After watching the FliteTest episode called "Viewer Request Speed Challenge" I decided I was going to scratchbuild my own "FT Versa Wing" and use the same power plant the FliteTest crew used to get into the triple digit speeds of over 100mph. From the episode I know that they used the "NTM Prop Drive 35-36A 1800Kv / 875w" motor from HobbyKing with an 8x8 prop. What is hard to discern from the episode is what type of battery and speed controller they used. I also know from the video that using an 8x8 prop with the setup they used was not the most responsible thing to do. At the end of the show you see when David's plane bursts into flames... LOL
Next I set out to research the "NTM Prop Drive 35-36A 1800Kv / 875w" motor and I found that even though people were saying very good things about it, there was not a lot of information out there on prop sizes and battery combinations. Even the HobbyKing website says "Prop data coming soon".
I tested the motor with different props ranging from 7x6 to 8x6 using a 4 cell battery and from 8x4 to 9x7.5 using a 3 cell. I thought it might be helpful to post the results for anyone who is thinking about getting this motor. For the testing I am using the "HK-010 Power Analyzer" from HobbyKing. For a speed controller I am using the "Turnigy Brushless ESC 85A w/ 5A SBEC" also from HobbyKing. For batteries I used both a 4 cell "Turnigy nano-tech 2200mah 4S 45~90C" and a 3 cell "Turnigy nano-tech 2700mah 3S 65~130C". Every test was performed using a freshly charged battery and as you can see from the pictures I used my "Spektrum DX8" transmitter and a "Spektrum AR6115e" 6 channel park flyer receiver. Everything is bolted down to a 2 x 4 piece of wood and then I clamped the entire rig down to my work bench. For safety I also put on safety rated glasses when I do these prop tests. ( I always wear safety glasses when I do these prop tests and you should too. Safey first! )
Keep in mind that the "HK-010 Power Analyzer" I am using has a max current rating of 100amps. As you can see from the results below I maxed out the current using a 4 cell battery and an 8x6 prop. Even though this is way above the 65amp max rating on the motor I thought I would test it because I found a few posts where people claim they are using this size prop on a 4 cell.
Last but not least I also found a few YouTube videos of people using this motor with a 6 cell battery and small 5.5 x 4.5 props to get 150mph speeds on the HobbyKing "Rad Jet 800". Needless to say I will be ordering some 6 cell batteries very soon. Once I get them I will update this article and post the results using the 6 cells batteries as well. I will post links to YouTube videos I found below as well.
4 Cell Battery
7x6 APC prop = 78 amps / 1170 watts
8x4 APC prop = 80.5 amps / 1187 watts
8x6 APC prop = 100 amps (maxed out) / 1446 watts
3 Cell Battery
8x4 APC prop = 55 amps / 663 watts
8x6 APC prop = 72 amps / 804 watts
8x8 APC prop = 85 amps / 945 watts
9x6 APC prop = 86 amps / 960 watts
9x7.5 APC prop = 97 amps / 1056 watts
Video links I found on YouTube of this motor with a 6 cell setup using small 5.5 x 4.5 props:
http://www.youtube.com/watch?v=B85pvUKu5GE
http://www.youtube.com/watch?v=oXyNNqI2Hxk
http://www.youtube.com/watch?v=_tXda2pT-xY
Well I hope that someone who is planning on purchasing the "NTM Prop Drive 35-36A 1800Kv / 875w" finds this information useful. Like I mentioned before, once I get the 6 cell batteries I will update this article with prop testing data for those batteries as well. I am also planning on posting an article/video of my scratchbuilt "FT Versa Wing" running the motor and batteries listed in this article. Stay tunned for that...
Rock ON!
fretsman
Some close up pictures of my testing rig:
"NTM Prop Drive 35-36A 1800Kv "
Specs:
Model: NTM Prop Drive 35-36A 1800
Kv: 1800rpm/v
Max current: 65A
Max Power: 700W @ 12v (3S) / 875W @ 15v (4S)
Shaft: 4mm
Weight: 120g
ESC: 70A
Cell count: 3s~4s Lipoly
Bolt holes: 18.9mm & 25mm
Bolt thread: M3
Connection: 3.5mm Bullet-connector
"Turnigy Brushless ESC 85A w/ 5A SBEC" and the "Spektrum AR6115e" 6 channel park flyer receiver.
4 cell "Turnigy nano-tech 2200mah 4S 45~90C" and the 3 cell "Turnigy nano-tech 2700mah 3S 65~130C".
Build thread with plans: http://spadworld.net/forum/viewtopic.php?t=18927
FLight video: http://www.youtube.com/watch?v=UjPKJZOAs1w&list=UUGbBDqVw5EwCQBLE4fbqGhw&feature=share&index=7
The best prop I found on 4S that didn't draw too much power from the motor was an APC 7x5. It flies around 100mph (calculated) with unlimited vertical and a nice "happy prop" sound. :-) You can sort of see in my build thread how I added a heatsink to the Turnigy Plush 60A ESC.
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I remember you posted on my forum post about this motor. I also saw your video of the delta wing. Awesome... Great plane and nice build...
Rock ON!
fretsman
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To answer your question.... I only ran the props for about 15 seconds at full throttle then backed of slowly so even when I recorded very high numbers neither the motor nor the ESC got very hot at all.
That being said I can tell you from actual flight testing what combination I have found works best for me. I put this motor on my new scratch built FT Viggen and I have been flying it with two different setups. On both setups the motor and the ESC only get warm to the touch.Using the 4 cell setup the motor does get a bit warmer but it is still what I would consider safe. Setup details are below...
3 cell setup = Turnigy nano-tech 2700mah 3S 65~130C with an APC 8 x 4 prop
4 cell setup = Turnigy nano-tech 2200mah 4S 45~90C with an APC 7 x 6 prop
Since the 4 cell setup does result in the motor getting a bit warmer I would consider running it using an APC 7 x 5 prop instead of the 7 x 6. I did not test with a 7 x 5 prop yet but from Team Monkeys post below it looks like that just may be the sweet spot for a 4 cell and this motor. I will try one next time I fly and post results here.
Rock ON!
fretsman
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Thanks in advance for any clarity.
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First let me say that I am no expert by any means. What knowledge I do have has been learned over the past several months by doing a lot of reading, Google searches, forum posting and of course the FliteTest crew and community. I just got back into this hobby about six months ago after about 15 years. Back then it was all gas and nitro so "electric" is kind of new to me.
That being said I will try to answer your question. I also welcome feedback and input from other readers as well. After all this is a learning process and having an open discussion is the best way to learn and share ideas.
In your post you mention that you have always assumed that the max-amp rating given by the manufacturer was something that could not be exceeded without potential consequences. You also ask how it would be possible, given my results, to achieve the exact manufacturer rating of 700W @ 12v (3S) or 875W @ 15v (4S).
From what I have learned the manufacturer rating of the motor is a number they give you to let you know what they consider to be the safe limit and optimal power level for the motor. It also lets you know that if you decide to take the chance and run it at higher power levels it is at your own risk. In other words, if you run it higher than what they recommend and the motor burst into flames it is now your problem, not theirs.
The ability of the motor to safely run at higher power levels than the manufacturer rating is dependent on many factors. Some of which are air flow (is the motor and ESC getting good ventilation), ambient temperature (is it a cool winter day, or is it blistering hot like it gets where I live, South Florida), the battery discharge rating or "C" rating (can the battery deliver the amount of power the motor is asking for), last but not least the quality of the parts (motor, ESC and battery). All these factor will determine how "hot" your electronics will get and heat is what can kill them.
As you can see the most important factor here is heat. Heat is your enemy. For example even if your setup gives you numbers below the manufacturer rating if you do not have enough ventilation flowing over the ESC and the motor you still run the risk that they will burst into flames. On the other hand if your setup is producing numbers that are higher than the manufacturer rating but you provide plenty of ventilation and it is also a cool winters day then you should not have a problem. Unless of course you run numbers so high that even good ventilation is not enough to keep the motor and/or the ESC from overheating.
As far as the second part of your question, "how do you get to the Max Power", keep in mind that the power output is constantly changing and even when you do get the exact "max power output" it does not stay constant for very long. What I mean by this is that when you have a battery that is fully charged the second you open up the throttle and spin up the motor the voltage of your battery starts to decrease. As the voltage of your battery decreases the power output of the motor also decreases. Another factor to think about is prop resistance. When you are holding onto your plane on the ground and you spin up the motor it has to work a little harder to spin the prop than it would if the plane was up the the air in flight. So the numbers you get on the ground while holding the plane are usually a bit higher than when the plane is flying in the air. When on the ground while holding the plane you get 70 amps at 720 watts then you can assume that in flight those numbers will drop to around 65 amps at 700 watts. Still keep in mind that those numbers will never be constant for long because the voltage of your battery is always changing.
To sum this all up I think the best way to think about the "manufacturer rating" is that they are giving you a ball park number that you should try to stay as close too as possible. Whether you decide to exceed those numbers or not you still need to make sure that the electronics do not overheat because in the end it is not amps or watts that kill your electronics, it is heat produced by the electricity that will damage them. More amp/watts means more heat = taking off as a plane and landing as a ball of flames... lol
I hope that my long winded reply can shed a little clarity on this subject for you and as I mentioned at the start of this I welcome any input from other readers as well.
Rock ON!
fretsman
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Rock ON!
fretsman
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