lownslo

My two transmitters are Futaba and the servos are 3003's and 3004's. I bought a Hitec flight pack with 425's for my third plane. When installing the control rods I noticed the servo arms are "offset". (I hope I can describe this well enough). On the Futaba arms... the opposing arm is straight across the center axis and of course the holes are too. The Hitec are "staggered or offset" somewhat. Can anyone tell me the reason for this? Won't it make one direction of the throw longer that the other? (Maybe I have the reasoning incorrect) ..thanks.... lownslo

Bob

Big_Bird

My Feedback: (1)

Bob, I have experienced this problem with several Hitec servos, primarily HS605's and HS605MG's. The problem has to do with the position of the feedback pot in the servo.

I'm not recommending that you do the following but here is how I was able to move the pot position to make the servo arm center at neutral position.

After removing the gear train and opening the bottom of the servo, you will notice that the pot is held in place by two screws. Normally you would think that if you loosen the two screws, then the pot could be rotated a sleight amount to fix the position problem. This is not the case because the pot has an anti-rotation tab on the front side. Remove the two screws and remove the pot. Break off the tab. replace the pot, rotating it sleightly and replace the two screws. Reassemble the gear train and check to see if the position is correct. If not repeat the sleight rotation and recheck. When you are satisfied, carefully tighten the screws and apply a small dab of Zap-A-Dap-Goo to two sides of the pot to lock it into place. Leave the bottom of the servo open until the glue dries.

I'm sure Hitec would not condone this modification and I don't recommend it either but the information is there and you are on your on.

Ken

lownslo

Hi Ken, That is some detailed info!!!! I think I will go with what I have.
I have been in this hobby about a year and have never even seen the inside of a servo..... maybe after more time in this I might try it.
I do thank you for your time. I am sure your time is not wasted. Someone out there may have the same problem and use your info...... lownslo

jrjohn

My Feedback: (24)

where can I find good alluminum servo arms (1 1/4 inch) for hitec digitals (the one with the + on the top of the spline), Is there anybody other than Airwild that makes them??

JOhn

Jim Schwagle

My Feedback: (1)

From his description I believe what he is saying refers to the Hitec servo arms. All Hitec servos (that I have seen) come with one "X" shaped servo arm where the arms are indeed offset. The axis of the individual arm does not go through the rotation axis. This is on purpose.

vinnie

My Feedback: (1)

I don't have one in front of me but, while the arms are offset, aren't the holes in the arms aligned with the shaft?

Giant Scale

jrjohn
I use hitec servo arms from www.swbmfg.com
Scott has a wealth of knowledge about giant scale planes and makes a high quality product. He also has custom servo trays and pull-pull setups.

JohnBuckner

My Feedback: (1)

There is a purpose for offset arms however in the case of that Hitec arm I think if you lay a straight edge across the hole centers you will find no offset, if any it is minute. Yes the outside shape is not symetrical and I can only speculate that was done to reduce flexing on the 'push'.

Most companys do include offset arms though. Ever notice the extra holes on the round ones or the star shaped arms. The main purpose of that is to induce differential aileron mechaically just as Lownslo suspected. This is very usefull on high wing cabin type airplanes to reduce adverse yaw without the need to resort to electronic methods with a computer radio.

In the case of a high wing with strip ailerons just make the pushrods a bit longer to attach to the round or star servo arm just beyond the servo's output shaft.

John

Jim Schwagle

My Feedback: (1)

After posting the message I hauled out a servo and took a close look at the arms and the holes indeed are aligned with the axis of rotation but the arms themselves are skewed. As John Buckner stated this is no doubt due to an attempt to reduce flexing.

vinnie

My Feedback: (1)

Ok, I'll bite.
Why would we want to reduce the flex on push and not on pull?

Jim Schwagle

My Feedback: (1)

Good point. I would just be guessing. That said, I would much rather run a chance of flexing when going with down elevator and less of a chance with up. Up elevator gets used many times more than down, but then I am at best an intermediate level pilot. It could have nothing to do with flexing. Just as Futaba has arms that align themselves differently depending upon which arm is used, (Arm #'s 1 - 4, round etc. I am sure other brands are the same) the skewing may allow different alignments etc.

JohnBuckner

My Feedback: (1)

Vinnie, A flexing servo arm may not even be noticable on an average 40/60 sport plane but flexing anywhere in the system is not desireable. Now why a differance in flex with direction. Unless the push rod is grossly out of line there will be very little flex and what I mean by flex is twisting of the single type arm because the arm is pulling and the push rod tends to stay in alignment. Now on the 'push' if the rod not in perfect alignment and there is any loosenes at all in the housing or perhaps the rod itself is to flexable it will tend to bend up or down on the push. Given this with the soft plastic single, or cross arms there is very little resistence to this pushrod bending from the servo arm itself. The result will be a softening of control response and only in one direction.

Once agine this is not a big problem with sport planes but I can give you one example where it is noticeable is pylon racing. An activity that uses up most of my retirement time. A soft single arm that can twist and only in one direction will result in a 'hunting' effect on recovery from the high 'G' pull in one pylon which makes an accurate entry into the next pylon very difficult agine not dangerous but you do not win races that way. Its for that reason most pylon racers use the small (very low throws are used) round types which cannot twist within reason.

Sorry for the long winded post but you asked.

John