[NSRCA-discussion] berg 7 channel Rx
J.Oddino
joddino at socal.rr.com
Wed Sep 13 20:46:06 AKDT 2006
Fred is right that the maximum torque is a function of voltage, the motor
and the gear train. It occurs when the amplifier delivers a 100% duty cycle
to the motor. Increasing the pulse rate does not increase the duty cycle
past 100%. Ed is right that most of the time we don't get to 100% and
adding more pulses will increase the duty cycle closer to 100% and therefore
increase the torque. However, if a servo is set up for 50 pulses per
second, its minimum pulse to the motor and damping will probably not be good
at 100 Hz and the servo will buzz.
The new so-called digital servos pulse the motor three times longer per
frame (with more but shorter pulses) for every receiver pulse and therefore
advertise three times the holding power. This is only true at small error
signals (difference between input position commanded and output position)
and the same logic would apply to doubling the frame rate. You would get
twice the "holding torque" until you got to 100% duty cycle.
For what it's worth, I've had nothing but good performance with a Berg six
channel receiver.
Jim O
----- Original Message -----
From: "Ed Alt" <ed_alt at hotmail.com>
To: <nsrca-discussion at lists.nsrca.org>
Sent: Wednesday, September 13, 2006 8:48 PM
Subject: Re: [NSRCA-discussion] berg 7 channel Rx
> Basically, the way our standard servos work is that they trigger a one
shot
> on every pulse received. The output of the one shot is a pulse of
opposite
> polarity to the input pulse whose width is controlled by the feedback pot
> position (corresponds to the servo arm position). These two pulses are
> summed and if any error signal exists (if they don't match exactly in
pulse
> width), the error signal is stretched (made wider) and amplified to drive
> the motor in one direction or the other to resolve the error signal.
>
> The electronics are "dumb" in a standard servo and within certain timing
> limits, you should be able to increase the effective output torque by
> increasing the sampling rate of the pulses that are fed to it. I don't
know
> that it would be exactly double, but it should go up. This is because the
> motor is not driven at 100% duty cycle when it's running, i.e., it
receives
> a train of stretched pulses, but not a pure DC voltage level.
>
> Ed
>
>
> >From: "Fred Huber" <fhhuber at clearwire.com>
> >Reply-To: NSRCA Mailing List <nsrca-discussion at lists.nsrca.org>
> >To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
> >Subject: Re: [NSRCA-discussion] berg 7 channel Rx
> >Date: Wed, 13 Sep 2006 22:16:11 -0500
> >
> >Max output torque of a servo is a function of battery supplied voltage,
the
> >motor in the servo and the gear ratio.
> >
> >Changing the signal line frequency will not alter the servo output
torque.
> >
> >Also.. max torque of a servo can sometimes be a GEAR TRAIN limit.
> >otherwise it would be impossible to strip a sevo gear in flight. No
change
> >to the voltage supplied is going to alter the strength of the gears in
the
> >servo.
> >
> >It may effectively increase the servo resolution and thus sensitivity to
> >being off center, but it will not increase its available torque.
> >
> >It MAY have the servo circuit apply more power at a smaller deviation
from
> >"demanded" position... But that is an effect of resolution.
> >
> >So.. it may apply full torque available at half the deviation from
demanded
> >position... (may be what you MEANT to say...)
> >
> >Note that using a dual-inverter "glitch buster"
> >http://www.uoguelph.ca/~antoon/gadgets/noiserx.htm (especially with
Futabe
> >127 DF RX's) will boost the signal line from the RX output (appx 3.8 v
for
> >the Futaba 127 when using 4.8 v NiCd pack) to full RX pack voltage. This
> >can increase effective resolution. (especially with long servo leads)
> >The circuit is INTENDED to filter interference from long leads... and it
> >works. The side effect is almost as good as the intended purpose.
> >
> > If you can find the chip to make the circuit... I'm having trouble
> >finding the DIP (.10 inch pin spacing) I got some .05 in pin spacing
> >chips... which are going to be harder than heck to solder into the
circuit,
> >but should do the job.
> > ----- Original Message -----
> > From: Scott Pavlock
> > To: NSRCA Mailing List
> > Sent: Wednesday, September 13, 2006 4:59 PM
> > Subject: Re: [NSRCA-discussion] berg 7 channel Rx
> >
> >
> > {trimmed}
> > The nice part about this is it gives the ability of any analog servo
to
> >output twice its normal torque.
> > {trimmed}
> >
> > Scott Pavlock
> >
> >
> > On 9/13/06, White, Chris <chris at ssd.fsi.com> wrote:
> > Hi Mike Mueller,
> >
> > Oops.I meant to imply "They seem to be okay in low cost electrics"J
> >I'm not ready to try a $50 receiver in a big-buck R/C application either.
> >
> > Chris
> >
> >
> >
> >
>
>---------------------------------------------------------------------------
-
> >
> > From: nsrca-discussion-bounces at lists.nsrca.org
> >[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of mike
mueller
> > Sent: Wednesday, September 13, 2006 1:44 PM
> > To: NSRCA Mailing List
> > Subject: Re: [NSRCA-discussion] berg 7 channel Rx
> >
> >
> >
> > I know that Castle took a long time to introduce them to the
market.
> >The initial designs that they had right after taking over Berg were not
up
> >to the standards they wanted. I'm really impressed with these and can't
> >wait to try one. I'll also test them in a small IC plane before having
> >confidence in a pattern plane. The people at Castle are top notch. It's
> >also good to see an electronic component actually made here in the US.
Mike
> >
> > "White, Chris" <chris at ssd.fsi.com> wrote:
> >
> > Hi Mike,
> > I know some foamie guys are using these and treat them like they are
a
> > standard.....They should be okay.
> > Chris
> >
> > -----Original Message-----
> > From: nsrca-discussion-bounces at lists.nsrca.org
> > [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of
Michael
> > Wickizer
> > Sent: Wednesday, September 13, 2006 12:24 PM
> > To: nsrca-discussion at lists.nsrca.org
> > Subject: [NSRCA-discussion] berg 7 channel Rx
> >
> > Anybody have experience with these receivers? At only 8 grams, sure
> > would
> > be a weight savings in electric applications.
> >
> > http://www.castlecreations.com/products/berg_7-channel.html
> >
> > Mike
> >
> >
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> >
> >
> >
> >
>
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