DIY TRV with 28BJY-48 & ULN2003 & D1 Mini: would this work?

Hi guys, I cannot replace the valves since they are part of the piping system.
I was wondering if it would be possible to control the existing knob with a steppermotor and want to give it a try with a DIY project.
Since I have never used these kind of motors I have no clue it this could work so therefor this topic.

I found a webshop that sells these kind parts where I also will be ordering some zigbee devices.
From what I found here and elsewhere, I thought of getting following parts:

  • 28BJY-48 with ULN2003 (they come as a unit)
  • D1 Mini - ESP8266-12F - CH340
  • a power adapter (have no idea what is needed, except that the motor needs 5V)

The valves have very low resistance so I thought of connecting the motor directly to the knob in some way, but with a 1 to 1 ratio (the physical ‘connection’ between motor & knob will by trial & error)

  1. does anyone know if this could work; I mean, does this motor have enough torque to turn the knob?
  2. what kind of power source do I need to power the motor/driver & the D1 mini (given I can power them with the same adapter)

Thanks in advance for your help/ideas!

You need to figure out the torque needed to turn the valves.
You could make the gear you intend to use on the valve mount it and then fix a string on it.
Let the string hang free under the valve.
At the free hanging end you then tie a somewhat solid empty plastic bottle and then you slowly fill this bottle with water until your valve start to turn (remember to place the valve so it actually can turn further in the direction :)).
When the valve turns then find the weight of the bottle with content.

Now measure the radius of the gear or take half the diameter.
Now the torque your valve provide will be 9,81radiusweight
If you use meters for radius and kilograms for weight, then the result will come out as Newton meters (Nm).

radius = ½cm
weight = ½Kg
torque = 9,81 * 0,005 * 0,5 = 0,024525 Nm

You can find torque conversion homepages in google to convert this.

You then need to find the specifications for your stepper motor.
You need to find the holding torque, which is the estimated max value for the weight the motor can stay in position with. Your motor value need to be higher than the value you calculated above.

Beware that there are multiple different motors with the same housing, so you need to be sure you look at the right data. Motors can have different voltage, different gearing and just be made different internally, but still look the same on the outside.
The 28BYJ is typically a unipolar motor, but can easily be converted to a bipolar, which increase the torque.

I hope this is correct, because I use that procedure right now to try and smartify by wooden blinds.

A bit about the 28BYJ’s abilities: 28BYJ-48 Stepper Motor Torque testing and achieving maximum torque - Baba Awesam - YouTube
The driver board I have looked at for my project: Easy Driver stepper motor driver
A little about using a stepper motor (hint: notice the common ground): Arduino Tutorial 35: Understanding How to Use a Stepper Motor - YouTube
28BYJ changed to bipolar and used for blinds: Motorize and Automate your Blinds for $10! (WiFi) - YouTube

And remember to power off your motor after actions or it will use power to hold the position and it will the get pretty hot (up to 130c).

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