I am starting a new project to develop some automated roller blinds.
I would like the roller blinds to be "off grid" use solar cell on the window to charge battery's then initiate a motor twice a day, day and night to open and close the blinds.
There are already tutorials for this using a stepper motor, but the problem with the stepper motor is they require power to hold position, use more power and are generally expensive.
I would like to know if this would be possible with a continuous servo motor to accurately close them fully and open them again. maybe by calibrating using power on for a set time interval. or would there be any better alternatives or motor options.
Secondly would the project be feasible using a solar cell to power the arduino and motor.
example solar cell: http://goo.gl/iCnDAk
Using a continuous servo (which is just a DC motor with a gearbox and electronics) you will need a limit switch to tell the Arduino when the blind gets to the top or the bottom. You can't control the position of a continuous rotation servo.
You may still have the problem of needing power to hold position unless the friction of the gears is sufficient.
A DC motor with a worm gear will hold position without power.
Figuring out the size of solar panel and battery is not simple. I suspect they will be much bigger than you expect.
You need to figure out how much energy the motor and the Arduino need each day and then you need to choose a combination of solar cell and battery that can provide enough energy after taking account of battery inefficiency and variations in sunshine due to weather and the time of year.
The size of the panel depends on:
The size of the motor (power requirement).
The battery being used.
Power required to run the Arduino.
Where in the world you are.
Daily hours of sunlight.
I would expect that the panel you have suggested would be no good. For a start it is only 5.5V and 180mA. What battery are you planning to use? This panel would not be able to do much more than power the Arduino unless you make large efforts to reduce power.
Robin2:
Using a continuous servo (which is just a DC motor with a gearbox and electronics) you will need a limit switch to tell the Arduino when the blind gets to the top or the bottom. You can't control the position of a continuous rotation servo.
You may still have the problem of needing power to hold position unless the friction of the gears is sufficient.
A DC motor with a worm gear will hold position without power.
Figuring out the size of solar panel and battery is not simple. I suspect they will be much bigger than you expect.
You need to figure out how much energy the motor and the Arduino need each day and then you need to choose a combination of solar cell and battery that can provide enough energy after taking account of battery inefficiency and variations in sunshine due to weather and the time of year.
How about controlling the position using a trip switch, attaching a contact to the blind at the opened and closed positions to trip the motor when it reaches the set point, would that work?
That's a great idea using a worm gear although will a standard dc motor have enough torque without gearing?
The power consumption may be hard one to work out until I know how long the motor will be on for (how many revolutions it has to make)
weedpharma:
The size of the panel depends on:
The size of the motor (power requirement).
The battery being used.
Power required to run the Arduino.
Where in the world you are.
Daily hours of sunlight.
I would expect that the panel you have suggested would be no good. For a start it is only 5.5V and 180mA. What battery are you planning to use? This panel would not be able to do much more than power the Arduino unless you make large efforts to reduce power.
Weedpharma
I hadn't decided on a suitable battery yet. given I live in the UK where it is generally dull and gloomy would you be able to suggest a solar cell and battery that would be sufficient to run the arduino and standard 5v motor 2 times a day for, lets say 30 seconds.
We need to know which motor you want to use and its actual current draw.
We also need to know what Arduino you are using and its current draw.
The battery to be used is also required to match the panel.
Practicalities are:
Arduino needs 5V, or 7V+ for the Vin. To get 5V for the 5V input, you need 7V to feed the regulator. This suggests that you need at least a 7V battery. Common batteries are 6V, 12V or more.
You need current sufficient to charge the battery while powering the Arduino while the battery needs to be able to keep it all going if there is no sun for a few days. The battery should not be discharged more than 50% during this time.
It also depends on the location, on the equator you get a lot more power than Greenland using the same panel.
The time of year determines how many hours a day the sun shines.
At this time, we do not have enough information to make any recommendations for panel or battery.
I understand that there is no "standard 5v motor" I have not chosen a motor and wanted a estimate given an example motor.
But everyone seems to be very negative on this forum, Instead of just shooting down anything I say and correcting me on my mistakes maybe you could suggest motors, solar cells and batteries that may be suitable for this application, as the reason I came on here is for help not to be told what will not work all day but ways to make it work. I have just started out with electronics and I am always looking for help and ways to improve, this the reason I have joined the forum.
I have no set parts I am using for the project and would like suggestions.
I have many 3V motors rated at:
Rated Voltage: 3.0V
Rated load current 1.07A
but i don't believe these would be suitable for this application as I don't think they have enough torque to be able to open the blind.
I also have spare a continuous rotation servo which runs at 4.8v or 6v delivering 3.3kg/cm or 4.8kg/cm of torque.
but I am willing to buy new motors for the project based on suggestions.
Remove the friction or locking mechanism from a roller blind so it rotates very freely.
Consider adding a counterbalance weight on a small pulley wheel (ideally so it balances with blind half way down).
Fit a small motor with worm drive gearbox.
Somehow use photo sensors to sense when the blind is fully up or fully down.
Use custom electronics, not an Arduino, for much lower power consumption and significantly greater operating voltage range.
Use the voltage from the solar cell to determine when to close the blind at dusk and open at dawn (yes, I know it would be nice to have a real time clock to open at a set time in the morning).
Add a button to open blind if necessary on a very dark morning.
The problem is if I set them to go down based on sunlight is that if I have multiple blinds around the house they would all go off at different times and would there be issues with them going down during cloudy or dark stormy weather?
How about if I set them to go off via rf or wifi from a central raspberry pi running a node js server as I pretty good with JavaScript and node js. Then the circuit wouldn't need to take photo readings or track time and they can all be adjusted at once. World this use less power?
but i don't believe these would be suitable for this application as I don't think they have enough torque to be able to open the blind.
The very first step is to measure the force required to open the blind (in Newtons) and the distance over which the force is to be applied (in meters). The product gives you the total energy in Joules.
One watt is one Joule/second, which gives you the power needed to open the blinds. Double that to get the basic motor power spec. Calculating the torque requires knowing the pulley and gearbox specification.
aztekgold:
How about if I set them to go off via rf or wifi from a central raspberry pi running a node js server as I pretty good with JavaScript and node js. Then the circuit wouldn't need to take photo readings or track time and they can all be adjusted at once. World this use less power?
How many different sets of blinds do you want to control and how far apart are they?
Adding more computers will increase your energy consumption.
If you need more than one Arduino because of the distance between blinds maybe you could use one as the master controller and pass the up-down command to the others over a couple of wires. You will probably need wires in any case to bring power to the various blinds. I don't think it would make sense to have a separate solar panel and battery for each blind.
But everyone seems to be very negative on this forum, Instead of just shooting down anything I say and correcting me on my mistakes maybe you could suggest motors, solar cells and batteries that may be suitable for this application, as the reason I came on here is for help not to be told what will not work all day but ways to make it work. I have just started out with electronics and I am always looking for help and ways to improve, this the reason I have joined the forum.
The problem is that you have not really provided any technical details about 1) your blind or 2) just what you want the blind to do. I'd suggest you drop the roller blind and go with a wand operated Venetian blind. A long time ago I used a servo to operate one of these (attached pix) turning the main blind shaft. A six turn continuous rotation servo could probably be used to turn the wand.
