Thread: Telemetry?
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Old 01-07-2017, 06:19 PM   #39 (permalink)
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Join Date: Jul 2012
Location: Austin, UT USA
Default FrSky Telemetry

To the OP - take a very close look at a Taranis X9DP. It has a form factor and switch layout very similar to your beloved 9303. If you were to go this route, here a shopping list I would start with:

Taranis X9DP - $200
Custom hydrodipped case - $45
XSR 16 channel Rx - $25
RPM + Dual Temperature sensor: - $20
6S Pack voltage sensor - $15

For around $300 you'll not only have a super bitchin' singularly unique powerhouse Taranis (each hydro-dipped case is unique), you'll have everything you need to record 2 temps (e.g. motor, battery, ESC,..), electrical RPM (from which both motor and rotor RPM are computed), total pack voltage, and most importantly (and pertinent to the current discussion), you'll also get the voltages of each and every LiPo cell in the system. Usefully, a: "lowest cell voltage" value is also reported. Note that all of FrSky's X-series receivers are 16-channel via the 1-wire SBUS connector - which is the simplest way to connect to the FBL and they all support FrSky's S.Port telemetry protocol. The XSR is the smallest and lightest (5g).

Every day is be kind to your LiPo day

It seems that if health of the LiPo is the primary concern, then the primary rule to follow is to: NEVER LET ANY CELL GET BELOW 3.0V. EVER! To me, this actually means to never let any cell get below 3.3V. But to do this we must measure each and every cell in the system. FrSky's SP-FLVS voltage sensor does just that and measures both the overall pack voltage (2S-6S), as well as the voltage of each and every cell in the pack. This telemetry data is reported back to the Taranis at a frequency = 3Hz. Additional FLVS sensors can be added to support additional multi-celled packs (but each sensor must be assigned a unique ID using the FrSky channel changer gizmo ($15), and you must be running OpenTX version 2.1.x or higher). With three FLVS sensors, you can (easily, cheaply and lightly) monitor every cell in a large model running 12S power (2 6S in series) and a 2S Rx.

Using telemetry for flight termination

With a Taranis and a model fitted with a FLVS voltage sensor and the RPM sensor, (but no current sensor), multiple alerts can be combined to provide all necessary ingredients for a practical flight termination procedure which is kind to your LiPos:
  1. COUNTDOWN TIMER: Conventional countdown timer that runs when the throttle channel output is > 0. This includes a voice bark at every minute followed by: "Ten", "Nine", etc final countdown barks at the end. The duration for this countdown timer would be manually adjusted using trial and error such that the battery ends up at say, 65% depleted (you chose this value). The pilot can ignore this alert and continue flying and will start getting nagged with warnings as the battery "runs out".
  2. BATTERY LOW: (Vave <~ 3.65V) - "You're battery is getting low!"
  3. BATTERY CRITICAL (Vcellmin < 3.3V) - "LAND NOW! You're nearly out of gas!"
  5. BATTERY TEMP HIGH (Tbatt > 120F) - "Battery is getting hot!"
  6. BATTERY OVERTEMP (Tbatt > 200F) - "LAND NOW! Battery overheating!"
  7. MOTOR TEMP HIGH (Tmotor > 120F) - "Motor is getting hot!"
  8. MOTOR OVERTEMP (Tmotor > 200F) - "LAND NOW! Motor is overheating!"

If the system does have a current sensor in addition to voltage, then additional useful parameters can indeed be computed: e.g. Instantaneous power (V*I) and total mAh consumed (a measure of energy). If the capacity of the battery is also known, then an additional useful parameter can be computed: "Estimated percent battery remaining". Additional voice alerts could be added to alert at user defined thresholds. Assuming you knew ahead of time exactly how much energy was actually in the battery to start with, then the "Estimated remaining" = "true remaining". But this is a very big assumption! But as long as the: "lowest cell voltage" is used and the threshold warning alerts heeded, any errors with "estimated" values will be harmless to the LiPos.

One other point worth mentioning; the current sensors are quite heavy. But do be sure to check out all the other cool telemetry sensors available. After using multiple Tarani for more than 3 years I can voice that FrSky quality is actually very good - and their stuff is unbelievable inexpensive! The only quality issues I've encountered are the switches on the X9D are somewhat cheesy. I'd look at the Horus and upcoming Q7X as well, but they got rid of a couple buttons that were near and dear to me

My $0.02

Yes I am a Taranis fanboy - (because IMO it is just that great - and get this - new hall effect gimbals for the X9D/X9DP are reportedly coming soon! )
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