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OnTheSnap
07-15-2009, 01:34 AM
I certainly don't disagree with your assessment of ripple. But I'm not convinced on how this plays into the life or heat generation of the ESC. We both agree that lower throttle settings on the ESC produces a lot more heat. I believe this heat is generated by the potential difference between the back EMF voltage and FET output voltage. I don't see how ripple matters here? :confused: There are no components on the output of the ESC that care about ripple?

dauste
07-15-2009, 04:49 AM
Can I ask you guys a question:


But the original arguement is the best place to run the esc with all else being equal. So for example a 11T at 100% curve or 12T with 80% (just random numbers, i didnt do any math), you have to assume that both sets would be running the same HS which requires the same power regardless of the esc settings.


Looking at this example, with the same load on the rotor (say hovering) and same HS, would you get more flight time out of the 100% throttle with lower gearing as the motor is running more efficiently?

DominicD
07-15-2009, 12:40 PM
A motor's max efficiency is based on RPM not throttle position.

dauste
07-15-2009, 12:51 PM
Ah, I think you know what I was getting at though! Do you have an answer? My electronics knowledge stops at 'O' level. ;)

OnTheSnap
07-15-2009, 12:56 PM
The power system is most efficient at 100% throttle. This minimizes losses in the ESC. This why everyone always recommends gearing down and increasing the throttle curve to achieve the desired RPM.

Note that there are other problems with running 100% throttle. Mainly, there is no head room for the governor to operate. So while less efficient, actual performance might be better at 85% vs. 100% throttle at the same head speed.

dauste
07-15-2009, 01:10 PM
Thanks for that, I will try dropping a tooth. Not had much luck so far with the Scorpion governor as it seems to settle at different speeds when spooling up.

DominicD
07-15-2009, 01:17 PM
The gov on the scop esc is useless, the best way to get performance out of the scorp esc is to leave everything default but enable the SS. Then set for 100% flat TC and gear the pinion to get the desired HS.

dauste
07-15-2009, 02:21 PM
Cheers Capi! That's what I'll aim to do now.

Danal Estes
07-15-2009, 10:43 PM
For what it's worth, I've been through this exact same debate many times, to the tune of hundreds (or thousands) of posts... and I'm too burned out to repeat all of that. I've also spent a LOT of time with everything from motors to O-Scopes to the code (firmware) that runs inside the ESC.

IMHO, HFG has nailed it with everything he's said in this thread.

For what one more opinion is worth... :)

Danal Estes
07-15-2009, 10:49 PM
The power system is most efficient at 100% throttle. The ESC is most efficient. The motor may or may not be... depends on many, many thingsThis minimizes losses in the ESC. This why everyone always recommends gearing down and increasing the throttle curve to achieve the desired RPM.Agreed, again assuming the motor is reasonably happy at the resulting motor RPM

Note that there are other problems with running 100% throttle. Mainly, there is no head room for the governor to operate. So while less efficient, actual performance might be better at 85% vs. 100% throttle at the same head speed.

The last paragraph is misleading. 100% in Governor mode is NOT, repeat NOT 100% throttle. The % sent from the TX in Gov mode is an RPM request. The gov may be able to reach that requested speed... or not... many other facts must be considered.

That's why the general guidance for setting up a gov is:

1) Slowly increase %. Use a tach and note the % where the headspeed no longer increases.
2) Whatever number comes from step (1), no matter how far above or below 100 that number is, multiply it by 0.8. Or perhaps 0.85, depending on how much "headroom" you wish the gov to have, and how flat your batteries hold their voltage. Fly with that number, again no matter what number that turns out to be.

Phrased another way... %s in gov mode just don't tell you ANYTHING. Want further proof? Castle's "Gov Hi" and "Gov Lo" overlap (on purpose). So, on a given setup you might be able to fly the EXACT same governed headspeed at 92% in Lo and 23% in Hi. Now, what did that % mean again?



Actually... one of the reasons I've begun to stay away from Gov mode is because there is SO MUCH misleading information in forums regarding Gov. The "100% leaves no headroom" (or its corollary "80% gives perfect headroom) myth is one of the most common.

OnTheSnap
07-15-2009, 11:15 PM
For what it's worth, I've been through this exact same debate many times, to the tune of hundreds (or thousands) of posts... and I'm too burned out to repeat all of that. I've also spent a LOT of time with everything from motors to O-Scopes to the code (firmware) that runs inside the ESC.

IMHO, HFG has nailed it with everything he's said in this thread.

For what one more opinion is worth... :)

Ok, please explain to me how ripple plays into this?

Well, just received the latest RC Heli Mag and it seems to agree with me. Since you've developed ESC's can you please enlighten us?

DominicD
07-15-2009, 11:51 PM
You are going to trust a magazine over two EEs ? :)

OnTheSnap
07-16-2009, 12:08 AM
Uh, well I'm an EE also. Although I've never dealt with motors in my designs. But did play with them in school.

DominicD
07-16-2009, 12:10 AM
My school work deals with MOS and RFIC so my knowledge on the topic is limited as well. But i did my fair share of research before i wrote my esc 101.

OnTheSnap
07-16-2009, 12:21 AM
Go to www.rchelimag.com and you can view 3 pages of the mag. Go to the esc article, which is co-authored by a guy from castle. Let me know if you agree.

DominicD
07-16-2009, 01:41 AM
Are you referring to Arthur Koral's "Brushless Systems" ? I found the best place to leanr about brushless esc is to pick up a application or datasheet on a brushless controller NOT a magazine that targets the public. Both AVR and PIC have great application datasheets about brushless controllers, and as always the first half of the document explains the basics.

OnTheSnap
07-16-2009, 10:21 AM
See attachment.

So you disagree with the Castle Creations Engineer and the RC Heli Mag editorial staff?

:DH

DominicD
07-16-2009, 12:30 PM
They arn't comparing apples to apples tho. The case i'm arguing the motor is geared and TC'ed such that the motor is the SAME RPM. They are talking about a high vs low motor RPM which i have no argument with.

OnTheSnap
07-16-2009, 12:56 PM
Well I guess we've done a horrible job communicating with each other. The point they've conveyed is the same point I was making. Which is explaining why putting a big pinion on and running the throttle lower is harder on the ESC.

DominicD
07-16-2009, 01:01 PM
What area of work is your EE in ?

OnTheSnap
07-16-2009, 02:18 PM
I'm a system designer working in the networking field. My last shipping box was a 48 port 10G 1U non-blocking switch.

DominicD
07-16-2009, 03:45 PM
Finishing up my phd in RFIC design, my last design was 2x2mm 10GHz :)

brtmac
07-16-2009, 07:05 PM
So, if back EMF is the primary reason that running an ESC at partial throttle is bad, would it be possible to get around this somewhat by using a two stage ESC. The first stage would be a single FET (or gang of FETs in parallel to handle the desired current) which would regulate the voltage from the battery. Then the motor drive FETs would effectively always work in the full throttle realm. They would basically switch on at the beginning of their phase and stay on until the end of the phase.

Or, would that just cause the back EMF to pass through to the first stage resulting in the same overheating problem there? Would a set of caps between the two stages reduce that problem?

OnTheSnap
07-16-2009, 09:07 PM
Interesting idea to try and match the motor back EMF to increase efficiency. Any voltage conversion is also a big loss in efficiency. If it worked out to be better then the BEMF losses, it would still come at a big expense with respect to part count and space in the ESC.

I've heard that Jazz controllers do much better at lower throttle settings. I have no idea what they're doing to achieve this.

ken22golf
07-17-2009, 12:20 AM
I've heard that Jazz controllers do much better at lower throttle settings. I have no idea what they're doing to achieve this.

On my 4S 450 Pro w/ the Jazz ESC, everything runs the coolest at 60% throttle. When I start increasing the throttle, the ESC starts overheating.

I've been following this thread because I kept hearing how a higher T% would be more efficient, but it sure hasn't been working for me with the Jazz. I tried dropping the pinion and increasing the T%, but I end up with the ESC overheating after 30 seconds...(yes I reprogrammed it after swapping pinions and the gear mesh was perfect)