MR60

Tiger motors-propellers combinations for an heavy lift octocopter

Hello all,

I have been doing quite a bit of analysis for what would be the best tiger motor model/propeller combination for improving my heavy lift octocopter.

I am sharing here an excel analysis sheet I made for that, as it may be useful to share this with the community.  The objective is to find the combination of tiger motor model/propeller size (propellers are assumed to be APC slow fly, I think they are the best ratio price/quality wise) to :

-to lift a 10 pounds octocopter

-Throttle close to 50% at hover point

-Have some amps/watt reserves on the motors and ESCs when throttle 100%

Fixed constraints for me : ESC 40 amps, Battery weight is asssumed to be 1130g, All Up weight including battery is 4850 g, propellers must be APC slow fly.

Here is the result of my the analysis in the excel sheet below (the file is also provided in annex). The calculation were made with the online eCalc tool for multicopters:

Conclusion : I will get the tiger motor model 3510 360Kv, with 6S battery and 14x4.7 propellers. It provides me all I wish for:

-good flight time duration : 18 minutes (for a heavy beast!)

-50% throttle at hover point

-All amps and wattage are well below the limits of the motors and ESCs.

Hope this would help others who are looking what would be best motor/prop combinations for their setup,

Accesorily and as a consequence, I must sell my current 3110-17 (700Kv) tiger motors to help me finance the acquisition of this other model (see picture above). They are like new (were purchased recently in june 2013) and they flew a total time of less than 50 minutes of use. I sell them in their original boxes with the original 6 mm tiger motor propeller mounts plus their carbon prop mounts. If interested, pm me. I am thinking for a price of 45 US\$ each (price of new is around 64 US\$ each).

Cheers,

Replies

•     Forest

Can i get a photo of your test stand.

• I would be interested in buying your Tiger Motors if they are still available...

Peter

klimon@equitableservices.com

• MR60

Shyam - Interesting build.

M2M distance: 100 cm

Props: 17x5.5 CF Props"

Motors: 5010-14 360kv RC Timer

ESC: Hobbywing Skywalker Quattro 20A 4 In 1 esc

Custom build CF Frame + 3D printed center mount (220 gms)

Total estimated net weight: 1.3 kgs

From the ESC, I'll assume 3S batteries?

For this discussion to explain the math, let's assume that All-Up-Weight (AUW) of the copter at take-off less rotor weight is 1 kg (so motors not included but the camera and batteries are or what ever the payload is).

o each motor needs to supply 250 (1000 / 4) grams of net-thrust (rotor thrust after lifting itself) to hover

o each motor needs to supply at a minimum 2X that or 500 grams net-thrust to provide adequate control in moderate winds.

So calculate the AUW less motor weight.  Divide by four for net-thrust hover.  Multiply by two for minimum net-thrust hover.

Then go to the tables and find your motor (or let's test one that looks good).  Somewhere in this thread is an attached worksheet call Thrust Tests.

So report back with net-hover and max thrust numbers.  It sounds like you are in about the same range as the X2 Black Momba.  Then we'll go from there.

• Thank you for sharing all this info! Hoping someone can help. I have a 3DR Y6 and am very much interested in extending its flight time. What would be a good motor and prop size combination for this? I was looking into the tiger motors but unfortunately I don't have much knowledge on the subject; any input would be greatly appreciated. Don't mind spending if the return is proportional.

Currently have 30 amp ESCs that will only do 3S. I don't mind replacing the ESCs if I must. Currently using a 3S 5800mah & 850kv motors and getting about 9 minutes. Props are 10x4.7 top and 11x4.7 bottom.

• MR60

One of my goals on this new X2 Black Momba is to see how far past 30 minutes I can fly.  So you will get a kick out of this.  Just checked actual flight weights (the system is built) and at the weight it would fly carrying between 12000 to 18000 mAh of battery, the best rotor is the ,,, da da ...

T-Motor MN3510-25 motor swinging the 15x5.5 RCTimer Heli Prop.

While I need more prop testing at lower levels, using the T-Motor appears to deliver about 3% more efficiency at X2 thrust levels, which is an additional minute.

The X2 hovers at 113 grams net thrust per motor.  Total thrust per motor carrying 18000 mAh times 2 for margin only comes to 390 grams.  So it would be well under anything close to running hot.

So thanks Hugues!  I owe you big time.  Need something milled or tested, let me know.

• MR60

Forrest, would you have the possibility to measure this for the X4112S 400KV motor ?:

At 22,2 Volts, the following, at full throttle:

Prop size     Full thr     Amps  thrust (grams)

 14*4.7 100% 19.7 2460 15*4 100% 13.3 2100 15x5 This comes from the published table of sunnysky and I would like to compare with reality 100% 17 2400
• MR60

Good news. I could finally make a link between simulation and reality. Forrest made real measurements that up to now I could not link to either the tiger tables nor the simulation tool I used. Thanks to the answer I got from the father of the eCalc tool in Switzerland, I can now explain the missing link and show that the data measured by Forrest in the excel for me are quasi identical to the simulated ones.

The missing link is the fact the eClac alone is useless to define a motor configuration. Indeed it does not say anything about thrust. You need to use the complimentary propCalc tool (see picture below) to check thrust and wattage (or amps). ONLY if these two tools give a green light (for a motor and prop combination), i.e. ok with the watts, ok with the thrust, ok with the RPM simulataneously in the two tools, then you can make a conclusion that the motor/prop combination will work.

For example, we made a mistake about the MN3510-360KV. I could not understand why everything seemed ok on eCalc, but then when effectively measured on the testbench it almost fried Forrest and his lab (I hope you have a fire insurance at least). I should also have used propCalc and I would have seen that 15x5,5 props exceed largely the maximum wattage of 330 watts of this motor (although it seemed fine on eCalc). Reversely, reducing the prop size in propCalc to get just at the 330 watts limit, gives me then a thrust value of around 1700grams which is exactly what Forrest measured on his testbench!

Another conclusion is that I could really well use the 3510 motor, but with maximum prop size of 15x4 (just at wattage limit).

Here the comparative pictures between Forrest's toasted measurements at 70+°C and propCalc :

• MR60

A promised, I give you hereunder the answers from the eCalc "father" on my questions about eCalc reliability measurements. I provide their statements in italic fonts :

-"eCalc does NEVER calculate thrust for intermediate throttle settings - only for full throttle."

This is important to know because i always used eCalc to look for a motor combination that gives about "50%" throttle and based on the AUW, the thrust at 50% is deduced. So this is incorrect (and explains why eCalc did not provide the expected results versus true measurements <- this is my interpretation)

-"When compairing Benchtests you have to compare at the same Voltage Level!"

This is important because by default eCalc selects an average voltage based on the number of cells. The guy from eCalc showed me where to correct this:

so if you comparing the tiger data, you have to manipulate the Voltage for Max (or Hover) to come up with the same voltage level in the corresponding calculation....

I asked him the question: "I also found this here where again it gives completely different results than eCalc : https://www.youtube.com/watch?v=ejA1xPvcJXE. It is a tiger MN4014-400KV tested with two sets of props (14x6 -> 2,585Kg thrust @18,9 A and 15x5->1,215Kg thrust @5,4A). Where is the catch ?"

-"...hard to make a statement based on this video. propCalc does calculate quite good thrust results but far off with the amps...???"

Here the guy refers to propCalc, different tool than eCalc that does provide Full thrust information (not at 50% throttle unfortunately). I di dnot know its existence, I will take a look. He showed me a comparison between propCalc and the MN4014-9 motor that is quite good indeed on thrust but totally off on amps.

He also showed me on two different motors : MN3117 (the one I have now) and MN4012-13 that eCalc was indeed quite close to the tiger motor tables on the amps and wattage (there is nothing that eCalc says about thrust, so this cannot be compared. PropCalc must be used instead). This by changing the voltage param as shown in picture above, to be at exactly 22,2V (for 6S).

hope this will help others to use/interpret better the results of eCalc and propCalc.

Anyway I'm still undecided about which |@@#{#{# motor to choose from. But now that I know for sure that we cannot use eCalc for thrust comparison and that tiger tables are maybe not so nonsense, I will redo a quick motor scan.

• MR60

Thx a lot Forrest for the results. It's great information.

to understand correctly the high voltage tab : column H "Thrust" show the measurements you got with 6 S ? Do the red numbers (in same column) mean that you capped the thrust value ?

Was the voltage 22,2 Volts for all measurement points ? (so I can derive amps)

I'm going now to compare your measured values with what eCalc generates and with the RC tiger tables so I could maybe determine the best comparative source for motors (eCalc or tiger tables or none).

I notice that thrust values range for all motors between 450 and 1500. Only the last thrust point (in red, column H) varies. How should I interpret this ?

Would there be a way for you to measure the thrust at a gross 50% throttle position (roughly define by the stick in mid position) and the 100% position (stick fully up) ? except if there is a way to link your data points to throttle % ?

You suggested earlier that the MN4012 400KV had a better efficiency based on rc tiger motor tables. Based on eCalc, with my AUW, this motor is not at all efficient  : eCalc give around 60% efficiency at hover, which I don't really believe. Would be interesting to test that if you have this motor.