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Sep 01, 2017, 11:02 AM
E sailplane thermal hack
So the operating V range of regular low voltage servo is
4.8-6v ,, range for HV is 6-8.2,,, so CLEARLY the HV servos have a WIDER operating range,, PLUS I'm quite sure the reduced speed and torque the HVs would experience at 5V wouldn't be a big deal. So to me at least it would seem the HV servos give a wider range of battery BEC options.
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Sep 01, 2017, 11:46 AM
NorCal Electric Soaring (NES)
SoaringDude's Avatar
I just looked on the MKS site and compared the rated operating voltage range for the DS6100 (4.8-5.0v) to the HV6100 (3.8-8.4v). So for those MKS servos yes, it looks like a better LOW voltage margin which is what we are talking about here for backup operation.

But you have to check each of the servos you are using. e.g. my DS-11 aileron non-HV servos are rated down to 3.5v op. voltage.

Personally I'd be a little nervous using any backup system unless I can verify that the plane can reliably work over the expected range of backup voltages.
Sep 01, 2017, 11:46 AM
solastagia
kcaldwel's Avatar
Thread OP
I just did a quick test with just the centre panel on, 4 servos, flaps on SBus.

At 3.64V into the diode, 3.23V at the Rx, everything works fine. The servos are a bit slow, but no issues, and pretty good servo power.

At 3.60V into the diode, 3.20V at the Rx, the right flap is delayed behind the left by about half a second. The other servos are normal. This may be an SBus artifact. The glider would likely still be flyable, but you'd want to be very careful with the flaps. A 1S cell would be pretty discharged by the time it got to 3.6V.

3.54V into the diode, 3.12V at the Rx seems to be the lower limit for my system (Airtronics servos). The left flap works, but the right doesn't. The tails servos still work, but are slow.

At 4.10V into the diode, the current draw jumps around from 0.18A to 0.24A. Moving the servos, it is very easy to get over 0.5A on a relatively slow updating display, with just 4 servos connected. I have some in-air current draw data, and it is pretty easy to get around 1A with 6 servos.

Kevin

Edit: I did a range check at 3.64V, 3.60V, and 3.54V. The range seemed undiminished. FrSky X4R SBus with a FrSky SBus to PWM converter in the wing to Airtronics digital servos.
Last edited by kcaldwel; Sep 01, 2017 at 11:53 AM.
Sep 01, 2017, 11:51 AM
NorCal Electric Soaring (NES)
SoaringDude's Avatar
Kevin, good info. What servos are in your wing and fuse?
Sep 01, 2017, 12:10 PM
solastagia
kcaldwel's Avatar
Thread OP
Quote:
Originally Posted by SoaringDude
Kevin, good info. What servos are in your wing and fuse?
Hard questions! I'm pretty sure the wing servos are Airtronics 94761 digitals. I forgot the tail servos are actually MKS 6100s.

I haven't done as detailed a test on my other airplanes with 1S back-up, just drained the cell down to 3.6V or so to see if they worked. They have MKS and JR digitals in them, which worked fine. No SBus converter on those airplanes

One thing I forgot to mention is my FrSky voltage telemetry only works down to 3.5V, and then it just stays there.

There is a 1g 5V regulator available now that will put out up to 1.5A, if anyone wants to use a 2S LiPo for back-up with regular servos. You could set the BEC for 5.5V, which would be about 5.1 after the diode, and if you got a voltage drop to below 4.7V at the Rx trigger a battery alarm:

https://www.rcgroups.com/forums/show...for-2S-back-up

Kevin
Sep 01, 2017, 01:04 PM
Oleg Golovidov
olgol's Avatar
Kevin, can you test your fuselage servos without the wing?
MKS6100

The specs say 4.8-5.0 V operating range, but they work fine above 5.0 V (I have done it myself by accident, and heard from other people too), and they certainly work well down to at least 3.5V and probably lower (used in hand launch planes). Kevin's test went down to 3.12 V and they still worked.
Sep 01, 2017, 01:19 PM
solastagia
kcaldwel's Avatar
Thread OP
I tested just the MKS 6100 tail servos. They are in the fin of my e-Xplorer, at the end of maybe 800mm (?) of 24g wire, so there will be some voltage drop there as well. The FrSky X4R works down lower than the servos it appears.

3.5V into diode, 3.12V at Rx measured with multimeter -servos work.
3.48V into diode, 3.11V at Rx - works, rudder quite slow
3.45V into diode, rudder servo quits, elevator still works, 3.08V at Rx
3.40V into diode, both servos quit forgot to measure the Rx voltage, probably about 3.04V or so.

Kevin
Sep 01, 2017, 01:31 PM
Oleg Golovidov
olgol's Avatar
Thanks!

3.15-3.20V at the receiver looks like the minimum safe voltage.

allowing 0.4V for the diode voltage drop, 3.6V battery voltage is safe.
3.6V is on the order of 50% charge level or less (?) for a LiPo.
Sep 01, 2017, 02:08 PM
NorCal Electric Soaring (NES)
SoaringDude's Avatar
I just ordered the 1S HV 220mAh cells and discovered while talking to Randy at RCDude.com that Hyperion came out with a tiny step-up 2g regulator (link) designed for 1S Lipos and generates 5.0v @ 2A. That is, the input voltage range is 3.0~4.2v. This eliminates the worry of low voltage servo and RX issues. It also makes a single smaller 1S lipo more usable since the full capacity of the cell is available i.e. no diode between the 1S cell and the reg*. I bought one and will test it soon.
* You still need diodes between the BEC and RX, and between the reg and RX.
The downside is that the regulator has a small standby current (<5mA) so the lipo 1S cell will have to be topped off more often. But I think that is more than a fair tradeoff for getting a solid 5.0v out.
Sep 01, 2017, 03:22 PM
Adam
xStatiCa's Avatar
I do not recommend using a Turnigy 1s round cell for this use. In my discharge tests, they drop voltage more than any regular rectangular LiPo cell. The round cells work great for DLGs that have low amp usage but for larger stuff I wouldn't use one even for backup.
Sep 01, 2017, 04:56 PM
solastagia
kcaldwel's Avatar
Thread OP
Quote:
Originally Posted by SoaringDude
I just ordered the 1S HV 220mAh cells and discovered while talking to Randy at RCDude.com that Hyperion came out with a tiny step-up 2g regulator (link) designed for 1S Lipos and generates 5.0v @ 2A. That is, the input voltage range is 3.0~4.2v. This eliminates the worry of low voltage servo and RX issues. It also makes a single smaller 1S lipo more usable since the full capacity of the cell is available i.e. no diode between the 1S cell and the reg*. I bought one and will test it soon.
* You still need diodes between the BEC and RX, and between the reg and RX.
The downside is that the regulator has a small standby current (<5mA) so the lipo 1S cell will have to be topped off more often. But I think that is more than a fair tradeoff for getting a solid 5.0v out.
Looked on eBay, and they have the 2A step-up regs, 5 for $4 or $1 each:

http://www.ebay.com/itm/5pcs-Regulat.../201756204986?

http://www.ebay.ca/itm/Regulator-2A-...sAAOSwo4pYWfVf

Supposedly less that 80uA static current.

Kevin
Sep 01, 2017, 05:25 PM
NorCal Electric Soaring (NES)
SoaringDude's Avatar
All from China. Found other eBay listings too. I'll order some and test them too and let the best step-up board win.
Sep 01, 2017, 11:52 PM
Registered User
Aaro's Avatar
These can be "noisy". Keep away from rx/servo wires, and make the range test.

Aaro


Quote:
Originally Posted by SoaringDude
All from China. Found other eBay listings too. I'll order some and test them too and let the best step-up board win.
Sep 03, 2017, 05:52 PM
solastagia
kcaldwel's Avatar
Thread OP
There is an alternative to the Schottky diodes that has a much lower forward voltage drop of about 0.026V at 8A, compared to about 0.4V for the Schottky. They are more expensive, and you need two of them to make an ORing device. They are a more complicated device, so I suppose the failure rate will be higher. The low voltage drop would give more margin with a 1S back-up:

https://www.digikey.ca/product-detai...8-1-ND/3911155

ORing data sheet:

http://www.ti.com/lit/an/snva699/snva699.pdf

If anyone finds a low cost source for these, let us know. I guess ideally you would set them up in a redundant configuration, but that would take 4 of them. I suppose the odds of both of them failing simultaneously and taking out both power sources is pretty low.

Kevin
Sep 03, 2017, 11:52 PM
Westranm's Avatar
Kevin,

Thanks for sharing. That looks very interesting.

-Randy


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