Lawnmower clippings- maximize packing density

  1. taylaron

    taylaron 388
    Gold Member

    Greetings PFers,

    I'm trying to find the most efficient way to pack the lawn clippings after mowing my lawn. I need to fit the most mass in the smallest volume possible. I'm curious if decreasing the length of the grass clippings (via post shredding) will increase the packing density. I also assume vibration packing will also help as long as the grass is dry. Any other ideas to increase packing density other than compression?

    Vibration packing simulation

  2. jcsd
  3. Danger

    Danger 9,663
    Gold Member

    Well, I think that you hit the main factor when you mentioned it being dry. Moisture is a very large percentage (I don't know the number) of the weight of cut grass. As to size, my experience with dry vegetation is that it will crumble almost to dust under compression. Maybe you could use some sort of intermediate storage such as a canvas bag that you can stomp on or beat with a stick or something and then transfer it to what I assume will be its final resting place of a plastic bag. (I say that because I think that a plastic bag might rupture if you beat it with a stick.)
    On the other hand, if you do manage to pulverize it sufficiently, you could probably just spread the dust back onto the lawn without it being noticed.
    Gotta go for now, but I'll think on it some more.
  4. taylaron

    taylaron 388
    Gold Member

    Thanks Danger. That's good insight. I'm designing a robotic lawnmower and i'm trying to find the best way to pack the clippings into bags onboard the mower. Whither or not they pass through a shredder before being blown/ packed into the bag and being shook is the question.

  5. Danger

    Danger 9,663
    Gold Member

    Okay, I see. At first I thought that you just wanted to get rid of stuff that you raked up.
    I have an idea or two, but need just a tad more information to decide whether or not there's any practicality to them. Most importantly is what kind of power you have available. Is the machine electric, and if so cordless or plug-in? How big? Is a bit of extra noise allowable? How autonomous does it have to be (as to length of time between human interventions)?
  6. taylaron

    taylaron 388
    Gold Member

    First of all, the robotic lawn mower is in conceptual stage right now so there are few fixed constraints.

    1. The mower will most likely be battery powered with a 20-40 Amp hour battery on it.
    2. It should be less than 24'' x 24'' square by 1ft tall (Excluding baggage system).
    3. The machine should be fully autonomous with brief maintenance every few months.
    4. The mower is designed to be modular, capable of peripheral modules being attached to the exterior specializing in certain tasks (poop duty, weed sprayer, thatcher, etc...)
    5. The clipping removal system could either
    a. bag the grass (immediate drop off to dumpster location, or human collection). Should be able to accept 10-20 gallon standard garbage bags (no draw string). Robot will Likely close bag with a wire twist-tie. Bags could be filled on external carrier being towed, or carried around on top of the mower while in use.
    b. send the grass to the dumpster via a flexible tube (fan-blown, conveyor, screw, etc...)- in which case it could be corded...
    c. pulverize it and disperse it back onto the lawn (mulching)
    d. vaporize/ burn it (not desirable or practical for many reasons thus out of the question)
    6. The mower should be substantially less noisy than the typical mower- able to run at night without disruption.
    7. The device should be safe for people and animals.

    I've worked out much of the navigation and technical details conceptually, having considered a plethora of options. That is for another discussion though. For this thread I would like to focus on clipping storage methods for the baggage option.

    Thanks for your thoughts.
  7. Danger

    Danger 9,663
    Gold Member

    Right, then. I'll just mention a few of my ideas in a vague "off the top of my head" manner rather than get specific.
    If you want to pulverize it, there are portable cross-cut paper shredders available that use their own battery power or could be adapted to tap the robot's supply. That might be easier than building a custom cutter. Or you could feed the clippings in between a set of helical or herringbone gears, especially if you file the edges to sharpness.
    If corded power is available, a leaf-blower and some heating elements might be able to form a drying system, but I suspect that it would be too loud and there's always a potential fire hazard with that sort of stuff.
    My first thought was that perhaps some sort of tamping device could be used to squeeze out excess water and compact the fibres. With the aforementioned caveat of fire risk, heating could be added to that process as well. This whole idea would be highly power-hungry, though, since hydraulics or a powerful screw-jack would be required.
    A system somewhat similar to the previous one would be to add a small baler (similar to the type used for hay on a farm). The robot could then just "crap out" bundles for later collection or stash them on a trailer. Those bales could then be dried, mulched, fed to sheep, or whatever at the user's discretion.
    That's all I have for now, but I'll keep thinking on it.
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