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.
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!
@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.
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?
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.
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.
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.
You could also create another device that pivots/opens a door radially instead of my current device that only provides a lateral translation for the latch, if it was necessary to open/close a pivoting door.... or use a guillotine or sliding door and keep the current design because a sliding door would only require lateral motion. In other words, my current device would pull open and later shut the door. The challenge would be getting solenoids strong enough and with long enough travel to do that if you needed to stick with battery-powered operation (which was a major challenge in my development)... however, if you were free to use AC power like I had for my prototype then it becomes a lot easier. There are already "gate openers" on the market that people use to open gates at the ends of their driveways, let out livestock, etc... one of those might be just what you need!
Yes, we've heard from a couple of folks who have chickens.... apparently the organic chicken market is pretty vibrant! It's very easy to train a dog to nudge open any door when they hear the click of the opener unlatch it, especially after they've gotten used to listening for it - which only takes a couple of times. I haven't tested with any chickens yet, but the other chicken farmers tell me chickens would be able to open a light door and come out. Shutting doors later is another topic I've thought about a lot and have some ideas about, but haven't built any prototypes for yet because that aspect is more dependent on the particular application - i.e. what type of animal, what type of door, how/when do you want it to close, will the animal go back in on their own or not, etc. For example for applications where the animal would naturally go back in on their own during the day you could just spring load the door they come out in the morning such that it would shut after they leave their coop in the morning, lock it remotely with 1 of my boxes equipped with a "push" solenoid inside it instead of its normal "pull" type that pulls open the latches, or use a combination push/pull solenoid (they're a little more expensive but available) and then let the animals return inside in the evenings through a 2nd flap/etc. with a simple setup that allows them to pass through to go back into the coop/pen/etc. in the one direction but not the other. For example a very light spring-loaded pivoting flap.
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