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RV10-List:Trim troubles and mods

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pitts_pilot(at)bellsouth.
Guest

Posted: Fri Nov 02, 2007 6:17 am Post subject: RV10-List:Trim troubles and mods

gary wrote:



 	  Quote: 	
		  



It seems to me that the two problems with the stock RV10 trim that Tim

outlines should be able to be solved with less expense than a whole new

system (no offence Tim).  The resister that William Curtis suggested solves

one of them (speed), can anyone of you electronics guys design a time out

circuit that we could build and add to our Ray Allen system?



Designing the delay function is the easy part (probably 555 timer 
	


available at Radio Shack). What function do you want to 'time out' 

(incremental trim???), how long is the time (,25 second??), and what 

presently controls that function (switch???)???

I have no clue (I'm not there yet) what the actual functionality of the 

servo is.  Does it run too fast (the resistor mod) or coast past the 

wanted position????  What's the basic complaint???

Linn



 	  Quote: 	
		  

William, what value of resister are you starting with to test the system?



Gary

40274

rnewman(at)tcwtech.com
Guest

Posted: Tue Nov 13, 2007 7:29 pm Post subject: RV10-List:Trim troubles and mods

I'd like to share some insights into the engineering design considerations 

regarding speed control circuits for DC motors.    (the

Ray-Allen style trim servo uses a brushed DC motor)

I would discourage the use of a resistor type speed control for adjusting 

the travel speed on the trim servos used in our RV aircraft for the 

following reasons:



  Adding a series resistor to the trim motor limits the available current to 

the motor and although it will slow the motor down it also limits the 

available motor torque (i.e.. its ability to move the attached control 

surface).    This could be undesirable as the loading on the control surface 

will vary with aircraft configuration and performance.    Although you may 

"tune" the resistor combination to work in one flight regime it may not be 

what you need in another.    Now perhaps there is a suitable compromise 

value you may find "works" for your plane, but have you tested it thru 

temperature, airspeed and aircraft loading extremes?      The fundamental 

problem is that series resistor forms a voltage divider with the attached 

motor, as you load the motor down, its impedance drops,  this means that 

more of the voltage available from the aircraft bus will be dropped across 

the resistor and less will be available for the motor as you load it down. 

This effectively makes this method susceptible to problems over full 

operating range of loads and supply voltages.    Again, you may be able find 

a "suitable" value that seems to work, but be careful to test over a wide 

range of conditions.

     A second, more long term problem associated with this method of speed 

control has to do with motor life.     A brushed DC motor can develop a 

condition which will dramatically shorten its operating life if it is speed 

controlled by reducing the available current available to the motor.    The 

phenomena is most prevalent in motors that are used for short durations or 

intermittent duty.   The condition that is likely to develop is that the 

dust from the motor brushes will pack the slots of the motor's commutator. 

This dust is a combination of conductive particles (carbon from the brushes) 

and any oil from the motor bearings.  This substance is like a conductive 

paste and it gets wedged into the spaces between the commutator bars.    The 

paste effectively shorts out the motor over time.   Normally, when the motor 

is run at its designed voltage or when it controlled by reducing the 

available motor voltage, there is plenty of current available to burn off 

this conductive paste, and the motor lasts its full rated life.    However, 

if the motor is speed controlled by limiting the available current (eg. 

using a series resistor dropper circuit)  the ability to burn off this brush 

paste is greatly compromised.  The brush pasted remains packed in the 

commutator and the motor effectively gets shorted out and stops moving. 

This usually is noticed when the motor is turned on, and the brush paste 

just cannot be cleared.   The motor is then done.     I've seen this effect 

ruin dc motors within a dozen accumulated run hours.



    In the DC motor industry the accepted method of speed control for 

brushed DC motors is to reduce the motor voltage without limiting the 

available motor current.   This is done by a number of methods which include 

linear regulators, high frequency switching regulators or direct PWM (pulse 

width modulation) to name a few.   All of these techniques can reduce the 

average voltage to the motor without limiting the available motor current.



    Sorry for the long post, but sometimes the engineering that goes to what 

seems to be relatively simple can have significant consequences.

Bob Newman

TCW Technologies

www.tcwtech.com

speckter(at)comcast.net
Guest

Posted: Wed Nov 14, 2007 5:19 am Post subject: RV10-List:Trim troubles and mods

Thanks for the informative write up.  As they say, now I get it>



Gary

40274

Do not archive



--

billderou(at)yahoo.com
Guest

Posted: Wed Nov 14, 2007 9:46 am Post subject: RV10-List:Trim troubles and mods

Bob-

  I developed an automatic elevator trim system for my aircraft 15 months ago and it has been performing flawlessly. Its so benign that its virtually invisible and has never failed.

   

  The black box creates a stream of 12-14.5 volt square pulses at 20hz. Pitot pressure is sensed and a fine microprocessor backs off the duty cycle expotentially as the speed increases. There are no switches normally needed, although I have an off and constant 12 volt override switch for emergencies. The feel on the trim switch is constant - no matter what speed the aircraft is moving.

   

  Do you see any long term motor or electrical issues with this arrangement?

   

  Bill DeRouchey

  N939SB, flying

  billderou(at)yahoo.com (billderou(at)yahoo.com)

  



Bob-tcw <rnewman(at)tcwtech.com> wrote:

  [quote]--> RV10-List message posted by: "Bob-tcw" 



I'd like to share some insights into the engineering design considerations 

regarding speed control circuits for DC motors. (the

Ray-Allen style trim servo uses a brushed DC motor)

I would discourage the use of a resistor type speed control for adjusting 

the travel speed on the trim servos used in our RV aircraft for the 

following reasons:



Adding a series resistor to the trim motor limits the available current to 

the motor and although it will slow the motor down it also limits the 

available motor torque (i.e.. its ability to move the attached control 

surface). This could be undesirable as the loading on the control surface 

will vary with aircraft configuration and performance. Although you may 

"tune" the resistor combination to work in one flight regime it may not be 

what you  need in another. Now perhaps there is a suitable compromise 

value you may find "works" for your plane, but have you tested it thru 

temperature, airspeed and aircraft loading extremes? The fundamental 

problem is that series resistor forms a voltage divider with the attached 

motor, as you load the motor down, its impedance drops, this means that 

more of the voltage available from the aircraft bus will be dropped across 

the resistor and less will be available for the motor as you load it down. 

This effectively makes this method susceptible to problems over full 

operating range of loads and supply voltages. Again, you may be able find 

a "suitable" value that seems to work, but be careful to test over a wide 

range of conditions.

A second, more long term problem associated with this method of speed 

control has to do with motor life. A brushed DC motor can develop a 

condition which will dramatically shorten its operating life if  it is speed 

controlled by reducing the available current available to the motor. The 

phenomena is most prevalent in motors that are used for short durations or 

intermittent duty. The condition that is likely to develop is that the 

dust from the motor brushes will pack the slots of the motor's commutator. 

This dust is a combination of conductive particles (carbon from the brushes) 

and any oil from the motor bearings. This substance is like a conductive 

paste and it gets wedged into the spaces between the commutator bars. The 

paste effectively shorts out the motor over time. Normally, when the motor 

is run at its designed voltage or when it controlled by reducing the 

available motor voltage, there is plenty of current available to burn off 

this conductive paste, and the motor lasts its full rated life. However, 

if the motor is speed controlled by limiting the available current (eg. 

using a series resistor dropper circuit)  the ability to burn off this brush 

paste is greatly compromised. The brush pasted remains packed in the 

commutator and the motor effectively gets shorted out and stops moving. 

This usually is noticed when the motor is turned on, and the brush paste 

just cannot be cleared. The motor is then done. I've seen this effect 

ruin dc motors within a dozen accumulated run hours.



In the DC motor industry the accepted method of speed control for 

brushed DC motors is to reduce the motor voltage without limiting the 

available motor current. This is done by a number of methods which include 

linear regulators, high frequency switching regulators or direct PWM (pulse 

width modulation) to name a few. All of these techniques can reduce the 

average voltage to the motor without limiting the available motor current.



Sorry for the long post, but sometimes the engineering that goes to what 

seems to be relatively simple can have [quote][b]

wcurtis(at)nerv10.com
Guest

Posted: Wed Nov 14, 2007 5:33 pm Post subject: RV10-List:Trim troubles and mods

When this was last discussed, a few folks ask me for resistor values.  I did a rough calculation and determined that about a 10 ohm resistor would be required to get it down to ~7 volts (assuming .6 amp draw) but that resistor would have to be quite large to dissipate nearly 3 watts.  



I redesigned the speed controller by using the ubiquitous 780x power regulator instead.  In this case a 7806 regulates the input voltage down to 6 volts for up to 1 amp.  The speed controller is activated by a switch on the flap torque tube where ,when the flaps are up, power to the trim motor is via the 7806 power regulator, any other flap position and trim motor runs at full speed.  Much more efficient and elegant compared to a resistor.



http://wcurtis.nerv10.com/90Electrical/RV10PitchTrim.pdf



I encourage your development of products for the RV-10 and I think your trim controller is an excellent product.  However, we all have the tendency to implement the "gold plated" solution when the more effective stainless steel would do.



William

http://wcurtis.nerv10.com/ 



------

speckter(at)comcast.net
Guest

Posted: Thu Nov 15, 2007 9:40 am Post subject: RV10-List:Trim troubles and mods

Could you also design a time out feature in this circuit to eliminate the

runaway problem?



Gary

40274



--

sergiolov

Joined: 15 Nov 2007
Posts: 1

Posted: Thu Nov 15, 2007 11:44 am Post subject: Re: RV10-List:Trim troubles and mods

I am going to use your circuit for my trim. However, seems that there is a mistake in the wiring of the relays,that in this configuration shorts the +12 to ground, unless there is something of which I am not aware.

Sergio

RV8 82041, flying

RV10, finish kit

 	  wcurtis(at)nerv10.com wrote: 	
		  When this was last discussed, a few folks ask me for resistor values.  I did a rough calculation and determined that about a 10 ohm resistor would be required to get it down to ~7 volts (assuming .6 amp draw) but that resistor would have to be quite large to dissipate nearly 3 watts.  



I redesigned the speed controller by using the ubiquitous 780x power regulator instead.  In this case a 7806 regulates the input voltage down to 6 volts for up to 1 amp.  The speed controller is activated by a switch on the flap torque tube where ,when the flaps are up, power to the trim motor is via the 7806 power regulator, any other flap position and trim motor runs at full speed.  Much more efficient and elegant compared to a resistor.



http://wcurtis.nerv10.com/90Electrical/RV10PitchTrim.pdf



I encourage your development of products for the RV-10 and I think your trim controller is an excellent product.  However, we all have the tendency to implement the "gold plated" solution when the more effective stainless steel would do.



William

http://wcurtis.nerv10.com/ 



------

rnewman(at)tcwtech.com
Guest

Posted: Thu Nov 15, 2007 2:11 pm Post subject: RV10-List:Trim troubles and mods

Don't forget to account for the heat-sinking of the linear regulator.   If 

your design assumtion is for 0.5 amps of current at 6 volts on the servo, 

that leaves 8 volts across the regulator for a supply voltage of 14 volts. 

The power dissipation in the regulator will be  8 x 0.5 = 4 watts.  Also, 

don't forget to handle raw electronic components such as voltage regulators 

with proper static safe procautions. Avoid making walking wounded that are 

likely to fail at the least timely moment.     Good luck rolling your own.



-Bob Newman

www.tcwtech.com



---

KiloPapa

Joined: 24 May 2006
Posts: 142
Location: Pearblossom, CA

Posted: Thu Nov 15, 2007 7:59 pm Post subject: RV10-List:Trim troubles and mods

Thanks for the informative and technical post.  I like that.



Kevin

40494

----- Original Message Follows -----

From: "Bob-tcw" <rnewman(at)tcwtech.com>

To: <rv10-list(at)matronics.com>

Subject: Re: RV10-List:Trim troubles and mods

Date: Tue, 13 Nov 2007 22:28:24 -0500

rnewman(at)tcwtech.com>

 	  Quote: 	
		  

I'd like to share some insights into the engineering design

considerations  regarding speed control circuits for DC

motors...........  



Bob Newman

TCW Technologies

www.tcwtech.com

_________________
Kevin
40494

do not archive

Keith Snyder

Joined: 15 Jan 2007
Posts: 3
Location: Fleetwood,Pa

Posted: Fri Nov 16, 2007 1:20 pm Post subject: Re: RV10-List:Trim troubles and mods

Hey William,

  Looking at Mr. Newman's website it looks like he is just up the road from you. Not far from me either.

rnewman(at)tcwtech.com
Guest

Posted: Fri Nov 16, 2007 2:56 pm Post subject: RV10-List:Trim troubles and mods

Guys,  your welcome to visit,  I'd love to have fellow builders stop by. 

Your welcome to check out the progress on my RV-10   (deep in the fuse)  or 

see a Safety-Trim in operation in my Glastar  out at 1N9  , Queen City 

Airport in Allentown PA.



just send me an email   rnewman(at)tcwtech.com



Bob Newman

www.tcwtech.com



---

wcurtis(at)nerv10.com
Guest

Posted: Fri Nov 16, 2007 5:49 pm Post subject: RV10-List:Trim troubles and mods

Yeah, I was trying to make the drawing simpler so I flipped one of the relays and then got it all mixed up.  I've corrected it and updated the drawing at the same link.  For whoever asked about the timeout circuit, This would more complexity than I would be comfortable putting together.  For that you should probably go with Bob's controller--or just make sure you have a pull able circuit breaker on the panel for the Trim motor.



http://wcurtis.nerv10.com/90Electrical/RV10PitchTrim.pdf



William

http://wcurtis.nerv10.com/ 



------

wcurtis(at)nerv10.com
Guest

Posted: Fri Nov 16, 2007 7:12 pm Post subject: RV10-List:Trim troubles and mods

Bob,



Did you know my Cardinal was based at Queen City (1N9) up until the last week of October.  I just got a hangar at Quakertown.  Very nice and reasonable.  I was on the waiting list at Queen City for the past year and a half.  Queen City is a nice utilititarian airport where folks just come, fly, then go home.  I never did get around to getting the permit to drive on the airport.  Silly, you can taxi your aircraft all around the airport but you have to take a test and get a permit to drive your automobile on the airport grounds.  Queen City is nice but Quakertown is much more personable.



Did you get the note that Queen City was selected one of four airports in PA to get an ADS-B ground station?  Oh well, with the ADS-B, even if I'm not based there, it's close enough to use as an alternate in lieu of Allentown (ABE) when required.  My old-old airport in NJ (47N) just got a new WAAS RNAV 25 approach with an MDA down to 480-1.  That's only 200 more feet than an ILS would get you down.  That plus the glidescope on RNAV(GPS) approaches and WAAS is WAA(s) cool.



In the meantime, I'm busy building shelves in the hangar and changing the oil in the Cardinal.  Will have to come and visit you soon though.



William

http://wcurtis.nerv10.com/ 



------

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