CTE

[Henderson,Eric]

Winter came early.

-----Original Message-----
From: discussion-request at nsrca.org
[mailto:discussion-request at nsrca.org]On Behalf Of JOddino
Sent: Tuesday, December 02, 2003 11:57 AM
To: discussion at nsrca.org
Subject: Re: CTE


Hi Jerry,
I think you did a bait and switch.  Using your numbers, the smallest
increment at the servo is .088 degrees.  But if you are reducing the throw
from 90 degrees at the servo to 30 degrees at the surface, the smallest
increment at the surface is .088/3 = .029 degrees.  That is very good.
In the real world you can't get all of the 1024 steps due to trim and
subtrim overhead.  If you want better resolution you need to go to a
programmable servo like the Hitec or a servo set up with less throw like the
4000 Super Servos that had about 60 degrees total.  You could make full
travel of the Hitec 30 degrees for 1024 steps.  The problem with that is
gear slop and linkage slop get to be a larger percentage and you have no
mechanical advantage so your torque at the surface is decreased.  Speed
would be great though.  As with most things it is a trade off.  I always
figured .1 degrees at the surface was fine.
Jim
----- Original Message ----- 
From: "Jerry Budd" <jbudd at QNET.COM>
To: <discussion at nsrca.org>
Sent: Monday, December 01, 2003 10:06 PM
Subject: Re: CTE


>
> Disclaimer:  YMMV
>
> Let's digress a bit.
>
> [Note to Robert Gainey:  The "Geek Alert" is now in effect!]
>
> Why is the servos resolution worse than the command resolution?  If
> you set your ATV to 150% and your servo moves +/- 45 degrees your
> servo has a max resolution of 90 degrees/1024 bits = 0.088
> degrees/bit.  So we're really servo limited.
>
> Lets look at this another way.  If you have a 10 bit resolution
> system (1024 steps) and you are using 2/3rd's of your resolution (on
> a JR that'd be equivalent to leaving your trace rate set at 100%) to
> drive your surfaces +/- 15 degrees the minimum theoretical surface
> deflection you could command is 0.044 degrees/bit.  But as shown
> above your servos are only good to ~ 0.09 degrees at the servo output
> wheel, or about half of the command resolution.  Again, we're limited
> by the servo resolution.
>
> Jim Oddino, you out there?  Wanna check my numbers?
>
> Jerry
>
>

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