Encourage or discourage my crazy litterbox design
December 20, 2024 7:24 AM Subscribe
I have a notion for how to design an easy-to-sift pine-pellet litterbox. It's inspired in some part by the ideas behind the Omega Paw Roll'n'Clean and compost tumblers. It's lodged in my head and I need to either be talked out of it or given a sense of how I might turn this idea into reality.
First off: I know it's quite impossible to offer any advice about cats without being able to see pictures of the cats in question. So, to address that concern, here are the regal and complacent Kokopelli (left) and tiny-legged newcomer Hecate (right); adventurous, easily bored Wisakedjak; and adorable but skittish Baba Yaga.
Second: pine pellets, for those not familiar with them, have a sifting process rather unlike clumpling litters. Pine pellets are small compressed cylinders of woodshavings, about 6mm or so in diameter. When they get wet (e.g. when urinated upon), they dissolve into sawdust. Routine cleaning of a pine-pellet box is a two-stage process: empty the whole box into a sifting tray and sift. Then (doing the opposite of what one would do for clumping litter), you throw out the sifted bits (which are sawdust) and put the larger pieces back in the box. Then you can use a wide-slatted litter scoop to extract feces (which are usually larger than the pine pellets, which fall between the slats of the scoop.
This is easier than I make it sound, but the key notion is, you want to keep everything above sawdust size and smaller than a smallish poop. So here's what I'm envisioning, in three stages of development:
Phase I design (sawdust-sifting only): the chamber itself is a cylinder lying on the lateral surface , with an opening on one end (with some redesign it could be open on both, but let's stick with this for simplicity), and that opening has a lip that's a few inches wide. The chamber rests on a freely-rotating casters on a fixed frame so that the chamber can rota freely, but and is suspended a little above the ground. Somewhere on the frame should also be a lock which can be slid into a notch on the side of the chamber to inhibit rotation. There's room to slide a shallow, wide bin under the chamber, and a crank on the back of the chamber to make it easy to rotate (optional; you could rotate it by hand from the side). Most importantly, on the top of the chamber, running the entire length of it and at least a quarter of the circumference, there's a hinged panel which can securely lock in place (this could be done with a single mechanical latch together with sufficiently strong magnets, I think), but this panel isn't solid like the rest of the chamber---it's made of a mesh material with holes large enough to pass sawdust but not pellets. Operation of this device is pretty easy: for adding pellets and removing feces, you open the panel and do what you do. You fill with pellets to below the lip, so that they don't easily fall out (can't help cats kicking them out, but that's always a problem). To remove the sawdust, though, which can sometimes be a fiddly operation involving multiple separate trays, you just turn the crank a few times. The chamber rotates, and as the mesh top reaches the bottom, the pellets slide over it while the sawdust falls through. Ideal rotation speed and number of rotations might take a while to dial in, but it seems that as long as the rotation provides some agitation to the contents, over multiple spins most of the sawdust will come out. When not sifting sawdust, the aforementioned rotation lock is engaged so that it doesn't accidentally become a cat exercise wheel and fling litter everywhere.
Phase II design (feces-catcher): add to this design a J-shaped (or reverse-J-shaped) section of much coarser mesh, attached on the hinge side of the sifting surface, and extending down into the chamber, then curving under the sifting surface and back up maybe half of the distance it came downwards. This design is sifted in exactly the same way as before, except now it has a preferred direction it needs to be rotated to work properly. If you rotate so that the hinge side comes downwards last, the contents roll over the Phase I sifting surface like normal, but then they also pass through the Phase II catcher, which will be in a scoop-like orientation at 180° rotation, and then from there back to upright, it'll be basket-shaped (going from upright back to upside-down, it'll spill, although designing the edge to be curled back, midway beween a J shape and a lowercase-d-shape, will mitigate that). So when we rotate this, it will not only sift sawdust out into the pan, but also catch larger-than-pellet-sized chunks in this little basket, which can then be emptied. Since it's mounted on the hinge side, it should swing only a small distance and in a way which doesn't spill when the hinge is opened.
Extra design feature (litter-flinging prevention): Hang a rubber sheet down on the interior of the entrance to the chamber. Glue a few metal plates to the bottom of the sheet, and put indentations in the front of the chamber's lip where these plates will hang. Before rotating, put strong magnets in the indentation to hold the sheet in place; afterwards, remove them so that the sheet provides no resistance to cats entering.
Automation details: this could form the core of an automated system easily enough. The rotation lock on the frame could be solenoid-actuated, the rotation motorized, and the flap magnets replaced with electromagnets. If it's automated I'd definitely want to make the flap electromagnets weak enough that a cat in duress could easily overcome their grippiness, because you don't want to be trapping a beastie in there --- the chamber-rotation process looks like it's not likely to hurt a cat trapped in there, but even so it'd be very unpleasant and I'd just as soon that, if an automated process started with a cat inside it, the cat could reasonably get out.
So this is in the realm of pure fantasy at the moment, but much of it seems reasonable. With the right size and material for the cylinder's lateral faces (and I have no idea what those would be, but I'm thinking repurposing some size and shape of cylindrical trash receptacle could be a place to start) the lip and back face could easily be made out of plywood. All the components seem plausible, and if sourced correctly, potentially inexpensive.
So am I being stupid? Is this a terrible idea? Is this a thing which already exists? Are there fabrication details which are obvious to other people? Id love to make this idea a reality, and document the process and tools, so that others could replicate it, because it seems like if it works right it could be a very good pine-pellet system.
First off: I know it's quite impossible to offer any advice about cats without being able to see pictures of the cats in question. So, to address that concern, here are the regal and complacent Kokopelli (left) and tiny-legged newcomer Hecate (right); adventurous, easily bored Wisakedjak; and adorable but skittish Baba Yaga.
Second: pine pellets, for those not familiar with them, have a sifting process rather unlike clumpling litters. Pine pellets are small compressed cylinders of woodshavings, about 6mm or so in diameter. When they get wet (e.g. when urinated upon), they dissolve into sawdust. Routine cleaning of a pine-pellet box is a two-stage process: empty the whole box into a sifting tray and sift. Then (doing the opposite of what one would do for clumping litter), you throw out the sifted bits (which are sawdust) and put the larger pieces back in the box. Then you can use a wide-slatted litter scoop to extract feces (which are usually larger than the pine pellets, which fall between the slats of the scoop.
This is easier than I make it sound, but the key notion is, you want to keep everything above sawdust size and smaller than a smallish poop. So here's what I'm envisioning, in three stages of development:
Phase I design (sawdust-sifting only): the chamber itself is a cylinder lying on the lateral surface , with an opening on one end (with some redesign it could be open on both, but let's stick with this for simplicity), and that opening has a lip that's a few inches wide. The chamber rests on a freely-rotating casters on a fixed frame so that the chamber can rota freely, but and is suspended a little above the ground. Somewhere on the frame should also be a lock which can be slid into a notch on the side of the chamber to inhibit rotation. There's room to slide a shallow, wide bin under the chamber, and a crank on the back of the chamber to make it easy to rotate (optional; you could rotate it by hand from the side). Most importantly, on the top of the chamber, running the entire length of it and at least a quarter of the circumference, there's a hinged panel which can securely lock in place (this could be done with a single mechanical latch together with sufficiently strong magnets, I think), but this panel isn't solid like the rest of the chamber---it's made of a mesh material with holes large enough to pass sawdust but not pellets. Operation of this device is pretty easy: for adding pellets and removing feces, you open the panel and do what you do. You fill with pellets to below the lip, so that they don't easily fall out (can't help cats kicking them out, but that's always a problem). To remove the sawdust, though, which can sometimes be a fiddly operation involving multiple separate trays, you just turn the crank a few times. The chamber rotates, and as the mesh top reaches the bottom, the pellets slide over it while the sawdust falls through. Ideal rotation speed and number of rotations might take a while to dial in, but it seems that as long as the rotation provides some agitation to the contents, over multiple spins most of the sawdust will come out. When not sifting sawdust, the aforementioned rotation lock is engaged so that it doesn't accidentally become a cat exercise wheel and fling litter everywhere.
Phase II design (feces-catcher): add to this design a J-shaped (or reverse-J-shaped) section of much coarser mesh, attached on the hinge side of the sifting surface, and extending down into the chamber, then curving under the sifting surface and back up maybe half of the distance it came downwards. This design is sifted in exactly the same way as before, except now it has a preferred direction it needs to be rotated to work properly. If you rotate so that the hinge side comes downwards last, the contents roll over the Phase I sifting surface like normal, but then they also pass through the Phase II catcher, which will be in a scoop-like orientation at 180° rotation, and then from there back to upright, it'll be basket-shaped (going from upright back to upside-down, it'll spill, although designing the edge to be curled back, midway beween a J shape and a lowercase-d-shape, will mitigate that). So when we rotate this, it will not only sift sawdust out into the pan, but also catch larger-than-pellet-sized chunks in this little basket, which can then be emptied. Since it's mounted on the hinge side, it should swing only a small distance and in a way which doesn't spill when the hinge is opened.
Extra design feature (litter-flinging prevention): Hang a rubber sheet down on the interior of the entrance to the chamber. Glue a few metal plates to the bottom of the sheet, and put indentations in the front of the chamber's lip where these plates will hang. Before rotating, put strong magnets in the indentation to hold the sheet in place; afterwards, remove them so that the sheet provides no resistance to cats entering.
Automation details: this could form the core of an automated system easily enough. The rotation lock on the frame could be solenoid-actuated, the rotation motorized, and the flap magnets replaced with electromagnets. If it's automated I'd definitely want to make the flap electromagnets weak enough that a cat in duress could easily overcome their grippiness, because you don't want to be trapping a beastie in there --- the chamber-rotation process looks like it's not likely to hurt a cat trapped in there, but even so it'd be very unpleasant and I'd just as soon that, if an automated process started with a cat inside it, the cat could reasonably get out.
So this is in the realm of pure fantasy at the moment, but much of it seems reasonable. With the right size and material for the cylinder's lateral faces (and I have no idea what those would be, but I'm thinking repurposing some size and shape of cylindrical trash receptacle could be a place to start) the lip and back face could easily be made out of plywood. All the components seem plausible, and if sourced correctly, potentially inexpensive.
So am I being stupid? Is this a terrible idea? Is this a thing which already exists? Are there fabrication details which are obvious to other people? Id love to make this idea a reality, and document the process and tools, so that others could replicate it, because it seems like if it works right it could be a very good pine-pellet system.
Best answer: Go to a maker space near you and start chatting up the machinists / CNC experts!
Colleges with engineering or product design programs are another good place to start if you run into a dead end of maker spaces. Sometimes they’ll have a community open-house, a class that needs projects to work on with outside community members, etc.
posted by seemoorglass at 8:27 AM on December 20, 2024 [1 favorite]
Colleges with engineering or product design programs are another good place to start if you run into a dead end of maker spaces. Sometimes they’ll have a community open-house, a class that needs projects to work on with outside community members, etc.
posted by seemoorglass at 8:27 AM on December 20, 2024 [1 favorite]
Best answer: Pine pellets were my litter of choice for about 5 years (for my cats, people!), so I'm familiar with the basic movements for separating old and new litter, and poopy and not-poopy parts.
Overall I like the idea, but I'm wondering if you considered an option (that I think would be simpler?) to shake/agitate the tray in place into something below. It's much closer to the existing set-up of, for instance, the Purina Breeze box placed on top of a regular litter box (as in this video, the original I think - don't miss the part where she runs her hands through dirty litter). Like the method in that video, I never emptied litter into a sifting tray but rather agitated into a larger litter box below, then threw that out with the puppy pad. So I'm thinking a linear back and forth motion would be easier to pull off than rotational, and wouldn't require you to create a large tube that
☐ some
☐ all
☐ none
of the cats might use.
Linear agitation's not as cool, true. I say go for it with the design you have in mind, and I agree with seemoorglass about prototyping it. You'll inevitably see improvements for the one you envision when you do that.
posted by cocoagirl at 10:01 AM on December 20, 2024 [1 favorite]
Overall I like the idea, but I'm wondering if you considered an option (that I think would be simpler?) to shake/agitate the tray in place into something below. It's much closer to the existing set-up of, for instance, the Purina Breeze box placed on top of a regular litter box (as in this video, the original I think - don't miss the part where she runs her hands through dirty litter). Like the method in that video, I never emptied litter into a sifting tray but rather agitated into a larger litter box below, then threw that out with the puppy pad. So I'm thinking a linear back and forth motion would be easier to pull off than rotational, and wouldn't require you to create a large tube that
☐ some
☐ all
☐ none
of the cats might use.
Linear agitation's not as cool, true. I say go for it with the design you have in mind, and I agree with seemoorglass about prototyping it. You'll inevitably see improvements for the one you envision when you do that.
posted by cocoagirl at 10:01 AM on December 20, 2024 [1 favorite]
Best answer: I am remembering the sawdust plume that I get when dumping used (but not feces-laden) pellet litter into the green waste bin, and I think you are underestimating the dust factor. Unless you bake in a shop-vac port to actively help (and you are willing to have a urine-steeped shopvac forever).
posted by janell at 10:51 AM on December 21, 2024
posted by janell at 10:51 AM on December 21, 2024
Response by poster: Apropos of a sketch: my drafting skills are terrible, but I might try to draw something. Or build a 3D model (I futz with OpenSCAD a lot for 3D printing; I could probably build a not-crappy model there).
With regard to linear vs. rotational agitation: rotational honestly seems a lot easier to engineer. One concern I have is that any sort of mesh sized to let sawdust through might not be durable enough to handle cats walking on it. It'd be reasonably sturdy if resting directly on a solid surface, but then there's nowhere for sawdust to fall through to. I'd originally thought about a suspended mesh pan you just need to shake on its moorings, but I'm uncertain on the long-term durability of such a design with cats (one of whom is 20 pounds!) walking in, walking out, flinging litter, etc. And, also, if it can't be locked in place, its apparent instability would probably skeeve the cats. The advantage I saw to a rotating drum is that the mesh can be a completely different surface than the one the cats walk on. And it'd be easier to automate than linear agitation --- I'd only need a standard rotary motor, instead of a concrete vibrator or other exotic/potentially pricey component. Also, my phase-2 feces-catcher idea doesn't seem like something that'd translate to a linear-agitation model. Not that I'm certain that idea will work at all, but it only makes sense in a rotary context.
With regard to dust plumes: I've not found my pine litter to be too dusty. Any dust pluming that'd happen with rotation seems like it'd also happen with the sifter trays I already have and use by hand, so it doesn't seem like it'd be worse. But I might be totally off-base there.
posted by jackbishop at 2:59 PM on December 22, 2024
With regard to linear vs. rotational agitation: rotational honestly seems a lot easier to engineer. One concern I have is that any sort of mesh sized to let sawdust through might not be durable enough to handle cats walking on it. It'd be reasonably sturdy if resting directly on a solid surface, but then there's nowhere for sawdust to fall through to. I'd originally thought about a suspended mesh pan you just need to shake on its moorings, but I'm uncertain on the long-term durability of such a design with cats (one of whom is 20 pounds!) walking in, walking out, flinging litter, etc. And, also, if it can't be locked in place, its apparent instability would probably skeeve the cats. The advantage I saw to a rotating drum is that the mesh can be a completely different surface than the one the cats walk on. And it'd be easier to automate than linear agitation --- I'd only need a standard rotary motor, instead of a concrete vibrator or other exotic/potentially pricey component. Also, my phase-2 feces-catcher idea doesn't seem like something that'd translate to a linear-agitation model. Not that I'm certain that idea will work at all, but it only makes sense in a rotary context.
With regard to dust plumes: I've not found my pine litter to be too dusty. Any dust pluming that'd happen with rotation seems like it'd also happen with the sifter trays I already have and use by hand, so it doesn't seem like it'd be worse. But I might be totally off-base there.
posted by jackbishop at 2:59 PM on December 22, 2024
I can't fully picture the setup you're describing, but I have some thoughts anyway. First, I'm having a hard time seeing this as less problematic than a basic sifting litter box, like the Arm & Hammer sets. Mine has a sifting tray that just nests in the regular litter bin (and there is also an extra regular bin); to sift, you just lift the sifting tray and shake a bit. Afterwards, you just pop the sifting tray back on the extra regular bin, and take the one with sawdust to empty. No need to pour the pellets around. You still have to scoop the feces, but that's pretty simple with pine litter.
Is there a challenge you want to overcome other than having to pour the pellets back and forth? It's seeming like whatever you might save in ease of sifting/scooping might be outweighed by difficulty of cleaning. Odd shapes are going to make that harder, and so will any attachment points for mesh to frame. Any automated filtering of feces over some kind of mesh has a risk of becoming super nasty if your cats ever have diarrhea, and I think that's worse with pellets than a clumping litter, since at best, feces seems to pick up a fine layer of sawdust. So you want to somehow plan for it being super easy to disassemble and deep clean.
Finally, for anything automated with a motor, I'd be super hesitant to DIY it for safety reasons. For liability reasons, there's no chance I'd be directing anyone else on any such DIY.
(As for my experience, four of my cats use a Litter Robot left 100% in sleep mode, so I've got to press a button to "flush" it; two use pine pellets in the sifting box system I described, and one uses a traditional box with clumping litter.)
posted by ktkt at 4:55 PM on December 26, 2024
Is there a challenge you want to overcome other than having to pour the pellets back and forth? It's seeming like whatever you might save in ease of sifting/scooping might be outweighed by difficulty of cleaning. Odd shapes are going to make that harder, and so will any attachment points for mesh to frame. Any automated filtering of feces over some kind of mesh has a risk of becoming super nasty if your cats ever have diarrhea, and I think that's worse with pellets than a clumping litter, since at best, feces seems to pick up a fine layer of sawdust. So you want to somehow plan for it being super easy to disassemble and deep clean.
Finally, for anything automated with a motor, I'd be super hesitant to DIY it for safety reasons. For liability reasons, there's no chance I'd be directing anyone else on any such DIY.
(As for my experience, four of my cats use a Litter Robot left 100% in sleep mode, so I've got to press a button to "flush" it; two use pine pellets in the sifting box system I described, and one uses a traditional box with clumping litter.)
posted by ktkt at 4:55 PM on December 26, 2024
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