Powering Embedded Controller, ESC and Motors

Thread Starter

AF_Maxwell

Joined Dec 12, 2018
25
Hi, I have a problem which I have been making progress with but am confused as to why and what's going on.

Aim: to control 4 racestar motors using the racestar 4in1 35A esc using PWM from a bluepill, system powered by one lipo with a bec stepping voltage from 12v to 5v 3A.

Problem: inconsistent motor performance, sometimes the motors calibrate and arm properly then run exactly as they should from minimum throttle to maximum throttle - sometimes they calibrate and arm but don't run and sometimes they calibrate and arm and run at higher throttle values.

Cause and effect: the main thing that introduces problems is expanding the total amount of components that run off the bec. Adding more components both reduces the bec output voltage and seems to be causing voltage spikes (not entirely convinced of the latter).

Signal chain:
3S Lipo > 1000uF ESR cap > 4 in 1 ESC > 12v output of ESC to switch with snubber > Switch output to BEC > Bec output to bluepill, HC05 bluetooth module, mpu6050 with 100uF caps on each of their inputs > bluepill pwm to esc pwm input > motors.

Experience so far: when the BEC output isn't 5V or very close to it the ESC can't properly interpret the PWM values. The amount of time the embedded power source differs from 5V and the range it differs basically determines how many faults seem to occur. However even if the power rails are something stupid like 3.5V to 7V the PWM output of the bluepill is still a PWM output and behaves perfectly fine except increased or decreased in amplitude. There is no noise at all in the PWM output. So it's probably because the ESC fails to capture the timing of the PWM if its voltage range is off. The switch was causing spikes and a snubber stopped this problem altogether, the motors were also causing a fluctuating battery voltage so a large ESR cap on the lipo output was used and this solved that problem. The HC05 has a large inrush current causing the voltage to fall for a brief second but this was solved with the cap on its input.

Now I want to add the ESP32 cam with Wifi capability but the module requires 300mA at 5v. Now the BEC should be able to output 300mA and the embedded system as a whole is likely only draining a 100mA or less when the bluetooth module HC05 is transmitting (my assumption) so there should be ample space for the ESP32 Camera and Wifi board but no matter how I attempt to connect it the PWM can't be interpreted by the ESC. Also the wifi card isn't displaying a wifi signal when powered from the BEC.

It seems like a simple problem but I'm fresh out of ideas as of what to do. The only solution seems to be to get a BEC that has good regulation.

Also I've tried to add a 7805 regulator separately to the BEC to power the ESP32 Camera Wifi module but it heats up and the wifi signal can't be found.

Note every single part of this embedded system works when powered via USB individually so the components don't seem to be damaged.

Problem components;
https://www.nextfpv.com.au/products/f295-dsun-clone-mini-adjustable-dc-dc-step-down-bec
https://www.olimex.com/Products/IoT/ESP32/ESP32-CAM/
 

trebla

Joined Jun 29, 2019
177
Can you show some scematics? First thing i noticed that you are using 1000uF cap in lipo side of the BEC. Better is place this cap to 5V side because there is more voltage fluctuations possible then in battery side, where voltage drop is more smooth, depending how much charge is left. And second thing - what is capacity of LiPo battery you use?
 

Irving

Joined Jan 30, 2016
940
What's your estimated maximum current draw on the 5v side? I think your issue may be that you are making some assumptions about the BEC's capability based on the marketing guff on the web page and not what the chip is actually capable of.

What motors are you using on that ESC?
 

ci139

Joined Jul 11, 2016
1,671
the ESC can't properly interpret the PWM values. The amount of time the embedded power source differs from 5
(although trivia) i'm sorry to propose that such may be pointing to a design shortcoming to stay immune to supply voltage variations --e.g.-- is there any control currents/-voltages that "source" from the supply voltage value ...
 

trebla

Joined Jun 29, 2019
177
One thing comes on mind, what kind of PWM the Bluepill board outputs? ESC usually needs servo-type PWM signal (50Hz, 1-2ms pulse).
 
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