Need Advice on P40 ARF Control System

[Kafin Noe知an]

I have finally finished and am about to fly my ARF P40 for the first time, however when I check the control system the pushrod from the bellcrank to the flap appears to be flexing/bouncy when I give full up control. The pushrod wire is 0.072 and I put 2-56 threaded coupler at the end. I was looking for 4-40 threaded coupler that will fit into 0.072 but couldn't find one.

At first, I thought the culprit was the pushrod wire, but it was actually caused by the clevis hitting the spacer of the 4-40 ball link that I installed.
I then replaced the clevis with DU-BRO 2-56 threaded ball link, and this actually solves the flex problem, but I don稚 feel it痴 secure enough to fly with.

Has anyone used that DU-BRO 2-56 threaded ball link for control system purposes?

The other options/combinations I was thinking are:
1. Go back with the clevis but replace the 4-40 ball link into smaller 2-56 in a hope that I'll get get smaller spacer that I can use as a standoff so it doesn稚 hit the clevis.
2. Go back with the clevis but replace the 4-40 ball link into clevis as well.

What are your thoughts on this?
Looking forward to hearing more from you, and any ideas are welcomed.


Best,
Kafin

[Motorman]

Mark a point forward of your solder joint to measure the length you need then, remove the coupler and solder on a piece of wire with an S bend.

[Colin McRae]

Kafin, on my P40, I used a 2-56 threaded coupler for the ball link that goes to the bell crank. I used JB weld to attach the coupler to the pushrod**. Then a 2-56 ball link from the bell crank.

Then I used a 2-56/4-40 ball link on both ends of the CF pushrod to the elevator.

There is a bit of flex on the kit pushrod from the bell crank, but not too bad. I don't really notice flight issues w/ overall model control.

** When I made up the JB weld on the coupler, I took my Dremel cutting wheel and put a few good nicks on the wire, and also drilled a small hole on the coupler nearest the threaded end so the epoxy could flow out when the wire was inserted. Reason being so the epoxy has a positive surface to 'grab' on both the wire and coupler.

[Kafin Noe知an]

Then I used a 2-56/4-40 ball link on both ends of the CF pushrod to the elevator.

Thanks a lot Colin!
Does that mean 2-56 Swivel Ball Link for 4-40 Rod? Like this one DUB 2139?

[Kafin Noe知an]

Kafin, on my P40, I used a 2-56 threaded coupler for the ball link that goes to the bell crank. I used JB weld to attach the coupler to the pushrod**. Then a 2-56 ball link from the bell crank.

Then I used a 2-56/4-40 ball link on both ends of the CF pushrod to the elevator.

There is a bit of flex on the kit pushrod from the bell crank, but not too bad. I don't really notice flight issues w/ overall model control.

** When I made up the JB weld on the coupler, I took my Dremel cutting wheel and put a few good nicks on the wire, and also drilled a small hole on the coupler nearest the threaded end so the epoxy could flow out when the wire was inserted. Reason being so the epoxy has a positive surface to 'grab' on both the wire and coupler.

Another thing, I also notice that both ball links from the bellcrank pushrod and CF pushrod to the elevator are going into the same hole?
I was wondering how it shows on the plan? Do you mind sharing that info since you happen to have the plan.

[Colin McRae]

Yes, same top hole on the flap horn. I wanted the minimum flap deflection (farthest hole from the flap). And I am using the farthest hole from the elevator to get minimum elevator deflection. Other holes can be used, but this setup seems to work OK control-wise for me.

And yes, I will dig out the plan and advise.

[Colin McRae]

Here is the plan setup.

It can be set up this way, you just need to see how the model flies and adjust accordingly. The hole setup I am using seems to fly the model well enough for me. Try to get a 1 to 1 setup first and adjust accordingly based on flight performance.

And another adjustment is always handle spacing.

[Colin McRae]

Thanks a lot Colin!
Does that mean 2-56 Swivel Ball Link for 4-40 Rod? Like this one DUB 2139?

yes

Also, the CF rod I use is 3mm ID and 5mm OD. The 3mm ID is perfect for a threaded 4-40 rod when I make up the CF pushrod w/ ball links.

[Kafin Noe知an]

Here is the plan setup.

It can be set up this way, you just need to see how the model flies and adjust accordingly. The hole setup I am using seems to fly the model well enough for me. Try to get a 1 to 1 setup first and adjust accordingly based on flight performance.

And another adjustment is always handle spacing.

Great! Thank you so much Colin.


Best,
Kafin

[Colin McRae]

Great! Thank you so much Colin.


Best,
Kafin

Welcome!

[Kafin Noe知an]

Is it okay to use 2-56 screw into 4-40 ball link?
I can稚 find the 2-56/4-40 ball link here.

4-40 screw is definitely too big to fit into my control horn, the other option is using the M2.5 screw.

[Ken Culbertson]

Is it okay to use 2-56 screw into 4-40 ball link?

It might work but I would not advise it.  If you do screw it in as far as you can and don't be "banging" any outside corners!  All controls have limits. Normally it is the bellcrank to flap but it could be the elevator as well.  You do not want the controls to be pulling against that ball link without it's ability to move.  It will pull out followed by the crashing sound peculiar to your circle.

Ken

[Colin McRae]

I agree w/ Ken. The 2-56 screw going thru a 4-40 swivel will have a bit of slop affecting the accuracy of the controls. But the affect will be small.

Can you drill out the horn for 4-40?  Or use a different horn that will allow for a 4-40 screw? Or relocate and drill a new 4-40 hole near the top hole on the flap horn.

[Jake Moon]

Kafin, I'm going down to NTC Hobby sometime in the next couple days, do you want me to look for that 256/440 ball link? I can mail it to you.

[Colin McRae]

My local hobby shop caries Dubro parts but did not have 2-56/4-40 ball links in stock. But they were able to order them for me. Another option is to order on-line direct from Dubro. But I don't know if Dubro ships internationally. And maybe eBay?

One other thing to note. Sometimes the ball does not swivel 'freely' in the ball joint. If you happen notice this, just throw the link away and try a different one. The Dubro ball links are relatively cheap and every now and then there is a bad one from the factory that binds somewhat. I even tried to lubricate it but it did not really help. 

[Dick Pacini]

I looked through my supplies and found my package of Dubro Ball Links 4-40 X 4-40.  I also have a couple of the stand off bushings that are used between the ball end and the bellcrank.  That allows the ball to swivel without binding.

[Kafin Noe知an]

Kafin, I'm going down to NTC Hobby sometime in the next couple days, do you want me to look for that 256/440 ball link? I can mail it to you.

That would be great, Jake. Big thank you!
You can also update me on facebook Messenger as well.