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Old Aug 03, 2012, 09:29 PM
Koo
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Maiden with my Radjet 800!

Was running a 4s 45C nano-tech with a 1250kv 600watt motor. Apparently I didn't get enough rmps with the 4.75x4.75x prop I was using and stalled right after the launch. My bixler with stock setup gets more thrust than this with the 4s at full throttle ^^

If anyone has any recommendations for a good motor (under $20) and maybe a better prop I'd love to hear them
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Old Aug 04, 2012, 02:10 AM
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Sounds like a heavy setup that's way, way underpropped. Do you have a wattmeter to check the current and power? My guess would be that you want at least a 6 or 7" prop on four cells with that motor to get any reasonable amount of power out of it, but you need to be able to monitor the motor's current draw to avoid burning it out while maximizing performance.

Personally, I'd run a TowerPro 2415-7T 3850Kv heli motor on 3S with a 5x5 prop. The motor is six bucks and worth every penny. If you want to run a 4S pack, I'd go with a Suppo 2217-6 1500Kv outrunner swinging a 6x5.

Also, if you're running a 100% bone-stock Bixler on four cells, you're lucky nothing has smoked yet. Its setup was designed for 3S operation; 4S will result in greatly increased current draw.
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Old Aug 04, 2012, 05:17 PM
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Yeah thats a really low rpm motor with a really small prop isn't it?
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Old Aug 04, 2012, 05:39 PM
Koo
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Quote:
Originally Posted by C₄H₁₀ View Post
Sounds like a heavy setup that's way, way underpropped. Do you have a wattmeter to check the current and power? My guess would be that you want at least a 6 or 7" prop on four cells with that motor to get any reasonable amount of power out of it, but you need to be able to monitor the motor's current draw to avoid burning it out while maximizing performance.

Personally, I'd run a TowerPro 2415-7T 3850Kv heli motor on 3S with a 5x5 prop. The motor is six bucks and worth every penny. If you want to run a 4S pack, I'd go with a Suppo 2217-6 1500Kv outrunner swinging a 6x5.

Also, if you're running a 100% bone-stock Bixler on four cells, you're lucky nothing has smoked yet. Its setup was designed for 3S operation; 4S will result in greatly increased current draw.
Thank you a lot. I ordered a 2200kv turnigy motor from HK for $9 from their USA warehouse after seeing a lot of people use the same motor with their 4s setup. And sorry if I confused you, I use the bixler only with a 3s battery so thats why nothing has burned yet.

Also, I currently only have 4.75x4.75, 6x4, and 9x7 props so which one do you suggest with the new 2200kv turnigy motor?
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Old Aug 04, 2012, 06:59 PM
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Which 2200Kv motor is it? A link would help. The Kv value alone says nothing about size, weight, performance, power, or anything else.

Are you planning to run it with the 4S battery?
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Old Aug 04, 2012, 09:07 PM
Koo
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Originally Posted by C₄H₁₀ View Post
Which 2200Kv motor is it? A link would help. The Kv value alone says nothing about size, weight, performance, power, or anything else.

Are you planning to run it with the 4S battery?
Sorry I was in a hurry. Here is the link. And yes, I am planning to use a 4 cell on it. I know that it only says up 3 cell but I have seen multiple people using this motor with 4 cell and with excellent results.
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Old Aug 09, 2012, 08:15 AM
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I'm using a 6x4 with a 2066kV motor on 3S in my FunJet. Very tame setup, but good thrust for getting in the air for sure. I'd try a 6x4 on 3S for the maiden and then start experimenting.

/edit:

Quote:
Originally Posted by C₄H₁₀ View Post
Which 2200Kv motor is it? A link would help. The Kv value alone says nothing about size, weight, performance, power, or anything else.
It says a lot actually. 11.1V * 2200 rpm/V = 24420 max rpm. max rpm and prop pitch determine max airspeed.

However, it doesn't say how efficient the setup will be, how many amps will go through the motor and if it might melt in the process of spinning.
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Old Aug 09, 2012, 03:01 PM
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It says a lot actually. 11.1V * 2200 rpm/V = 24420 max rpm. max rpm and prop pitch determine max airspeed.
Actually, no, it doesn't tell you much of anything at all.

If you want to correct me in the future, please check your information first.
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Old Aug 09, 2012, 06:22 PM
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If you want to correct me in the future, please check your information first.
I'm sorry to offend you, sir. Please direct me to information on how to calculate the number of revolutions per minute of an electric brushless motor, then, so this kind of mishap won't happen again in the future. Thank you.
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Old Aug 09, 2012, 07:24 PM
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The Kv value, when measured and used correctly, tells you how many RPMs it takes for the motor to generate a given back voltage.

In common use, it's just used to tell us how fast the motor will try to spin with a given voltage input and no load on the shaft. This is very useless information, though, if you don't know a few other key pieces.

For example, in your post you mentioned the motor's max RPM as being 24420 because 11.1 x 2200 = 24420. This is clearly assuming a 3S lipo is being used. What you've failed to account for is that A) a 3S lipo's fully-charged voltage is actually 12.6V, and B) this voltage will fluctuate based on how much current is being drawn from the battery. Running an unloaded motor might bring pack voltage down to about ~12-12.4V depending on the battery and the motor. Kv doesn't give you that information, though.

From there you said that this determines the motor's max RPM. False, unless it's unloaded. With an unknown prop mounted, it's anyone's guess what the actual RPMs will be due to the load of the prop, so it's also anyone's guess what the pitchspeed will be.

Even if you measure the RPMs with a tachometer and calculate pitchspeed from there, you still don't have a clue what the airspeed will be unless you have dynamic airframe drag and prop thrust information. You don't even know your true maximum pitchspeed because the prop will speed up by some incalculable amount once it starts moving... So no, you don't actually know your max pitchspeed OR airspeed.

The Kv of the motor tells you... yeah... nothing
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Old Aug 09, 2012, 10:37 PM
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It still tells you the relative RPM of a motor compared to other motors regardless of their other specs unless it was some really weird exception. You can't deny that even not knowing anything else about a motor besides KV, that if it is a high KV motor it is more for high RPM and less torque, requiring a small prop to be efficient, where as one with a lower KV rating is always going to spin at a lower max RPM but will have more torque doing it, requiring a larger prop to be efficient.
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Old Aug 09, 2012, 11:22 PM
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You can't deny that even not knowing anything else about a motor besides KV, that if it is a high KV motor it is more for high RPM and less torque, requiring a small prop to be efficient, where as one with a lower KV rating is always going to spin at a lower max RPM but will have more torque doing it, requiring a larger prop to be efficient.
Yes, but only if the battery voltage is a constant. If the only piece of information we have is the Kv value, even relative between motors, then we still don't know much of anything.

(sigh)

Let's pretend we have two motors which are identical except for their Kv values. Motor A has a Kv of 1000, and Motor B is wound for 2000. Now, one might assume that Motor B is more suited for swinging a smaller prop on a faster plane because its Kv value is higher. However, both motors can have the exact same performance with a given prop if we want them to. Motor B will simply do it on half the voltage while drawing twice the current that Motor A would.

The only real limits are those of practicality. I COULD fly my Slow Stick on a 1S lipo and a 3300Kv motor with the same 9x5 prop it has now, but I would need an ESC that can handle 54A (versus the 18 it draws now) and can operate on the loaded voltage of a single lipo cell (most 54A ESCs can't). I would also need the lipo to be three times the capacity, so 5400mAh, if I want the same total energy storage.

I could go by a factor of 3 the other way, too: 9S 600mAh pack, ~367Kv motor, 6 amps... but then I need a tiny ESC and BEC which are capable of handling nearly forty volts.
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Old Aug 10, 2012, 12:23 AM
Koo
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I bought the 2200kw 350 WATT motor. Still have to mount it in the plane. The problem is that it's different size than the one I had on it, so I'll use just two screws to mount it. Hopefully it will be fine.
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Old Aug 15, 2012, 05:21 PM
Koo
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Had a succesful flight yesterday! Today I crashed because lost control of my 9x. I wasn't using FrSky and had antenna right on top of my ESC. Is this a problem? Pretty sure this caused the crash
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Old Aug 15, 2012, 06:47 PM
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Originally Posted by koo29 View Post
Had a succesful flight yesterday! Today I crashed because lost control of my 9x. I wasn't using FrSky and had antenna right on top of my ESC. Is this a problem? Pretty sure this caused the crash
Did the TX turn itself off or just lose link? I've had mine turn off because I was using AA ni-mh batteries that were slightly oversized, which made them get intermittant contact in the battery holder
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