View Full Version : Medussa data logger vs Eagle Tree Logger

Pages : 1 2 3 [4] 5

12-30-2007, 11:28 PM
> as I am sure it processes the signal and sends just the data to the logger.

It's plugged into the same RPM port that the magnetic or optical sensor plugs into, so I'm pretty sure it's just pulses which the main unit counts/measures.

So, why do some say it is not accurate? If our systems have zero slip by definition, how could it be wrong? Noise? I think that's the bigger question.

>It cold and raining.


- John

TX HM-52
12-31-2007, 09:18 AM
more than likely it's a simple optoisolator.

01-03-2008, 10:24 PM
Well, Santa brought me the Eagle Tree V3 for Christmas and I gave it a quick test tonight. I had one problem....my RPM's were reading way too high (around 6000). I have the brushless motor sensor. I stripped some insulation from the end of the motor wire one lead on the sensor and connected it inside the bullet connector of one of the motor wires. I have a Medusa 28-32-3400. During the initial setup I told the data logger that my motor had 2 poles because it is an inrunner. Also, since I have a 12 T pinion and the trex has a 150 tooth gear, I divided 150 by 12 and got 12.5 so I put 12.5 to 1 in the setup. Can anyone tell me what I did wrong?
Also, when in graph mode is it possible to save the graph as a file?



01-03-2008, 10:43 PM
Anyone interested in a almost brand new V2? I have the cable and software CD. The unit looks brand new. Probably used 3-4 times. The V3 is $69+shipping. Some people dont need the amount of sensors on the V3 so Im wanting $55 Shipped.

01-04-2008, 04:17 PM
Did you read my post?

I am quoting one of the Eagle Tree engineers. One of the guys who DESIGNED the system, not some tech who is a phone answerer.

According to the ENGINEER, the brushless sensor counts pulses. It does NOT measure pulse width.

And you stated that the tech only sort of agreed with you, that he did not outright say that they measure pulse width.
For measuring RPM, measuring the width of the pulse would be pointless. I mean yeah, you can do it, but it's extra information that you don't need.

01-04-2008, 08:23 PM
Well, I just did some experimenting with my Eagle Tree logger RPM sensor. I left the ratio setup to 12.5 to 1. I kept increasing the pole number until I got around 2800 RPM's on the logger at hover pitch, which is about what my Trex is turning. I ended up putting 48 poles in the RPM setup to get my target RPM reading. Can someone please let me know if this is the correct way to set this sensor up.



01-04-2008, 08:31 PM
For measuring RPM, measuring the width of the pulse would be pointless. I mean yeah, you can do it, but it's extra information that you don't need.

MOST people understand that. :)

TX HM-52
01-04-2008, 09:29 PM
I thought this thread was dead but actually if you want to get down to it the ESC outputs a PWM synthesized sine wave and it's frequency and amplitude (hence motor speed) are DIRECTLY related to the pulse width as I understand it.

This is an excerpt from an Intel PIC/MCU datasheet detailing how to generate sinewaves via PWM.

"The 80C196KC family's on-chip peripheral set includes a Pulse Width Modulator (PWM) for generating a pulse train of varying width, which can be filtered to generate analog voltages. This can be used to generate sine waves and even more complex waveforms by periodically changing the PWM value."

This article mentions driving motors as well as audio.

link to full somewhat interesting article here http://www.intel.com/design/mcs96/technote/3351.htm

I would still imagine that the brushless sensor is basically an optoisolator (with a high impedance clamped input so it doesn't burn out the LED) that pulses on the positive transitions of the sine wave giving what I think would be a square wave of varying frequency depending on the speed of the ESC signal and hence the motor (as I've said all along). Just a guess on this part since I've never had my hands on a brushless sensor from ET. Either way the pulse width is the basis for the whole signal and determines the frequency or speed and is ultimately at least part of what's measured if the ESC output is whats measured of course this whole line of thinking goes right out the window if they do in fact use back EMF to get speed..



01-04-2008, 10:25 PM
Wow! This dicussion is both getting extremely annoying or very interesting, depending upon your viewpoint. :)

I vote for the latter, since it is obvious that we have some people here who know a little bit about RC electronics! :D


I'm sorry, I am just a bored academic, RC addict who likes to talk about theory and application. :rolling

01-04-2008, 11:25 PM
> if you want to get down to it the ESC outputs a PWM synthesized sine wave and it's
> frequency and amplitude (hence motor speed) are DIRECTLY related to the pulse width
> as I understand it.

This is one of the areas that seperate the "men" from "boys" when it comes to ESCs. There are very simple, rudimentry ways to do the switching and then there are elegant, even patented ways to do the switching. The elegant ways increase efficiency and smoothness of the motor. This is one reason some ESCs can operate at much lower "throttle percentages" than others. Kontronik, for example, is known as the king of partial throttle operation because they have a more elegant switching scheme which actually varies the timing, frequency, and switching pattern real time.

- John

TX HM-52
01-05-2008, 01:05 AM
I've put a scope on the output of my Castle ESC and it looks very straightforward and linear as far as speed vs frequency to me, not sure about other brands or even if they're compatible with the logger sensors which is what we're discussing here. I'm sure there are all kinds of methods of modulation for more high end controllers for various apps, there are tons of patents out there for all kinds of crazy stuff and not all of it works as the patent office is not in the business of making sure the patented item/idea even works...all I was doing was taking a shot at how the loggers inexpensive BL tach works and once again this was only because the guy I spoke to at ET said that was how they did it when I asked if that was the way they read RPMs (why do I feel like a broken record?).

I never claimed to be an ESC expert, just basing my ideas about BASIC ESC operation and how I would log RPMs through a BL motor on a budget with what I know about general programming and hardware as well as what I was told by ET and what I've seen myself by putting my other heli's ESC on the scope and observing for the sake of this argument. I currently work on projects in a slightly more lucrative market that involve much more complex custom interfaces for high end automation and control systems (mostly digital signals / data I/O) not designing ESCs for motors and ESC loggers.

I would think even the engineers at any fancy ESC manufacturer would agree with my opening sentence in my last post and overall premise above (maybe I'm wrong, I've only skimmed articles on the topic in the past and never needed to study advanced ESC design principals for any jobs yet), but I agree there are surely modified / enhanced methods out there but the pulse width is still the heart of any digital motor drive system period from what I know and have ever seen.

I also wouldn't say Intel is not a "Big" boy when it comes to digital signal processing as per the article I posted about above.

01-05-2008, 08:29 AM
I wasn't disagreeing at all with your previous post. I was trying to add to what you posted. Yes, all of our ESCs use PWM. It's all about how you implement PWM. It doesn't have to have a constant time period between pulses.

- John

01-05-2008, 08:46 AM
And the PW doesn't relate directly to RPM in a constant mannaer across ESCs.

But the number of pulses/sine wave peaks does. So for a univeral device, counting pulses is easiest.

As for what people at Eagle Tree say, the design engineer trumps the tech any day. :)

TX HM-52
01-05-2008, 09:06 AM
And the PW doesn't relate directly to RPM in a constant mannaer across ESCs.

But the number of pulses/sine wave peaks does. So for a universal device, counting pulses is easiest.

As for what people at Eagle Tree say, the design engineer trumps the tech any day. :)

I'm glad we're finally in agreement here, that's all I was trying to convey :) (first time in post #13 and last time I repeated myself in 7th sentence of post # 83 above most recently). I agree with what you say about the low level techs (they work off of basic scripts and are generally not there for design expertise or salary) I had probably 10 long phone calls , the last with a couple of senior people (not entry techs) at ET for my dead V2 as I keep saying, I'm pretty sure I talked to your buddy Bill as well and they were all very unhelpful and really didn't seem to understand the I2C bus issues I was having with the LCD output to the Power Panel and this was the only reason I posted in this thread to begin with.

That being said I would also have to agree with JKos that there may be some modified modulation schemes out there that may not allow accurate RPM counting with this method. :)

Happy flying (hopefully it's warm enough this weekend for you to fly),


05-08-2008, 11:57 AM
I would love to put one of these on my gasse, but temps in diffrent places of the motor go above 125-150. Venom temp would be the only way. Why are they using such low temp sensors?


05-08-2008, 02:12 PM
TX HM-52 (http://helifreak.com/member.php?u=20825) your understanding of how an ESC works is painfully wrong. Take a look at my Brushless 101 on Bob's forum.

05-08-2008, 02:22 PM
IMHO, regarding the sensing of motor commutation, and RPM detection: JKos is right. Tx hm52 is incorrect.

A three phase motor controller NEEDS to know which phase to drive. It may be able to make a motor move without this, (ESC's do this to get the motor started, because there is no back EMF when its stationary) but they cannot efficiently continuously drive the motor, or regulate its speed without accurately sensing the winding phase. Which they do using back EMF.

I haven't used them, but I would fully expect a motor drive based RPM sensor to be completely accurate. If it isnt accurate, its because they designed it poorly, not because there is anything fundamentally wrong with the technique.

And if it matters, I have a EE degree, have designed three phase motor controllers, PWM power amplifier circuits, and speed regulation control loops.

05-08-2008, 03:19 PM
Markb give me a HUG !! Not too many folks out there really understand an esc but have no issue with discussing them at length. The esc needs an accurate sense of the windings in relative phase to the stator magnets, they use the back EMF and filtering to get the zero crossings. On start up the esc is an open loop controller and will run as a closed loop control to be able to vary the speed and be efficient after start-up. There are NO sine waves on our ESC.

The eagletree measure the motor RPM exactly !! The only difference between the HS and the motor RPM is any slippage on the one-way bearing (this is what the eagltree people are talking about drag).

And if it matters, I am in my final year of my Phd in EE. My focus is on PLLs, VCOs, mixers, transconductance amplifiers, and frequency Synthesizers. I teach a 4th year class and grad class on VLSI and another 4th year class on embedded systems (68HC11, and MEMS sensors).

TX HM-52
05-08-2008, 08:55 PM
The discussion was if the eagle tree was counting pulses from the ESC.... look back in the start of the thread. I design dedicated micro controllers for a living and have quite a few successful products as well as some awards. I just said that ET probably just counts the pulses from the ESC to determine speed (I can see how it could be done with reasonable accuracy on a budget, and the guys at ET said that was what they did).

I have never designed an ESC and really don't care to unless someone offers me a ton of cash to do so, then I would study ESC theory. For now I'm into much much more complex multi processor PIC projects as well as very high end Crestron programming in C++. This is ontop of complex home automation interface software of mine that runs many famous peoples multi-million dollar homes using a Windows touchscreen GUI. I can assure you I have a real good understanding of PIC programing.

I only responded to this thread to say I was screwed by ET, that's all.

BTW HFG, you should stick a scope on the output of one phase of your ESC and you'll see a SINEWAVE just like what drives ANY 3 phase motors! (I've done it and can post pics if you lack proper test equipment). That's just basic ESC knowledge.

Have a nice day!

05-09-2008, 09:14 AM
LOLOL I am not taking advice from someone who uses the world COMPLEX and PIC in the same sentence :)

TX HM-52
05-09-2008, 09:26 AM
put a friggin scope on it you bonehead...,oh wait let me guess you don't have one except in the little school lab..

You should listen to people that are in the real world, with real experience schoolboy..stick to something you understand like helis.

yes, i have built some multi pic products that talk to dozens od sensors for complex projects such as geothermal system controllers managing a few dozen wells and all the rest of the system.. stuff they just don't teach in school.

05-09-2008, 09:31 AM
Your stuff is for hobbiests. BTW here was my last project.


TX HM-52
05-09-2008, 09:36 AM
I'm no hobbyist.. I've been producing REAL products in the REAL world for many many years in many fields that are much more complex than a simple chip.

So if you CAN stick a scope on your ESC and see just how right I am and how totally wrong you most basic assumption of ESC operation is.. Do I need to draw you a hookup diagram?

05-09-2008, 09:42 AM
Hehe enjoy your little world. I'am out of this unproductive "discussion".

05-09-2008, 09:45 AM
put a friggin scope on it you bonehead...,oh wait let me guess you don't have one except in the little school lab..

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.......