siltuz
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Motors

Thu May 29, 2014 1:12 pm

Hey all,
I have had great success with this forum so far on all my projects, and it occurred to me today that my Pi could control the blinds in my workshop, which are fairly laborious to reach, by having a motor spin a wooden piece that would slot into the blinds beaded string thingy... yeah technical. anyway, the wood bit I can do easy enough, but I have never had the pleasure of working with motors, and as such I don't know what would be the best way of going about that side of things. My aim is simplicity, and reliability. My only programming experience is in python and a very small amount of Java.
so my first thought was Servo motors, but with python's unreliability (especially as this same pi constantly runs other programs in the background such as temperature monitoring), would that work to be able to achieve a set number of rotations that would wind the blind up or down perfectly, preferably linked to the time, (I.e. 7am till 10pm) or based on light (although the problem there is the street light right outside the window could maybe distort it right?).
So the first and most important part, which I hope to sort as soon as possible, is the parts list. I've seen many different motors supported by different bridges or something, but I have no idea how to link which with which, nor what motor would be suitable.
So far, I know I will need some more wires, some kind of motor, some kind of bridge to said motor (possibly) and a power source (most likely batteries) for the motor. Is there anything else?

thanks a lot guys!

BMS Doug
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Re: Motors

Thu May 29, 2014 4:46 pm

Probably the easiest route would be to purchase a commercially available blind motor and modify it to be run by the pi.
Doug.
Building Management Systems Engineer.

siltuz
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Re: Motors

Thu May 29, 2014 5:20 pm

That is a little over my budget for it, and modifying an existing product may be over my experience level, plus I would like to learn more about motors for further projects too. In terms of the blind as well I feel I should mention that the blind is a roll blind as well (if this makes a difference)

kbfirebreather
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Re: Motors

Thu May 29, 2014 5:23 pm

You could get a motor with encoder to be able to position it how you want. Or you could try a motor without an encoder and knowing how much it turns with each pulse, you could calculate/experiment to figure out how many pulses will raise/lower your blinds.

siltuz
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Re: Motors

Thu May 29, 2014 5:59 pm

kbfirebreather wrote:You could get a motor with encoder to be able to position it how you want. Or you could try a motor without an encoder and knowing how much it turns with each pulse, you could calculate/experiment to figure out how many pulses will raise/lower your blinds.
would Python work for the pulses? I know the speed of pulses can vary with python but in terms of amounts of pulses, is that possible to code reliably?
and what kind of motor without an encoder would you recommend?

Ravenous
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Re: Motors

Fri May 30, 2014 8:41 am

The beaded string thing that angles the blinds could be run between two rubber pulleys. With the right diameter pulley, slightly less than one turn would go between open and closed. Then a gear motor and two limit switches (to stop it going too far) might do the trick.

Alternatively, you could just use the motor and pulleys - no controller. Just put two switches (on/off and reversing) in a convenient place you can reach.

I suppose the messy bit is building the mechanical thingie with the pulleys and screwing it to a wall. (Or make it heavy and sit it on the windowsill????)

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Cancelor
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Re: Motors

Fri May 30, 2014 3:09 pm

Two other possibilities ...... have a couple of limit switches, one that activates when the blinds are up and the when they are down.

or ... just let the motor stall when it gets to the end.
Can't find the thread you want? Try googling : YourSearchHere site:raspberrypi.org

siltuz
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Re: Motors

Fri May 30, 2014 4:47 pm

Ravenous wrote:The beaded string thing that angles the blinds could be run between two rubber pulleys. With the right diameter pulley, slightly less than one turn would go between open and closed. Then a gear motor and two limit switches (to stop it going too far) might do the trick.

Alternatively, you could just use the motor and pulleys - no controller. Just put two switches (on/off and reversing) in a convenient place you can reach.

I suppose the messy bit is building the mechanical thingie with the pulleys and screwing it to a wall. (Or make it heavy and sit it on the windowsill????)
The pulley system and motor seems a good idea, but i'd like to use the Pi as the controller purely for the experience of doing it through that, for the day when maybe I could control the entire room with it.
For the messy bit, it's no problem really, I can mount it up fairly simply and I don't care if it looks a bit off or ought
Cancelor wrote:Two other possibilities ...... have a couple of limit switches, one that activates when the blinds are up and the when they are down.

or ... just let the motor stall when it gets to the end.
I'll definitely look into the limit switch idea, not quite sure what they are but the internet is a beautiful thing

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Cancelor
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Re: Motors

Fri May 30, 2014 5:55 pm

I just used google to see what you would get ;-) ... some are well expensive!!! .... I meant one like this https://www.egr.msu.edu/eceshop/Parts_I ... switch.jpg Maplin or RS do them.

I'm thinking of a switch that gets activated when something presses against it i.e. the blind gets to the top, pushed against it and closes a switch that in turn sends a signal to the RPi to stop the motor.
Can't find the thread you want? Try googling : YourSearchHere site:raspberrypi.org

johndough
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Re: Motors

Sat May 31, 2014 8:45 am

Cancelor wrote:I just used google to see what you would get ;-) ... some are well expensive!!! .... I meant one like this https://www.egr.msu.edu/eceshop/Parts_I ... switch.jpg Maplin or RS do them.

I'm thinking of a switch that gets activated when something presses against it i.e. the blind gets to the top, pushed against it and closes a switch that in turn sends a signal to the RPi to stop the motor.

Hiya

Well the limit switch could be directly in the motor direction line, and the PI has a run time of X.XX seconds as a back up.

If you blind rotates 6 times from top to bottom then a gearing of 12 to 1 will give a position for a limit switch, and another about 180 degrees further on.

No great force would be needed so plastic parts would suffice.

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Cancelor
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Re: Motors

Fri Jun 13, 2014 12:30 pm

Can't find the thread you want? Try googling : YourSearchHere site:raspberrypi.org

rgrbic
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Re: Motors

Fri Jun 13, 2014 11:13 pm

DC motor can be used for this purpose. To drive the motor you need appropriate circuitry. If you want to have variable speed then something like L298N can do the task but you need to generate PWM signal. If you want to drive the motor with only one speed then simple switch like transistor can do the task (but keep in mind that you need to provide both directions of rotation). Pi can activate this circuitry over GPIO (consider galvanic isolation).
Put some limit switches for top and down. These switches will provide Pi information about state of the blinds. Apart from that, some kind of overcurrent protection should be implemented (what if blinds get stuck?)
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johndough
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Re: Motors

Sat Jun 14, 2014 8:59 am

siltuz wrote:Hey all,
I have had great success with this forum so far on all my projects, and it occurred to me today that my Pi could control the blinds in my workshop,

thanks a lot guys!
Hi

Well Chivas Regal had large manual fire doors, and to wind them up took hours.

So they duplicated the driving mechanism and then motorised it, setting the motor at low level.

As it is a roller blind you would probably do very little damage if it overran slightly. Fit a driver cog/wheel to the ballchain, plastic knobbly string;)) at low level, setting the tension carefully.

Then by turning it by hand the roller blind should move.

Next is a small electric motor (DC) and a pair of switches.

The weighted bottom bar could be capable of tripping switches, especially if one end was extended slightly and it ran in guides.

So if you can achieve the mechanical steps to this point, and then ask about the switches etc we can then move on to the actual Pi and sensors.

If you dont get the Pi to work autonomously, you still have a motorised blind to ease your daily grind.

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mikronauts
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Re: Motors

Sun Jun 15, 2014 2:11 am

Just found this thread... good time to find it as well, as wifey has been asking me to automate opening/closing the curtains in our living room!

I have a pile of different gear motors in my lab, I just don't know how much torque it will take to open/close the curtains (still debating weather I should measure it, or just experiment) - mind you, it does not have to open/close very quickly.

The limit switches will be easy to add, I just got a shipment of 2" lever micro switches.
http://Mikronauts.com - home of EZasPi, RoboPi, Pi Rtc Dio and Pi Jumper @Mikronauts on Twitter
Advanced Robotics, I/O expansion and prototyping boards for the Raspberry Pi

rgrbic
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Re: Motors

Sun Jun 15, 2014 8:58 am

Few years ago I was partially involved in such project. I will post few images tomorrow.
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rgrbic
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Re: Motors

Mon Jun 16, 2014 7:53 am

Here are the images of the motor and magnetic sensor (magnetic contact switch)
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