Thread: Discussion Telemetry systems
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Old Dec 14, 2011, 05:21 PM
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Lakewood, Colorado
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I've used the built in telemetry with XPS, Jeti and FrSky systems, and in all cases,
the audio alarms for the two most basic things
1. low Rx battery voltage (XPS didn't have this, but the others have programmable alarm levels)
2. impending or total loss of signal (all 3 have some form of this, although XPS's was really primitive)
are the most useful to me.
As a slope pilot I might fly a plane for hours, and I want to know when the
Rx battery level reaches a programmed threshold. I fly until it beeps, and then land.
For someone flying an electric, you set it to monitor flight pack voltage instead
of Rx voltage, and do the same.

And no matter what I'm flying, I like to know if there's some reason I might
be losing the signal. It could be due to bad antenna orientation, blocked by my own
body or someone else's, external Rf, a damaged or missing Rx antenna (happens more
often than you might think), or damaged Tx antenna (fatique due to repeated bending
or turning). The low or loss of signal alarm tells me all that. I even get a different
audio alarm if power is lost to the Rx and restored in the air (brownout).

It's also incredibly useful for locating downed planes. With very simple body blocking
techniques you can use the low or lost signal alarms to pinpoint the exact location
of a lost plane (quite common on the slope, and not unheard of at RC fields) to within
a couple dozen feet (closer with a live RSSI display). I even found one of my
slope planes *inside* someone's garage after I landed at the bottom of the hill, and
a nearby resident picked it up and took it home. Imagine their surprise when, after
my puzzled 10 minute search I showed up at their door and told em I was pretty
sure my plane was in their garage. Lots of excuses. Can't imagine they'll do it again.

Heck, I even have a little 1S lipo strapped to the side of one of my FrSky 6ch telemetry
Rx's that I power up by itself, and throw into my FPV plane. The FPV plane
has a completely different control system, but should it go down somewhere
out of sight I can narrow its general location down by reviewing the last
received video, and then when I'm within a half mile or of it so, I throw my FrSky
Tx module back in the radio, and use the same direction finding techniques
as above. If I want more range or to pinpoint the direction more easily, I throw
a 12dB Yagi antenna on the Tx module. The Rx only draws about 30-40mA sitting idle
so a 160mAh lipo will power it for a couple hours above the low voltage cutoff.

With the addition of a telemetry display one can monitor the signal strength in real time to
evaluate your Tx and Rx antenna placement and orientations. See where there
are problem Rf areas at a given location. Monitor voltage from multiple
batteries, current to the motor, and so forth. I rarely ever need to look at
the display, but given a choice between a tricky slope landing and re-launch to
check something, versus a quick glance at the display, it should be obvious
which is the safer option.

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Last edited by Daemon; Dec 14, 2011 at 05:28 PM.
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