Do we have access to rigging/machinery to help us simulate the g-forces in
the proper axis also while in test-harness mode?

On Wed, Jul 8, 2009 at 5:08 PM, Nathan Bergey <nathan.ber...@gmail.com>wrote:

> > If i were to pick a root cause: inadequate testing.
>
> If you are saying that we didn't throw enough things out of airplanes
> then I couldn't agree more. :)
>
> What do you suggest would count as proper testing?  Someone (alright,
> me) can work on building tests before we even make the thing so that
> we can do a really good round of testing as soon as we have a
> prototype.
>
> On Wed, Jul 8, 2009 at 3:45 PM, <rq1...@q7.com> wrote:
> > (2009.07.08) kirk...@pdx.edu:
> >> Quoting rq1...@q7.com:
> >>> If i were doing it i'd use 4 mechanically independent servos. I
> estimate
> >>> the reliability of doing this is about 1/2 of the single servo system
> >>> being proposed. (Can we put the cool linkage drawing on the wiki page?)
> >>>
> >>> Despite the reduced reliability, i still think the 4 independent scheme
> >>> is a winner.
> >>>
> >>>   * Reliability is still very high
> >>>
> >>>   * Mechanically ready for full flight control
> >>>
> >>>   * Mechanically simpler
> >>>
> >>>   * Same system that must be developed down the road anyway
> >>
> >> Add higher cost to the list.
> >
> > Certainly it might cost more. Probably no more than 400 $ extra.
> >
> > Keep in mind that the per-servo torque requirements might be
> > considerably reduced in the 4 independent scheme.
> >
> >
> >> The reason I was pushing for a linked system is because there were
> >> reservations on the team about what could go wrong if the micro messes
> >> up and the servos go out of sync. Keep in mind we have NEVER
> >> successfully flown an ARM micro in 3 airborne tests.
> >
> > Yeah, what's up with all the ARM failures? (See Doug's question below.)
> >
> > The linked system is safer with respect to controller failure.  A
> > controller failure in the independent system has the potential to make
> > the flight path into a large radius circle, possibly at high spin rate,
> > not good.
> >
> >
> >> I will be happy to machine both the linked single servo system and the
> >> four servo system, so multiplying the work required is not a big
> >> problem. I really want to take baby steps on this, and I think the
> >> additional  insurance is worth the work. We'll do the independent
> >> version, but I don't think we should do that one first.
> >
> > I appreciate what you're saying.
> >
> > Since you're doing the work, you should do it the way that seems best to
> > you.
> >
> > The linkage will be hard to get working well, but if it does work well
> > it will be a thing of beauty.
> >
> >
> >>> In the 4 independent scheme, the servos must be individually trimmed.
> To
> >>> do this i would consider an absolute magnetic shaft encoder:
> >>
> >> Why add a shaft encoder when the existing servo positioning system gives
> >> minute of angle precision? I think the additional sensor violates the
> >> KISS principle. Modern digital servos are strong, fast, and accurate. I
> >> plan to align the fins the same way RC helicopter blades are aligned;
> >> using an inclinometer style pitch gauge.
> >
> > My experience with off the shelf servos is they won't re-point with
> single
> > degree accuracy but i haven't tried the more expensive digital servos.
> >
> > --
> > I just checked what i think is the Futaba site
> >
> >   http://www.futaba-rc.com
> >
> > I can't find a specification for pointing accuracy, which does not
> > inspire confidence.
> >
> > Ditto for
> >
> >   http://www.rc.futaba.co.jp
> >
> > Every servo i've ever taken apart had a sub-50 cent potentiometer in it.
> > Will that A) work. B) work under vibration, C) work reliably, D) work to
> > sub-degree precision? Honestly i think the answers are: Sometimes. No,
> > no, & no.
> >
> > Clearly doing anything but buying and using an off the shelf servo is
> > way more work than desirable. I'd like someone to prove me wrong and
> > show that off the shelf servos are just fine. Please.
> >
> > I did notice these guys, who are interesting
> >
> >   http://www.openservo.com/
> >
> >
> > (2009.07.08) daus...@gmail.com:
> >> What has been the root-cause of each of the three failed ARM flights? A
> >> robust controller solution would seem to be a primary factor for the
> >> roll-control project, with either a single- or a multi- servo approach.
> >
> > If i recall, first was either a blown GPIO pin or an odd reset due to a
> > wiring problem.  Second was a blown GPIO.  Third was a firmware bug.
> >
> > If i were to pick a root cause: inadequate testing.
> >
> >
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