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

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
Xpress..'s Avatar
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.
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.
Jul 25, 2017, 05:55 AM
Registered User
the_crack_fox's Avatar
Keep in mind, if you're flying flybarless helis, many modern gyros will output very high resolution, even if your tx/rx doesn't. So the hi-res servos might be more useful than you think.
Jul 25, 2017, 06:27 AM
What could possibly go wrong?
Thank you, that's a good piece of info, I don't fly any choppers but it's an insight into the equipment. Would anyone know what resolution the Hitec 3-axis gyro can do? I was considering one of these for fixed wing, but it's only out of curiosity. Bit resolution isn't the only reason to choose up-market servos, quality is always nice to have and the 7- and higher series are Hitec's high performance range.
Jul 25, 2017, 06:44 AM
Registered User
the_crack_fox's Avatar
I'm using 8330's with a 3digi FBL gyro, A9x and optimaD receiver. The 3digi outputs 2800 steps, almost 11 bit resolution. The servos are super slick in operation. When setting up on the bench you can see and hear how nice they move.

I also have a set of 5565's in an old raptor 50. They move like arthritic old men in comparison.
Jul 25, 2017, 06:53 AM
What could possibly go wrong?
That's interesting, the other issue is whether the servos themselves have the angular pitch fine enough to divide the arc of travel into 12 bits worth of resolution. I'd really like to get some 7 series but I really have zero budget right now, very difficult season with little to no work, but I'm planning it ASAP as an upgrade. I think the A9X has gotta be one of the most under-rated Tx's out there for the price... it's a pity Model Engines / World Hobbies is gone, I got all my Hitec stuff as a package deal at an amazing price that never rose in almost 2 years until they shut down. Fantastic deal.
Aug 18, 2017, 10:14 AM
What could possibly go wrong?
I had never looked into the newer D-series 32-bit processor servos, actually they do seem interesting. You get the 12-bit (4096-step) output resolution, and the prices are much lower than any I've seen for 7-, 8- and 9-series servos. Next time I need some good standard sized servos, I'll probably go for these. They're available with good torque and speed, reasonably priced and with the high resolution. I'm sure it's a subtle difference, but I've met some advanced pilots who tell me that when you get to a certain point and you're using performance models, high-accuracy servos make a difference you will notice.
Aug 18, 2017, 04:55 PM
Xpress..'s Avatar
Originally Posted by BernardW
I've met some advanced pilots who tell me that when you get to a certain point and you're using performance models, high-accuracy servos make a difference you will notice.
You absolutely will, but it depends on the model. It's generally airplanes with large control surfaces where you will notice a difference between a mid grade servo and a high grade servo.

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