Some total noob questions about servos

[ACITceva]

Hi guys,

I'm building a Forza 450 and it's my first kit so I have a few questions about servos - some general and some related to this particular helicopter.

1) I bought four KST215MG servos and have found that the servo horns are a REALLY tight fit on two of them. Its definitely the servo and not the horns since the same horn goes easily on two servos but requires a lot of force on the other two. Is this just an expected difference in manufacturing tolerances? Any hints for dealing with that or do I just force them on/off?

2) It looks like the single arm horn is a really tight fit between the frames when used on the rudder servo. Since the tail rod is going to connect to one of the inner holes on the horn can I cut the end off the horn to make it fit better? Any suggestions for doing that without busting the thing?

3) I haven't purchased an FBL unit yet but plan to use an AR7200BX. I was kind of wanting to take my time doing the mechanical setup first. As I've worked through the process though I've stumbled across a flaw in my plan. The servos are going to be difficult to get to once they're installed and the frame is together so attaching the horns at 90 degrees will be tough. Maybe others could do it but I doubt I have the dexterity so I'd really like to get the horns on first. Problem is without an FBL I don't have a way to center the servos.

I do happen to have a spektrum receiver sitting around that I'm not using for anything. Is it possible to plug the servos into that receiver to get center, attach my horns at approximately 90, install the servos and continue the build and then do the FBL setup and final servo adjustments at a later time? Or can I not assume that a servo's center position will be the same on both receiver and FBL unit?

[LaDon]

You might get lucky but chances are no the center won't be the same. I don't know what brand horns will fit the kst servos but if they are jr spline or not but if they are I would order the adjustable horns from jr Americas for the 450. I am not sure but they may have a futaba spline option too you would have to ask them. I think they do for the bigger servos. Not sure on the smaller ones but they sure make setting the heli up easy and the work and look nice. I would just dremel the end off the horn with a sander and then it won't break. If you end up getting the adjustable horns that problem will be solved also

[Corvette & Copter Guy]

Personally I would use the JR servo's that would come with the combo kit. Not saying anything bad about the KST servo's though. The adjustable servo horns that fit the "kit" servo's make set up super simple. Never before has the phrase, "so easy a caveman could do it" fit so well.

[spootman]

Just replaced some of the gears in my KST's from a recent crash and some of the horns were a little snug like you described. The JR horns will NOT fit them and they do not offer Futaba adapters for the micro size. Hitec horns should work with the KST's. As far as snipping off the unused sides of the arms, it won'affect anything. Oh, and welcome.

[ACITceva]

Originally Posted by LaDon

You might get lucky but chances are no the center won't be the same.

Would anybody be able to explain why this is? (I believe you - I'm just curious about the technical reasons behind it)

I sorta thought that each servo has an inherent "center" point and the device (either FBL or receiver) just sends a pulse which drives the servo to that built in center point. So why would they be different?

[ACITceva]

Originally Posted by spootman

Just replaced some of the gears in my KST's from a recent crash and some of the horns were a little snug like you described. The JR horns will NOT fit them and they do not offer Futaba adapters for the micro size. Hitec horns should work with the KST's. As far as snipping off the unused sides of the arms, it won'affect anything. Oh, and welcome.

Thanks for the welcome!

So any hitec horn should fit on the KST servo?

As far as snipping off the end of the horn any suggestions to the technique? LaDon mentioned a dremel but any other techniques? I was thinking if I was to score them deep enough with an exacto knife they might snap off relatively cleanly.

[ACITceva]

Also in the manual for the rudder servo it says the following:

"If you are using servos other than JR please use the servo horns that the length 10mm to 11mm"

I'm making two assumptions about this so please tell me if I'm wrong.

- They want me to use the hole in the horn that is at about 10 or 11mm

- I measure that distance from about the center of the mount screw hole (the one that fastens the horn to the servo)

[HeliWobbles]

Originally Posted by ACITceva

Also in the manual for the rudder servo it says the following:

"If you are using servos other than JR please use the servo horns that the length 10mm to 11mm"

I'm making two assumptions about this so please tell me if I'm wrong.

- They want me to use the hole in the horn that is at about 10 or 11mm

- I measure that distance from about the center of the mount screw hole (the one that fastens the horn to the servo)

Yes, JR mean put the ball at the hole that is closest to 10-11mm from the centre servo screw.

As far as centring servos go- yes your spare Rx will help. just make sure you have no mixes or sub-trim in your radio. The best thing is to create a fresh model, that way there are no corruptions. Easier still is to get a servo tester. I have a cheapie and always centre my servos before putting on the arms.

By the way, there are no stupid questions. We have all been through these problems ourselves and mostly glad to give back into the community what others have given us.
Have fun.
Ted

[Corvette & Copter Guy]

Nothing wrong with asking questions. One of the reasons I suggested using the "kit" servo's is the simplicity. All of these servo questions would never have been asked. I really enjoy a smooth issue free build. I have found purchasing a combo type kit relives a lot of build issues. I do understand trying to save a few bucks, nothing wrong with that.

[ACITceva]

Originally Posted by Corvette & Copter Guy

Nothing wrong with asking questions. One of the reasons I suggested using the "kit" servo's is the simplicity. All of these servo questions would never have been asked. I really enjoy a smooth issue free build. I have found purchasing a combo type kit relives a lot of build issues. I do understand trying to save a few bucks, nothing wrong with that.

No worries I knew what you meant and I appreciate the advice! I even agree that purchasing the combo with servos would have been easier - but honestly I kind of wanted to work through this process and ask these questions. Flying only BNF's previously I was starting to feel that I wasn't understanding the whole picture and yet it's hard to ask questions because you "don't know what you don't know". So I wanted to go through the process of building the entire kit and also learning about and choosing my own ESC, servos etc.

I don't really fly during the winter so I'm just taking my time and overcoming each hurdle as they come.

[spootman]

Originally Posted by ACITceva

Thanks for the welcome!

So any hitec horn should fit on the KST servo?

As far as snipping off the end of the horn any suggestions to the technique? LaDon mentioned a dremel but any other techniques? I was thinking if I was to score them deep enough with an exacto knife they might snap off relatively cleanly.

The horns for the Hitec 65's were a snug fit like you described the stock horns, but the Tarot horns fit a little better (post #195). As for snipping off the ends, I use wire cutters on mine so I don't see using an Exacto knife being a problem.

[Corvette & Copter Guy]

Originally Posted by ACITceva

Flying only BNF's previously I was starting to feel that I wasn't understanding the whole picture and yet it's hard to ask questions because you "don't know what you don't know". So I wanted to go through the process of building the entire kit and also learning about and choosing my own ESC, servos etc.

I totally understand. There are still many things I still have not 100% grasped in this hobby. I have a very strong soldering background so at least that was one hurdle I didn't have to overcome. I hope your build goes smooth and feel free to post as many questions as you need