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Feb 20, 2019, 04:34 PM
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Spektrum Linear Servo Reversal


The linear servos mounted on a Spekrtum RX have a black wire and a white wire lead. If I reverse the black and white connection points on the RX will the servo move in the opposite direction as previously with the same gimbal offset?
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Feb 20, 2019, 04:50 PM
Aedificem ergo sum
cybermike's Avatar
No, because you would also have to reverse the connections to the potentiometer, which you can't because they are traces on the circuit board instead of wires.

However, this guy had a clever solution - physically reverse the orientation of the motor and gear shaft - https://www.rcgroups.com/forums/show...9&postcount=16
Feb 21, 2019, 12:29 AM
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ruzam's Avatar
At the risk of over thinking this, wouldn't it be easier to just mount the servo backwards?
Feb 21, 2019, 08:40 AM
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AntiArf's Avatar
Servo reversal programming: https://www.rcgroups.com/forums/show...-reversing-how
Feb 21, 2019, 12:18 PM
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Quote:
Originally Posted by ruzam
At the risk of over thinking this, wouldn't it be easier to just mount the servo backwards?
The problem is this: There are two servos mounted on the RX. Only one has to be reversed. So if the RX is mounted "backwards" then the one you wanted reversed is fixed and works like you want, but the other one is now going in the wrong direction. Note that you cannot just unscrew the servo you want to change and mount it "backwards" - the mounting holes are not symmetric and there may be potentiometer problems also.

In addition, I am trying to preserve the AS3X/SAFE functionality, so making changes in the TX won't work.
Feb 21, 2019, 12:26 PM
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Quote:
Originally Posted by AntiArf
This is good information for servos that ARE NOT integrated into the RX. Linear servos that ARE NOT part of the RX can simply be mounted "backwards" or the Spectrum server reversal cable used. The reverser cable cannot be used for RX integrated servos
Feb 21, 2019, 01:02 PM
Wanton construction
Pouncer's Avatar
Quote:
Originally Posted by alset
The problem is this: There are two servos mounted on the RX. Only one has to be reversed. So if the RX is mounted "backwards" then the one you wanted reversed is fixed and works like you want, but the other one is now going in the wrong direction. Note that you cannot just unscrew the servo you want to change and mount it "backwards" - the mounting holes are not symmetric and there may be potentiometer problems also.

In addition, I am trying to preserve the AS3X/SAFE functionality, so making changes in the TX won't work.
That's a very specific challenge..
But in your situation, seeing as the brick's servos are for elevator and rudder I'd either use a yoke to mechanically reverse the direction, or an even simpler fix put the moving surface horn on opposite side?
Or would that make it work against AS3X?
Feb 21, 2019, 05:32 PM
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Originally Posted by Pouncer
That's a very specific challenge..
But in your situation, seeing as the brick's servos are for elevator and rudder I'd either use a yoke to mechanically reverse the direction, or an even simpler fix put the moving surface horn on opposite side?
Or would that make it work against AS3X?
Thanks for your reply. I am not sure what you mean by a yoke, but thinking about it a while I came up with the configuration shown in the photo. Is this what you meant?

I am putting a UMX Gee Bee SAFE RX in a test scratch built. I didn't look at the RX closely enough. Unlike most planes the Gee Bee has the rudder horn on the right and the elevator on the left. I built it the scratch the opposite. I COULD change the horn positions but my goal is to put this RX in one of the discontinued Flyzone Aircore planes, all of them with rudder left, elevation right configurations, so I want the RX to accommodate this. In any case I have to swap the servo positions (either unscrew them and swap or re-route the motor wires - I don't know which is best)

The rudder reversal is the issue. I suppose I could ignore this since I guessing that yaw correction by AS3X/SAFE is not that important, but I'm not sure.
Feb 21, 2019, 11:59 PM
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AntiArf's Avatar
Quote:
Originally Posted by Pouncer
That's a very specific challenge..
But in your situation, seeing as the brick's servos are for elevator and rudder I'd either use a yoke to mechanically reverse the direction, or an even simpler fix put the moving surface horn on opposite side?
Or would that make it work against AS3X?
Yep, a lot simpler than reversing with mechanical reversing inside the fuselage.
I used a mechanical mix to drive a rudder and 0.015" music wire cable operated ailerons from the rudder servo on the brick some years ago, along with a take off for steerable tailwheel. The little Stuka flew well, but if I were doing what this guy is planning however, there's no need for complexity and I would just move to the horn to other side of the rudder or elevator, as you suggested. No need for unnecessary complexity unless one has to.

Quote:
Originally Posted by alset
I suppose I could ignore this since I guessing that yaw correction by AS3X/SAFE is not that important, but I'm not sure.
If a model requires yaw correction from safe, there's probably another problem. Never had any need for safe, on models down to 16" span.
Feb 22, 2019, 07:42 AM
Aedificem ergo sum
cybermike's Avatar
It's not a question of whether you *need* yaw correction - it's a question of whether you can turn it off or not. Reversed AS3X on the rudder may not be as fatal as on ailerons or elevator, but it ain't gonna be pretty.

I don't know if anyone has definitively answered whether the 2-cell (Timber, GeeBee, etc.) SAFE Rxs can be programmed with the USB dongle or not, but I would assume not just like the 1-cell (Sport Cub S, etc.).

Funny - SWMBO and I just had the same issue with the GeeBee Rx in the ME-209 she is building. I ordered it thinking it was the same layout as the Timber Rx and she proceeded to build the plane with that layout assumed. Fortunately, we powered up the Rx one last time before gluing in the control horns and noticed the channels were swapped. Even more fortunate, the pushrod layout was symmetrical enough that there wasn't any issue in swapping the control horn positions other than patching the now unnecessary slot on one side of the elevator.

I wish I had checked the Rx programmability before she installed it, but I didn't, and don't want to get the beating from suggesting that we remove it to test the programming cable
Feb 22, 2019, 09:07 AM
Wanton construction
Pouncer's Avatar
Quote:
Originally Posted by alset
Thanks for your reply. I am not sure what you mean by a yoke, but thinking about it a while I came up with the configuration shown in the photo. Is this what you meant?
Yes exactly like that!

Quote:
I am putting a UMX Gee Bee SAFE RX in a test scratch built. I didn't look at the RX closely enough. Unlike most planes the Gee Bee has the rudder horn on the right and the elevator on the left. I built it the scratch the opposite. I COULD change the horn positions but my goal is to put this RX in one of the discontinued Flyzone Aircore planes, all of them with rudder left, elevation right configurations, so I want the RX to accommodate this. In any case I have to swap the servo positions (either unscrew them and swap or re-route the motor wires - I don't know which is best)
Aaah, OK then.
So to be clear: one would expect the rudder servo mounted on the left to pull the horn on the moving surface when giving left yaw stick on the transmitter?
But on this particular brick the servo is positioned on the right side and actually pushes the rudder horn on a left stick input since the horn is mounted on the opposite side of the rudder.

In this case, assuming you won't swap the motor/receiver/servo module between airframes it would seem that the by far simplest solution is to either connect the moving surfaces the way they are on the GeeBee, or use a yoke.

Quote:
The rudder reversal is the issue. I suppose I could ignore this since I guessing that yaw correction by AS3X/SAFE is not that important, but I'm not sure.
Mechanical reversing as above will work with and not against AS3X.
Feb 22, 2019, 09:57 AM
Aedificem ergo sum
cybermike's Avatar
If it helps, note that you can also rotate the Rx 180 degrees (along the yaw axis, so the motor connector points aft) and reverse the Tx channels if needed. The important thing is that the AS3X corrects all the axes in the proper direction (including aileron, if you are using it).

You can't flip the Rx upside down though - SAFE will immediately try to rotate the Rx right side up!
Feb 22, 2019, 01:55 PM
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Well, I just discovered what NOT to do. I thought I would be clever and swap the two integrated linear servos. I carefully changed them so as not to damage the contacts on the servo. When I powered up, the servo tabs slammed into the extreme positions.

OK. So I'll just swap them back. NOPE! Now when connecting the battery, nothing - no red or green lights on the RX - no power. I assume that the RX is now worthless.
Feb 22, 2019, 04:30 PM
Wanton construction
Pouncer's Avatar
Quote:
Originally Posted by alset
Well, I just discovered what NOT to do. I thought I would be clever and swap the two integrated linear servos. I carefully changed them so as not to damage the contacts on the servo. When I powered up, the servo tabs slammed into the extreme positions.

OK. So I'll just swap them back. NOPE! Now when connecting the battery, nothing - no red or green lights on the RX - no power. I assume that the RX is now worthless.
You lifted the entire mechanisms and kept the motors wired to their original pads?
If so I can see the board getting confused as heck!
Feb 22, 2019, 04:41 PM
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Quote:
Originally Posted by Pouncer
You lifted the entire mechanisms and kept the motors wired to their original pads?
If so I can see the board getting confused as heck!
YES lifted them and exchanged their positions - rudder to elevator and elevator to rudder. But when I put everything back to the original, The RX would not power up. NEW DEVELOPMENT : I totally removed the servos from the RX (did not disconnect motor wires). NOW RX powers up, binds to TX and ailerons work. Confused on what to do next.

Note: I appreciate all the knowledge and help from the forum members that replied to this subject.


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