Hi,
I would like to turn a domestic common ball valve (shown below) with a motor and also have an option to manually turn it.
Please help me with these questions:
Hmmm not easy … how are you with metal work ?
Have a look at commercial motorised valves and see how they work for inspiration .
I’d prob use a geared motor - slow speed hi torque .
Have a search of this forum , it has come up before
Hi, @johnmgm
Welcome to the forum.
Can I suggest you turn your logic around.
Look for a motor controlled ball valve that you can also operate manually.
Unless you have the necessary mechanical building skills, or access to same, a ready made device would serve you better.
Tom.... 
Would appreciate your help to build the needed skills 
What size ball valve? The bigger they are the harder they are to turn, requiring a larger motor or more gear reduction. Larger motors require more electrical power, which require larger and more expensive power supplies.
What type of equipment/tools do you have to work with?
How will the motor mount? Will the mounts be welded or brazed to the valve body? Or maybe secure brackets to a clamp to clamp around the body.
It will probably have either a brass body of a galvanized steel body. If galvanized steel, any welding will burn off the galvanizing and allow corrosion to take place. If it is a brass body, any welding/brazing is a skilled endeavor using the proper equipment.
Either way, if welding or brazing, It will have to be taken apart and reassembled. The ball is either plastic or rubber. It will melt.
I assume you are lacking on manufacturing skills so maybe welding is out.
Maybe fashion a clamp of some sort to clamp to the body. Bolt the motor mounts to the clamp. It is basic fab skills. Using a drill and a tap to make threads.
@TomGeorge has a good suggestion. But if you want to learn I say go right on ahead and learn.
BUT--Sometimes, buying the premade version is MUCH more efficient/less expensive/makes better sense than buying hundreds of dollars worth of equipment to build a 20$ part. Unless you need an excuse to buy stuff!
Hi @scottcalv
I watched https://m.youtube.com/watch?v=kDaRmqbQVFU and I want to understand their approach little deeper especially the mechanical side of things
The video has a link to ready made and inexpensive Wifi Faucets
I watched most of the youtube link. That can be replicated, but not easily for a manufacturing beginnner. It even has a “manual” transmission that moves a gear so it can be in neutral. They do use a clamp to secure it to the valve or pipe. There is no encoding system, only micro switches at the end of the travel. So the valve will only be OPEN or CLOSED. It did look like you can stop it in midstroke with a button to get a partially OPEN/CLOSED state. BUT you have to observe it to know when to stop it. I am unsure if you can stop it via wifi, I did not watch that part of the video. So without visually seeing the handle position, you do not know if it is almost closed, 1/2 open, etc…
The switches and buttons could be coded with a pretty easy state machine I think. Look up state machines. There are plenty of examples for things like garage door openers where the states are OPEM, CLOSING, CLOSED, OPENING, STOPPED. I certainly can not help with the wifi coding and the app development. Those two things are beyond my level of coding. You might be able to use a premade wifi relay for direction control.
Once again, what type of tools and manufacturing equipment do you have or have access to? A lot can be done with a hacksaw and a file and a drill.
I would also recommend maybe modeling it in a 3D modeler of some sort. There are free ones on the internet. I like Fusion 360 myself. I use a paid version (it has features the free one doesn’t), but the free version is FAR MORE CAPABLE than I am. If you can model it, even by hand with a pencil and paper, that is a good start. You need to envision how all the moving mechanisms will work. And then envision where all the parts will go neatly and not get in each other’s way.
In fact, watch the video again, get some ideas, and model one up first. Start with a design.
Edited: Start with your requirements, then make a design.
Thanks a lot, @scottcalv Yes, I need to get started with the modelling of it.
As a software developer, I don't have issues with coding.
On the mechanical side, I've been able to understand that we need to have a gearmotor connected to a gear that moves the valve handle that in turn moves the arm of the valve with limit switches on both the sides.
Could you shed some light on the pull ring clutch part?
That type of valve, a quarter turn valve, are relatively easy to turn when new.
Over time and depending what you are using it for - water? - they can become tighter.
Cheap ones can have chrome plated balls and when the plating starts to come off, it graunches up the sealing 'O' rings.
Look for stainless steel balls and hex sockets internally to dissemble them.
Also, some are described as full bore valves, i.e. same bore as the pipework.
Left long enough without being used, they seize up altogether.
Sometimes, depending on medium, a PVC valve fairs better.
In some industries, waste or dirty water, PVC is preferred.
A gate valve might be a better choice for motorising as the stem is turned multiple times to raise and lower the gate. A good stepper would be easier to fit and use.
All valves need use to be reliable. A daily "exercise" routine helps.
Central heating valves like Honeywell V4043A are already motorised and reasonably priced.
It's not a clutch, it just pulls one of the gears out out place so that it does not engage with the other gears. However I don't see how you could pull the ring when it's mounted to the pipe.
If DIY is not the main purpose here, just pick a ready made motorized valve. You can find different configurations and powering options with manual function at ~$40.
Hi @scottcalv
Thank you so much for helping with a sketch.
Could you please take a look at https://m.youtube.com/watch?v=kDaRmqbQVFU and guess what kind of gears they would have used?
No need to guess. The picture shows metal spur gears. Then there is enclosed part just under the motor which we can’s see which contains more gears.
look like plastic ones or maybe carbon fiber?
The narrative in the video states they are metal.
You right!
Looks like quite good value.
I'd want to know what they mean by "remains in its new position while expending almost no energy."
This sounds like a synchronous motor type commonly used in UK central heating system. 3/4" is close to UK 22-mm. They work by the motor powering in one direction with a spring return. There's a manual lever that can be latched for draining.
The UK ones like the Honeywell 4043A suffer from a design compromise where the motor drives to one position, a microswitch turns off the AC power, but a diode and resistor put a small DC current onto the motor which stalls it and the gearing keeps it in place. I think this is what they mean by almost no energy. The Honeywell design is widely copied.
Where it looks better than the Honeywell is that it is a ball valve rather than a rubber ball on a lever. It should have much better operating pressures.
The other downside is it's either fully closed or open. If it is the stalling type, it should be possible to do away with the microswitches and stall it in any position by swapping the power to DC.
This stalled condition generates heat and eventually causes the insulation to fail. Plumbers love it. The pawl and pinion gearing wears out as well.
