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RV-12 Trim

Jaknjoan

Well Known Member
This is directed to Stein, or anyone else that can give me some insight.

After powering up my system this past weekend, everything appears to be working with the exception of my stabilator trim. I'm getting power back there to the servo, but very little. Question .... is the full range of the potentiometer trim about 3/4 of a turn? That's all I can get. In one extreme direction, pressing the trim control switch it makes no noise and no movement. In the other extreme direction the motor makes some noise and is trying to move the trim, but is able to move the shaft maybe 1/8 - 1/4 inch if I hold it long enough. There is no resistance since the trim tabs are off and the pushrod is just laying on something.

Any suggestion in where I go from here.

JT
 
Trim

Stein did not do the board. I had the same prob. You have a low voltage problem and need to turn your blue dial as far counterclockwise as possible. Even then you may need a battery charger on it. Your battery is doing 12 volts, your flying will more likely do 14. My dial was turned completely off...all the way clockwise.
 
I had an actual motor problem

If I laid the motor on top of the tail, not hooked up to ANYTHING, it would run in up and down cycles. Was binding inside. I would try that. Did you follow the instructions and hook it up to a battery from a 12v drill and run it that way ?

John Bender
 
Stein did not do the board. I had the same prob. You have a low voltage problem and need to turn your blue dial as far counterclockwise as possible. Even then you may need a battery charger on it. Your battery is doing 12 volts, your flying will more likely do 14. My dial was turned completely off...all the way clockwise.

My battery was fully charged, showing about 13.1 volts (using a good meter). It is possible that 14.6 volts would make it more active, but I hardly believe that is the problem because when I was originally testing the servo I operated it with a 9 volt battery and had strong but slower than normal movement. I have a fair amount of experience with these servos as this is not the first or second RV that I've built.
 
trim

you could also consider pulling the red and white pins in the d-sub up front and see if you get better movement (in other words, a board problem). That was going to be my next step.
 
JT,

What voltage does the Dynon indicate when you fire the system up? Is your battery ground lug tight?

A couple of builders that have had trouble run a Battery Minder / 2 amp charger overnight to top off the battery then run the test. The trim should however, work in the lower voltage (12v-13v) mode so you can adjust the trim prior to take off.
 
JT,

What voltage does the Dynon indicate when you fire the system up? Is your battery ground lug tight?

A couple of builders that have had trouble run a Battery Minder / 2 amp charger overnight to top off the battery then run the test. The trim should however, work in the lower voltage (12v-13v) mode so you can adjust the trim prior to take off.

Larry,

I have not had time to work on my problem this morning until now, but my master voltage on the Dynon is 12.2 volts. I had used a battery minder and brought the voltage to the max that the charger will charge it. I really don't think the problem is my voltage, because, as previously said, the servo worked fine using a 9 volt battery and with 12+ volts it should have all the power the servo will ever need. The power appears to be going back to the servo, but it is only a trickle in relation to what the servo needs. I don't know whether it's the wiring or something else. Peterk had a suggestion of disconnecting some wires running to the servo in the Tunnel harness that I may try if nothing else works. My ground cable is tight and sound.


JT
 
What is the voltage at the servo under a load?

I just finished checking the continuity of all 5 wires originating at the servo to their pin locations in the 37 sub-D connector going into the Av board. All show continuity. (I had help from my wife who handled the servo end with the ohm meter and I used a long wire at the instrument panel) I have checked the voltage at the servo when the trim switch is activated in the up and down mode, at appears to be about 6.2 to 6.5V without a load. I disconnected the servo from the actuating arm and was able to get full movement in and out using a Duracell 9 volt battery. It would seem to me that the potentiometer should allow 12 volts to get back to the trim servo when it is turned all the way in one direction, and I'm only getting just over 6V.

Right now I'm thinking the board may be responsible. I have not yet contacted Van's about my problem.

JT
 
Trim

JT,

Let us know what you find out. I don't think any of us are completely satisfied with the
 
I am having the same problem with mine. I called vans and they where little help. At first mine would not work then I hooked up a battery charger to bring the voltage up to 14v. I also adjusted the pot. My trim is now working but it sounds like it is surging or laboring.
 
Welcome to the club

I spoke with Ray Allen again today. Mine has the same problem. The gear inside that turns around the threaded rod is not running true, and has a slight bind with each revolution around the threaded rod. The problem here is Van's is feeding low power to the servo to slow it down, which cause the speed up and slow down because of the internal binding. For likely most applications, it is not an issue. Van's wants us to set the timing for a full stroke at 25 - 30 seconds at 12 volts. That requires a lower voltage to get it to slow down. Ray Allen told me it was designed to full stroke in 8 seconds. That requires a serious reduction in power to achieve that. Hope this makes sense.

John Bender
 
Hi JT,

It would be interesting to apply the 9 v. battery to the forward ends of the wire at the connector to the tunnel cable. If you apply 9 v. and the trim motor works like the 9 v. applied in the rear then the wire is OK and if the 9 v. applied to the front comes out 4 v. at the back you would know that you have an issue with the wires and my first guess would be that one of the connectors that is crimped on is not the best of connections, it will ring out but not carry any load.

Have a good day.

Best regards,
Vern
 
Van's wants us to set the timing for a full stroke at 25 - 30 seconds at 12 volts. That requires a lower voltage to get it to slow down.

This is not correct.

A lower voltage is not used to slow down the trim on an RV-12.

It uses a PWM (pulse width modulation) circuit. It uses full voltage but pulses it on and off to make the motor move slowly. When the speed pot is turned, it is adjusting the amount of time the voltage is off versus on. This is a standard technique for moving DC motors slowly without losing much torque. The laboring sound is because the internal friction varies slightly while it is running, but it is normal (for the RV-12 at least)
 
I spoke with Ray Allen again today. Mine has the same problem. The gear inside that turns around the threaded rod is not running true, and has a slight bind with each revolution around the threaded rod. The problem here is Van's is feeding low power to the servo to slow it down, which cause the speed up and slow down because of the internal binding. For likely most applications, it is not an issue. Van's wants us to set the timing for a full stroke at 25 - 30 seconds at 12 volts. That requires a lower voltage to get it to slow down. Ray Allen told me it was designed to full stroke in 8 seconds. That requires a serious reduction in power to achieve that. Hope this makes sense.

John Bender

I think you have it right
 
This is not correct.

A lower voltage is not used to slow down the trim on an RV-12.

It uses a PWM (pulse width modulation) circuit. It uses full voltage but pulses it on and off to make the motor move slowly. When the speed pot is turned, it is adjusting the amount of time the voltage is off versus on. This is a standard technique for moving DC motors slowly without losing much torque. The laboring sound is because the internal friction varies slightly while it is running, but it is normal (for the RV-12 at least)

If what you say is true then why does my trim require more than 12v to even make it operate.
 
Trim

This is not correct.

A lower voltage is not used to slow down the trim on an RV-12.

It uses a PWM (pulse width modulation) circuit. It uses full voltage but pulses it on and off to make the motor move slowly. When the speed pot is turned, it is adjusting the amount of time the voltage is off versus on. This is a standard technique for moving DC motors slowly without losing much torque. The laboring sound is because the internal friction varies slightly while it is running, but it is normal (for the RV-12 at least)

Scott,

Just wanted to mention that I really enjoy your explanations of some of the engineering thought processes behind this delightful machine. If you don't get too frustrated by us anxious builders please continue to offer the insight - sometimes its pretty fascinating...above for instance. Thanks.
 
Scott M

I understand fully what you said about motor contolling. My statement was general. Less power is a term I choose. The issue is the servo has a bind internally that greatly affects the way it will go thru its cycle with "lower power" applied. As I was told, it was designed to go thru a full stroke in 8 seconds with 12v. Slowing that down causes the internal binding issue to be come serious. Very hard to get the motor to start when it may have stopped in a binding condition. They are sending me another one, with the understand that it needs to operate at the "lower power" settings called for.

John Bender
 
Summary of what I have done to trim and still no luck

I've been unsuccessful in making my trim servo function properly since this past weekend.

Here are the steps that I have taken that points to the wiring being okay, some power is getting back to the servo, but it appears in a reduced voltage that is insufficient for its operation.

1. All 5 pins from the 37 pin connector to the servo have been checked for continuity.
2. The Odyssey battery is new, but I have put on a battery minder to bring the battery to a maximum charge of about 13 volts when the charger is in place.
3. I disconnected the trim servo connector and ran it from a 9 volt Duracell battery and it works fine but slower due to 9 volts.
4. I then put 9 volts to pins 31 & 32 on the 37 pin Tunnel harness connector at AV Board (with the connector removed) and the servo worked about the same as putting the 9 volt directly to the two power conductors at the servo.
5. The potentiometer is turned all the way counter clockwise, with the connector attached to the Av board, and the battery charger on I get a very, very slow movement of the servo, that is almost undiscernible. With the pot turned clockwise, there is no movement.

I understand from Scott's post that there should always be 12 volts going to the servo, the pot merely pulsates to slow or speed up the servo depending on the setting on the pot.

I was able to measure just over 6 volts going back to the servo with the master on and the trim switch activated.

I understand that Steinair did not fabricate the Av Board, so who is the mystery fabricator of the board? I'm at a loss as to where I go from here other than to Van's to see if I can get a new board to try.

JT
 
Hi JT,

Yes you should go to Van's during the support hours, but be prepared to hear that the good support people know very little about their "Magic Box". If you are unable to get solid help then we as a group may have to approach Mr. Green, Van's President, to get him to hire or provide an avionics person for the support staff as he is now in the avionics business and I for one feel that he should provide that support that is required to get these kits working properly. I am 13 days into a magnetometer problem and last night I received the first response from Van's asking me to check the voltage on one pin, which I will do when they have confirmed that I do understand the instructions correctly to be sure that we are doing the test correctly in the hope that we do no damage to the Dynon.

Best regards,
Vern
 
As I was told, it was designed to go thru a full stroke in 8 seconds with 12v. Slowing that down causes the internal binding issue to be come serious. Very hard to get the motor to start when it may have stopped in a binding condition. They are sending me another one, with the understand that it needs to operate at the "lower power" settings called for.

John Bender

Ray Allen sells (or used too anyway) a speed control that as far as I know only varies the voltage. This causes much more loss in output torque. If they sell a speed control, they must expect the motor to be able to operate at a reduced speed.

The trim system as designed will appear that the motor is laboring because it is running so slow but this is normal. If yours seems to be laboring so much that it can not be stopped at any point in the travel range and restarted, I would say that your trim motor has a problem.

If the trim is adjusted as described in the manual, it will run from stop to stop in about 20 seconds when the engine is running and buss voltage is at the normal operating level. That is why 25 - 30 seconds is used for the adjustment value when only operating on the aircraft battery.

If you adjust for full travel range in only 8 seconds the pitch trim will be extremly sensitive in cruise flight. This is the case with all the RV models not just the RV-12 and is why most everyone using electric trim on RV's (and many other kit plane models) uses a speed control.
 
Scott

As I have stated, my motor speeds up then nearly stops until it get past the binding position. I took the top off and watched it. With each revolution of the main 'drive' gear around the threaded rod, it tries to force the threaded rod away from the other reduction gears. With higher 'power' to the servo, it goes right past the tight spot easily. By slowing it down, per the desired requirement, the binding issue becomes a problem. The servo needs to turn very freely thoughout the entire stroke. I think many of us are having the same issue, but since we have not been around these servos in many cases, we have not understood how they should be wokring until the 'problem' shows up.

John Bender
 
As I have stated, my motor speeds up then nearly stops until it get past the binding position. I took the top off and watched it. With each revolution of the main 'drive' gear around the threaded rod, it tries to force the threaded rod away from the other reduction gears. With higher 'power' to the servo, it goes right past the tight spot easily. By slowing it down, per the desired requirement, the binding issue becomes a problem. The servo needs to turn very freely thoughout the entire stroke. I think many of us are having the same issue, but since we have not been around these servos in many cases, we have not understood how they should be wokring until the 'problem' shows up.

John Bender

It sounds to me like it is a problem with the trim motor. I have been involved with running a few different motors on the PWM speed control and they typically act as you describe (surging change in speed while it is running) but they all have been able to be slowed down to the specified and run the full range without stalling or getting stuck if stopped in the wrong position. Hopefully a different trim motor will solve your problem.
 
Thank you Scott

Ray Allen said they would send me another one after a long ( second ) discussion. They said they would try to get one that does not bind too much. Should be here tomorrow or the next day. I'll report back how that goes. I think some of the others are having a similar problem. If it happens to stop at the binding point, sometimes they do not want to start again.

John Bender
 
Trim Speed Adjustment RV-12

My trim is very sensitive. In cruise, it takes just a quick tap to change the trim pressure, and sometimes that quick tap is too much trim movement.

I just learned about the 30 second rule that it should go from one end extreme to the other end extreme in about 30 seconds. I attempted to time my yesterday. I started timing as I held down the trim switch to get full movement. It moved about half way and stopped. I held down the switch again and the same thing happened, except now is has gone full movement in one direction. I did that several time and each time it stops at approximately the take off position. I have just learned about the trim adjustment procedure contained in the AV-50000 and I am going to work on adjusting to slow it down dramatically. Currently full range is about 16 seconds when you continue after the stop about way. So I have two questions. Is the trim switch and controller supposed to stop 1/2 way when the switch is held down, and if so, is the stop supposed to be in the takeoff position? Second, If I do the test twice to get movement through the full range and double the times, do I then set those two times to equal 30 seconds. Currently, my trim is moving full range, counting the stop, in about 15 seconds. Can anyone advise me on the proper steps to take to solve the problem. Also can someone refer me to the proper place in the KIA to find the adjustment procedure. I have look but so far it has aluded me. Thanks in advance for your help.
 
My trim is very sensitive. In cruise, it takes just a quick tap to change the trim pressure, and sometimes that quick tap is too much trim movement.

I just learned about the 30 second rule that it should go from one end extreme to the other end extreme in about 30 seconds. I attempted to time my yesterday. I started timing as I held down the trim switch to get full movement. It moved about half way and stopped. I held down the switch again and the same thing happened, except now is has gone full movement in one direction. I did that several time and each time it stops at approximately the take off position. I have just learned about the trim adjustment procedure contained in the AV-50000 and I am going to work on adjusting to slow it down dramatically. Currently full range is about 16 seconds when you continue after the stop about way. So I have two questions. Is the trim switch and controller supposed to stop 1/2 way when the switch is held down, and if so, is the stop supposed to be in the takeoff position? Second, If I do the test twice to get movement through the full range and double the times, do I then set those two times to equal 30 seconds. Currently, my trim is moving full range, counting the stop, in about 15 seconds. Can anyone advise me on the proper steps to take to solve the problem. Also can someone refer me to the proper place in the KIA to find the adjustment procedure. I have look but so far it has aluded me. Thanks in advance for your help.

Since there are a number of instrumentation configurations of the RV-12, it is difficult to offer suggestions without knowing what you have. Your airplane is a rather low serial # which would imply Dynon D180 EFIS but what it actually has depends on when the airplane was finished.

On the Skyview and G3X systems, if they have the optional autopilot control panel, the system has a built in trim runaway prevention. This will not allow the trim to run continuously for more than about 6 seconds. On these airplanes, when testing the trim speed, you need to continuously press and release the trim switch every 4-5 seconds while doing the test. This resets the limit timer and allows the trim to continuously run (except for the fraction of a second that you released it which will have no appreciable effect on the overall time)
It sounds like this is what you are seeing but without knowing how your airplane is equipped it is just a guess.

For additional info, refer to the README document appropriate for what panel equipment you have. They can be found here https://www.vansaircraft.com/public/downloads.htm
 
Trim

Scott,

Thanks for your reply. My aircraft is a low serial number but last summer I upgraded it to the Skyview HDX and installed the auto-pilot control module and the knob module. Now I know why the trim stopped.

I am going to the airport this afternoon to work on this so you reply is very timely.

Thanks.

John
 
Trim Speed

My trim speed is too fast. It goes full range in about 16 seconds. I have the Dynon Skyview HDX with the auto-pilot controller and the knob module. My understanding is that with the auto-pilot controller, it contains a separate trim controller that has total control of trim feature. I have gone into the setup menu of the Skyview HDX and it has two places to adjust trim speed. One is for high airspeed and the other is for low airspeed. I have set the high airspeed to 40% and the lowspeed is set to 28%. I am hesitant to set them much lower. I tried setting the pot on the Vans 50,000A before I learned that the auto-pilot module controls the trim function. I set the Vans 50,000A all the way counter clockwise and it didn't make any difference.

It is still too fast and too sensitive.

I am wondering if some of you who have similar equipment will tell me what the percentage settings are in your Dynon and if you are happy with them.

Thanks in advance for your help.
 
John,
Have you ever read through the entire read me document that I posted a link to in post # 26?

It references the settings file(s) that can be downloaded from the Van's web site. I am pretty sure that if you load the file into your screen, it will automatically load settings in your HDX that will be pretty close to what you need.

Even though you have HDX, the info you want to select is for Skyview.

BTW, all the way counter clockwise on the AV-50000 is max. speed (think of it as the same as a water valve CCW for wide open.... Fully CW for shut off).
This should still be adjusted to the proper speed because it will revert to using it if there is aver a power failure of the autopilot system.
 
Last edited:
Trim Speed

Scott,

I apologize that I did not read the entire file. I just downloaded both files, the pdf readme and the file with the settings. I will install those according to the directions on Tuesday.

I did make a mistake in my last post. I turned the pot all the way clockwise. You are right that counter clockwise is the fastest speed. I just made a mistake when typing the post.

I do appreciate your help on this and other matters. Getting the trim speed right will make flying at cruise much easier.

John
 
Trim Speed, A question for Scott

Scott,
First of all, Scott I want to thank you for all the help you provide on this forum. I have been reading the read-me file that you posted and have downloaded all the files for my system from the link you provided. Tuesday I am going to go to the hangar and install them.

I have carefully read the section on trim settings, etc. several times. I want to be sure I understand it. It says "If the SV-AP-Panel were to fail, (and I interpret that to be turned off in addition to an outright failure), the switch on the panel would still control the trim motor at full rate trim. The following calibration test will not affect the function of the trim switch on the panel."
So does that mean that when the auto-pilot is off and I am manually flying and trimming, that full speed trim is the only thing that is available to me? In other words, the adjustment pot on the Vans 50,000A will not change the trim speed in manual mode?

After reading that last paragraph I am not sure it is clear. Here is how I fly. I take off and manually adjust the trim within seconds of takeoff. As I continue to fly to altitude, I manually adjust the trim. When I reach my cruising altitude, I manually adjust the trim and then turn on the auto-pilot, using altitude hold and normally either track or gps mode. While at cruising altitude, I let George (the auto-pilot) fly the airplane and the auto-pilot makes all the trim adjustments. When I start to descend, I set my new desired, lower altitude, put the auto-pilot in descent mode, and select a rate of descent. I let the auto-pilot fly down to some altitude when I decide it is time to be hand flying. Then I turn the auto-pilot off and begin manually flying the airplane. All trim adjustments from this point until I land are done manually.

The problem in my airplane is that the trim speed is too fast. Full range trim is about 16 seconds and I have the pot adjuster full range clockwise to yield the slowest trim rate. So If I am understanding the quoted portions of the manual correctly, when the auto-pilot control module is installed, the only trim function in manual mode is full speed.

Please understand that I am asking these questions as a learner. I want to learn my airplane and know what it will do and not do. I am not asking the questions to be argumentative or confrontational.

I am looking forward to your answers so I can understand this system more completely and know what to expect from my trim.

John
 
You could buy several 1/2 watt resistors ranging in value between 1 ohm and
15 ohms. Set Van's trim pot to the center of its range. Using trial and error,
put one of the resistors in series with one of the trim servo motor leads.
 
Scott,
First of all, Scott I want to thank you for all the help you provide on this forum. I have been reading the read-me file that you posted and have downloaded all the files for my system from the link you provided. Tuesday I am going to go to the hangar and install them.

I have carefully read the section on trim settings, etc. several times. I want to be sure I understand it. It says "If the SV-AP-Panel were to fail, (and I interpret that to be turned off in addition to an outright failure), the switch on the panel would still control the trim motor at full rate trim. The following calibration test will not affect the function of the trim switch on the panel."
So does that mean that when the auto-pilot is off and I am manually flying and trimming, that full speed trim is the only thing that is available to me? In other words, the adjustment pot on the Vans 50,000A will not change the trim speed in manual mode?

After reading that last paragraph I am not sure it is clear. Here is how I fly. I take off and manually adjust the trim within seconds of takeoff. As I continue to fly to altitude, I manually adjust the trim. When I reach my cruising altitude, I manually adjust the trim and then turn on the auto-pilot, using altitude hold and normally either track or gps mode. While at cruising altitude, I let George (the auto-pilot) fly the airplane and the auto-pilot makes all the trim adjustments. When I start to descend, I set my new desired, lower altitude, put the auto-pilot in descent mode, and select a rate of descent. I let the auto-pilot fly down to some altitude when I decide it is time to be hand flying. Then I turn the auto-pilot off and begin manually flying the airplane. All trim adjustments from this point until I land are done manually.

The problem in my airplane is that the trim speed is too fast. Full range trim is about 16 seconds and I have the pot adjuster full range clockwise to yield the slowest trim rate. So If I am understanding the quoted portions of the manual correctly, when the auto-pilot control module is installed, the only trim function in manual mode is full speed.

Please understand that I am asking these questions as a learner. I want to learn my airplane and know what it will do and not do. I am not asking the questions to be argumentative or confrontational.

I am looking forward to your answers so I can understand this system more completely and know what to expect from my trim.

John

As I wrote in my previous post (# 29), and as mentioned in the read me file, the trim speed reverts to using the normal speed control (the one on the AV-50000) when the AP system is off line.
That is why I said you still need to properly set the speed for that system.

A properly operating AV-50000 speed controller can be adjusted slow enough that the servo will stall and not move, so you either think you are turning it all the way clockwise but your not (the control is a 25 turn pot, so it takes 25 full turns to go from max speed to minimum speed), or something with the speed controller has failed. A failure is rather unlikely because as a rule they either work or don't, but I guess it is possible.
Since the pot can be difficult to access, my recommendation would be that you try again... maybe using a different adjusting tool (note, if you use a small metal screw driver, do not make adjustments with power turned on), and see if you can get it any slower. Because it is a 25 turn pot, it takes a couple of turns to see much of a change.

I would discourage adding resistors to slow the servo speed. It will reduce the torque output of the servo which could cause stalling problems at higher loads on the antiservo tab, and it would be just masking the actual problem (assuming it really wont adjust any slower)
 
Trim Speed

Scott,

Thanks for that reply, that clarifies things.

I turned it two or three turns and it was then much harder to turn so when I realized that I stopped because I didn't want to damage it.

Tomorrow I am going to install the file and configuration files that I downloaded and I will see about turning it more. As you said it is hard to access. I got a screwdriver small enough to fit and then cut part of the handle off so it would fit in the small space. When I was adjusting it, I had the sheet metal off the top and took out the start module for good access. Some have said you can access it with the skyview out so that is what I will try tomorrow.

Thanks again for your help.

John
 
Scott,

Thanks for that reply, that clarifies things.

I turned it two or three turns and it was then much harder to turn so when I realized that I stopped because I didn't want to damage it.

Tomorrow I am going to install the file and configuration files that I downloaded and I will see about turning it more. As you said it is hard to access. I got a screwdriver small enough to fit and then cut part of the handle off so it would fit in the small space. When I was adjusting it, I had the sheet metal off the top and took out the start module for good access. Some have said you can access it with the skyview out so that is what I will try tomorrow.

Thanks again for your help.

John

You can't damage the pot on the AV-50000 buy turning it too far... it will just continue to freewheel when you get to either end (Note... people with the AV-12 switch panel for the D-180 have a pot that is only 4/3 of a turn and it can be damaged if you try and force it too far.)

You can damage it by pushing excessively hard on the pot.

It sounds like you probably didn't turn it enough to make much adjustment.
 
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