pcm or pre coded crash I would love to see you fly 2 planes on the same freq. say
plane 1 on 32 plane 2 on 32 as you stated ppm
would let you manage some what. pcm would make you crash due to lock out been there
done that as i am sure many will tell you
shortly. pcm pre coded crash was never in tended to fly on the same freq. as another
plane and when lockout occurs there is not a
thing you can do but watch in horror as you pile into the ground
best of luck
Dale
Ralph Weaver wrote:
> At 08:55 PM 7/11/00 -0700, you wrote:
> >1) Is PCM that much better than FM? I've heard it's a marginal difference
> >and the receivers are heavier.
>
> A standard FM transmitter sends a series of pulses to it's RF section where
> it is sent out the antenna. The receiver turns an RF signal back into a
> series of pulses, sending the first pulse to the first servo, second pulse
> to the second servo etc. If you get interference, the pulses will be
> wrong, but will be sent to the servos anyway causing the servos to move
> randomly.
>
> A PCM transmitter sends a coded message. The PCM receiver can tell if the
> message has been damaged. If the message has been damaged it is ignored
> and the servos don't move until the next good message. If there are no
> good messages for 1/2 second (selectable) then the receiver puts the servos
> in preset positions which was programmed at the transmitter. As soon as a
> good message gets through, the receiver goes back to normal operation.
>
> I've flown a glow plane on PCM while someone else was standing beside me
> with his transmitter on the same channel. The plane responded slowly, but
> was flyable.
>
> A common misconception is that PCM receivers lock into failsafe. This is
> only true if no good messaged are getting through - and if that is the
> case, what would be a better alternative? PCM receivers respond to all
> good messages, ignore bad messages and set the servos to a preset position
> if no messages are getting through.
>
> Another common misconception about PCM is that you can't tell if there is
> an interference problem until it is too late. This is not true. You can
> set the failsafe so that one of the channels moves enough that you know
> there is a problem - on powered planes you usually go to low
> throttle. When you get interference, the motor goes low, pretty hard to
> miss that.
>
> Some claim that they's rather "fly through" the interference with a
> standard FM radio rather than be "locked out" with a PCM radio. Since PCM
> radios will respond to all good messages, the chances of '"lying through"
> are better with PCM.
>
> PCM receivers are a little larger, and more expensive so I only use them in
> expensive or potentially dangerous (large and/or fast) planes.
>
> Bottom line: If you get interference on normal FM receivers, you have no
> idea what the servos will do. If you get interference on a PCM receiver,
> you know exactly what the servos will do.
>
> There is also a new technology available from several manufacturers. It is
> an intelligent FM receiver. If the pulse widths received are not within
> industry standard specifications, the servos are held at the current
> position until good pulses start coming in. These type receivers are a bit
> better at resisting interference, but can't tell good pulses from bad
> pulses if they fall within the industry spec. They also don't have presets
> in case the signal is completely lost and can't be programmed to signal
> interference by moving a particular servo.
>
> There are a lot of testimonials about flying with a particular radio type
> and the plane crashed, so that radio type is bad. Seldom is there any
> evidence to show that the radio type had anything to do with the crash.
>
> Which is better? That depends on your requirements. Envision the various
> scenarios that your plane might be in and ask yourself if you would rather
> have your servos move randomly, or hold their position, or hold their
> position and eventually go to presets.
>
> Ralph Weaver "Great minds talk about ideas,
> Fishers, IN average minds talk about events,
> USA small minds talk about people." -- Eleanor Roosevelt
>
> My site http://members.home.net/rmw00
> MTI products http://www.magtechinc.net
>
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