What kind of motor would I need to turn this central heating valve?

Question

I often forget to turn my central heating down when I leave the house, so I thought it would be cool to make a device that could do it for me and to have a website where I can check and change the heating. I was thinking about using the Arduino with an Ethernet shield for this. Programming won't really be a problem. I am however totally new to motors, and I have no clue as to which kind of motor would be suitable for this. This is the knob:

The idea is to have a motor sit next to it and attach four arms to it that fit in the corners of the knob. I'll also add a potentiometer to be able to control it when I'm home.

So, is this possible? Thanks!

Edit: So I understand this is not the best solution and that it would be better to hack a thermostat or use an electric valve, but unfortunately both of those things are not an option for me. I have just one radiator (this one) and that's it. So I'd still like to know what kind of motor would be suitable for this. I was thinking a servo would be good but that limits me to 180 degrees of rotation, and I need a little bit less than 360. There are ways to get more than 180 degrees, but that would remove the position feedback thingy. Do I even need that?

Answer 1

I once visited a hackerspace that was trying to make a light bulb throb between bright and dim for a replica TARDIS. Their solution was to get an ordinary dimmer, such as you'd mount in your wall, then mechanically link this to an RC hobby servo controlled by an Arduino.

It worked, for a few hours. Then something would break, every time.

Then, I showed them how to put a triac on an ATtiny. Not only was this solution about three orders of magnitude cheaper, it never broke.

Here's the lesson: just because you do something with your hands doesn't mean a machine should. This is why industrial automation robots look like this:

and not like this:

There are machines designed to control the flow of heated water to your radiator, and they don't look like hands to grab the knob that's already there. By searching for "electric radiator valve", I found this, available from decorisland.com:

It looks like the interface is two wires, and you apply a voltage to open the valve. This should be pretty easy to interface with an Arduino. But, it's also probably compatible with a standard wall-mount thermostat. You could even get one of the many internet enabled thermostats on the market (such as by Honeywell or Nest) and skip the Arduino, avoiding this problem:

Answer 2

While it may seem unlikely that your landlord will care much, most are at least somewhat approachable. If you offer to pay the building superintendent fit a wireless smart digital thermostat and are prepared to leave it in place or remove it again at your cost when you leave there should be relatively little resistance.

This picture search should give you ideas.

PS. trying to roll your own for a one off will be educational but will not likely save you any time or money.

EDIT:
The building may already have some in use and can recommend a compatible type. The new digital smart units can usually be programmed to do time slots even when in standalone operation.

Answer 3

The device in your photo is a thermostatic radiator valve (TRV). Usually the standard screw valve is replaced with a push-valve which is shut off by pushing a pin. An actuator head is screwed onto the valve to drive the pin.

Figure 1. A mechanical TRV. A thermal element (often a plug of wax-like material) expands with temperature and pushes the pin and valve disk down to shut off the water. Setpoint is adjusted by rotating the knob and moving the actuator closer or further from the pin.

A wide range of programmable heads are available to easily replace the actuator provided the push-valve is already there.

Figure 2. Electronic TRVs are available in standalone and networked versions. The heads can be retro-fitted onto existing TRVs.

Further reading:

• http://openhab.org.
• http://opentrv.org.