Seeking way to automate rotation of temperature knob on gas boiler

[winelight]

I'm looking for a home automation solution to rotate a knob through 180°.
It's a plastic knob of 25mm diameter.

Rotation speed is not an issue. It can take minutes to do the 180°.

Resolution is also not an issue. If I can only stop it every 30 degrees or so, so six or seven positions overall, that's fine.

I've been looking at reversible DC motors that have a built-in gearbox.
I would drive this from an Amazon Echo controlling a Sonoff RF Bridge sending signals to a a 433mhz controlled relay board, in order to turn the motor in either direction.

I would only have the crude timing resolution of 5 seconds offered by Alexa routines. For example, if a full rotation takes 1 minute, 5 seconds would approximate to 30 degrees.

I realise that this would almost certainly result in drift (because the 5 seconds you get from Alexa is only very rough), so I would need limit switches, and a routine to drive it to one end or the other, to reset its position occasionally.

Firstly, is there a better or easier way of doing this please?

And secondly, how do I transfer the rotary drive from my controlling device, which would have to be mounted about 500 mm away in the vertical plane? I imagine some sort of pully or sprocket wheel, clamped on, or around, the existing knob.

It's the temperature control in the attached photo.

 

[ericmark]

I would use an elastic band to drive the knob or a wheel using some other friction drive so it can slip at end of travel. However the main question has to be why?

I have the same control with my boiler, and I can't understand why I am given the control to start with? I know the hotter the radiators are the faster they heat the room, but the temperature of the radiator is controlled by the lock shield valve and thermostatic radiator valve (TRV) and we are told there should be a gradient of temperature across the radiator so in real terms the temperature of the water leaving the boiler makes very little difference to room temperature.

I have used time to control a motor rather than stops, with a drive which could slip, also used stepper motors, but 433 Mhz is a shared band, and I seem to remember I can use a far bit of power on this band 40 watt, excepts within 100km radius centred near Charing Cross, London. I only have a 5 watt transceiver my self, but it is not a reliable frequency to use. Without a licence I think limited to 10 mW so it can be swamped so easy.

 

[mattylad]

@winelight, in your picture the top of the panel appears to have brown staining on - is this correct?
If so then I think you need your boiler looking at by an RGI soonest.

As for the variable temperature control, yes using a stepper motor fed from a driver board and an arduino/pi is a project but I'm not entirely sure that your allowed to do that to a gas appliance - perhaps an RGI can chip in on this?
What make/model boiler is it? you may be able to get an electronic temperature control to fit it.

 

[winelight]

Thanks for the comments.

Well first off it's an antique boiler, hence the discolouration, and it is stripped down / tested / measured / checked / parts replaced as necessary by an expert in this model every year, but it's a Servowarm and hence there are no other controls at all, no room thermostat, no TRVs, and so adjusting this 2-3 times a day is what that you need to do to get reasonably constant temperatures in the house.

Sure it could be a microcontroller project but really I want to find a way to avoid that.

A rubber band drive sounds reasonable as the least intrusive technique, because I really don't want to touch the boiler itself, even if it would be legal for me to do so.

FYI 433MHz is what's used by any remote controls you have that aren't infrared, so for garage doors, security gates, my car, curtain / blind motors, linear actuators in general, and most commonly for remote controlled sockets/plugs. So you can already buy reversible motor drives operated by 433MHz, for example for opening / closing curtains and blinds, but these are expensive, hence my preference for a DIY solution of some kind.

 

[ericmark]

In general however old the boiler there is a over temperature device to stop it over heating, so by-pass valve and TRV's would seem the best option.

Don't forget the by-pass valve, when that opens and sends hot water back to boiler the boiler will shut off, but without that valve there may be no flow.

I use programmable TRV heads, not expensive £15 each I paid for bluetooth, £10 without bluetooth I used eQ-3. I will be first to admit not perfect, but not looking for perfect, near enough engineering is what I want.

Like you I have a boiler (oil) which does not modulate, and is simple off/on, I do have thermostatic control with Nest, but that is mainly to turn temperature down at night and when not home, it does not control room temperatures.

The boiler is around 18 kW which is not very big for a three story house, and the TRV heads have transformed to heat up times, so easy when you think about it, I get home and start the meal, then I eat the meal, then watch TV, so there is a 15 minute delay kitchen first, then dinning room then living room and then bedrooms so boiler heats the rooms in order of use, so the rooms used are warm faster.

Once hall is warm heating goes off, not the best idea, I really don't care if the hall is cold, I don't sit or stand in the hall for long, however it is central to house, so best location for average temperature. However the hall radiator is two doors away from the wall thermostat, so there is far too much of a delay in the thermostat registering the heat, as said not perfect, so I cheat in a way, and set thermostat to raise the temperature 0.5°C per hour it is more to ensure the boiler fires up on a regular basis than controlling temperature, the TRV heads control the temperature.

This

is my main control. And the button with moon and sun swaps eco to comfort and I walk in room and touch the button, which I have set to 17°C and 20°C the bar graph at top shows when it auto changes, no wiring, so simple, but it works.

 

[MeldrewsMate]

An interesting project. I am also confused as to why, but that's not my concern. There are many proprietary products that will combine to give you adequate room and hot water temperature control with the Servowarm (Glowworm?) boiler that you have...but that's not what you asked.

I would suggest you gen-up on the Arduino, then buy an Arduino Uno or Nano, plus a stepper motor and drive to suit (there is also a variant called We-Mo that has wireless comms built-in). The torque will be just enough to turn your control knob via the elastic band, thus avoiding any intrusion into the boiler.
There is plenty of wireless and stepper motor software available on the www.arduino.cc website.

From that position I assume you will want to drive your boiler temperature automatically in response to room or hot water temperature, and for this you will have to measure those variables.
All straightforward and fairly easy to do....but again, why go to all that trouble to make an old boiler do what a modern one does for itself (see OpenTherm), unless it's just an avenue to improve/develop your coding skills.

Good luck though.

 

[winelight]

Thank you for your thoughts.

Firstly it's not my boiler nor house so that's why I'm looking for a solution that I can simply affix to the existing knob and remove if necessary.

The boiler is a Servowarm Elite 50 and there's manuals and diagrams available on the web for anyone interested.

I don't have the time, space or inclination to buy a PC, install and maintain an Atmel development environment, and then embark on a development project, which is why I'm seeking a solution using out-of-the-box off-the-shelf components, as far as possible.

As to why, although there is no room thermostat, it is possible to maintain a reasonably constant temperature in the house by adjusting this control a few times during the day, typically when I'm out of the house or busy doing something else, or even if I am available, on those rare occasions, I forget anyway.

 

[ericmark]

I see your problem, I would fit TRV's mainly to keep things simple and standard. In my youth I had some really good ideas I thought to keep equipment running, however no one else could work out what I had done, I thought it was simple, but no one else did it seems, so in latter life looked for standard way around a problem so others could come along latter and fix it.

I looked for TRV and found them at £4.70 and an electronic TRV head at £10 so it simply does not seem worth the time and effort to fit non standard controls.

Looking at manual it seems designed to use a time clock or thermostat, so again seems a lot of work for nothing.

 

[MeldrewsMate]

I don't have the time, space or inclination....which is why I'm seeking a solution using out-of-the-box off-the-shelf components, as far as possible.

Out of the box temperature control of the room could be achievable using the programmable TRVs suggested by ericmark. I can't help you with an out-of-the-box elastic band driver.

 

[Why Not Indeed]

I would look into acquiring a knob that mounts on the same shaft as the existing one, then affixing something to that in order to avoid damaging the one that's there now [simply put the original one back when you're done].
You could translate this motion 500mm vertically with something as simple as Lego chain drive and a couple of sprockets. If "500mm away" is on the sheet metal front of the boiler then whatever is at the other end driving this could be held on with strong magnets.
Ideally you want something that knows its position like a servo so that it doesn't go out of tune.

 

[winelight]

I do hear what most of you are saying. Yes TRVs is probably a rather more sensible idea.

When the guy comes to do the annual service in the summer I'll ask him whether that's something he could easily do. (If I do plumbing then you can be sure things will break, will be incompatible sizes and fittings, and then will leak when, after several trips to the plumbers merchants, I eventually get it all back to together.)

 

[Why Not Indeed]

Smart TRV heads are a quick and easy thing to do if you've already got TRVs [swapping a TRV head is barely even plumbing, IMO]. If you don't have TRVs already, then it's a case of replacing one of the valves on every radiator. How much longer do you plan to live there? Not sure I'd be spending my money on upgrading someone else's heating system.

 

[picasso]

If only someone could invent a programmable room stat that could turn the boiler off and on at whatever time and temp you wanted, there would be no need for elastic bands!

 

[winelight]

I think this boiler is designed to run continuously, firstly, secondly I don't have the freedom to go drilling holes through walls etc. So that's not an option. Sorry if that wasn't clear from my first post. Otherwise of course I would just have fitted a thermostat years ago.

 

[jonm01]

How about a wireless room stat ? No need to drill walls then.