ESC PWM Control Help - RC Groups
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Dec 21, 2010, 02:07 PM
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ESC PWM Control Help

Hi guys,

So i got all of my esc's and motors in today, but im having a problem. The ESC Im using is the Mystery 40A with built in BEC. The BEC has 3 wires (brown, orange and red). The red one is the 5,5v BEC output. I disabled that as I dont need it.

The orange one has 4,9v, i thought the brown wire was earth. However when I hook up the orange one to my Microcontrollers PWM output (and set a voltage on there), nothing happens. So which one is the correct wire? And if brown is the throttle cable, then why has the orange one got 4,9v on it?

Also I havent heard a Beep or whatever coming from the ESC. What have I done wrong?
Last edited by Julian90; Dec 21, 2010 at 02:25 PM.
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Dec 21, 2010, 05:10 PM
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I read somewhere that the PWM frequency needs to be about 50hz. is this correct? It wont start up otherwise? (no sounds etc)
Dec 21, 2010, 05:19 PM
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Middle wire should be 5v. It would be up to the person who soldered it as to what the outside two are connected to. When I use the brown,red,orange ribbon wire, brown is ground and orange is signal with red 5v in middle. You will read a voltage on your meter if you go between signal and ground. The meter will average the PWM signal and give you a voltage reading. The higher the duty cycle (pulse on longer) the higher the voltage reading.
Dec 21, 2010, 05:33 PM
Registered User
Thanks for your response pug398,

When deciding on which wires to connect i used the same logic as you did. But the weird thing is the orange wire has 4,9v on it from the ESC aswel. Does this mean the pwm signal works by pulling it lower? I cant wrap my head around this one.

Also, the mystery guide says the PWM signal is either 8khz or 16khz, should i create a 8khz pwm signal then? Or 50hz like i read elsewhere? i really dont know where to go on this.
Dec 21, 2010, 06:45 PM
Registered User
If you are talking about a factory built esc then the signal wire is an input and yes it is at a high level when measured with a high impedance meter with no drive signal. The input signal can be way higher than 50 Hz and if it is controlling a brushless motor can be up to high as 400 Hz. Driving a standard analog servo it would need to be low hertz. Driving digital servo can be higher. You will not hear a beep (motor tone) unless a motor is connected.
Dec 21, 2010, 06:50 PM
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The ESC is a Mystery 40A SBEC.

I have connected the motor (A Hobbyking NTM 35a, 910kv brushless dc). I have tried ranging the PWM output that was connected to the control signal (the orange one thats on high) from 0v to 3v (which should be just more then 60% duty cycle).

Ive tried HZ between 38 and 400hz still nothing. Any suggestions?

I heard a short beep coming from the ESC and the motor spinning for like half a second once but not been able to replicate, pretty strange.
Dec 21, 2010, 07:05 PM
Registered User
A servo or esc control signal does not change amplitude for control. It is at either 0v or 4-6v depending on circuit. The pulse goes positive ever 20ms (for 50 hz) and should stay positive for at least 1ms. This would be a low or off signal condition. Keeping the pulse rate (frame rate) the same, the pulse width is then increased up to 2ms (for full on or high). In other words you are modulating the pulse width to set the amount of drive. You could use a 555 timer chip to simulate a servo controller signal or else you will need to program a microcontroller. Hope this helps.
Dec 22, 2010, 03:02 AM
That tree again!!!!
thanhTran's Avatar
The ESC needs the PWM pulses in the range between ~1ms - 2ms to work. When it's out of this range, it might not work. Also the pulses have to be at 1ms or less for some time (couple seconds) when you have power on the ESC before it arms itself. Only after arming is done, the ESC can start running based on the PWM pulses you put in (still has to be between 1ms - 2ms).

Dec 22, 2010, 06:20 AM
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Okay, Anybody know where I can do the calculations to get the correct AVR timer settings for 1-2ms? Im using a Pololu SVP 1284 (Atmega 1248p)
Dec 23, 2010, 02:37 PM
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Dec 23, 2010, 08:22 PM
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You need to generate a signal of 50Hz, and then vary the duty cycle, if you go read the source code from all those open source Multi-copters you can see how its done, or you can go to the forum which is the official Atmel forum for the Avr chips and do a search about pwm+servo or servo+control, even google will give you good results.
I'm saying you to go to search not because I'm a mean person, but reading 2 or 3 topics ans pages/blogs about this will teach you a lot about the timers.
Some links so you dont have to do the search:
Dec 24, 2010, 10:25 AM
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Kevo500's Avatar
Originally Posted by Julian90
Also I havent heard a Beep or whatever coming from the ESC. What have I done wrong?
While it may not be helpful to your current problem .. Just wanted to note that the beeps you hear actually come from the motor , not the esc itself.

The esc uses the motor as its "speaker" when beeping.

Just wanted to bring that up .. in case you were listening for beeps whithout a motor attached.
Dec 25, 2010, 06:21 AM
Registered User
Thanks for your replies, first of all Senso, I really didnt know what to search for really.. Did lots of searches on PWM control, Timer HZ etc etc. Didnt really pan out.. Thanks for the keywords and the urls.

Thanks kevo, I did think the sounds came from the ESC, however i still had a motor attached so. This is good to know tho

I will have a go at this, i'll let you know
Dec 25, 2010, 06:24 AM
Registered User
The problem creating a 50hz PWM frequency was the fact that with the Pololu SVP 1284, I can use timers 0 and 2 (both 8 bit timers), but according to the registries, they dont have a manual 'top' function on ICR, i tried anyway. This got me kinda confused on what to do. Ill have a go later on

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