HBK2: Z-Bend to Ball Link Conversion - Pics and install notes

[gregor]

The stock setup uses a Z bend in the 3 swash links that insert directly into one of holes of the servo arm. Over the course of a couple months, the holes in my servo arms had enlarged which translates to a fair amount slop in the swash movement. I was surprised how difficult it was to locate some balls and ball ends to complete this upgrade. There are a number of different ball ends available form HeliDirect but it’s hard to tell what size it is. After much searching I fell back to one of my favorite sources for HBK2 miscellaneous parts, the Blade 400. The B400 uses a number of either same or similar parts as the HBK2 (and probably the Belt CP). The balls are the same size and the ball links by all appearances and fitment, are pressed from the same mold as those on the HBK2. B400 parts are still filtering into the hobby shops and online etailors, so I got my parts directly from Horizon.


Balls
http://www.horizonhobby.com/Products/Default.aspx?ProdID=EFLH1436

http://www.horizonhobby.com/ProdInfo/EFL/250/EFLH1436-250.jpg


Ball Links
http://www.horizonhobby.com/Products/Default.aspx?ProdID=EFLH1437

http://www.horizonhobby.com/ProdInfo/EFL/250/EFLH1437-250.jpg



The next piece required to complete the upgrade is the connecting rods. The distance between the center of each ball is about 35mm. With added length of the ball links, the rod needs to be about 20mm. Your size may vary so please do your own measurements. For connecting rods, I found 3 options

1) Raw threaded rod cut to length. I didn’t fully investigate this option and I’m not sure if threaded rod is available in this size.

2) Use the existing rods and cut off the Z bends. Then use CA glue to attach ball link to the rod. This worked surprisingly well. The glued-on end wouldn’t budge and under the extreme twist and pull tests the ball end broke off before the rest of glued on part came free of the shaft. I didn’t want to go this route as you can’t replace the ball end links. Over time the ball links get loose and need replacing. However, it’s fairly easy to replace the entire rod. If you are doing a full head linkage replacement using the Eksy linkage kit EK1-0290, it includes new rods as well as new loop shaped connecting rods and new blade grip/control arm links.
http://www.helidirect.com/images/helicopter_parts/esky_honey_bee_king/EK1-0290.JPG

3) Rods already cut to the right length. There are a number of different length rods in this package for the B400. I used the second from the shortest length and it was still a few mm too long. Plus there was only one per package.
http://www.horizonhobby.com/Products/Default.aspx?ProdID=EFLH1438




When the balls arrived I was impressed. They were small, finished well and judging how much effort it took to trim them down (more on that later) I’d say they are made of some hard metal. No wimpy aluminum here. They are low profile which is required for the tight fit and take a 1.5mm allen wrench like a number of other screws on the HBK2.
http://www.pbase.com/greg_campbell/image/92899456/original.jpg



Left Rear Servo
First up is the easy one. No clearance issues and the ball goes right in. Like the other three, the threads got a drop of CA to help ensure they are securely attached. I would have prefered to install a backing nut on the back side of the ball, but there aren't enough threads exposed, so CA it was.
http://www.pbase.com/greg_campbell/image/92898554/original.jpg




Front Servo
Next up was the front servo. This one is a little tricky because when the servo arm goes all the way down, a few threads on back side of the ball link is sticking out, very close to the motor. With all the possible frame flexing, I didn’t want to leave it to chance and dremeled off a about a mm of the ball. Just enough so that it was flush with the back of the servo arm. These balls are pretty hard and took more than just a little effort to remove the material. As a result this will heat up the ball link and could melt the servo arm. So do this step with the ball link removed from the servo arm.
http://www.pbase.com/greg_campbell/image/92898547/original.jpg



Right Rear Servo
Last up was the hard one. No cutting here but the fit is very tight. I’ve cheated a little since I’m using swash servos that are smaller than the stock servos. The problem is the gap between the front servo and the rear servo is pretty small. The servos I’m using aren’t as deep as the stock servos so there’s a little more room which allowed me to mount the ball facing forward. With the stock servos you’ll most likely need to mount the ball on the back side of the servo arm. But be carefull that the new links aren’t hitting the canopy rod. It will be extremely close and may require a little shaving on one side of the ball link if there is any contact with the canopy rod.
http://www.pbase.com/greg_campbell/image/92898561/original.jpg

Correctly attaching ball links to balls
Also be careful with the ball links. Contrary to popular belief, they are not bi-directional. Meaning there is a right way and a wrong way to attach them to the balls. One side of the ball link is slightly smaller than the other. As you might expect, the larger sized hole is the "inside" and the smaller size is the "outside". If you install them in reverse you'll have to force the smaller sized hole over the ball and will stretch the "loop" part of the ball end. This will add some slop to the ball link and when added up through all the connections in the head can cause tracking issues or contribute to lack of head precision.

Here are two new links. The difference in diameter is hard to see, but its there. Its a little easier to see the "inside" is very flat and the edges are squared off. The outside diameter is a tiny bit smaller and the edges are rounded off.

http://www.pbase.com/greg_campbell/image/92899441/original.jpg

http://www.pbase.com/greg_campbell/image/92899443/original.jpg

So why have we been adjusting in 1/2 turn incriments? In my case, the original instructions came from the Blade CP manual. In the tracking instructions, it says "one half to one full" turn. However, the links the Blade manual are referring to are bi-directional. So no harm. But in our case, the half-turn adjustments as well as other links in the head being installed backwards may be contributing to the slop and tracking issues some HBK2 owners (like myself) have been plagued with.

Just an fyi. One thing to notice here is ball links on the Esky purple CNC swash appears to the same ones on the B400 head. Something to keep in mind in case you need a replacement. These are pretty hard so I'm guessing we shouldn't see the wear normally associated with the aluminum ball ends.
http://www.horizonhobby.com/ProdInfo/EFL/450/EFLH1435-450.jpg
http://www.horizonhobby.com/Products/Default.aspx?ProdID=EFLH1435

Let me know if you have any questions or comments.

[xrbcoronalogoflyer]

thanks for the posting...excellent report...ken

[C R Mudgeon]

What size were the balls? 3.5mm or 4.7mm?

[gregor]

I don't have a way to measure them. I've been meaning to get a micrometer, just haven't got around to it. Two guys on RR measured thiers. One got 3.85mm and the other got 4.00mm.

[C R Mudgeon]

They maybe "3.5" balls. I got a bag of these balls "LINK" (http://www.helidirect.com/product_info.php?cPath=249&products_id=1302) from heli direct. They were from the hdx300 they are 3.5mm balls using them on a AXE cp project to get rid of the Z bends. The nice thing is that they are two piece. screws and balls. You can grid the pedestal off them for more clearance using the Finless toothpick trick.

I was wondering because I need a source for the ball ends. If the Blade 400 has "3.5mm" balls then I can use them.

[C R Mudgeon]

Oh BTW Excellent post! How is the HBk2 working out since?

[gregor]

I don't think they are 3.5mm. I noticed the balls in your link are listed as aluminum. I wanted to stick to steel to reduce the ongoing maintinance. I would have prefered a two piece design for the reason you mention, the stand off. That provides a little more flexibility for tighter mounting locations. Unfortunately I couldn't find any steel versions in the correct size.

The HBK2 is doing great. I've since gone to a full CNC head and bumped the pinion up to an 11t. Its very precise and responsive. Now all I have left is figuring out how to get rid of the tail bounce. But that's a topic for another thread :)

[DumbDawg]

BTW for making your own rods I saw recently a die especially for making threaded rods. You measure, thread and mount ur ball ends on, seemed simple enough. If you like I will try and find it again. I didn't bookmark it because I'm not at that stage of the game yet.

I am going to go find it again as I may just pick up some stuff you linked here and replace when needed.

[DumbDawg]

TADAAA!!! I did bookmark it:)
http://www.helihobby.com/html/rc_heli_tools.html

At $20 it might just be worth it to pick it up... I'm sure there are other dies you can get.

oh... its for cutting 2mm threads onto rods so won't work for the 3.5's

Anyway just looked at metric Tap & Die sets and there are plenty around to between 60 and $20 dollar. Your local hardware store probably has a set or two lay'n about

[driftless]

Very nice...for those of us that did the CopterX head upgrade, which size balls are on that (CopterX/Align balls)

Tom

[gregor]

I'm not positive, but I think Align uses 4.75mm balls

[DumbDawg]

I think swapping out the Z bends for balls is a great idea. Now there is a source for the balls but where do you get the rod stock to make the linkage??

[xrbcoronalogoflyer]

I think swapping out the Z bends for balls is a great idea. Now there is a source for the balls but where do you get the rod stock to make the linkage??

i've been using stock esky or b400 rods...my latest project is to use a bent ball-link, like the ones used by the gaui200 and mikado logo10/500, to replace the 'hoop linkage' that goes around the blade grips...gregor, have you thought about that? ken

[DumbDawg]

Bent ball link??? Hows that work, I've never seen a gaul200.

[xrbcoronalogoflyer]

here's a pic of the 'bent link'...the logo10/500 uses the same bell/hiller layout (which leads me to believe that the gaui folks might have copied a tried and proven system)...ken

[DumbDawg]

I can see what you are talking about but fail to see the advantages of this type of system, other than positioning perhaps. But why else would you go this route??

[xrbcoronalogoflyer]

actually, you're right about not needing to do such a mod - especially on a hbk2...but i thought since we're already replacing z-bends with ball-links, might as well go all the way...possible advantages:
- more than once, after replacing a spindle, i forgot to reinstall the hoop link, and had to remove the grip again.
- ball-links might reduce slop
- adjustability
here's a pic of the swash links from my logo10 manual...ken

[DumbDawg]

I called Horizon to order some of the ball and links. Mostly wanted the balls and had a question about the links. So I asked for tech help in heli's. I got this guy that was I'm sure semi brain dead. He kept telling me I should support my 'local' hobby shop, which I'd told him was better than 2.5 hrs drive away. I wanted to know what size rod went into the link ends cause I was going to order that as well. Didn't want to order the wrong size, right. Well he disappeared for 5 min then came back and said that they would all pretty much fit???? Which means what? Then said he thot it was about 2mm. Where did he go then??? the potty?? Anyrate... my rant. I surely hope they are not all like this, so I'm waiting to see what my order will actually have in it. Maybe a cnc head for a trex, I'm told they will fit HBK2's.

If so I'm def not going to shop there anymore.

[jh1947]

Hi
Enjoyed the write up. Did a similar conversion a month or so back using parts package EK1-0548 (~$5.50) Can be found at this site http://jaghobbies.com/rc_planes/belt_cp_cart.htm

Tnx Jim

[JCUNNY]

I did this on mine, and have never looked back.


JC

[nas_matko]

Hi
Enjoyed the write up. Did a similar conversion a month or so back using parts package EK1-0548 (~$5.50) Can be found at this site http://jaghobbies.com/rc_planes/belt_cp_cart.htm

Tnx Jim
I can't see three equal rods in the package. Did you use two of them?

[orlbuzz]

Yes, I would like to know if you had to use two packages also.

orlbuzz

[netdog]

hey gregor, I noticed in your pics that u r using the ds 285 servos. Do u use a seperate bec or will the 25a controller run those ? I currently have a 30a esc and run xtreme's new motor 4000kv. My controller"s bec is good for up to 2 amps . Do u think it'll be ok ?

[gregor]

I'm running an Ele 30a ESC with a linear 2a BEC. I install the servos and I'm setting it on the bench, the ESC goes into thermal shutdown. I noticed the ESC was getting very hot on the opposite side of the heatsink. This is were the regulators for the BEC are located. Next I get out my multmeter and measure current, only 1.34 amps. I ended up measuring the current draw from each component to get a better picture of what was going on. The old servos were from my Blade which is why they are listed in the table below. The Eflight servos don't draw much, which is why it was working before the servo swap.

The idle current is the device powered up but no Tx input and no load applied. The loaded current is the device with Tx input and the movement almost stopped by manually holding the servo arm. BEC voltage from the ESC is 5 volts.

Device..............................Current (Idle)....Current (Loaded)
============================================
AR6100 (rx)..............................24ma............ .24ma
2100t (gyro)..............................66ma.......... ....66ma
HiTec HS-81 Analog tail servo....36ma............425ma
Eflight S75 Analog Servo.............6ma............125ma
JR S285 Digital Servo................11ma............275ma


So to summarize here are the numbers comparing the two setups on my heli.

Setup with the S75 Servos
Idle..........144ma
Loaded...890ma (.89 amps)

Setup with the S285 Servos
Idle..........159ma
Loaded...1340ma (1.34 amps)


I've tried 2 ELE speed controllers and they both behaved the same. I've since found that many linear BECs are rated using a 2s. With a linear BEC, the higher the input voltage the lower the output current. I'm currently running a 3A BEC. I went with the switching BEC from HobbyWing and its working fine.

Here's the full story as it unfolded.
http://www.runryder.com/helicopter/t405751p1/

[jh1947]

Yes, I would like to know if you had to use two packages also.

orlbuzz
As I remember it, one package had everything I needed