[Don Howard]

I seem to be mechanically challenged of late.

I need some photos of how C-16 owners attached their servos to the Johnson Bar.
I know that Hitec HS-81MG will fit, and probably the 85MG, too.

I have attached a picture by Pete Thornton of his servo install, but if the arm is connected, I cannot see the connector rod or mechanism.

Thanks

 

[Dwight Ennis]

I usually solder a small ring lug on the end of a pushrod and secure it to the Johnson Bar via the screw used for finding the detents (you don't want the detents with R/C anyway). I also remove the spring from the pivot so allow less friction in the bar movement - less torque required for the servo to move it.

I drilled one Johnson Bar once for a standard clevis. Dulled three HSS drill bits doing it. You really need a carbide bit to punch through that stainless.

 

[Don Howard]

Thanks Dwight.

I have either lost some portion of the detent, or it never had one when I got it.
I did have a screw in the detent location that acted fine as a deternt.
I had gotten the engine used and the servo for the Johnson Bar had been glued to the back of the cab, but was not part of what I received.

Ran the other day with NO screw in the detent locatiion and the bar did not shift at all in either forward or reverse.
Without the detent, or detent screw, the bar moves easily, so I was surprise to have it stay in place!

 

[Dwight Ennis]

I have in my previous installations (C-16, C-21) made angle brackets to hold the servo and JB Welded them to the side of the cab. In the future, I think I'll adopt Pete's approach and secure the servo to the cab floor instead (space permitting). It's a lot easier to adjust pushrods, etc. with the cab off and out of the way.

BTW, here's a link to an archived topic showing how I did it in my C-21. I did pretty much the same thing in my C-16.

 

[Don Howard]

Thanks for the link to the C-21 RC archive-never thought to look beyond C-16.
It contains exactly the photos I had hoped someone would link me to.
top down view:
http://www.qte.com/rr/C-21_RC/DSCN3271.JPG
and
side view:
http://www.qte.com/rr/C-21_RC/DSCN3273.JPG

 

[Dwight Ennis]

Glad to help Don. Actually, the C-21 was the one Johnson Bar I drilled. On the C-16, I used a ring lug. I also used a ring lug at first on the C-21. Servo problems later caused me to try something else, and I drilled the J-bar.

See this archived thread for photos of the first installation using the ring lug.

BTW, the ring lug would have worked. I was burning out the reversing servo, so I drilled higher up on the J-bar to give the servo more leverage. Turned out I was using too small/low torque of a servo, and the pushrod was too thick initially, causing lateral stress on the servo horn, causing the servo to constantly buzz. Ultimately, it would overheat and give up the ghost. Using a higher torque servo and a smaller, more flexible pushrod solved the problem.

 

[Pete Thornton]

I cannot see the connector rod or mechanism.

Don,

I have lots of photos like that!

But all you had to do was ask...

As Dwight says, you can use the screw that originally fitted in the indent (upper screw on the top pic from my Ruby/FWRR loco.)

And while the C-16 (which I did a few years ago) has a direct rod from servo to lever, I nowadays use a bent piece of piano wire, to introduce a little more flexibility and less strain on the servo or lever if they don't exactly move the same distance.

 

[Don Howard]

Thanks guys!
I bought an Hitec HS-85MG today, just 'cause it has more torque.
Tested 81MG for fit and pleny of room.
North East Sailplane had both in stock and let me take the 81MG out to the car to test the fit.
Loose. Then bought the 85MG and test fitted and fits, too.
I may have to take off the tension spring, unless someone tells me it is really needed.
81MG measured 12mm, 85MG measured 13mm.
http://www.nesail.com/detail.php?productID=344