View Full Version : Medussa data logger vs Eagle Tree Logger

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TX HM-52
05-09-2008, 09:45 AM
Hehe enjoy your little world. I'am out of this unproductive "discussion".

So, you can't use a scope? are you afraid to see how WRONG your most basic understanding of ESC operation is? Sad really, i like to learn new things even if it embarrasses me.

Oh well your right, I better get back to making money hand over fist designing real controllers. Your probably late for school anyway.

TX HM-52
05-09-2008, 09:54 AM
What is with these freeken people from Texas!! Last go around about how brushless speed controls worked, another A$$ Wipe from Texas could not hold his tongue and have a little respect for the other people on HeliFreak. TX HM-52, got over yourself!!! There a couple other people in the world that know a few things.......

you're pretty funny, if you girls stuck a scope on it you could easily see I'm right and maybe learn some respect for others yourself. (read the posts leading to my reply and see just who couldn't hold their tongue ,HFG saying I don't know what I'm saying .READ MAN! DON"T JUST CHEERLEAD AND TYPE spouting BS)

05-09-2008, 10:16 AM
The flaming is out of control here, but I hate to leave dis-information with the last word.

Look at this picture from HFG's brushless 101. I think it was taken not directly at the motor terminals, rather earlier in the controller, but it captures the essence of the issue.

The yellow, green, purple traces correspond to the 3 motor wires. The shorter pulses are the PWM (pulse width modulation). PWM controls the current to the motor. The PWM pulses appear in groups. The groups are the motor commutation. Each group drives a "phase" of the motor, which is locked to the physical geometry of the windings of the motor.

The PWM frequency has NOTHING to do with motor speed. nothing. It is strictly there to control the current to the motor. However, the frequency of the GROUPS of pulses, the commutation... is locked directly to the phsyical rotation of the shaft. If you were to drive the incorrect phase, it will produce braking torque, or no torque. Clearly the ESC must know what phase to drive at all times. And, by observing the passage of the groups of pulses, a logging device can correctly determine motor speed.

05-09-2008, 10:16 AM
easy on the pissing contest.
i am actualy interested on what an esc looks like on a scope. not to prove someone right or wrong. just to see.
i personaly value HFC's opinion (not in this thead, but in general). usualy when he writes a comment on here. i generaly take it as fact.
he is opiniated on his comments though, but i think that comes from his actual experience in matters.
no offence given HFC.
(edited) posted before seeing marc's post

05-09-2008, 10:22 AM
can you define the "emk" trace line in more of layman's terms abit?

05-09-2008, 10:50 AM
From the web page HFG referenced
When the motor turns, it will generate 3 position signals, so-called EMK signals.They tell the processor ("Motor-Steuerung" in the diagram) what the position of the rotor is. On the scope screen picture this is the lower, purple, curve.So, its a feedback signal telling the controller what phase of the motor to drive. Before sensorless brushless motor controllers, brushless motors incorporated a position sensor to produce such a signal so the controller could know what phase to drive. Sensorless controllers (our ESCs) start the motor using random phasing. Basically kick it to make it wiggle. Once moving, the motor produces back emf (voltage). The motor acting like a generator. The sensorless controller picks up the back emf, figures out the motors actual phase, and starts driving it correclty... I haven't tried it, but you may be able to occasionally observe the motor start (very slightly) in the wrong direction, then reverse and go right.

The picture is somewhat simplified. You cannot drive one wire of the motor. Its always 2. name the three wires A,B,C: commutation would go: AB AC BC BA CA CB , repeat. You see its actually 6 states. Each wire is driven positive for 2 states, off for 1, negative for 2, off 1. The states are overlapped such that you always get one wire positive, one negative, one off "floating".

The commutation also ensures that each wires drive circuit goes from +,off,-,off,+ never directly from + to -. Which turns out pretty important to the life of the driver circuits. Further, some controllers put a delay (or overlap) in the commutation between turn off, and the next phase turn on.

The voltage at each wire is a mess. PWMing on/off at high frequency. Commutating at lower rate, locked to motor speed/angular position. And back EMF, and inductive "flyback" superimposed. The current in each wire however is smoothed out by the inductance of the motor, and does look much more sinusoidal.

TX HM-52
05-09-2008, 11:12 AM
here is a pic of what an actual controller puts out to the motor with a REAL scope as well as the setup showing my little EP100 with a CC10 ESC...

The real world sucks eh?


sorry for the bad camera work but I have no time to setup a tripod and need to work.

05-09-2008, 12:33 PM
That is sooooo NOT a sine wave.

05-09-2008, 12:39 PM
why is that marc??

TX HM-52
05-09-2008, 12:49 PM
that's what a PWM generated sinewave looks like with back EMF signals superimposed..go back to school Mark

Again, everythings double since I didn't have time to setup the tripod to shoot the scope screen in low light while holding the heli down so it doesn't cut my scope probe wires and chickendance on my bench.

05-09-2008, 01:07 PM
you said it yourself. "PWM superimposed". Technically, that makes it no longer a sine wave, as you originally called it.
A couple posts back, you will find I provided a similar list of signal elements that you have named on this waveform.
PWM, commutation, back emf... all superimposed on... the sinusoidal element you see.
But the combined waveform is not a sine wave. To call it a sine wave completely discounts all the other elements in there!
Its just a poor description of the wave, even if the brightest blurry thing you see on the scope (at this sweep speed) is sinusoidal. All those pulses above and below it are enormously significant! I cant simply ignore them and call the whole thing a sine wave.

05-09-2008, 01:07 PM
Lets everybody tone it down a bit and learn. Pretty interesting stuff.

Thank you in advance. I like to learn and I want us all to remember that leaving out all the emotion will help more people read the important posts that educate in this or any other thread.

Thank you!! :hug:

05-09-2008, 01:21 PM
Ummm well I know jack crap about electronics.. but it seems to me that if those so called pulses are designed to give the motor a magnetic push and a finite one at that it's not hard to see that once that push if given how an outside force such has drag would throw monkey wrench into any calculation that only counts the pushes to measure speed. Then again like I said I don't know jack about electronics so you won't see me waving about my resume about trying to {LOL} convince anyone of my arguments but please do correct me if I'm wrong. :smokin:

05-09-2008, 01:23 PM
thanks for stepping in will.
i truely love to listen (read) true professionals have a debate without the nonsence inbetween. this is truely a good thread to read....no ofense given to the professionals on the debate platform.

05-09-2008, 02:03 PM
I think we actually agree on whats in the motor waveform... I just object to calling the composite a sine wave. th hm 52 is ok with calling it that. Terminology/semantics. lets be nice.

The original issue is whether one can accurately sense the motor speed, based on the electrical signals going to the motor. I stick by my original statement that it can be done. I have no experience with a data logger, so I cannot say that they actually DO it right, but I will say that it CAN be done right.

Reiterating, the ESC must in fact sense the motor position in order to drive the correct windings to produce torque in the correct direction. Knowing the position of the shaft, the controller can select which two of the wires to drive (and polarity) ... called commutation. Further, by counting the rate of commutation changes that the controller is using, one can determine the motor rpm.

PWM is faster, and superimposed on top of commutation. PWM is used to control the current. It is independent of motor commutation and RPM.

Lets look at third parties to corroborate some of the things I've said.
page 1 second paragraph
Traditionally, BLDC motors are commutated in six-step pattern with commutation
controlled by position sensors. To reduce cost and complexity of the drive system,
sensorless drive is preferred.Six step commutation, with position sensors. Sensorless replaces the position sensors, using the motors back emf to determine shaft position...

page 6 has the same commutation sequence I wrote above.

page 3 paragraph 1
innermost one determines the rotor position to commute correctly the stator flux. Once
the rotor position is known, the magnitude of the stator flux has to be generated and
controlled.motor position required to correctly commutate ...


Not enough ? Google BLDC sensorless
you'll get a whole mess of documents, integrated circuit specs, controller articles, yadda yadda... that confirm the following: That the ESC must know the motor phase to commutate it correctly. It doesnt just spit out a train of pulses willy nilly. They are coordinated with the shaft angle. In sensorless designs, the controller determines the motor position from the back EMF of the motor windings, sensed in between (in time) the driving pulses.

I disagree with HFG that a PIC cant do anything complex. They can. In fact, theres probably a micro controller in your transmitter, and your gyro. And disagree with TH hm 52 that a phase locked loop chip is simple. Anything but. Especially in RF world.

I'm done.
And, I'm sorry if I participated in the mud slinging.

05-09-2008, 02:21 PM
Sorry wasn't the original question whether the DataLoger can?? ... then later turned into whether it can be done in general?

05-09-2008, 02:26 PM
Yeah, and that's what I'm trying to address. If sensing can be done in general, then a data logger can do it. In fact, the data logger has it easier, because the ESC already IS doing the job based on back EMF... the data logger can take advantage of that fact, and only has to look at the commutation aspect of the total waveform. Which is a much larger, more easily interpreted aspect of thesignal. And is why it can get away with only looking at one of the motor terminals.

FWIW, I plopped my 450 w/2221-8 on the floor and watched the motor very carefully at the beginning of spin up. (note to safety minded: I only went up to about 20 RPM indoors) When I started with the motor in certain positions it would always spin backward at first, then turn around and go the right way. When I started in other positions, it would start out right in the first place. It all depends on the start position. Give it a try...

05-09-2008, 02:36 PM
... nevermind, I think I'm getting it..no I'm not meh

05-09-2008, 02:41 PM
Ok, I had to see for myself so I dusted off the o-scope and checked it out. This is the output of a Castle Phoenix 35 at low speed and the second picture has the speed kicked up a bit.

05-09-2008, 02:51 PM
The bottom line is that the voltage applied to the motor is pulse-width-modulated, but the resulting current flow in the motor windings 'resembles' a sinusodial shape.

Our motors are basically 3 phase AC synchronous motors, only permanent magnets are used on the stator instead of using an external supply.

I'm glad to see people breaking out the scopes, though!

05-09-2008, 03:35 PM

05-09-2008, 03:53 PM
ouch... not the vibe I was going for. I actually tried hard not bite on the flames. I guess, next time I'll just not respond.

05-09-2008, 05:03 PM
next time I'll just not respond
please dont marc. your opinion to me is very valuable.
i partialy read the thesis. all i can say is holy crap they make you do that indepth writing to get a masters??? im glad i dropped out....lol
my wife had to do her's years ago in accounting. and i only read the first 4 paragraphs before i started to yawn.....lol

05-09-2008, 10:12 PM
Now we need to scope the output of the ET brushless RPM sensor and the motor lead to which it is attached at the same time. That would really help answer the question about the sensor.

Here are two basic facts:
1) Our ESCs use back EMF as the "sensor" for commutation.
2) There is no slip in our BLDC systems. And, therefore, the commutation directly relates to the motor RPM at all times.

Both of these facts are extremely well documented.

Therefore, if the ET brushless RPM sensor correctly senses the commutation, it's output will directly track the RPM of the motor. But, do we know that the sensor correctly senses at all times? That is the question. And what the Logger does with the output of the sensor is yet another question but I think it relates right back to the reliability of the sensor's output since we know the Logger correctly measures RPM from other sources (magnetic and optical).

- John