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Gadget Freak Case #215: Automating the Doggie Door

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Charles Murray
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Inexpensive
Charles Murray   6/5/2012 6:56:46 PM
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Nice job, Les. I always like to look at the BOM to see how expensive the parts are, and it looks like their's nothing expensive there (some of the parts weren't clickable, but none appear very costly). Cost is usually the governing factor on these ideas, and this seems doable on the production level.

novahokie
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Iron
Re: Inexpensive
novahokie   6/5/2012 10:04:48 PM
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Yes, at high volume the parts add up to about $10 per opener, including the remote control.

GlennA
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Gold
How are you with hand tools ?
GlennA   6/6/2012 9:51:57 AM
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Nadine J;  How are you with a tape measure, jig saw, drill etc ?  I opened the lower storm window, removed the window screen and fitted a piece of polycarbonate (Lexan also works) into the window frame.  I can remove the polycarbonate at any time to revert to a regular window.  I installed a cat door into the polycarbonate.  Then I added some insulation.  The inner double hung window still clears the assembly.  In the morning I open the window to let the cats out, and close it at night after they are in.  During the day they come and go as they please.  I didn't like the idea of a magnet-key in case the cats' lost their collar.  The outside window ledge is about 6 feet off of the ground - the cats use the central A/C unit as a step, but an uninvited human would find other windows more inviting if motivated to break in.  I also installed a cat door into a piece of 1/2 inch plywood that sits in the sliding door frame for use when we are home.

William K.
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Platinum
Automating a dog door, or cat door
William K.   6/6/2012 10:04:35 AM
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Really, vertical opening is the only practical way to do it, since the door can close by gravity, which is much safer, and yet be constrained very well by the guide channels. A swing-action door would need a latch, which would add a lot of complexity, and still need a separate mechanism for opening and closing. A solenoid would not be suitable for either opening or closing because the force increases as the stroke progresses. The radio coller is the most common, although an RFID type system would work very well, but cost more. A proximity system would probably let all kinds of animals in and allow a major disaster. Picture a racoon attempting to escape after raiding the kitchen pantry.

Keeping humans from using a cat entrance could easily be done by electrifying the whole window frame. Cats are two small to touch both the window frame and ground at the same time, while a human would stand on the ground and make contact with the frame quite natrually. Yes, it would harm the burglar, but one could always claim that it was an electrical fault caused by thier tampering with the door drive mechanism. 

Rob Spiegel
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Blogger
Re: Inexpensive
Rob Spiegel   6/6/2012 12:40:15 PM
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That cost makes the gadget surprisingly inexpensive, Les. Were you seeking a design that would favor low-cost parts, or did it just work out that way as you put the gadget together?

NadineJ
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Platinum
Re: How are you with hand tools ?
NadineJ   6/6/2012 2:08:52 PM
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@GlennA - I like it.  That's a great point about cats loosing collars.  I suppose you could embed a chip in the cat but that would increase the overall cost.  Shocking burglars is a tempting benefit.

I love discovering soloutions for renters in urban areas to live well without risking eviction. 

You've all inspired me to start that ebook...add to list.

novahokie
User Rank
Iron
Re: Inexpensive
novahokie   6/6/2012 2:35:16 PM
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When I made my 1st prototype I didn't care about looks too much, I was using 120V AC for power, and it probably added up to close to $100 to make it.  But once I started considering making them to sell and learned that the final retail prices you see in stores for things is usually 5X-10X what the materials cost it became obvious really quickly that I needed to optimize everything possible.  My investor, distributor, company heads, and others I ended up working with also convinced me that it needed to run on batteries, AND get smaller, all at the same time to be a viable product.  Those 3 conflicting goals let to what remains the biggest design challenge: getting enough pulling force AND enough stroke, using a minimum number of the smallest batteries possible (to reduce size).  As 1 of the readers mentioned earlier, the force solenoids can exert drops dramatically with their shaft extension, and I need my maximum pulling force when the shaft is fully extended, so I basically had to sacrifice some stroke length from what I really wanted to make sure it would have enough pulling force at that extended position to pull back the latch reliably when activated.  The flap version of this Gadget Freak has a little longer stroke than the original version for crates because the force needed to pull the smooth rod back out of the screw eye you see in the video is much less than what might be necessary to pull a latch back on a typical wire crate, due to friction I've seen a lot due to warpage of the crate panels, misalignment of the doors, etc.  But after all the dust settled though I reduced the $100 down to about $10, batteries included!

Rob Spiegel
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Blogger
Re: Inexpensive
Rob Spiegel   6/6/2012 2:46:32 PM
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Thanks for the detail, Les. I would guess this is a common way for a product in development. First you prove it without undue concern about costs. Once you have your working prototype, it's time to review the BOM and manufacturing process to come up with an economically realistic version.

robatnorcross
User Rank
Gold
Re: Automating a dog door, or cat door
robatnorcross   6/6/2012 6:21:21 PM
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My families dog (Charlie) invented this decades ago. He trained the humans in the house to come and open the door at his command. He stood by the door and barked once. If we didn't respond in a timely manner he barked twice (you get the idea. When he wanted back in he did exactly the same thing.

May be people should just get smarter pets.

If WE were as smart as he was we would have taken out a patent.

William K.
User Rank
Platinum
Automated pet doors
William K.   6/6/2012 10:19:16 PM
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The successful doors that I have seen did not use a solenoid to open the door. Not only is the force to displacement curve the opposite of what is required, but also any solenoid able to do the job will draw way too much current. The commercial units that I saw used a small motor to raise the door, which does a far better job and consumes less power.

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