Tarot 650 PRO motor-config

Hello! I hope that I’ve posted this in the right thread!

I have a hexacopter built on a Tarot 680 PRO frame which have the followings specs:

Motors: 5010-350kv
ESCs: XT-Xinte 40A 3-6 Cell
Props: 1355 Carbonfiber
Battery: Limskey 4s LiPo 10400mAh 30c
Flight Controller: APM 2.8 with a M8N GPS

+Alot of other things…
APM power module, APM sound and light indicator, navigation leds, 915MHz Telematry link, Mini OSD, Ultrasonic sensor, FPV Camera, 3 axis gimbal for a gopro and a 48channel FPV transmitter.

All of this adding up to a weight of 3366g!

Now to my problem…
I’ve just upgraded my Tarot 680 pro’s motors, escs and props to these specs in hopes of a better flight time. The problem that im having as of right now is that I feel like I’m loosing power whilst flying. This while flying in “Atti Hold mode”, when I give full throttle I expect the copter to climb at resonable speed, however the copter then starts to decent slowly… (Almost resulting in crashes) Like there is not enough power in the motors. This makes me concerned that the motors are not strong enough to carry my craft. Could someone tell me if this hardware is good enough to carry my craft? Cause I’m not sure how to calculate it… Cause if the hardware is sufficient enough I suspect that there is some setting that I have done wrong on the flight controller.

The old setup had the following specs:
Motors: Readytosky RS 2212-920kv
ESCs: SIMONK 30A 2-4 Cell
Props: 1045 Black plastic

Same everything else!
This configuration resulted in approximately 10 minutes of flight.
Up until this day I have grounded my craft when the cells have reached a minimum of 3.8V, is this to low or could I go lower without damaging the battery?

Thank you for taking your time to read this!

Sincerely, Christopher

4S battery, KV350, 13x5.5 props, 3.8volts low voltage = bad choice

4S Batt, KV700, 13x5.5 props, 3.5volts low voltage (3.7 remaining), better choice…

or 6S and KV350…


Try ecalc.ch in the future to get an idea of a working setup.

Thank for your answer! I’m sorry, I cant seam to understand this! How do you calculate this? So what you are saying is that i probably should get a 6s battery instead? I would like to keep the 350kv motors! Is these calculations relating to my loss of power issue or to my question of minimum voltage on the battery?


Thank you! I’ve tried to use it, but I guess that I probably need a membership to get the calculations. However it’s worth it right? So I should be looking into getting a membership?


I just entered your config in to ecalc and it surprises me, that your copter is flying at all:

Here is the same setup with a 6s lipo:

IMNSHO eCalc is crap. I paid to use it and it was not even close to what I was seeing in the field.

Your power system is all wrong.

I have 5010-350Kv motors on a 662mm QUAD. I’m swinging 1655’s on 6s. Take off weight is 3315 grams. Flight time using 80% of battery capacity is 24 minutes.

I have a 680 Pro. 4006-740kv motors swinging 1355s on 2 5200mAh 4S Lipos (10400mAh total capacity) in parallel. Take off weight is 3248 grams. Flight time using 80% of the battery capacity is 18 minutes.

I tried using 5010-530Kv motors on 6S 10000mAh swinging 1355s, and the flight time increase (just under 2 minutes) did not justify the cost.

The point is, the 5010s need to be run with props between 15" and 17" on 6S, period, end of story.

Read this:

Note: This is NOT my work… Used by permission of renatoa on RCG
The attached spreadsheet with do the math for you…

I have used this for quite sometime and it has proven to be accurate to within seconds of real life performance.

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.
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Calculate Flight Time.zip (1.2 KB)

Here are the specifications for my 680 Pro:

AUW (g) 3248

Battery Capacity (mAh) 10400
Number of Cells 4
Battery Weight (g) 895
Battery Energy Density (Wh/kg) 171.9776536

Number of Motors 6
Hover Thrust per Motor (g) 541.3333333
Motor Eficiency (g/W) 8

Expected Flight Time 22.74679803 minutes
Flight Time with 20% Reserve 18.19743842 minutes
680 Pro Bare Weight (No LiPo) 2353 grams
Turnigy 4006-740Kv
13" x 5.5" CF Props
X-Rotor 40A OPTO ESCs
Pixhawk Flight Controller
915mHz Telemetry
FrSky X8R
Tarot ‘Small’ Retracts
SJ4000 ‘clone’ camera
2 Axis Gimbal w/8bit SBGC
Tattu 4S 10400 15C
Craft&Theory Telemetry
OLED Display

So then, here is the bottom line:
Unless you extend the motor arms you are stuck with using 13" props. With 13" props, using 6S is a waste of money. To get better flight time you need to find motors that will run on 4S and when swinging 13" props they will have a high g/w.


  1. Motor data charts are notoriously inaccurate because they do not accurately reflect real world performance. Bench testing anything never matches what happens “in the field.”
  2. There is no one solution that fits all configurations, and any one who says so should not be trusted.
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Would ecalc have told him, that his setup was far off and therefore saved him money, buying parts that do not match? Yes!

eCalc has always worked great for me, estimating my flight times to within 10%. You must give it good information or it will not give you good estimates. As count74 says it sure is better than wasting money guessing which motors will work.

A general rule of thumb is that
300KV motors are 6s
500KV is 4s
800KV is 3s

For an aerial photography rig.

Indeed. eCalc has predicted well for me from 600 size multirotors down to the tiny 130 3" I recently completed. GIGO would apply here.

Thank you! Those calculations are very useful! Oh that is not looking good at all… If I’m understanding this correctly, these calculations only apply for half of the crafts weight! Which would imply that my setup is very wrong! I draw the conclusion that I need new motors with a higher kv rating! I do however have a octoframe (Tarot X8 with a wheelbase of 1050mm), that I can donate these motors to if that is possible! I would be grateful if you would mind posting the calculations of a octocopter with the following specs:

Motors: 5010-350kv
ESCs: XT-Xinte 40A 3-6 Cell
Props: Tarot RC 1555 Foldable
Battery: 6s LiPo 10400mAh 30c
Weight (with battery): ~5kg

If that does not work, what type of battery do you recon would be suitable for this config?

Thanks in advance!

Thank you for taking your time explaning! I’m going to look into this equation! So if I change motors to ~750kv I could use the same props and battery? Cause that would be great! I have other crafts/future builds that I can donate the 350kv’s to! When you say 5010’s should run of a 6s does that apply for a motor with 750kv as well? Or could/should I get something like 4006-620kv instead of 5010-750kv?

Thank you, thats useful! I Will keep this in mind in the future!


I can’t speak for other brands, but stay away from the Tarot 4006-620Kv motors. I have 6 of the bloody things and they are crap. I got them in a bundle when I bought my 680 Pro. Every thing else was good but those motors just couldn’t cut the mustard.

The ironic thing the bundle shipped without the motors because they were on back order, so to get into the air I asked the guys at RCG what they recommended, and the answer was MultiStar 4006-740Kv.

I ordered a set and I got them in about a week. It was another month or so before the Tarot motor arrived so I had plenty of time to test the 740s. When I put the 620s on I knew right away they were not going to cut it.

The first thing I noticed was the hover throttle point was noticeably higher, and I was able to confirm this by using the Pixhawk data flash logs and making a comparison between the throttle PWM and total current draw for each set of motors. The 740s won hands down.

I have 4 5010-750Kv motors but I really haven’t put them to the test yet. My gut feeling is to use 4S unless you want to swing a prop longer than 13", and I’d be real cautious about using them with 6S…

This is the kind of crap I get from eCalc:


Here are the specs for my 680 Pro:

AUW (g) 3248

Battery Capacity (mAh) 10400
Number of Cells 4
Battery Weight (g) 895
Battery Energy Density (Wh/kg) 171.9776536

Number of Motors 6
Hover Thrust per Motor (g) 541.3333333
Motor Efficiency (g/W) 8

Expected Flight Time 22.74679803
Flight Time with 20% Reserve 18.19743842

680 Pro Bare Weight (No LiPo) 2353
Turnigy 4006-740Kv
13" x 5.5" CF Props
X-Rotor 40A OPTO ESCs
Pixhawk Flight Controller
915mHz Telemetry
FrSky X8R
Tarot ‘Small’ Retracts
SJ4000 ‘clone’ camera
2 Axis Gimbal w/8bit SBGC
Tattu 4S 10400 15C
Craft&Theory Telemetry
OLED Display

so, if eCalc is so good, how come it adds 2353 to 895 and comes up with an AUW of 5933? And how the frack does eCalc compute a hover flight time of 26 minutes when I’m only seeing 18 minutes actual in the field? And the next question is, where does eCalc come up with a g/w of 4.79 when I know the g/w is 8? How do I know this?

Well, I have my electrical system calibrated to with 1± 0.100 Ah (100 miliAh) REPEATABLE between current used and current charged FOR EVERY FLIGHT I HAVE EVER MADE WITH THIS AND 2 OTHER AIRCRAFT.

And, my actual hover flight times from take off to landing after a low battery failsafe triggered RTL are within a few seconds of the 80% used battery capacity predicted by renatoa’s formula. And finally, after motor disarm and battery disconnection, ALL individual cell voltages quickly recover to 3.7v+ .

So gentlemen that is why I believe eCalc is crap.

Here’s the challenge:

Take my specs, plug 'em into eCalc and see what you get, and then take the spreadsheet I posted earlier and see what you get. My money is on renatoa…

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You bad mouth eCal every chance you get yet you have made a common mistake using it. The battery weight is the PER Cell weight, not the weight of the whole battery. You have told eCalc your battery weights 3580g and that confuses the heck out of it.

Garbage in garbage out.

Something I haven’t seen anyone ask… How many amps are you using to hover?

The reason I ask this is, the amount of current (amps) you’re using to hover is THE number that gives you the real world efficiency of your ship. It combines everything- the actual total performance of all motors (not the advertised performance), the propeller performance, the PID tuning, and the weight of the entire ship including the battery.

This is why I always try to reduce the amps used to hover. You can do that by:

  • selecting the proper motors for the payload weight
  • matching motors with recommended props
  • balancing props
  • reducing weight
  • proper PID tuning


I’ve trusted your counsel for a long time and you hit the nail on the head. I went back and corrected the battery data, and now eCalc is well within the ball park.

Great. Under the covers eCalc does the same things that Renatoa’s calculations. So maybe eCalc can now add to your tool box. Cheers