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Servo Control  with Micropython - with the ESP 8266 ...- compared to Arduino 

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tarifa    0
Posted (edited)

hello dear community, :)

 

first of all - i hope that my beginner-question will fit into this sub-forum.  I hope so. 


Servo Control  with Micropython - with the ESP 8266 ...- compared to Arduino 


I work with young kids and I'm always looking for economical platforms to build intriguing projects. While we can say that Arduino clones are pretty cheap, it uses the C/C++ language that the kids are not familiar with. This is pretty challenging. Also and furthermore, it doesn't have a built-in WiFi which is a must for all the IoT projects that i have in mind. On the other hand, while Raspberry Pi has WIFI and kids can program it using Python, it is still an expensive platform to just control few GPIO ports to turn devices on and off. I need something in between that has both WIFI and Python capabilities. It appears that I found my answer in MicroPython flashed onto a cheap ESP8266-based board.


so going the Micropython way is a good thing i thought;


now - for the RC-Car Projects i have in mind  i found a interesting library. + see this  Micropython Library for Hobby Servo Control for ESP8266

cf: https://bitbucket.org/thesheep/micropython-servo/src/default/

This is a simple class for controlling hobby servos with Micropython on the ESP8266 boards. 


It's in fact a simple convenience wrapper over the machine.PWM functionality. Currently, the supported pins are 0, 2, 4, 5, 12, 13, 14, 15 

-- because only those pins are supported by machine.PWM. Pins 1 and 3 may become supported in the future.

usage: To use this library, we simply need to copy it to the ESP8266's filesystem, 
or include it in the scripts directory while compiling the Micropython firmware.
cf: https://bitbucket.org/thesheep/micropython-servo/src/default/

work and use case: The way the servos work is that we send them a square wave signal with a fixed frequency (for analog servos this is usually 50Hz, but the digital servos may be furthermore able to accept up to 300Hz signals): with that the duty cycle controls the servo position exactly. The tradition is that at duty cycle of 1500µs the servo goes to its center position.  


well - I have a question an an idea. 

is 3V3 enough to run this!? The thing that looks interesting to me in this class is the fact,
that in the example for the ESP min is said to be 40 and max to be 115...  and I allways thought how can we make 180° out off that (Chapter 7.2) cf http://docs.micropython.org/en/latest/esp8266/tutorial/pwm.html?highlight=servo#control-a-hobby-servo


generally spoken - and compared to the Arduino: Then I looked into the source and saw that this used totally differnent values for min and max microseconds 600 and 2400. Well if we compare this to the Arduino reference and they to also took totally different values 1000 to 2000. See: Is it a depending on the servo manufacture that some values are min is 400 µs lower and the max is 400 µs larger. 

the question to me: Why are the examples from the mircopython docu totaly different?
Finally i want to add an idea. What about an read method, at least the arduino has got one. ;)
https://www.arduino.cc/en/Reference/ServoWriteMicroseconds


BTW one question: - do we need that library - cannot we just start without that... - cf this post:

https://icircuit.net/micropython-controlling-servo-esp32-nodemcu/2385
Servos are exciting devices. We can get precise posting with minimal code, all we need is a controller that can produce PWM at 50Hz. 

the main thing is to understand how to use ESP32 to control Servo. We will be using micropython to program ESP32/NodeMCU. The greate thing about MicroPython is that it is platform independent (mostly),  which means code written for NodeMCU (ESP8266) can be used on ESP32 as well.

To use MicroPython on ESP32, First we need to load MicroPython Interpreter. Check out ESP32 
– Getting started with MicroPython post to load interpreter and tools you can use with micro python. https://icircuit.net/esp32-micropython-getting-started/1999
If you are using NodeMCU, then refer to this post https://icircuit.net/nodemcu-getting-started-micropython/2406   by the way: MicroPython has PWM support. You can find full documentation of PWM library here http://docs.micropython.org/en/latest/esp8266/tutorial/pwm.html


Environment requirements:

we need a ESP32 or NodeMCU

Machine with uPyCraft to load python files to the device

Controlling Servo: Connect servo signal pin to GPIO2 of the ESP, you need to power the servo as well

Code: All you need is couple of python lines to control the servo, how easy is that


import machine
p4 = machine.Pin(4)
servo = machine.PWM(p4,freq=50)
# duty for servo is between 40 - 115
servo.duty(100)

The PWM method of machine takes two inputs, the pin to which we want connect servo 
(in case of ESP8266 we can choose one from 0, 2, 4, 5, 12, 13, 14 and 15) and frequency of the PWM signal. Most of the hobby servos work with 50Hz PWM, so we choose that. Then we can use duty method to set the angle we can call servo.duty() method to change the set the servo angle

 


so the question is just  - do we need that library - cannot we just start without that

love to hear from you 

Edited by tarifa

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MeaganArky    0

Hi...the ESP32 is an all around much more capable part - more pins, better on-chip peripherals, more ram - one particularly helpful thing for your purposes may be that it has bluetooth. If the kids you are working with are old enough to have their own smartphones, that might be an attractive feature.
It comes down in large part to budget - Generic ESP8266 boards are dirt ###### cheap, such that you don't even have to care if your students trash them. ESP32 boards aren't all that much more expensive.
 

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