Subtrim vs. Programmer for Centering Servos

[flylow3d]

So Joe if I understand you correctly you don't use any subtrim or programming to achieve proper throws on an airplane of this size? Its all mechanical?

When you get to larger airframes is it the same process?

Is the above true for all control surfaces?

Thanks!

You are correct. I try to set it all up mechanically. I don't want to use the radio to cover up or fix anything. I can't stand seeing one endpoint at 140 and the other around 110 which is what happens if you set the arm to 90 degrees and use the radio to "fix" the incosistent throws.

This also holds true for setting up the elevator. Keep moving the horn on the spline until you get pretty close to equal throw in both directions of travel. If the rudder servo is setup in a push/pull configuration then this also holds true.

If you are setup to do pull/pull then here is some useful knowledge pertaining to that.

http://www.swbmfg.com/pages/Pull%2dPull-Wire-Explanation.html

I'll be back in a little while to explain the bigger planes.

 

[quadracer]

Can you elaborate on this. This is similar to the comment you made on another site. I cannot seem to rap my head around it. I think that you are saying that the manufacturers make the servo pockets with a few degrees of twist to them? Please instruct your Padawan :bouncy:.



This is something that never crossed my mind. So, question is, would using a programmer have the same affect? On one of the servos, I'm using like 65 clicks of sub trim to get it to where I want it, this seems like a lot, but I haven't noticed a diminishing throw. Do you think that this much sub trim will cause problems?

65 clicks of subtrim? Sheesh.... You could move the horn probably two notches and get rid of that.

 

[econpatric]

65 clicks of subtrim? Sheesh.... You could move the horn probably two notches and get rid of that.

Quadracer: If I understand Joe correctly, I should adjust mechanically for the issues by measuring throws until even, as long as the servo arm is close to parallel, the "two notches" in regards to the horn spline doesn't matter (to eliminate high amounts of subtrim), as long as the arm is set to produce equal throw.

As I was starting out (before asking here) and setting up for 90* it took 65 clicks of subtrim on my 9503 to get it the arm 90* to the servo case. I tried moving the horn on the spline, and also swapped arms and such. It was a large number regardless. I cringed to see that number so high also, so I posted this question to find out alternatives.

 

[flylow3d]

Quadracer: If I understand Joe correctly, I should adjust mechanically for the issues by measuring throws until even, as long as the servo arm is close to parallel, the "two notches" in regards to the horn spline doesn't matter.

As I was starting out (before asking here) and setting up for 90* it took 65 clicks of subtrim on my 9503 to get it the arm 90* to the servo case. I tried moving the horn on the spline, and also swapped arms and such. It was a large number regardless. I cringed to see that number so high also, so I posted this question to find out alternatives.

Yup, having equal throw in both directions means your servo arm is on the correct spline. This is often not 90 degrees.

When you get to larger planes with multiple servos per surface then the easiest way to match the servos is to make sure the arms are perfectly 90 degrees to the servo. This will still cause a little difference in the travel up and down but it will be a consistent difference between both servos so that they won't bind anywhere throughout the travel. Setting up two servos so that they don't bind at center or at their endpoints is a piece of cake. Setting them up so they don't bind throughout the travel is what gets difficult.

 

[quadracer]

I see what you mean, but I'm talking about removing the arm from the servo, then re-zeroing the subtrim and setting the arm back in place. According to above posts, you're losing a lot of travel in one direction.

 

[econpatric]

When you get to larger planes with multiple servos per surface then the easiest way to match the servos is to make sure the arms are perfectly 90 degrees to the servo. This will still cause a little difference in the travel up and down but it will be a consistent difference between both servos so that they won't bind anywhere throughout the travel. Setting up two servos so that they don't bind at center or at their endpoints is a piece of cake. Setting them up so they don't bind throughout the travel is what gets difficult.

Thanks for all your help Joe. I appreciate it! I am glad for today that I am just dealing with one per surface!

 

[flylow3d]

No problem at all. This is something I have spent a lot of time messing around with and it has really paid off. Makes the planes fly a ton better too.

 

[robj]

At a Huckfest Team pilots were building a 87, they grabbed a programmer first thing. When I got my 87 I bought a programmer, to date never used it. I did play with it once, a bit harder than radio programming, for me not as intuitive. But in the end I didn't use it and got the tip Joe mentioned about matching end points. I did spend a good 4 hours over a few days messing with the throttle servo to get the mechanical expo thing since my dx7 doesn't have a throttle curve. On that I could REALLY tell a difference from the initial setup vs the end setup. I'm about to move it to a 9503 with a throttle curve but will probably leave it as is. Until I can get with a team pilot to check it out.

 

[Mach3]

Great question econpatric, as this is something I haven't spent enough time doing on my own planes.
Thank you Joe for the great anwsers, I now know I need to spent some time setting my plane up a little better starting with my new 57" extra SC

 

[rcbirk21]

For this size of plane. I set the servo up based on getting equal throw in both directions with matching endpoints in the radio. I start with the arm as close to 90 degrees as possible. I then measure the throw for up and down travel. I always get more throw traveling down than I do up. To fix this, you have to move the servo arm on the spline in the direction in with you are receiving too much throw ( which for me has always been moving the servo arm so it points more towards the leading edge of the wing.) The servo arm is hardly ever at 90 degrees when I get finished setting it up.

When you are finished setting up you ailerons, your endpoints in the radio should be very close to maxed and they should be pretty close to being equal. Then when you measure the throw for both up and down travel, they should be equal.

so joe, when you do this do you do all of it with EPA's and dont touch the D/R until that is sorted out?