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Problem-Setting Trim/Servo Motor Speed

MartySantic

MartySantic

Well Known Member
The fastest trim speed I can obtain at a battery voltage of 12.3 VDC (as measured with a DVM at the battery) is 40 seconds (stop to stop). This is with the potentiometer at its stop (fully counter-clockwise). The trim motor merely buzzes with the pot fully in the other direction. The plans call for a min speed of 30 seconds at 12.0 VDC. The trim motor sounds as though it is laboring (wha-wha sound).

ANYONE else having this problem?? Has anyone solved the problem??

I measured the resistance of white wire and the white/red wire (power to the motor) from the tail to the 37 pin connector behind the panel and each is 0.9 ohms. So the wires and all crimps are good.

I have attached a battery charger and with a battery voltage of 13.8 VDC (at the battery), the trim speed is 31 seconds.

I have measured the DC voltage at the running servo with a DVM. The voltage is 5.0 VDC. From another post, I understand that the control panel board produces a pulse width modulation signal. A lower voltage is to be expected as the DVM is measuring an average of the chopped signal. I do not have a scope to view the waveform.

With the trim motor attached to a DC power supply, the trim motor speed is 12.0 seconds at 12.0 VDC and 10.0 seconds at 13.8 VDC.

I have talked to support at Van's and they have acknowledged others are having the same issue, but, could not suggest any other testing other than replacing the switch panel.

Has anyone replaced the switch panel and obtained better results??

Do the servos vary? Has anyone replaced the servo and obtained better results?
 
Last edited:
Trim problem

Marty

I am having the exact same problem as you. Sent email to Vans late yesterday and waiting for an answer.
 
Mine works, but labors like you describe (wha-wha) Not real sure what the difference could be. There is not much binding resistance from the hardware, but you might want to check that. Knowing Marty like I do that has been done twice. ;)

With only 5 volts going to the motor no wonder it is not working correctly. :eek:

Bad potentiometers?
 
Yes you have to get more to it. Before I set mine all I had was 6.48 V and it would not work at all just buzz. That was with battery charger hooked up. Then I set the potentiometer all the out to the stop and got 9.6 that produced 22 seconds travel time.

Brad Stiefvater
Salem SD
 
Trim

Marty,

Don't forget, those run on a PWM circuit and will sound kinda "laboring" because of the variable friction from moving a DC so slow with little torque. Brad, how does it work in the air?
 
Yes, I understand the PWM signal teminology. I still CANNOT meet the specification in the plans. At 12 VDC, you should get a 25-30 second stroke rate. I cannot meet this requirement. Any ideas??
 
Trim

I couldn't get there without a charger hooked up like Brad did...I was closer to 14 volts (14.1 if I remember)...be interesting to hear how it worked for Brad in flight.
 
Trim motor problem

MartySantic said:
The fastest trim speed I can obtain at a battery voltage of 12.3 VDC (as measured with a DVM at the battery) is 40 seconds (stop to stop). This is with the potentiometer at its stop (fully counter-clockwise). The trim motor merely buzzes with the pot fully in the other direction. The plans call for a min speed of 30 seconds at 12.0 VDC. The trim motor sounds as though it is laboring (wha-wha sound).

ANYONE else having this problem?? Has anyone solved the problem??

I measured the resistance of white wire and the white/red wire (power to the motor) from the tail to the 37 pin connector behind the panel and each is 0.9 ohms. So the wires and all crimps are good.

I have attached a battery charger and with a battery voltage of 13.8 VDC (at the battery), the trim speed is 31 seconds.

I have measured the DC voltage at the running servo with a DVM. The voltage is 5.0 VDC. From another post, I understand that the control panel board produces a pulse width modulation signal. A lower voltage is to be expected as the DVM is measuring an average of the chopped signal. I do not have a scope to view the waveform.

With the trim motor attached to a DC power supply, the trim motor speed is 12.0 seconds at 12.0 VDC and 10.0 seconds at 13.8 VDC.

I have talked to support at Van's and they have acknowledged others are having the same issue, but, could not suggest any other testing other than replacing the switch panel.

Has anyone replaced the switch panel and obtained better results??

Do the servos vary? Has anyone replaced the servo and obtained better results?
Click to expand...

Mine does not work at all and I cannot get to the pot to adjust it. The pot does not seem to be lined up with the hole. Does anyone have a suggestion as to how to get access to the pot?

I have no binding at the motor and it runs smoothly using a 9 volt battery at the motor. Also, I do not have two white wires in the bundle that runs back to the motor. I have one white wire and one white/red wire, which I assume is the other power wire.
 
Trim

Jim You hav ethe power wires correct.

To adjust the trim speed you have to remove the screws holding the switch module in the panel, then you can tilt the module to get access.
 
That was voltage from the panel. I had my volt meter on the wires at the servo and run the up/down trim switch. That was with the potentiometer maxed out. (all the way out to the stop)

I have done about 20 landings and take offs and I would not want it any slower than 22 seconds. Its works very good for me at that setting. If I had to speed it up I could not due to the potentiometer being maxed out.


Brad Stiefvater
Salem SD
 
Lift the right side panel out and then you can get at it.

jamescone said:
Mine does not work at all and I cannot get to the pot to adjust it. The pot does not seem to be lined up with the hole. Does anyone have a suggestion as to how to get access to the pot?

I have no binding at the motor and it runs smoothly using a 9 volt battery at the motor. Also, I do not have two white wires in the bundle that runs back to the motor. I have one white wire and one white/red wire, which I assume is the other power wire.
Click to expand...

Jim

The only easy way to get at the pot is to take the left panel out and lean it forward and then use a short mini screw driver. You can see the slot in the pot to do this when you lift the panel, with Dynon, etc attached and do what you have to do.

JT
 
mcems said:
That was voltage from the panel. I had my volt meter on the wires at the servo and run the up/down trim switch. That was with the potentiometer maxed out. (all the way out to the stop)

I have done about 20 landings and take offs and I would not want it any slower than 22 seconds. Its works very good for me at that setting. If I had to speed it up I could not due to the potentiometer being maxed out.


Brad Stiefvater
Salem SD
Click to expand...

Brad,
It is not in the landing pattern that it needs to be slow, it is cruise light. If it is too fast it is frustrating to get the airplane exactly in trim (which it can do very well if adjusted properly). The trade-off is having it a bit slow fro pattern work but at the slow speeds the trim forces are so low it really isn't an issue.
 
Scott,

Are you folks looking into this issue? Many of us cannot meet the requirement in the plans to set the trim speed to 30 seconds at 12 VDc. With the potentiometer fully counterclockwise, I see a 40 second stroke rate at 12 VDc.

At 13.8 VDc the stroke rate is 31 seconds.
 
MartySantic said:
Scott,

Are you folks looking into this issue? Many of us cannot meet the requirement in the plans to set the trim speed to 30 seconds at 12 VDc. With the potentiometer fully counterclockwise, I see a 40 second stroke rate at 12 VDc.

At 13.8 VDc the stroke rate is 31 seconds.
Click to expand...

I believe a drawing clarification has been issued or is about to be.
I don't know the exact specifics of it (please refer to the change notice for the details) but I believe it was going to clarify the 12 volts statement. I think that was a generic term intended to mean using battery only, not with the power buss at normal charge voltage (such as when a battery charger is connected). It means with a fully charged battery, not one partly run down after powering the system while working on it.
It also appears that some of the trim motors have more internal drag than others, and run a bit slower. If you use a battery that is fully charged (measures at least 12.8 v at the battery terminals) and you get within a few seconds of the recommended travel speed range you should be fine.

Once again, check the latest change notice for the official information.
 
MartySantic said:
One more thought.....Do not crimp the spade connectors on the 2 white trim motor wires until you know the polarity of the signals from the rocker switch on the instrument panel.
Click to expand...

You have a point there. Hopefully I'm lucky on this one (Besides that I still don't like those big connectors on those tiny wires).
 
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