Minimum Rx battery voltage warning - RC Groups
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Jul 07, 2017, 02:05 PM
What could possibly go wrong?
Question

Minimum Rx battery voltage warning


Hi, I'm using an Aurora 9X, Optima 9 and a 5-cell NiMH Rx. pack with Enerloop cells (2800mAh). The Tx using an Optima Rx and no other telemetry gear will show you the current Rx battery voltage, and you can set a warning point. Here's my question:
What would be a good voltage to use as a minimum for this Rx pack? As I understand it, it's called a 6V pack because each cell is nominally 1.2V, but really if it's charged you see closer to 1.5, giving well over 7V. When the cells drop to 1.2V you're really pretty close to needing to recharge. So I should set the practical minimum warning to higher than 6.0V, but what's right? I don't know if the warning now is set for a 4 or 5 cell pack. Granted you get a long time between recharges, but it'd be good to know when they're really due.

Also, my servos (5485HB) are rated for 4.8 to 6.0V... is this a *nominal* voltage, and we just interpret it as how many cells are in the pack, or does a fully charged 5-cell pack really warrant HV servos? Or put another way, is a 5-cell pack too hot for a standard 4.8 - 6V servo? Seems to me *actual* voltage of a charged up 5-cell pack is more like the ratings of an HV servo.

Finally, another recent post asked about resolution of Hitec digital servos and the reply noted that with a Spectra module, 7-series servos will have 2048 steps. How about 5-series servos like mine? And do you need Maxima Rx's to exploit higher than 1024 bits or can the Optima and/or Minima do higher res too? I'm not going to rush out and buy new gear to get more bits (I'm pretty happy with everything I've got esp. for the price) but I'm interested to know the spec. if anyone has it handy. Thanks in advance.
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Jul 07, 2017, 03:45 PM
Team Hitec, Customer Support
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I'd set the voltage alarm at 6 volts, this will give you plenty of headroom to land. 6.0v servos can handle a 6.0v receiver pack, it does not mean that 6.0v is their max limit. Our 6.0v rated servos can safely handle around 7.2 volts max.

Servo resolutions:

-Analog series: 512
-5XXX series: 1024
-7XXX series: 2048
-8XXX series: 4096
-9XXX series: 4096
-D series: 4096

Receiver resolutions:

-Optima/Minima series: 2048
-Maxima series: 4096

This is what the equipment is capable of operating at. However, what resolution you actually see will depend on what equipment you are using, for example if you use a 5XXX series servo with an Optima or Minima receiver you will always only see 1024 steps of movement out of the servo as this is the maximum resolution the servo is capable of. If you use a 8XXX/9XXX/D series servo with an Optima or Minima receiver, you will only see 2048 steps of movement out of the servo as this is the maximum resolution the receiver is capable of.

Similarly, if you use a 5XXX series servo with a Maxima receiver then you will only see 1024 steps of movement out of the servo as this is the maximum resolution the servo has to offer. The only way to see the Maxima receivers 4096 possible steps of resolution is to use a servo that can move the same number of steps.

Maxima series receivers are only compatible with digital servos, you cannot use an analog servo with them because the analog servo cannot handle the massive amounts of information being broadcasted to it by such a high speed receiver.
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Jul 11, 2017, 01:45 PM
What could possibly go wrong?
I missed this somehow, thanks for this. So as far as bit resolution, whichever is the lowest resolution device in your system is the limiting factor, as you explained. I would think for most people that 1024 bits is fine but it's nice to know what's what, it'd save buying hi-res servos then discovering your Rx. can't exploit them properly, for example. 6.0V sounds like a good warning level as you say, I noticed the Tx. defaulted to something like 6.5 I think, that's very conservative. I've only just recently got a "real" charger with intelligence, very educational as to battery behaviour.


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