. Only the 2 bigger ones on the plastic umbrella gear that connects to the torque tube were a little bit worn out. I took the chance to change the belt as well, but the old one didn't show any sign of use except a little dirt.
This time I was extra careful to assemble the gearbox correctly to minimize the risk of gear failure due to excessive play.

So that's it for wear an tear parts I needed to replace. All in all it comes down to about 60-100€ for all. I would recommend to change the following with priorities (1=high - 3=low) and ease of access (A=easy - C=hard).

Motor Counter bearing 15€ 1A
Tail shaft and umbrella bearings 4x around 15€ 1B
Thrust bearings Main blades 10€ 2B
Rotor blade shaft bearings 4x around 15€ 2C (also lubricate all)
Main shaft 3x (4 to buy) bearings 15€ 2B (lubricate one way bearing)
Torque tube 40€ 3A (only part that rotates that I didn't change due to price)
Tail blade thrust bearings 10€ 2A
Taile blade 4x bearings 15€ 3A
Gearbox bearings 4x 15€ 2C (only the 2 bigger bearings were bad, change belt too)
Belt drive 10€ 3C (only if visibly worn or changing gearbox bearings aswell due to access)

I hope this helps some of you for your upcoming winter maintenance :-). If you have the time an space, I would suggest to disassemble the heli and check for wear or damage due to disassemble (like me on the main rotor blade shaft) to save some bucks on unnecessary bought parts. All in all it took me 2 days to reassemble all, but I used the chance to install new servos as well, therefor i think it could be done on one long rainy Sunday if you are in a hurry.

And now for the second part of this post. I will copy and paste it in a separate thread as well; for those just interested in the servos.

This part is about the servos I changed. I used Futaba 172HV on the swash and Savöx 2272HV on the tail. They were doing good on all the flights, but I am always looking for something new, something better...I guess you know that feeling.
I went with the new MKS X8 series servos; HBL850 and HBL880 to be exactly.

In raw data comparison the differences are: Futaba more torque 37kg vs 22.5kg. But the MKS had the advantage on the speed; 0.110sec vs 0.079 sec. The MKS servos use 8mm output shafts vs the Futaba standard 6mm; more on that later on. I used metal servo arms on the Futaba already; better feel to them on stops than using the supplied carbon fibre plastic ones from the mikado kit. The Futaba servos have longer servo leads (around 3-5cm longer) and use plastic top and bottom plates; the MKS servos are all metal.

To use the MKS servos on the swash I had to use the "savox servo holders" due to 10mm servo hole spacing vs Futaba's 11mm. This was still not enough because it seemed the MKS servos were a little to "long" (although according the sheet says they are the same as the Futaba). The measurement that reads 49.50mm...I fixed it by putting 2 shims under the "servo holders" that connect to the main shaft bearing blocks to enlarge the distance just enough. See the attached pictures...I installed the MKS servos using the supplied rubber and inserts, but additionally put some carbon fibre plates on them as well to save the rubber an for the looks; rubber usually twists which look awful :-) . The servo plates are from the same person that made the custom servo arms for me; www.customheliparts.com

The tail servo was pretty much a drop in replacement regarding the size, but let's start with the raw data comparison and a brief flight experience first. The first servo I used in my XXtreme was the MKS HBL 980 with 0.036sec and 5.6kg. It was awesome; anyway I replaced it with the Savöx 2272 with 0.032sec and 7.0kg. It was kind of disappointing. I didn't put that much time into the perfect vbar setup, but it was obvious it would never be equal to the MKS 980; there was always a slight overshoot on both stops, gain was way lower 110 vs 80 and it wasn't that locked in on pitch especially during stuff like side tic tocs. So much for the a little history; now on to the new MKS HBL 880. The specs are 0.036sec and 10.1kg. I was able to use the metal servo horn from the addon http://www.mksservosusa.com/product.php?productid=133 . It's a direct fit and gave me 126/126 on the endpoints with the inner hole in vbar tail setup tab with a gain of around 90 points on the main page. And from a flight perspective it's just better than the Savöx, much better...and just a little better than the old MKS 980. In a direct comparison I probably couldn't tell the difference every time, but on the stopping it just work great - bam and stop.

And now as promised back to the swash servos MKS 850 and the small "problem" of a 8mm output shaft. Normal servos use 6mm, so all the horns on the market won't fit, except the ones made by MKS specially for the X8 series. They are: plastic cross with 20mm, metal with 18mm and metal small 18mm. All can be seen here http://mks-servo.com.tw/goods.php?goods_id=hbl850
Problem with all of the above? The don't fit the Logo's M3 screws on the ball links and 18mm is also more than the recommend 17mm. Yes, yes...the manual calls for 16mm, but as a quick measurement reveals the stock are 17mm...so misprint or leftover from prototyping. Enlarging the holes from M2 to M3 on the metal horns was also not the solution I wanted to use. As mentioned before, with the tail servo the horn is perfect, 18mm and M2 is just what I needed. Back to swash; I got in contact with Dan from www.customheliparts.com . He was very helpful an created the following carbon fibre arm with a 17mm distance and an M3 hole just for me :-) (and maybe other people to...). They can be found and bought here: http://customheliparts.com/store/ind...product_id=442 - don't be tricked by the M2 hole on the sketch, it's M3 in reality. For all European customers; I ordered on Wednesday, shipping info on Thursday and it arrived the following Wednesday. It was "first class mail international" with just over 12$ of charge.
They work like a charm and look just fantastic. On the pitch and cyclic setup screen I got around 95 points (98? don't remember) for 11 degrees pitch and 8 degrees cyclic. Just a little side note here, Futaba 172 gave me 83 points at 17mm and 89 points at 16mm; so it's not just geometry that defines the value, it's also "how far does the servo travel on a given input". Last but not least I would like to share my flight experiences so far: the MKS have no play at all after 20+ flights! the Futaba had 0.1-0.2mm play on the arm after 300+ flights. Let's see how long they stay sharp. They feel great, locked in, better than the Futabas; could be due to the play that developed, could be just a better servo...don't know. They perform great on rainbows and hard pitch reversals; no wobble and nice return to the other side. My piroflips seem easier and nicer; it seems the heli follows a little closer to the stick moves...like when you compare the "style" setting on vbar vivid vs precise...hard to describe; might be due to the age of the Futabas as well...so that's it for the MKS.

And now, after a lot of writing for me and a lot of reading to do for you, I would like to share my conclusion and ask you for your feedback. Is it to long? To boring? To little info on some parts? To much in one post? I was looking for a post like this, that's why I wrote it; so others don't need to search in 10 different places for the infos.

Conclusion:

After 1-2 seasons of flying an crash free and mild-hard flown Logo XXtreme needs some maintenance; DO IT! Best time would be winter....

Servos; MKS servos are awesome. I have them in my 450 (MKS 95 and 95i) and my 600 tail (MKS 980) and now in my XXtreme. Was it worth it? Yes and No; for the money (700€ with the horns and small parts like shrink tube, etc. and shipping) you can do a lot of other great things in your life, but the fact that you own a Logo 800/700 XXtreme shows you like heli flying a lot...so...whenever you feel the need for new servos or plan a new build check out the MKS X8 series. (By the way, I just noticed the are releasing some new 6mm standard servos soon MKS 960 / 990 http://shop.mikadousa.com/MKS-HBL960...vo_p_1184.html and http://shop.mikadousa.com/MKS-HBL990...vo_p_1185.html if you want to skip the 8mm shaft problem...)

Thank you for your time and appreciate your feedback!

Best regards,
Lukas

[nebuchadnezza]

All the parts



Servo horns



New MKS X8 Servos



Carbon fibre servo arms by customheliparts



Shimming required for the MKS X8 due to length



The old Futabas as a comparison with the metal servo horns from robitronic

[nebuchadnezza]

Main blade thrust bearings



Rotor head greasing



Gearbox removal



Gearbox - dirty...



The PowerDekker Motor 1,7mm2 411KV



Servos in all their glory



Tail servo with "stock" addon horn



Buffer capacitor

[nebuchadnezza]

Vbar and Powerbus placement



Heli



Heli



Another one of the tail servo



After receiver repositioning



And charging ;-) in 11 minutes



Best Regards
Lukas

[EEngineer]

"To use the MKS servos on the swash I had to use the "savox servo holders" due to 10mm servo hole spacing vs Futaba's 11mm."

On my MKS X8's, I used the non-savox aluminum servo holders....made a note of it on my manual.

Seemed to work ok.....

I used the MKS red adonized arms.....at the 18mm(inner hole).....drilled it out to accept the M3 ball...used a stop-nut to secure it.

The CHP CF arms are cool, too.

Had you used the MKS arms, you would have had to "mill" ~1.5mm off the elevator arm end to prevent it from stalling on a frame bulkhead....used a red felt tip pen to cover up the bare aluminum....the old felt tip pen adonization trick...

Also, with the X8s, I had to lengthen the swash links....from the lengths recommended in the manual....to get the followers parallel at mid-collective.

[rcmarty]

Searched high and low for counter bearing size.

After 1/2 hr on computer I just pulled out the CB.

Bearings are 8x16x5

Mikado part # 00954

https://shop.mikadousa.com/00954-Bal...16x5_p_24.html

Out of all my bearings these are the ones that go first. I guess it's the heat of the motor shortening up the lifespan.

I recall dave mentioned that he had replaced the CB on one of kyles machines.

I wonder if a ceramic bearing would be a thought.

Nice well thought out heli , I'm at 200 on my 800 , about 100 on the 700.


Martin

[rcmarty]

Question on the ' wobble ' comment.

Is this on a hard stop or hard direction change ?

I find on a hard direction change the heli seems to have a bit of a rocking back and forth right at the stop and just before the direction change.

Jr 8917hv on 2s lipo

Martin

[nebuchadnezza]

Originally Posted by rcmarty

Question on the ' wobble ' comment.

Is this on a hard stop or hard direction change ?

Hello rcmarty,

It is on a direction change, just before going the other way on rainbows!

Thanks for the part number of the counter bearing. Ceramic might be a good idea!

I can't tell you why, but for me the 10mm Savöx were the only ones that worked, EE.

BR
Luka

[Raptorapture]

Great post OP. I really appreciate your effort to share this info. I've been debating best servo's for the XXtreme. I've gone with the less powerful MKS 950's and 980. Great to hear just a small difference if that. I've also used MKS 980 on my 550SX and 500 tail. Works great. Cheers.