REFLECTOR: Elevator trim problem

[Burrall L Sanders]

John,
My main concern would be if your switches in the Mac stick are built and rated for the current that the trim motor demands to do its job.  Usually the switches are too light for the job...thus the need of a relay.
A switch that is overloaded with current can weld to the closed position and you could  have a runaway trim as a result that could go to the stops.  Be very careful because the fact that it worked a time or two should  not give you the warm and fuzzies yet.
Burrall

www.freeflightcomposites.com




From: John Dibble 
Sent: Sunday, January 15, 2012 3:45 PM
To: Velocity Aircraft Owners and Builders list 
Subject: Re: REFLECTOR: Elevator trim problem

I eliminated the solid state relay and wired the stick buttons directly to the trim motor.  Took 2 short flights today and it worked perfect.  I know that's not much time, but on the previous flight it began trimming up by itself right after leveling off at 1000 ft, so I'm cautiously optimistic.  If anyone, not using a relay with a Mac stick,  has had problems, I'd really like to hear from you. 
Thanks, 

John 

John Dibble wrote: 

  I'm seriously thinking about that.  Maybe with an additional switch to switch between the stick buttons and the toggle so I can keep the stick controls which work most of the time. 
  John 

  Douglas Holub wrote: 

    All arguments for a single DPDT (on) off (on) toggle switch on the panel for elevator trim, on the left side where it's easy to reach with the left hand. Only one robust component. 
      ----- Original Message -----
      From:Michael Watson
      To: Velocity Aircraft Owners and Builders list
      Sent: Thursday, January 12, 2012 12:29 PM
      Subject: Re: REFLECTOR: Elevator trim problem
      John, 
      I also have a Mac 7 stick. Last year I had a problem with an intermittent up button. 
      I called Mac and they sent me two new buttons to replace the up and down ones. 
      No problems since. I think your up button may be sticking. Unscrew the two screws 
      under the head four or five turns, twist the head left to right while pressing the up button 
      and see if it sticks. Find a position that it moves up and down smoothly then tighten the 
      screws. 
        
        
        
        

      On Thu, Jan 12, 2012 at 10:15 AM, John Dibble <aminetech at bluefrog.com> wrote: 
        While we're on this subject, I need help with an issue with my elevator 
        trim.  Over the past 100 hours, infrequently it seems to trim up 
        uncommanded.  I push forward on the stick to keep level and push the 
        trim down button.  For a second or two nothing happens.  Then it 
        responds properly.  I know if I press both buttons at once, nothing 
        happens, so I'm guessing that there is still an up input in the second 
        or two when nothing happens.  I have a solid state relay that failed 
        once.  In that case the output voltage reduced to where the motor 
        wouldn't run.  I have a Mac 7 stick.  On the ground the buttons operate 
        well with no sign of sticking.  I have several questions. 
        Where is the mechanism that prevents operation when both buttons are 
        pressed?  In the stick?  In the relay?  In the motor? 

        Can I eliminate the relay and run full current through the stick? 

        I may wire lights to the leads going to the motor so I can confirm when 
        current is being sent to the motor. 

        Thanks, 

        John 

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      -- 
      Mike W. 
      1997 Velocity Elite RG 
      Franklin /IVO Electric CS 
      Dual GRT EFIS HX Synthetic Vision 



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