Understanding ESC PWM and Timing settings

[superfreak]

What do PWM and Timing parameters in the ESC really do? What do they affect, and what is the relation of their settings to motor design, poles, efficiency, and resistance?

Knowing this would greatly assist with properly tuning the ESC to the motor.

Thank you for sharing your knowledge.

[nwcudaman]

that would be some good info. Several weeks ago I was talking to the guys at CC about both my 600 and my 550E align. Both are running Scorp 4025-1100 motors and both wth CC Esc's. Oddly enough, they suggested that due to their testing I should be running low timing, 8 pwm and not the outrunner mode!. So,, I gave it a bash. Works like a champ alright. They told me that Scorp motors seem to like the 8 pwm setting,,,and ya know what,,,,they were right. Flight times went up, power did too. Odd huh?

[phoenixheli]

Same thing on a century 800kv, went from the default outrunner to 12pwm, temps went down, flights up and more fun.

[Sparky Inman]

Here's a formula I ran across thats supposed to figure the proper PWM that so far has been working for me.
Kv x Volts (nominal you are using) x Pole count / 20
For my 500 my motor is 8 pole 1760kv running on 5s so
1760 x 18.5 = 32560 x 8 = 260480 / 20 = 13,024 so i have rounded down & set my PWM at 12k & it has performed flawlessly.
On the Scorpions I dont use it & just go directly to 8k as the Castle Guys recommended & it works. Should try the formula on them & see if it ='s out to the same or if 8k is just a good all around setting??

Sparky

[N017RW]

Thanks Sparky...

I used that formula and determined the proper [ICE50] PWM setting for my setup (430XL) is ~12.3k.
Previously I was using "Outrunner Mode". After switching to 12k instead, the motor temp. has DROPPED significantly after 6 min. flights of Scale type manuevers.

[Sparky Inman]

Originally Posted by N017RW

Thanks Sparky...

I used that formula and determined the proper [ICE50] PWM setting for my setup (430XL) is ~12.3k.
Previously I was using "Outrunner Mode". After switching to 12k instead, the motor temp. has DROPPED significantly after 6 min. flights of Scale type manuevers.

Excellent!
Like I said it has always worked for me.

[johnsma22]

There is a great article in the November 2010 edition of AMA's Model Aviation magazine on this very subject. It's called "Inside the Electronic Speed Control". It's an in depth article that is very technical and explains things better than anything I've read to date. It's worth getting the issue for this article alone.

[Cheetah62]

I remember that AMA article, and if memory serves it was written by an engineer at CC.
I just talked to CC about my KDE/Neu motor, which calls for 16KHz PWM in the specs. The formula above gives me ~12KHz. Lo and behold, CC also recommends 12KHz.
So, what I'm taking away from this is that the formula works well except when running Scorpion (and thus also Hyperion) motors, which are better at 8KHz.

[aramb]

I am running the 470kV 70MX motor in my Trex 700e F3C. The motor gets VERY hot (although the CC 120 ICE HV seems to be staying relatively cool). I currently have the PWM set to 8kHz in the Castle Link software. Using the above formula (Kv x volts x poles count / 20) results in the following:
470 x 44.4 x 10 = 208680 / 20 = 10434. On the Castle Link software, I can only choose 8 kHz or 12 kHz. Would I be safe moving it to 12 kHz in order to get cooler motor temps? Also, I have motor timing set to "5" in the software. Is this correct for this motor?

Thanks,

Aram

[ahahn]

The PWM rate has mostly to do with the motor inductance. The higher the inductance (actually it is the ratio of inductance "L" divided by the resistance. "R"), the lower you can run the PWM rate. This "L/R" time constant actually acts to smooth out the current flowing in the motor. A low PWM rate, giving long on/off pulses to the motor is pretty inefficient.

The motors really have no issue with high PWM rates. I run my Scorpions at 12 to 24 kHz and have excellent results. I have no idea why 8kHz is magic for Scorpions. Maybe the big ones have such a large value of L/R that 8kHz is fine. But so would 12kHz too.

On the other hand, the ESC prefers as low a rate as possible. The faster the switching, the the hotter the FETs run. That's because when the FET is transitioning between off (~infinite resistance) and on (very low ~milli ohms), there is a region of finite resistance. This short time span produces most if all of the ESC heat (why CC claims ~80% throttle is the hardest on the ESC). The faster the PWM rate, the more of these transitions occur in a period of time, so more heating.

Since most info about PWM rates we get comes from the ESC manufacturer, it is no surprise that they recommend going for as low a PWM as possible.

In one test I did, I found I was modestly more efficient at 24kHz than at 12kHz (Scorpion 3020 motor, ESC, and battery).

Another detail is the commutation speed. You do want the PWM rate to be higher than that speed by some factor, and I think that is what the formula given by Sparky is effectively calculating.

AFAIK, the outrunner mode is trying to use that calculation to change the PWM rate dynamically as your motor rpm changes, but I don't think it has been too successful. I really don't see a downside to the higher PWM rates, as long as the ESC isn't complaining!

JUST IMHO!

[ollie2893]

Originally Posted by ahahn

JUST IMHO!

+1 to all of that.

[aramb]

Originally Posted by ahahn

The PWM rate has mostly to do with the motor inductance. The higher the inductance (actually it is the ratio of inductance "L" divided by the resistance. "R"), the lower you can run the PWM rate. This "L/R" time constant actually acts to smooth out the current flowing in the motor. A low PWM rate, giving long on/off pulses to the motor is pretty inefficient.

The motors really have no issue with high PWM rates. I run my Scorpions at 12 to 24 kHz and have excellent results. I have no idea why 8kHz is magic for Scorpions. Maybe the big ones have such a large value of L/R that 8kHz is fine. But so would 12kHz too.

On the other hand, the ESC prefers as low a rate as possible. The faster the switching, the the hotter the FETs run. That's because when the FET is transitioning between off (~infinite resistance) and on (very low ~milli ohms), there is a region of finite resistance. This short time span produces most if all of the ESC heat (why CC claims ~80% throttle is the hardest on the ESC). The faster the PWM rate, the more of these transitions occur in a period of time, so more heating.

Since most info about PWM rates we get comes from the ESC manufacturer, it is no surprise that they recommend going for as low a PWM as possible.

In one test I did, I found I was modestly more efficient at 24kHz than at 12kHz (Scorpion 3020 motor, ESC, and battery).

Another detail is the commutation speed. You do want the PWM rate to be higher than that speed by some factor, and I think that is what the formula given by Sparky is effectively calculating.

AFAIK, the outrunner mode is trying to use that calculation to change the PWM rate dynamically as your motor rpm changes, but I don't think it has been too successful. I really don't see a downside to the higher PWM rates, as long as the ESC isn't complaining!

JUST IMHO!

This is great information! Thanks!!!

Aram

[badfrog]

Originally Posted by nwcudaman

that would be some good info. Several weeks ago I was talking to the guys at CC about both my 600 and my 550E align. Both are running Scorp 4025-1100 motors and both wth CC Esc's. Oddly enough, they suggested that due to their testing I should be running low timing, 8 pwm and not the outrunner mode!. So,, I gave it a bash. Works like a champ alright. They told me that Scorp motors seem to like the 8 pwm setting,,,and ya know what,,,,they were right. Flight times went up, power did too. Odd huh?

any idea if this holds true for the smaller Scorpions as well? I will be running a 2221-8 in my 450 Pro 3GX...

[sward104]

"I am running the 470kV 70MX motor in my Trex 700e F3C. The motor gets VERY hot (although the CC 120 ICE HV seems to be staying relatively cool). I currently have the PWM set to 8kHz in the Castle Link software. Using the above formula (Kv x volts x poles count / 20) results in the following:
470 x 44.4 x 10 = 208680 / 20 = 10434. On the Castle Link software, I can only choose 8 kHz or 12 kHz. Would I be safe moving it to 12 kHz in order to get cooler motor temps? Also, I have motor timing set to "5" in the software. Is this correct?"


CC says to use 12PWM & Normal timing (5) for all Align motors.

[aramb]

I have the 470kV motor also on my F3C. I have it set to 8 kHz and "5" on the motor timing. The motor feels pretty hot to the touch after 9 minutes of flight, but according to my motor temp sensor (telemetry), it is not getting any hotter than 120 degrees F which I think is okay.

[heliphlier]

I am running the scorpion-8 on my 3s 450 Pro and have been running at 8 kHz for some time as that was the suggested setting. After calculating with the above formula I got an answer of 1197.35 rounded up to 12 kHz and I am going to see how that runs and will give some feedback. Thanks for this great info.

[npomeroy]

Lots of good information above on PWM kHz but not so much on timing. Can anyone give a general explanation of the effect of higher and lower timing? I'm running a scorpion 4025-1100 on a T550 and it gets fairly warm. I run low HS and will be putting a scale fuse on - in fact will probably change to an 890 kv motor anyway.
What is the effect of change from medium to low timing?

I note that the Castle instruction sheet says "Electronic timing advance: Low advance - May slightly decrease current draw, and will give longer runtime and a cooler motor and batteries. This is the preferred setting for outrunner motors". This looks the way to go for me. But I would like to see a link to a more detailed description.

[realmoto]

Originally Posted by heliphlier

I am running the scorpion-8 on my 3s 450 Pro and have been running at 8 kHz for some time as that was the suggested setting. After calculating with the above formula I got an answer of 1197.35 rounded up to 12 kHz and I am going to see how that runs and will give some feedback. Thanks for this great info.

How did running the PWM @ 12 work for you? Am also running a small motor and want to know if changing the PWM make a big difference?

[realmoto]

Okay yesterday I made the changes on my esc. I had a 30min break and tried the PWM setting @ 12khz also the current limiting set to disable, also changed the timing from 0 to 5. Went out and tried it. The motor was very responsive did some pitch pumps and loops. The flight time was 10min. When I checked the motor & esc by touch they were warm not even hot the battery as well, I haven't had a chance to download the esc to see the data, but the battery had 3.658v per cell left. So am happy the the settings.

[DALE-PABAJO69]

Originally Posted by aramb

I am running the 470kV 70MX motor in my Trex 700e F3C. The motor gets VERY hot (although the CC 120 ICE HV seems to be staying relatively cool). I currently have the PWM set to 8kHz in the Castle Link software. Using the above formula (Kv x volts x poles count / 20) results in the following:
470 x 44.4 x 10 = 208680 / 20 = 10434. On the Castle Link software, I can only choose 8 kHz or 12 kHz. Would I be safe moving it to 12 kHz in order to get cooler motor temps? Also, I have motor timing set to "5" in the software. Is this correct for this motor?

Thanks,

Aram

you know I would have to agree with CC, BTW have you updated you'r ESC becuse I have the same ESC as you do and the PWM rate has 24khz 16khz 12khz 8khz and outrunner .
soon I'll be starting on my logo 600 and I got this turnigy 480kv motor for it will run on 12s, so I used the above formula to verify the PWM and the results where 10656 so I asume I'll be seting the PWM to 12kz and the timeimg I guess would be 5*