51.5" P-38 Lightning, what Servos?
04-13-2010, 04:33 PM
#1
Junior Member
Thread Starter
Join Date: Apr 2010
Location: NEW HARTFORD, CT
Posts: 15
Likes: 0
Received 0 Likes
on
0 Posts
51.5" P-38 Lightning, what Servos?
I bought the 51.5" P-38 Lightning, nice looking kit, ABYSMAL instructions. Please tell me what oz.-in torque servos this plane requires. Also, seeings how this plane apparently requires 2 elevator servos and 2 rudder servos, will any reversed servos be requiredsince I will be using y harnesses for them?
04-14-2010, 02:16 PM
#2
Join Date: Nov 2005
Location: Poolesville, MD
Posts: 12,624
Likes: 0
Received 0 Likes
on
0 Posts
RE: 51.5
Standard servos should be more than adequate... e.g. 28-32oz/in torque.
Re: Rudders
For the rudders no, because each servo is basically doing exactly the same thing at the same time and moving the control surface in the same direction.
Even when the servos are both facing "out" if you set up the linkages identically both surfaces will move in the same direction.
Re: Elevators
There are several ways to approach this, and what you do is up to you.
You can do the following in order of ease...
- Use two standard servos with your "Y" cable.
You will need to set up one linkage so the servo horn is "down" and the other is "up" on the servo.
In effect the linkages will move in the same direction.
You merely need to get the geometry correct, and both servo horns square with the control surface horns and each other.
In other words the pushrods must be parallel at stick center, even though one originates on the up side of the servo and the other on the bottom. That in turn means that the servo arms will tend to have a slight angle at stick center, but they MUST also be parallel to each other.
This seems a bit strange to people who have not done this before, but it works perfectly with NO binding when properly done.
- You can use two standard servos without your "Y" cable and use the TX to reverse one servo.
This requires a mix, and an additional channel.
Both linkages get set up exactly the same way, making this easier for a novice... but there are caveats...
Caveats:
+ End point adjustments must be fairly exact to prevent binding, as well as sub trim. The servos must never fight each other.
+ TX's ALWAYS transmit SERIALLY, that means one servo will get the position command before the other which can be problematic but not obvious to the pilot.
- You can use a JR Matchbox, MSX-10 or GOOD reversing device on one servo.
Both linkages can then be set up the same way, but the reversing device manages them.
You need a GOOD device ( not one of those cheapie in-line things ) because you want it to receive the signal, and re-transmit to BOTH servos at the same time. The JR Matchbox and the Futaba MSX do this, other devices tend not to.... so this incurs additional expense...
- You can use a reversed servo
Nowadays analog reversed servos are getting difficult to find, although digital programmable servos solve this problem..
However this also increases the expense of the servo and typically requires a servo programmer too.... so the Matchbox or MSX is typically cheaper and easier.
Re: Rudders
For the rudders no, because each servo is basically doing exactly the same thing at the same time and moving the control surface in the same direction.
Even when the servos are both facing "out" if you set up the linkages identically both surfaces will move in the same direction.
Re: Elevators
There are several ways to approach this, and what you do is up to you.
You can do the following in order of ease...
- Use two standard servos with your "Y" cable.
You will need to set up one linkage so the servo horn is "down" and the other is "up" on the servo.
In effect the linkages will move in the same direction.
You merely need to get the geometry correct, and both servo horns square with the control surface horns and each other.
In other words the pushrods must be parallel at stick center, even though one originates on the up side of the servo and the other on the bottom. That in turn means that the servo arms will tend to have a slight angle at stick center, but they MUST also be parallel to each other.
This seems a bit strange to people who have not done this before, but it works perfectly with NO binding when properly done.
- You can use two standard servos without your "Y" cable and use the TX to reverse one servo.
This requires a mix, and an additional channel.
Both linkages get set up exactly the same way, making this easier for a novice... but there are caveats...
Caveats:
+ End point adjustments must be fairly exact to prevent binding, as well as sub trim. The servos must never fight each other.
+ TX's ALWAYS transmit SERIALLY, that means one servo will get the position command before the other which can be problematic but not obvious to the pilot.
- You can use a JR Matchbox, MSX-10 or GOOD reversing device on one servo.
Both linkages can then be set up the same way, but the reversing device manages them.
You need a GOOD device ( not one of those cheapie in-line things ) because you want it to receive the signal, and re-transmit to BOTH servos at the same time. The JR Matchbox and the Futaba MSX do this, other devices tend not to.... so this incurs additional expense...
- You can use a reversed servo
Nowadays analog reversed servos are getting difficult to find, although digital programmable servos solve this problem..
However this also increases the expense of the servo and typically requires a servo programmer too.... so the Matchbox or MSX is typically cheaper and easier.
