Automated cat window opener.

[paulca]

It didn't take much research to find a casement (side/single hung) window opener/actuator.  They come in 24V form too.

Given they "claim" up to 400N force, although in cheap AliExpress form they probably only produce half that.  It's still 20Kg of force.  Even (I think) when you take the angles and torque/moments into account.

A cat tail or paw in the opening or the "jam" and this motor sounds like it could cause pain and even damage.

I found a very old thread elsewhere where someone suggested using a 12V car window motor.  The ideal being that they shouldn't be able to provide enough force without stalling out to prevent fingers getting nipped in windows etc.  Others had suggested truck wiper motors....  these do not have any concern for fingers and I have been hit by a wiper blade in motion and ... it did make an attempt to nearly slash my face open while physically pushing me out of it's way.

I was considering a complicated current sense shunt and a latch circuit to cut the motor power for a second maybe if it's current hits a value where the motor is going to deliver too much force for a finger in the window jam.

It occurred to me an even simpler limiter would just by a power resistor.  If the window opener draws a sensible amount of current, then a sensible amount of voltage will drop across the resistor.  If the motor stalls and the current rises more and more will drop across the resistor.

Then it occured to me that the motor and it's windings are ...  electrical engineering magic things beyond my understanding.

I'm going to guess, something like:  The stalled current spike is caused by the coil reading saturation (the rotar is not moving the magnetic field is not being driven, behaving like low ohm resistor.  Thus a series resistor of a fixed value would struggle to limit the current successfully.

Back to the current "trip" circuit.  Possibly with, possibly without an automatic recovery. 

For the opener to function as a "let the cat out" device it will have to have other automation.  Some of it will be in software, some may even be on a server.  So there is the capacity for the "current overload" status to "signal" to the automation and the "automatic recovery" could be triggered either by a "power down" or a "reversal".  Such that the hardware "lock out" remains in force until there is signs of awareness by intervention.

For the actual automation, that's far more about my cat's particular behaviour than it is electronics.  I have a range of sensors available for this, from basic smart buttons under a sheet of plastic that triggers when cat stands on it, to ultra-sonic prox sensors, motion sensors etc.  I expect a combination and a bit of fiddling.  "IR Beam sensors" are also an option, particularly for determining when the cat is standing IN the window opening.... as they have a tendency to do while deciding. 

Other things "nice to have" would be a "false start" when closing.  Make the window move suddenly, but only for a tiny distance.  This should be enough to spook the cat out the way.  Then the window will close 2 seconds later.  Relying on the beam sensors to stop it if the cat gets in it and the current limiter as back up such that if the cat is STILL in the gap somehow it only gets a gentle squeeze for a few milliseconds.  The window, if this is signaled to the automation, could then reopen, pause for 1 minute and then repeat the attempt to close.

How to tell if it's the cat or a cat burglar?  This is worth considering.  I'm still working with this.

[Psi]

You can also try running the motor from a lower voltage so its very slow and has little torque.
That way the cat has plenty of time to move his tail/paw out of the way as it slowly closes.

[eutectique]

How to tell if it's the cat or a cat burglar?

You should consider some sort of face control. It can be a neighbour's cat. It can be your cat inviting a neighbour's cat. It can be your cat with a gift for you in his/her mouth.

[pcprogrammer]

Or just get one of these.

Have your cat chipped and it will be the only one to use the flap.

[paulca]

How to tell if it's the cat or a cat burglar?

You should consider some sort of face control. It can be a neighbour's cat. It can be your cat inviting a neighbour's cat. It can be your cat with a gift for you in his/her mouth.

She is well beyond that now.  She brings me them alive.  I take this as the compliment it is, but I also fitted her with a bell now.

[coromonadalix]

some used  RFID tags on the collar   but face recognition  is going .....

[themadhippy]

Why reinvent the wheel,the cat already has an automatic window opener,you.

[woody]

Or just get one of these.

Have your cat chipped and it will be the only one to use the flap.

I can vouch for these. They work great. At least, the type that is connected to the internet, with an app to control them. Now the nice people at SurePetCare know when my cats are out of the house (and the mice dance on the table)

(I hope more people acquire these, as the only problem with these flaps is that they use batteries like a camel uses water. More users mean chances increase that someone gets fed up and designs a silent power supply to replace those four AA cells)

[paulca]

Why reinvent the wheel,the cat already has an automatic window opener,you.

Yep.  The cat has.  She also has an automatic door opener, she had figured out how to "rap the letter box"

Hence the need.

[paulca]

Or just get one of these.

Have your cat chipped and it will be the only one to use the flap.

I can vouch for these. They work great. At least, the type that is connected to the internet, with an app to control them. Now the nice people at SurePetCare know when my cats are out of the house (and the mice dance on the table)

(I hope more people acquire these, as the only problem with these flaps is that they use batteries like a camel uses water. More users mean chances increase that someone gets fed up and designs a silent power supply to replace those four AA cells)

Yes, it is a viable option.  The "Connect variety" can, apparently be hacked to work locally with MQTT.

Installation in the glazing or PVC windows seemed expensive to me, but apparently it shouldn't need to be.  Especially as I have a plastic only panel on the front door.

[Muxr]

Why reinvent the wheel,the cat already has an automatic window opener,you.

Organic window opener 

[Bud]

Or just get one of these.

Have your cat chipped and it will be the only one to use the flap.

I can vouch for these. They work great. At least, the type that is connected to the internet, with an app to control them.

Holy cat mama! They now put cats on the cloud 

[xrunner]

Dang. They should put one of them kitty kat doors on Schrodinger's box. Then there would be three states - alive, dead, or checked out with RFID. 

[wofritz]

Or just get one of these.

Have your cat chipped and it will be the only one to use the flap.

I have one of these. At the beginning it's quite funny to get a notification when a cat enters the door or an unknown animal is detected (It has some kind of proximity sensor besides the RFID). It makes my mobile phone meow.

The door works without the "cloud". Everything can be configured with the buttons on the door.

The door closes only by gravity. So if the cat is gentle (like mine) the door might not lock and "unprogrammed" cats enter the house (it happened!)

The RFID detection works flawlessly.

[pcprogrammer]

Or just get one of these.

Have your cat chipped and it will be the only one to use the flap.

I have one of these. At the beginning it's quite funny to get a notification when a cat enters the door or an unknown animal is detected (It has some kind of proximity sensor besides the RFID). It makes my mobile phone meow.

The door works without the "cloud". Everything can be configured with the buttons on the door.

The door closes only by gravity. So if the cat is gentle (like mine) the door might not lock and "unprogrammed" cats enter the house (it happened!)

The RFID detection works flawlessly.

Never happened here, but maintenance is needed when the cats are wet and dirty. Was a problem for us out here in the country side. Lots of muck on the forest floor. It gets in where the latch goes down and may corrode the inside a bit.

[paulca]

Dang. They should put one of them kitty kat doors on Schrodinger's box. Then there would be three states - alive, dead, or checked out with RFID. 

... and if the Internet is down or the cloud service isn't working, you are back to the original problem of not knowing if the cat is alive or dead.

[paulca]

Or just get one of these.

Have your cat chipped and it will be the only one to use the flap.

I have one of these. At the beginning it's quite funny to get a notification when a cat enters the door or an unknown animal is detected (It has some kind of proximity sensor besides the RFID). It makes my mobile phone meow.

The door works without the "cloud". Everything can be configured with the buttons on the door.

The door closes only by gravity. So if the cat is gentle (like mine) the door might not lock and "unprogrammed" cats enter the house (it happened!)

The RFID detection works flawlessly.

Thanks.  It is good to know it works "unsmart" without the cloud, meaning I can actually use it while I hack it.

The hack is, well, I call it a hack as it's technically invasive to a degree.  You DNS poison the cloud address and then place a trojan web-service in it's place locally.  Then you borrow the code someone diligently wrote to mimic the important parts of it as an HTTP->MQTT bridge.  I should be able to take it from there.