[NSRCA-discussion] Ackerman question

[Lance Van Nostrand]

Thanks, Troy.  I appreciate the completeness of your answer.  I am happy to 
have learned something new.
--Lance

----- Original Message ----- 
From: "Troy A. Newman" <troy_newman at msn.com>
To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
Sent: Monday, January 15, 2007 11:33 PM
Subject: Re: [NSRCA-discussion] Ackerman question


> Lance,
>
> The surface control horn and the servo do NOT need to be the same distance
> from the pivot point. Rather they only need to be the same "offset" from 
> the
> pivot point. A one to one ration is definitely not needed to maintain the
> cable tension on the trailing cable. I do it all the time. My maximum 
> travel
> on the rudder is usually about 25-30degs the servo will easily do 50degs
> each side. I use rather large control horns on the surface side and then 
> use
> the smallest servo wheel I can get use to the maximum throw I need. As I
> said usually only 25degs. My D/R values are sitting around 70-80% on the
> lowest rate I have. If I find that I'm flying on less than about 80% with 
> no
> need to go to 100% at anytime I change out the servo wheel to a smaller 
> one
> or go in a hole or two to get maximum resolution on the rudder that I can.
> This makes rudder inputs smoother and more consistent. It also allows me 
> to
> run a right tight linkage that has no spongy or springy feel to it. This
> helps in rudder corrections, finesse rudder inputs like rolling loops and
> circles, and it also helps in snaps. A tight rudder linkage that is 
> getting
> good leverage on the rudder will exit snaps cleaner and not give a wiggle
> when they are done. A spongy rudder linkage will give tail waggle on stall
> turns, in point roll transitions, rollers, and snap exits.
>
> Also using more of the servo will lessen any effects of servo gear and pot
> wear, and will maximize trim resolution so that very fine movements are
> possible. This stuff shows up in all surfaces and will translate in the
> amount of mix being needed. Not the percentage of mix but how minute a
> movement can be controlled in a mix situation. Basically this all allows 
> you
> to fine tune your model more closely.
>
> see this article I wrote a while ago regarding the proper setup of a 
> rudder
> pull-pull system It explains it pretty well. Not a bunch of theory and
> Ackerman stuff. Just the meat and potatoes of the deal. By the way it was
> published in the KFactor and then posted on Central Hobbies website.
> Specifically look at Figure #1 and #2
>
> http://www.centralhobbies.com/instructional/linkage2/link21.html
>
> Troy Newman
>
> ----- Original Message ----- 
> From: "Lance Van Nostrand" <patterndude at tx.rr.com>
> To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
> Sent: Monday, January 15, 2007 9:19 PM
> Subject: [NSRCA-discussion] Ackerman question
>
>
>> OK, this ackerman thing got me thinking again about this and a question
>> comes to light:
>>
>> Many times we say that the servo arm should match the control arm to
>> minimize cable slack.  However, if we use a smaller servo arm than the
>> control arm I am now thinking that this does not exacerbate the cable
>> tension problem. In fact, it does nothing except reduce the surface
>> deflection.
>>
>> If the goal is to use 100% of the servo travel (for precision) than an
>> equally spaced servo/control surface would only let the servo rotate +-
>> about 15 degrees for the average elevator.  This is less than 50% of the
>> servo's capability.  I always used smaller arms at the servo, or use a
>> wheel
>> if I end up with too much slack.  I thought I was making the best of a 
>> bad
>> situation, but now I am thinking that there is no bad situation.  If the
>> clevis is on the hinge line (or the servo connection and control horn are
>> equally offset in the same direction) then you should get a constant
>> tension
>> regardless of the mismatch in servo/control arms.  Is this right?
>>
>> --Lance
>>
>> ----- Original Message ----- 
>> From: "Richard Lindberg" <rclindberg at comcast.net>
>> To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
>> Sent: Monday, January 15, 2007 11:32 AM
>> Subject: Re: [NSRCA-discussion] Pull Pull Cable Tension Question
>>
>>
>>> Here's the URL for Ackerman setups:
>>>
>>> http://members.cox.net/bdfelice/Ackerman/ackerman.htm
>>>
>>> FWIW, Bob Pastorello, et al,  discussed this on the list in November
>>> 2004...!
>>>
>>> Richard
>>>
>> /listinfo/nsrca-discussion
>>
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