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Trim servo speed control question.

Mike S

Senior Curmudgeon
The Ray Allen SPD-1 speed control looks to be a voltage dropping device that not only slows down the servo, but also reduces the force the servo will generate.

Has anybody had an issue with using this speed control and then not having enough force to drive the trim tab?

Is there a better way to slow the servo down but not reduce the force it generates at the same time? Possibly some kind of pulsed full voltage signal?

Thanks in advance.

Mike
 
I installed this speed controller 20 some odd years ago and it's still working great.
http://www.matronics.com/governor/
But you do have to find a balance between fast and slow flight speeds, as it's not air speed sensitive like some of the newer devices, but it is simple.
 
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Data

On my -10, I use the vpx to schedule the speed trim. It also reduces the voltage to slow the speed of the servo. Through trial and error, I found that any percentage less than 80 causes the trim to not function. Not enough power to drive the tab and the servo would stall.

The better way to control the speed would be a PWM controller where the voltage is constant and the duty cycle is varied. I believe the garmin system uses PWM control for trim speed.
 
The better way to control the speed would be a PWM controller where the voltage is constant and the duty cycle is varied.

That is what I was trying to remember/describe.

Thanks for the info.

Is this what the Matronics unit does? They claim no loss of trim force.
 
Idk

I do not know, not familiar with that unit. If it is PWM then most certainly. Only thing to watch for is switching noise from the PWM unit…
 
I'M using the Garmin G3X system to control my trim servos. It uses PWM to adjust trim speed, and will adjust the speed of trim based on airspeed, with set points that allow you to adjust the speed reduction curve. Also, it has a max trim time limit to cut off power to the trim motor after a pre-set number of seconds. You then need to release the trim switch and reapply it to restart the trim motor moving. Provides some protection against a stuck switch or short to ground from causing trim runaway. It also does auto trim if you have their autopilot servos and turn the feature on.

Overall, I have been very happy with the G3X trim system.

Cheers,
 
I wish

I wish that I would have used the Garmin trim insted of the vpx but it is working so probably will not rewire...
 
Guys, thanks for the replies---they are appreciated.

Here is a bit more info for consideration.

The trim is operated by dual Tostin grips, and uses the Tostin relay unit to combine the inputs.

There is no VPX or Garmin stuff involved so while I am grateful for folks trying to help, there is no value to me talking about these setups.

I looked at the Matronics link, seems like it might be usable but not sure yet. I plan to call them tomorrow and see if their speed control will work in my setup.

Please keep the ideas coming.
 
I use a Trio Pro /w auto trim. It’s a PWM (pulse width modulated) output, with the positive pulse width controlled by airspeed (higher airspeed, smaller pulse width, slower trim speed). It works even when the servos are not engaged. For a simple home-brew approach it’s pretty straightforward to design a circuit with a manual control for the pulse width. Integrating that with airspeed for automatic control is harder. Unless you’ve got everything running in a microprocessor, then it’s easy. One approach is to have the stick hat switch provide full 12 volt DC, and a second, panel switch, provide a PWM output suitable for cruise. A simple relay deck can auto-switch between the two.
 
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I use voltage reduction on the 6 and it has plenty of power at reduced voltage. Not surprised to hear it doesn't work on the 10 (3-4 times the tab surface area). I just made a little board (1" x 1") with an LM317 (w/ req capacitors) and a pot. I recommend a separate switch wired in to the 317 and the output in line with the relays. While the reduced trim speed is quite welcome in cruise, it would not be at low speeds like in the pattern. I only use the low speed trim switch in cruise.

Larry
 
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I installed a TCW Safety-Trim with an a/s switch in my 7A. No problems with trim speeds which are adjustable if needed.

Rich
 
I installed a TCW Safety-Trim with an a/s switch in my 7A. No problems with trim speeds which are adjustable if needed.

Rich

I had one in the 10, that is going to be my fall back unless I can find something simpler and cheaper.
 
Digging up an old thread to ask if anybody knows if it's possible to speed up the travel of the Ray Allen servos by use of one of these devices?
Installation is for a reflexer on a Quickie 2 to give the ability to quickly dump full reflexer on landing to get some weight on the tailwheel. It currently takes 10 seconds to reflex 6 degrees. It'd be great if it could do it in two seconds.
 
You could increase the voltage with a "dc to dc voltage booster" available on
eBay for less than $10. But too high of voltage will damage the servo.
 
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