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08-18-2012, 11:01 AM | #41 (permalink) |
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You guys are confusing the heck out of me but staying tuned in in the hopes of learning some new stuff...
Sent from my DROID3 using Tapatalk 2
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"It's not the crash so much as the sudden stop" Compass 7HV, Compass 6HV, TRex450Pro, bunch of other junk in boxes ... Team Flybar Team Tail-In wannabe.... |
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08-18-2012, 11:20 AM | #42 (permalink) | |
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Quote:
Mainly, why does the current go so high at 50% throttle? ub3p: Where and how are you getting current readings from? AFW, is this just not having brakes, or not forcing the motor to slow down when throttle and or load decrease, or something totally different? Also, could you throw a hyperion on there? And cool dunno setup! Steve Sent from Tapatalk using my Inspire 4g through ATT (meaning it's a wonder you can see this!)
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08-18-2012, 06:48 PM | #43 (permalink) | |
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Quote:
I don't think of it as current going in, magicked up to double after the ESC, but rather as the load drawn by the motor due to the stress of the dyno. In this case, of Tony's torture test, the motor is drawing a peak current of 160A, the PWM of the ESC is chopping power to the motor to only supply at 50% of the time so the power going into the ESC, ignoring losses, and available for 100% of the time, only needs to be at 50% of the motor current, to supply the power for the same in intput voltage. This example gives an ideal of the stress, electrical and thermal our motors can experience - in this example that's 50 x 160A ie 8kW of power - thats around 400W of heating - makes you understand why the motors and pinions get warm!! For those with limited understanding of brushless ESC (that includes me) this site gives some theory of the circuitry and a nice pictogram of ESC function !
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08-18-2012, 08:41 PM | #44 (permalink) |
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AFW is very different from brake.
Brake is rectification of the motor AC to recharge the battery. This drains kinetic energy and brakes the motor. Freewheel is when the motor is allowed to spin during no power application. But during this time, in passive fw, the inductive current flows through the body diode because the freewheeling fets are off. In active fw, we select out the fets that are involved in fw, and turn them on during this time. So the the voltage drop decreases from ~1V of diode to I*R, which is a lot lower. This is my attempt at conceptualising pfw vs afw. I am keen to hear tony uber's formal explanation. |
08-18-2012, 10:12 PM | #45 (permalink) |
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So I'm still confused. . . is this a valid test of a realistic scenario I'm likely to see in my model, or someone just showing us how quickly they can smoke an ESC? . |
08-18-2012, 10:21 PM | #46 (permalink) |
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Interesting graph Kim we really need some foreplay to explain normal ESC function! So is freewheel basically dealing with inductive currents during FET off status by either shunting through the body diode (whatever that is lol) in passive FW and through the FETS in active FW? How does this benefit the ESC if is still having to "shunt" induced current ?
FireNWater: I think the CC illustration unlikely real-life scenario, as others have posted, no one goona hook up a Scorp 4530LE and pull 80A through at 50% throttle, BUT I bet a FW ESC like the Jive could have managed it. This is a voyage of discovery and learnng for all of us, exploring different aspects of ESC, rather than a didactic 'This One's Best'
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08-18-2012, 10:30 PM | #47 (permalink) |
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This thread is really making me consider majoring in EE over Computer Science. IDK though maybe both? Keep the tests coming I really want to see the Jive and YGE torture tested
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Nano CPX - Mild Brushless Phoenix Sim DX6i |
08-18-2012, 10:36 PM | #48 (permalink) |
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Man these dudes are WAY over my head w knowledge.... I just wanna know what won't grenade......
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"It's not the crash so much as the sudden stop" Compass 7HV, Compass 6HV, TRex450Pro, bunch of other junk in boxes ... Team Flybar Team Tail-In wannabe.... |
08-18-2012, 11:02 PM | #49 (permalink) |
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I hope tony doesn't plan on torture testing the kosmic in the same way? Would hate to see that burn.
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08-19-2012, 12:03 AM | #50 (permalink) | |
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Quote:
Seems like a bad idea to be sending power back into the lipo. But I guess the micro controllers can handle that with todays tech. So even if I have the brake turned off when I "downshift" the motor/esc are acting like a generator? And when freewheeling is engaged it acts like a flyback loop with current looping around the motor and esc, with the motor acting as the resistor (and the rotor of course) to dissipate power until it the lower input is achieved? My mechatronics minor is starting to come back to me The power thing turned out to be a doh moment. I was thinking Pout=Pin (wire, heat, etc are being disregarded here). Just from reading your posts I'm going to assume you agree with conservation of energy. The doh for me came when I realized I was just thinking about current, but you are totally correct here. I'll steal your example and elaborate a bit. The esc controls voltage going to the motor , which needs to match the Kv chart, and it doesn't care what current is going through it. So if you attach a load (dyno, rotor head, etc) that esc will kill itself trying to match that load by increasing the current, as you have already set the voltage using the throttle. current to the motor is the only thing that can satisfy the conservation laws, again, because the voltage is already set. Sorry for the long msg! and any errors as I'm freaking tired. Steve Sent from Tapatalk using my Inspire 4g through ATT (meaning it's a wonder you can see this!)
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08-19-2012, 01:49 AM | #51 (permalink) |
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Hello,
AFW is correctly called "active rectification" or "synchronous rectification" http://en.wikipedia.org/wiki/Active_rectification Regards, Hemut
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Banshee 700 LE #50 and some others ... |
08-19-2012, 05:30 AM | #52 (permalink) |
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Ive uploaded a video to YouTube explaining how Active Free-Wheeling works.
I apologise in advance if im not clear enough, ive never been great at explaining things. Ill be uploading the video file to HF shortly. Ill also write up a detailed explanation. [ame]http://www.youtube.com/watch?v=uqzOQGiwGnE&list=UU7lc_DFDwD3wDHd-ixH1gfA&index=1&feature=plcp[/ame] |
08-19-2012, 05:51 AM | #53 (permalink) |
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Wow, thats's a very clear explanation Tony
Cant' understand why any manufacturer would not use FW and for the price difference of a FET or a silicone diode why wouldnt all use AFW? Are there any downsides? Be fascinating to see the 'scope of none, passive and active FW
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08-19-2012, 05:56 AM | #54 (permalink) |
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Makes sense to me, and I'm still in highschool!
Very good explanation tony and much appreciated. PS: you have impeccable taste in music Sent from my iPhone using Tapatalk |
08-19-2012, 06:36 AM | #55 (permalink) | ||
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Im using my clamp meter for the current readings.
Quote:
Your motor is an inductor, and it has freewheeling currents during the PWM-OFF cycle. During the PWM-OFF, current normally flows via the body diodes in your FETs. AFW allows the free-wheeling currents to flow via the appropriate FET and save us the diode losses. Ill try dyno as many as i can, just need time. Quote:
If there are no diodes, the circuit would fail because you will have huge voltage spikes occurring to try and leak the inductive (free-wheeling) currents. In Passive FW, you'll see the ph voltage drop below ground level (during PWM-OFF) as the free-wheeling diode conducts. In AFC, the lower FET turns on and clamps the voltage to ground level. There is no price difference between them at all. Its all in the control. Last edited by ub3r; 08-19-2012 at 08:07 AM.. |
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08-19-2012, 07:17 AM | #57 (permalink) |
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@ub3r
Your explanation of AFW is 100% correct. But because you know in detail the advantage of AFW and of course the disadvantage of PFW, I'm just wondering why you are doing a test with 50% throttle and that high load on an ESC without AFW. Such a test will always end up in burning the ESC (without AFW). It's only a question of (quite short) time. So for me, the real title of this thread is: "How fast can I burn an ESC having no AFW" Regards, Helmut
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Banshee 700 LE #50 and some others ... |
08-19-2012, 08:09 AM | #58 (permalink) | |
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Quote:
Well the test shows us the advantage of AFW over PFW. |
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08-19-2012, 09:20 AM | #59 (permalink) |
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Thx for the great video explanation of the different types of freewheeling systems! Boy that HeliJive is starting to look better all the time…
Sent from my DROID3 using Tapatalk 2
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"It's not the crash so much as the sudden stop" Compass 7HV, Compass 6HV, TRex450Pro, bunch of other junk in boxes ... Team Flybar Team Tail-In wannabe.... |
08-19-2012, 09:31 AM | #60 (permalink) |
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Yes, but demonstrating this advantage by burning ESCs without AFW is IMHO quite unnecessary since AFW is nothing new on the market and the advantages of AFW are well known for years.
Regards, Helmut
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Banshee 700 LE #50 and some others ... |
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