posted on January 06, 2009 14:12
by Wayne Geffon - September, 2006
I was asked to do an article on IMAC set up in my 40% Carden 260. I’d like to start out by saying that this is purely how I do it and what works for me. The are definitely different approaches to setting up a large plane for IMAC. This is just an overview of what I do.
A lot of the techniques and philosophies have come to me from guys who are a lot smarter than me and have been very successful in IMAC for a long time. Peter Goldsmith and Mike McConnville have been a huge help to me over the last couple of years. I have learned a lot from them. They subscribe to the KISS method of keeping things simple and so do I. Pete’s article on trimming a plane is very well known in the IMAC circles but in case you haven’t seen it, here’s a link. <insert Peter Link>
I’ll start by listing what’s in the plane.
- JR 8611A servos (8)
- JR 4735 servo for throttle
- JR R2000 Synthesized receiver (1)
- JR Matchboxes (3)
- Fromeco 4800 mAh Li-ion Packs for the RX (2)
- Fromeco 2400 mAh Li-ion for ignition.
- Fromeco 3 power output Regulators with Heavy duty wire and Deans connectors (2)
- Fromeco single output regulator for Ignition (1)
- Fromeco Badger switches for RX. (2)
- JR HD Charge Switch for ignition. (1)
- Electro Dynamics Fiber Optic Kill Switch.
The set up for my plane started even before the plane was being built. I knew what I wanted in a precision aircraft and because of that, some early decisions were made. The main one was that plane would not be set up at all for 3D. By not doing that, I knew I would be using short servo arms, and control horns that allow for the pivot point to be exactly over the hinge line. This allows me to get maximum servo resolution during sequence flying instead of using a very low dual rate setting for IMAC if the plane had 3D rates. It makes a huge difference in how the plane reacts and feels. I know people are thinking, the pivot point does not need to be on the hinge line. That is true but, by doing so, you do not have to use up ATV percentages to equalize travel. It makes a huge difference when its time to set the surfaces up with a throw meter.
There has been a lot of talk about where to place the control horn in relation to the servo. Some guys like the pushrod to be at 90 degrees to the hinge line while the servo is centered. I personally like to have the pushrod parallel to the side of the servo when the servo is fully deflected. When the servo is centered, there is a slight angle between the pushrod and the hinge line. I feel you have more power this way when the surface is deflected.
I bought all the linkages, servos, Pro-Links and horns prior to the build being started so everything could be planned out ahead of time. For Ailerons and Elevator this I what I came up with. I found out that placing the control horn ½” off the side of the servo case would give me a parallel pushrod at full deflection . 140% ATV on a 1“ servo arm. For the Rudder I knew I needed a little more throw so I am using a 1-½” arm at 140% ATV. The Rudder hard points are 5/8” off of the servos side. A few discussions with Walt Beike (builder) www.builtbywalt.net about where I wanted things to go made setting the plane up after I received it a breeze. He set the servo pockets and hard points exactly where I had asked him to.
I used the new JR locking servo arms for the entire plane. The Control Horns were bought from Dubro to fit over the 8-32 horn bolts and the pushrods are Hangar Nine Pro-Links. All of these items are put together with Dubro 4-40 Ball Links.
One thing I did as the plane was being built was match the servos with JR Matchboxes on the bench. I initially looked for servos that were closest to each other without a Matchbox as far as being centered. By doing this, I was able to use less Matchbox increments to fine tune them at center. The more beeps you use to center the servos, the less end point travel you will have. (less resolution) I labeled the servos that were going to each surface and used the Matchbox to set centers. End point adjustment came later when I was adjusting throw on the surface with a meter. I feel that some type of matching device is required to lessen wear on servo gears and not tax the batteries with servos that fight each other. Sure, you can get away without doing so but, there’s no way to fine tune enough to reduce my concerns. Some guys use a Multi Point mix on JR Radios to accomplish this also. I know it works but I have never done it this way. (Out of laziness mostly)
The aileron Matchboxes are powered from a lead coming directly off of the Fromeco regulators. Each aileron Matchbox is powered from a separate regulator. The Rudder Matchbox is powered from the JR R2000 Receiver. The receiver has a total of 4 power outputs coming into it from the two regulators.
When the plane arrived I started out setting up throws. Here’s an overview of what I did.
Inboard aileron servo was adjusted by itself first. Without any adjustment I was getting 26 degrees of throw up and down at 140% on a 1” arm. I knew I wanted my maximum rate to equal 24 degrees of throw so I mechanically adjusted the horn away from the surface to lessen throw. Again, not wanting to use the Matchbox at this point. Now the throws up and down were pretty close to the desired 24 degrees. I then used the Matchbox to fine tune the inboard servo to exactly 24 degrees up and down. This was measured using the Hangar Nine digital Angle Meter.
The outboard wing servo was adjusted the same way by itself. After that, the two servos were both connected to the aileron and powered up. A little buzzing at the endpoints was adjusted away with the Matchbox. The throw was checked again and I had found that I had lost a little in total travel from 24 degrees. I then used the ATV travel for that wing to adjust both servos at the same time back up to 24 degrees up and down. Remember me saying my ATV’s were set to 140%? Reason being is by doing so, I have more percentages above 140% to use to fine tune at this point. If I had started at 150% there would be no room to go up if needed.
The Rudder was set up pretty much the same way as the ailerons. Mechanically at first. Then tuned with the matchbox individually. Then fine tuned together with the radios ATV function.
The elevators were tuned mechanically at first then adjusted individually through the radios ATV function. No matching required since only one servo is being used on each surface.
Here’s what I wound up with at 100% Dual Rate and very close to 140% ATV on all surfaces.
- 25 degrees up and down on the elevators.
- 40 degrees left and right on the rudder.
- 24 degrees up and down on each aileron. - You may be wondering why 25 degrees of up and down on the elevators. I do this because I like to flip into a higher elevator rate on landing rollout. The maximum travel is needed to be set here at 100 dual rate and 140% ATV. I use another Dual Rate setting to lessen the elevators to the desired IMAC rate. It’s a little bit of give and take at this point to get that accomplished. Not a big deal.
After all this has been done I set up the 10X to have it do what I want as far as switches and Flight Modes.
I activate the Flight Modes and also use the Extra Flight mode. (Now you have 5)
Flight Mode Trim is not used. If it was, I would have to trim for each Flight Mode individually.
My rates as described above have enough movement that I can fly the entire sequence. (including snaps)
My rudder has two rates I fly the sequence on. High rate of 40 degrees (100%) for Rolling Turns and Hammerheads and a lower rate for snaps.
I use enough expo to keep it all smooth. Generally 40-50%
- FM0 is IMAC rates, (low Rudder) and low idle
- FM1 is IMAC rates (low Rudder) and high idle. (Ever have the motor die in a spin during a contest? Not a good thing)
This mode also has the low throttle to down elev mix on it for straight down lines. 2% to be exact on this plane.
- FM2 is IMAC rates, (Low Rudder) low idle and the higher elevator rate I described above.. (Low idle here so I can flip into this rate on landing rollout and not have the throttle bump up.)
- FM3 is IMAC rates on elev and ail but now activates the higher rudder for Rolling Turns and Hammerheads.
- FM4 is not used but I set it the same as FM3 so if the switch gets moved to that position by mistake, the rates are what I need.
I make absolutely sure that the EXPO is set the same between modes on a particular surface so you cannot see anything change when modes are switched if I am holding stick pressure.
With this set up all I have to worry about is one switch in the sequence and only for the rollers and hammers.
I taxi out in FM2 (High elev rate and low idle) and flip to FM1 before I takeoff.
I am now ready for the sequence.
When I set up to land, I flip from FM1 to FM0. The only thing that changes is now I have a lower idle and the down elevator to throttle mix goes away.
I fly with thumbs only and do not use a neck strap so my radio is supported in the back by my four fingers on each hand. This is probably why I don’t like to flip switches when flying.
After all this its finally time to fly!
This is a good time to look over Pete’s trimming chart again and try and follow it.
My 260 felt pretty good after about 30 flights of getting used to it.
It was at this time I checked all the throws again with the Angle Meter. Stuff does change initially as the plane gets a few flights on it. A little ATV tweaking takes care of this and gets things back to where they were.
Here’s what I wound up with for mixing.
- 3% Up Elevator with left Rudder
- 2% Up Elevator with right Rudder
- 2% Opposite Aileron to Rudder movement.
- 2% Down Elevator with idle power for down line tracking.
- No Aileron differential.
- The Rudder to Ail and Elev mix stays on at all times. I sometimes hear this referred to as a Knife Edge mix. To me, that infers "only needed in Knife Edge" In actuality, its needed any time the rudder is deflected. Get the mix set and leave it activated at all times.
After all this, the plane flies like its on rails!
I hope this has made sense and as stated earlier.. Its not the only way to do it. Its just how I do it and what I like. Your results may vary.