Hi I'm new here
I'm building a octocóptero I need this lift enough weight then I'm getting engines running at 6s 22.2 v battery with drive 2800 grams per axis, but I encounter a problem, the power module only supports 4s Battery 14.8 v with this the push each moto drastically low.
You could put no power module but not know if I'm about to run out of battery and you could end up in a terrible accident.
because of that the power module is imperative.
Can anyone give me an idea of what to do in this case?
Thanks in advance.
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FWIW I think Mauch has great products, both in quality and features. Their pricing is very reasonable.
As for eCalc, use with grain of salt. It's a nice tool but has issues at least when estimating for KDE motors. If planning on installing high dollar props, do yourself a favor and use cheap ones first to test.
That's my experience anyway.
hate to side track, but what are the pros and cons of KDE motors? and at what S are you running the ones you have?
I use 4S currently.
Starting with the cons:
1) price
2) collar on the shaft should be checked and tightened before initial assembly.
Pros:
1) over 200 hrs bearing life before maintenance. By comparison, TM recommends 60 hrs bearing maint. on the MN3110-470 kv
2) triple bearings
3) efficient, quiet and powerful (535w for 2814XF-515)
4) great customer service and technical support
5) high quality, well balanced from factory
I only have used 2814XF-515 motors (have 14 of them) so can't speak for the others. They are the most versatile motor I've used yet compared to other brands in this class and can spin 15" props without getting hot on 4S coaxial Y6. They can run on 6S, am planning to try it possibly on a 3DR X8 frame with 8 motors and 10" props.
On my test quad using 13" APC MR props, the copter is nearly silent.
thanks. interesting about the quiet.
To show how grossly wrong eCalc can be, below is a flight done on 2/17. It is overpowered as normally a 12000 mah battery is used, but the error is still prevalent. With 13" T-Motor props, current draw and throttle go even lower.
Per eCalc:
Actual throttle out:
Actual current draw:
This was written by renatoa, a member of RCG:
For any platform of any size and weight, the flight time is the result of:
time = whkg / (1000*R / eff_gw) * 60, where
whkg = battery energy density, in Watt hour / kg, ranging from about 150 for the high C packs to 270 for LiIons. 10C Multistars are 185.
R = ratio between AUW and battery weight
eff_gw = motor/prop efficiency, grams per Watt, taken from mfr data.
Be aware to get from table the efficiency for the intended thrust, and for 50% throttle !
Efficiency greatly depends on load, so don't use efficiency stated for 1kg, to compute flight time of 2-3 lg platform !
Also, don't use values for more than 60% throttle, the platform will be unstable, no more room for motors to do their control job....
As I wrote, this formula works for ANY size platform and energy source, lets do the math for some particular cases:
Case I Ph2
battery wh/kg = 5.2(Ah)*11.1V/0.37(kg) = 156wh/kg
R ratio between AUW and battery = 1250/370 = 3.4
propulsion efficiency = 11g/W
time = 156 / (1000*3.4 / 11) * 60 = 30 min
Case 2 the 129 min record
battery wh/kg = 266Wh/kg - typical LiIon energy density
R ratio between AUW and battery = 3.4/2 = 1.7
propulsion efficiency = 14.1g/W
time = 266 / (1000*1.7 / 14.1) * 60 = 132 min
And finally, my 30 min case
battery wh/kg = 165, I use a Zippy Compact, having a bit more energy than the average LiPo
R ratio between AUW and battery = 0.75/0.195 = 3.8
propulsion efficiency = 11g/W - using Phantom 2 clone
time = 165 / (1000*3.8 / 11) * 60 = 28 min
As you can see from the above, reasonable precision of all estimations, proving this formula is valid for any configuration, so now you have a tool that should tell you what is wrong in your setup, and where to work to improve flight time.
The biggest unknown for most users is the propulsion efficiency, for this reason I think is mandatory to not buy stuff without manufacturer precise specification of this parameter.
renatoa is offline Send a private message to renatoa Find More Posts by renatoa
I have used his formula and it comes within seconds of calculating actual flight times.
I have added a spreadsheet that will get you started...
Calc.xlsx
The equation might work for your ships, but caution on generalizing. Let me explain.
Case 1: R = 1.01 (it's nearly all battery) using LiIon & efficiency of 20
equation says = 316 minutes (new world record)
actual time = 0 as the ship can't lift the battery
Case 2: R = 10 (the battery is small) using LiIon & efficiency of 20
equation says = 32 minutes
actual time = probably less than 1 minute
The more general equation is quite a bit more complex, especially when trying to attain world records or designing a ship to exceed a specific flight duration. The equation needs to take into account:
- net lift efficiency (the grams the rotor system can lift after it lifts itself)
- the AUW (ship, battery, & payload)
- the voltage profile of the battery under a draw and especially how it draws down near the end
- how the voltage drop impacts net lift efficiency or watts to fly the ship (it's an inverse relationship)
- battery capacity at different voltage levels
- maximum lift at different voltage levels (when the ship can no longer stay in the air given the voltage)
Don't mean to be critical. Like I said, if you have an equation that seems to work for you, then your equation works. But, if you are curious about the worksheet that is used for the general case, let me know. i'll be happy to share it.
Also, the best net-lift efficiency numbers are ones you generate yourself.
Well, I'm not an engineer or a professional. I'm a hobbyist, and you are correct, the formula does work for me and through the application of that formula I have two aircraft that consistently fly well within the numbers it generated.
AUW is accounted for, and as we all know, most (if not all) manufacturer generated g/w numbers are crap.
As a case in point, I'm running Turnigy 4006 740Kv motors on my hex. Turnigy says for an aircraft weight of 3 kilos, I should be seeing a g/w of 9.2. In reality the number is closer to 8. I verified this by taking voltage and current numbers from the data flash logs, and the data said the g/w was closer to 8 than it was to 9.2. I also compared total current used to what my charger put back, and those numbers were consistently within +- 200mAh. And, just in case you are wondering, both of my power monitors were calibrated for voltage and current under load.
And finally, my initial point still stands, there is no way a stock 680 Pro can lift 30 Kilos.
If you wish to debate the accuracy of renatoa's formula I suggest you take that up with him.
You sound a bit offended by the constructive feedback offered by Forrest... No need for that. If you take offense that's your prerogative, but his response isn't only for your benefit and I for one appreciate his insight..he's not "debating" anything with you, thanks!
I am offended. I don't take lightly to someone who dreams up totally unrealistic "data" and tries to use it to insult my intelligence.
His R value examples were totally useless. Flight time is based on more than just R value. For example, what are the current capacities and voltages of these mythical power sources?
And his use of the phrase "The more general equation," implies that I and those who successfully use renatoa's equation are somehow inferior or not in the main stream.
A much better approach would have been for Mr. Frantz to have taken the time and effort to explain his chosen method and why he uses it. Unfortunately he chose to ridicule rather an to educate.
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