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Old Feb 05, 2012, 05:03 PM
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Italy, Sicily, Palermo
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Wich is safier and reliable...a DX8 or a GRAUPNER HOTT MX 16 OR 20 ?

I already have a DX6 i a DX7 i and a Futaba 9CA with also an ASSAM module and receivers ( excellent )
Never had a single problem with them or their receivers....But is time now to buy a new one with TELEMETRY.....Maybe a DX8 ( BUT THEY SOLVE THEIR ISSUES ? ) or maybe THE NEW HOTT GRAUPNER MX 16 OR 20...I heard very good reviews about it....
Any suggestions ?
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Old Feb 06, 2012, 02:53 AM
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Romania, Dolj, Craiova
Joined Sep 2007
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If you want telemetry at the price of a single receiver of your two choices above, plug a Frsky in your 9C and be happy. This is the winning solution !
If you are not convinced there could be something so good and so cheap, check the other threads about Frsky.
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Old Feb 06, 2012, 03:40 PM
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Sverige, Värmlands Län, Filipstad
Joined Jan 2009
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Hi,

Two of my flying buddies use Graupner MX-16 Hott and they are happy with the radios.
I believe world champion in F3B Martin Herrig use Graupner MX-20 Hott so it can not be that bad.
http://www.graupner.de/de/newsdetail...6-dd586258e2fd

I have not a clue if any difference between US and European MX-xx Hott radios.

/Bo
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Old Feb 06, 2012, 06:19 PM
Air, Ground & Water
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Canada, ON, Rockland
Joined Aug 2008
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What issues are you reffering to for the DX8 that's got you worried? Nothing preventing me from flying with my DX8 and enjoying every second it's on..
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Old Feb 06, 2012, 10:42 PM
"Unnecessary Necessity"
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Canada, BC, Vancouver
Joined Sep 2006
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If the OP is in Europe, Graupner HOTT or Multiplex makes more sense but not if in the US. Since he already has DX6i and DX7 he might as well stay with Spektrum(at least they have good service around here)
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Old Feb 07, 2012, 02:44 AM
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ande:

if the OP is in USA ....Airtronics make sense..but not if in Europe.

... me like SD10g too much ... over Hott (i dont need telemetry)

(im from europe)
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Old Feb 07, 2012, 05:48 AM
Danish? Don't U eat that??
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Denmark
Joined Jan 2008
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No problem with getting Airtronics in europe; it's just labelled Sanwa - and they seem fairly priceworthy in comparison to me; just never were many buyers.....don't know why.
The only thing I could imagine would be either the fact that so few already have them here(low chance of help from colleagues), and maybe the risc of poor support; but as i see it the possibilities for support in europe are no different for sanwa/airtronics than for Hitec,Futaba, JR or spektrum; haven't really heard anything about Sanwa support (good or bad) though.....again, not many sold here.....

The RDS8000 was tempting to me for a while due to a very low price tag at a specific dealer, but the dealer ran out before I got myself worked up to ordering. Would look for something with telemetry now though, if i at some time had to get a 2.4GHz transmitter - I currently fly an MX16s(35MHz) and am extremely pleased with it(very good structure in the SW), but have no experience with Hott.
Lindinger.at has the SD10G on sale currently by the way.....about 350euro delivered i believe.....not a half bad price....
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Old Feb 07, 2012, 02:47 PM
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Germany
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As I see it, Spektrum does not even offer a module able of determining the capacity that was used during flight. Without this feature, telemetry is practically worthless when one wants to monitor flight packs.

I would chose Hott therefore, If I were into electric flight.
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Old Feb 07, 2012, 02:53 PM
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Canada, ON, Rockland
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I have telemetry on 3 of my electric planes and all 3 I monitor the main pack voltage and it's not worthless to me infact extremely usefull.

If you find it worthless for you then so be it, you are entitle to your opinion.
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Old Feb 08, 2012, 10:40 AM
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Germany
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The voltage alone says nothing about the state of charge of a battery.

In my opinion, the voltage is far too variable and therefore not a good indicator for the remaining or used battery capacity.

A new or warm pack has less voltage sag, a cold or older pack more. If you work with full throttle, the voltage sag will be more, and less when one floats around at low power. Look at any discharge diagram, and you will see how different the voltage levels are depending on the current used.
If one uses more power, a voltage-based warning will kick in too early, and too late, should one only use minimum power.

When there is still 20% capacity left in the battery, the discharge curve is still pretty level, so that there is no reliable way to judge the remaining capacity by voltage alone.
This insight lead to the development of capacity telemetry sensors, which make the lifes of electric pilots who use them much easier.

With my Jeti system, since 2008 I use sensors that do precisely this. When the capacity I programmed an alarm to has left the pack, a beeper goes off in my TX, and I know it is time to land.
For my 2200mAh packs, I set the alarm to 1800mAh. This way, I use exactly 80% of the capacity, and I still have energy left for some restarts.
Electric flying is so much more fun since I have telemetry. No more guessing or worrying, now I KNOW.

I have attached the first best discharge diagram I found on google. Let's say the capacity is around 3.8Ah, then one should stop at ~3Ah. At 3Ah, the voltages go, depending on the current, from 3.4-3.7V. Which would be the level to program for a warning? I don't know, since I cannot foresee If I will go full throttle, half throttle, or almost idle when I hit the 80% mark.
The capacity warning will always trigger reliably at 3Ah when I programmed it that way, and is therefore more reliable, easier to program without guessing, and generally more straightforward.

Voltage-only based telemetry systems are better than nothing of course. One could program an alarm level of, say, 3.3V, and be alarmed shortly before one falls from the sky with a dead pack. But this brings the pack way beyond the 80% level. Why bother with mediocre telemetry approaches, when much better and backed-by-reality systems are on the market?
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Old Feb 08, 2012, 11:29 AM
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And are you able to get 1800mAh from 2200 packs when outside is below 5C ?!
No need to confirm, because I know you can't.
I worked some time in OSD designing and the whole team members, mostly Polish, which is also a somewhat cold nordic country, as Germany, we agreed that counting mAh in lower temperatures is useless, even dangerous to rely on this.
Conversely, the pack voltage, but only when motor is cut, so no load, is always spot on for any pack brand and capacity.
No load on pack make the above graphs voltage variations under different load without meaning, the voltage under no load is always a chemistry thing and shows extremely precise the % of jiuce left in pack.
And, don't forget... the low voltage is the danger for lipos, not other criterias.
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Old Feb 08, 2012, 02:57 PM
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Canada, ON, Rockland
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Using voltage for telemetry works very well for me and has for the past many years and why I will continue to rely on this method as my main source for monitoring my packs. When the current sensors come out if they do then it might be something I will consider but it will be for the simple reason of having another aspect of my flying to monitor.

After several testing I am able to set my alarms at a setting where and when I land the resting voltage is exactly where I want it to be. I fail to see where this would be a fatal method to use for monitoring.

You are entitle to your opinion and also entitle to request such sensor and what ever but there is no need to claim voltage sensing to not be good.

There is plenty talk of this sort in the lipo section and will leave it at that.
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Old Feb 08, 2012, 06:06 PM
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United Kingdom, England, Kent
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Quote:
Originally Posted by RENATOA View Post
And are you able to get 1800mAh from 2200 packs when outside is below 5C ?!
No need to confirm, because I know you can't.
I worked some time in OSD designing and the whole team members, mostly Polish, which is also a somewhat cold nordic country, as Germany, we agreed that counting mAh in lower temperatures is useless, even dangerous to rely on this.
Conversely, the pack voltage, but only when motor is cut, so no load, is always spot on for any pack brand and capacity.
No load on pack make the above graphs voltage variations under different load without meaning, the voltage under no load is always a chemistry thing and shows extremely precise the % of jiuce left in pack.
And, don't forget... the low voltage is the danger for lipos, not other criterias.
I totally agree. This mA counting rubbish that is talked about with alarming regularity on modelling forums is one day going to prove extremely dangerous. Voltage is the ONLY true way to determine the state of a functional battery.

Temperature alone is one factor that can give misleading capacity when Ma counting. Also as batteries age their capacity falls, so what happens then. Forget mA counting, it's a waste of time and effort.
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Old Feb 10, 2012, 12:17 PM
Proud to eat Kraut ;-)
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Germany
Joined Dec 2003
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Quote:
And are you able to get 1800mAh from 2200 packs when outside is below 5C ?!
Of course! I always make sure to bring my packs up to the right temperature for takeoff. Additionally, I make sure that the cooling of the packs is reduced when it is cold outside, for example by putting tape over some or all cooling air inlets.

Allow me to interpose, that cold lipos also have a reduced voltage, so you have to readjust the voltage warning level as well.

What do I hear about resting voltage all the time? How do you check it? Do you have to cut throttle and look at a screen?
I cannot imagine how an automated alarm for resting voltage would work.

I for one would hate having to avert the eyes from the plane every minute or so, because I have to read a display. Is that how your voltage system works? How do you achieve "no load" on the batterys? Do you have a separate power source for the servos and RX?
How do you check resting voltage on a helicopter? Doing autorotation blindly while checking the TX display is surely an interesting challenge...

So am I correct then that, because you rely on resting voltage, which is always higher than voltage under load, you cannot use voltage under load to determine battery capacity? In this case, this would make an automated alarm impossible, or you would have to tie it to the trottle stick somehow, that the alarm is only activated when there is no throttle. This would be dangerous, as the alarm would be switched off when one flies regularly. I for one prefer an automated alarm, as I know that humans are not infallible. I do not want that I always have to remember checking the voltage during flight. I take of, fly without worries, and think about landing when my capacity alarm goes off. It is that simple. And it never misfired since 2008.

Quote:
Forget mA counting, it's a waste of time and effort.
Strange. Of all those people, who actually own sensors capable of both checking voltage and capacity, all use capacity as the primary warning parameter.
And of all people, who argue against capacity metering, I don't know a single one having actually tried it.

Nothing is as useful for determining the capacity as capacity itself.
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