Push-Pull Tail Setup

[PaulH]

Chris posted some excellent instructions a while back that descibed how to set up the upgrade push-pull tail on an Intrepid. With his permission I have reproduced them for everyone to read.

One note from Chris: Although the instructions show a Futaba GY401 gyro being installed, they have found that the push-pull tail assembly doesn't not offer enough throw for a GY401 to work well. The "limit" setting on the GY401 needs to be above 100% for best operation. The push-pull assembly requires that the limit be near it's lowest position. This leads to poor tail performance and low gain settings to compensate for the loss of resolution.

[Helisin]

Originally Posted by PaulH

Chris posted some excellent instructions a while back that descibed how to set up the upgrade push-pull tail on an Intrepid. With his permission I have reproduced them for everyone to read.

One note from Chris: Although the instructions show a Futaba GY401 gyro being installed, they have found that the push-pull tail assembly doesn't not offer enough throw for a GY401 to work well. The "limit" setting on the GY401 needs to be above 100% for best operation. The push-pull assembly requires that the limit be near it's lowest position. This leads to poor tail performance and low gain settings to compensate for the loss of resolution.

I don't suppose the newer pilot (like myself) would notice a big problem with the 401. My limit is set at 85 to obtain full travel with no contact on either side.

[Helisin]

Nice of you to post it. Thanks!

[PaulH]

The only thing that you might notice is that you have to drop the gain fairly low so that the tail doesn't wag. That means the gyro won't hold the tail as well as it could. There will be a higher chance of it drifting.

Chris, jump in here if I'm totally off-base, but I think that's what I remember you telling me.

[SeaHawk]

I was just comparing the pdf instructions to the instructions I got with my brand new, recently purchased push pull kit. In the pdf you posted, it says to put the two balls on the short end of the arm. In the instructions that come with the pushpull kit I just got, it says to put them on the long arm. Which is correct???
I know it works o.k. on my first Bergen on the long side. Was this a typo or a revision to instructions that come with upgrade?
Also, the instructions that come with the kit (#7033) have you mount the two balls on the arm on the left side of the arm, servo side, and the pdf version has them screwed in on on the right side of the arm,which is opposite side. Do different kit versions have different length control arm pivot posts?

[cbergen]

I'm not ignoring you Gary, I'm checking into it. I do know we changed where to put the balls, but off the top of my head I cannot remember which is the proper way...


Edit


Ok, Use the PDF instructions. We changed the balls to give a mechanical advantage due to the weak (27 oz/in) servo. It also allows for a higher limit setting required for the 401.

[SeaHawk]

I imagine it doesn't make that much difference, but we all know that assumptions are not always correct, so best to ask.

[miami6]

this is my setup

[F6Hawk]

How will the 601 perform using this push-pull setup?

[cbergen]

We do NOT recommend the Push-Pull system with Futaba gyros and servos, although I have not tried the new GY520 yet...

[F6Hawk]

Ok, I read that with the 401, now it is ALL Futubas, eh?

Forgive my noobiness, but why? The gyro just sends drive info to the servos, so how can it be a bad thing to use with push/pull? What gyro DO you recommend?

[cbergen]

We've found that with the 401 especially, it performs best when the travel limit on the gyro is set between 100 and 120. This is impossible to do with the push pull setup.

The 601/611 similarly works best with high travel limit settings, again difficult to do with the push pull system.

JR gyros do not seem to have this "limitation", so work well either way.

[cbergen]

For gyro recomendations......The only one I've had difficulty with was the JR 770 3D. But that was on my electric, not the Gasser.

I REALLY like the Spartan DS 760 with a JR 8900G servo. Simple setup, and just plain works!!

[Pinecone]

BTW the 770 also likes high limit settings, but I was able to get it pretty high by reversing the ends of the push-pull arm, so put the ball to the tail pushrod on the SHORT end, and use the outer hole on the tail bellcrank.

But haven't had it in the air enough to see how well it works.

If not, Spartan time.

[F6Hawk]

Originally Posted by cbergen

We've found that with the 401 especially, it performs best when the travel limit on the gyro is set between 100 and 120. This is impossible to do with the push pull setup.

Sorry, Chris, I guess I don't understand the gyro enough to grasp the concept.

I thought the gyro just sensed (uncommanded) heading changes, and put in opposite inputs to maintain heading hold to the servos. So really, the servos are doing the work, based on electrical output from the gyro, right?

If so, then why does a push-pull differ from a single-arm servo? Other than less slop, doesn't one get the same travel? I mean, the pushrods are the same length, right? Just two of them, instead of one.

Sorry if this is a dumb question, but I only have single-arm servos in front of me, and can't see what else may be going on via web pics.

[cbergen]

If you look at this pic, you can see our push pull setup for the tail rudder. The push pull linkages only go as far as the vertical bellcrank. THEN the pushrod (single pushrod) goes from there back to the tail bellcrank.

The placement of the balls gives some mechanical advantage (or disdvanatage, depending), Which also changes the limits of travel.

It's these limits of travel that seem to dictate how well (or how bad) the gyro operates. Consider the resolution of the servo (steps), Higher travel limits give greater resolution (more steps), whereas less travel limit, less rsolution.

The gyro/servo combination works as a team, and works best within a certain resolution. Some gyro/servo combinations work in larger lattitudes, others liek the 401 seem to be best at between 100 and 120 on the travel limit set on the gyro.

I found the same with the 601/611 gyro, that it worked better WITHOUT the push-pull system.

[Pinecone]

Basically, due to the arm that Bergen uses, you can't put the ball in close enough to get the gyro in its sweet spot.

What you need is a custom arm, with the two balls spaced for the outer holes of a large servo wheel, with holes for the ball to the tail pushrod at various distances from center to tune the gyro/servo/tail setup.

[ernatz]

If you move the ball out on the tail rotor bell crank
Then you can increase travel, NO?

BTW adjustable links on tail blades is great.

Don't have one yet, its coming, just trying to absorb all I
can from these posts so excuse me also if I'm missing
the obvious.

[Pinecone]

It helps. But seems it still isn't enough for the Futaba gyros.

[ernatz]

So I've got the right idea, Thanks