### What exactly do I control when sending a certain PWM signal to an ESC?

Hi All

I want to ask a question that, after reading about it and watching YouTube videos, I still don't have a clear understanding about:

What exactly do I control when sending a certain PWM signal to an ESC? Is it thrust? RPM? Current?

An example:

I have a drone with a 3S battery, 30A ESCs, 2300kV motors, and 5x3 props.

If I now send a PWM signal of 1500us, i.e. 50% throttle, what happens?

- Do the ESCs draw 15 A (=  30A * 0.5) ?

- Do the motors spin at 13800 RPM (= 2300 kV * 12V * 0.5)

- something else?

Say I now change the props from 5x3 to 6x4. Thus it generates more thrust at a given speed, compared to the 5x3 prop.

Everything else (battery, ESC, motor, PWM signal) being equal, what is now different?

- Does the prop generate the same amount of thrust but spin slower?

- Does the prop spin at the same speed but draw more current?

- something else?

Thanks for your help.

You need to be a member of diydrones to add comments!

#### Replies

• Thank you for that explanation, it's very insightful.

One thing I still don't quite understand: What causes the current flowing through the motor to increase with increasing load? Since the ESC apparently does not change its behavior depending on the load.

Nando te Riele said:

Using a 30A esc does not mean you are consuming 30A, it only means that the ESC should stay in one piece until 30A (with cooling) not that it actually does 30A at full throttle.

What PWM controls is Duty-Cycle. (normally, not true in governor mode for example)

Or to say it in another way, the Voltage going from the ESC to the motor. (close enough)

Kv= how many RPM you have to turn the motor to generate 1V, not the other way around

If you take the number and multiply by ~0,75 or 0,8 (dependent on the load on the motor) you get close enough for most people)

So you calculation of "13800 RPM (= 2300 kV * 12V * 0.5)" would be in the ballpark if you compensate for losses

2300 kV * 11.7 (voltage under load) * 0.5(duty cycle) *0.8 (losses, etc)=~10764

When you change propeller size from 5x3 to 6x4 your load increases: the motor will draw more current and do less RPM (@ the same dutycyle).

• Using a 30A esc does not mean you are consuming 30A, it only means that the ESC should stay in one piece until 30A (with cooling) not that it actually does 30A at full throttle.

What PWM controls is Duty-Cycle. (normally, not true in governor mode for example)

Or to say it in another way, the Voltage going from the ESC to the motor. (close enough)

Kv= how many RPM you have to turn the motor to generate 1V, not the other way around

If you take the number and multiply by ~0,75 or 0,8 (dependent on the load on the motor) you get close enough for most people)

So you calculation of "13800 RPM (= 2300 kV * 12V * 0.5)" would be in the ballpark if you compensate for losses

2300 kV * 11.7 (voltage under load) * 0.5(duty cycle) *0.8 (losses, etc)=~10764

When you change propeller size from 5x3 to 6x4 your load increases: the motor will draw more current and do less RPM (@ the same dutycyle).

• No bo not assume any thing ! Know or ask questions, ESC operates using PWM PPM SIGNALS reseved only ! They do not send any signals, what ever loop is being implied from Flight controller it sends and receives signals.

• Certainly the PWM signal plays a role. It ultimately determines what the ESC and the motor does.

I'm assuming the ESC runs some closed-loop control loop, where the input (i.e. the setpoint) is the PWM signal. My question is, what is the feedback variable in this control loop which shall be controlled to match the input (in other words, what am I commanding with the PWM signal?). Is it current draw, RPM?

Are you saying it's RPM?

OG said:

you are straining the motor and ESC bring it out of the it's efficiency range causing it to draw more current by adding larger prop the KV RATINGS AND MOTOR SPEED do not change. PWM signals have nothing to do with this ???

• you are straining the motor and ESC bring it out of the it's efficiency range causing it to draw more current by adding larger prop the KV RATINGS AND MOTOR SPEED do not change. PWM signals have nothing to do with this ???

This reply was deleted.

### Activity

DIY Robocars via Twitter
RT @gclue_akira: 柏の葉で走行させてるjetracerの中身　#instantNeRF #jetracer https://t.co/giVvuE4hP7
Jul 4
DIY Robocars via Twitter
Cool web-based self-driving simulator. Click save when the AI does the right thing https://github.com/pncsoares/self-driving-car
Jul 4
DIY Robocars via Twitter
RT @donkey_car: Human-scale Donkey Car! Hope this makes it to a @diyrobocars race https://www.youtube.com/watch?v=ZMaf031U8jg
Jun 25
DIY Robocars via Twitter
RT @GrantEMoe: I won my first @diyrobocars @donkey_car virtual race! Many thanks to @chr1sa @EllerbachMaxime @tawnkramer and everyone who m…
Jun 13
DIY Robocars via Twitter
RT @gclue_akira: JetRacerで自動走行したコースを、InstantNeRFで再構築。データセットは別々に収集 #jetracer #instantNeRT https://t.co/T8zjg3MFyO
Jun 13
DIY Robocars via Twitter
RT @SmallpixelCar: SPC 3.0 Now the motor also works. This car is doable. I just need to design a deck to mount my compute and sensors. http…
Jun 13
DIY Robocars via Twitter
RT @SmallpixelCar: My new car SPC 3.0. https://t.co/CKtkZOxeNQ
Jun 7
DIY Robocars via Twitter
RT @SmallpixelCar: High speed at @diyrobocars thanks @EdwardM26321707 for sharing the video https://t.co/o4317Y2U1S
Jun 7
DIY Robocars via Twitter
RT @SmallpixelCar: Today at @RAMS_RC_Club for @diyrobocars. Used @emlid RTK GPS and @adafruit @BoschGlobal IMU. Lap time 28s https://t.co/R…
May 28
DIY Robocars via Twitter
May 13
DIY Robocars via Twitter
RT @f1tenth: Say hi to our newest #F1TENTH creation for @ieee_ras_icra next week in Philly. It’s going to be huge! 😎 🔥 @AutowareFdn @PennEn…
May 13