Building A Homebrew Robotic Lawnmower?

mmonkey writes "With the seemingly small amount of summer we get here in the UK, the last thing I want to be doing on a sunny day is mow the lawn. So I started thinking "surely a light-ish lawnmower could 'gain' a couple of motors, and suddenly be computer-controlled?". Then I started thinking about stuff like obstacle avoidance, optimum path planning, guidance system, how to get pretty-looking stripes, and I realised that it's actually a potentially complex (read: fun) thing to do. So, have any Slashdotters done this before? Did you modify an existing lawnmower or build a whole new one from scratch? What motors work best? For that matter, what type of mower works best? I know you can already get these, but that detracts from both my geek-drive and my wallet, both of which I'd prefer to keep as full as possible."

Just for you?

[Johnathon_Dough]

If this is something that is for you only, and not for sale, then I would think it would be easy.

If you know what objects are fixed,such as pathways, bird feeders, what-not, you could build the controller from one of those old dump trucks from the 80's that let you pre-program a course by feet and angle of turn, etc. All you need to add is a bar attached to a kill switch for when the neighbors cat/kid/dog runs over to check it out.

Roomba + Mower

[dracken]

How about some duct tape job of roomba [roombavac.com] and a lawn mower ? You get obstacle avoidance and area coverage for free. You can even come up with interesting names like "Rower" or "Moomba" :^)

Well..

[herrvinny]

My first reaction was, "Well, you linked to what looks like a small business site, so either that site's going down or the hosting fees with bankrupt the company". But I digress.

that detracts from both my geek-drive and my wallet, both of which I'd prefer to keep as full as possible."

Well, I think your wallet's going to be drained either way. You need specialized components, software, etc for a completely automated solution. And even that's not going to be the end-all (corners, adjacent to fences, etc)

I would say start with a remote-controlled (as opposed to computer-controlled; mods, there is a difference) solution, see if you can rip apart some RC Cars [rc-car.com], take their steering equipment out, see if you can interface to them using a RC Helicopter Remote [heliguy.com] or RC Airplane Remotes [rc-airplane-world.com], connect up the servos, and perhaps sprinkle some detectors [hobbytron.net] around your lawn.

Computer controlled would be difficult, to say the least. Perhaps even a Masters level thesis or a really good undergraduate senior project. Hell, if you can make it fairly cheap and efficient, you have your own business.

Re:Uhhhh

[Eiki]

The safe way to do it is to have the thing run with very low power, and just nibble at the lawn, but do it all day. The big gas engine on the top of your push mower is really for the convenience of the operator, so that he can mow tall grass without stalling the thing or slowing down.

But if you mowed the grass yourself, one time, and then let loose your robot to simply maintain the height with a low power electric motor and some relatively safe blades, etc.... After all, it can stay out there all damn day!

Re:How About....

[mangu]

I read somewhere that in Scotland they use geese for the same purpose. You get a free trespasser alarm, since neither a goat or sheep will care about who enters the space, but a goose will attack first, then make a loud noise, and ask questions later.

Re:Uhhhh

[k4_pacific]

Suppose you made a grill for the bottom of the mower deck similar to that which covers the blades of an electric razor. This would allow the blades of grass to reach the rotating blades while keeping fingers and toes safe. Perhaps finding one of those big furnace registers like you see in old houses would be the way to go.

Re:Uhhhh

[sploxx]

Yes, I would implement the following:

1. A _safe_ mowing method as you describe
2. The position measurement could be done with (ultra)sonic sensors and a transmitter on the mower. Doesn't work if you have to change garden often.
3. A power and communication cable. Can be cheap because of low power requirements because of 1.
4. A tower from where the cable goes to the mower and a mechanism to ensure that the cable doesn't get in the way.

Of course there is no obstacle avoidance etc., but I would start such a project in a modest size, not with all the 1000 features which _could_ be implemented!

As I'm doing such things also (Homemade microcontroller applications are everywhere in my home), I would say that it is far better to have a little thing working than big plans for a big thing but get nothing implemented.

Don't build One Big Machine

[kraksmokr]

If you really want to be different consider an autonomous swarm of mowing machines. The guts of a Roomba would be a good starting point! I'd like to see a self-organizing mesh network created by the mobile mowing agents.

Good luck - I'd love to see this when you're done!

My advice

[Call Me Black Cloud]

First, build the logic. Take an RC car and use it as a lawnmower simulator. Connect your steering/avoidance circuitry to the car and see if the car acts like you want a lawnmower to.

Lego Mindstorms?

[ikekrull]

First, get yourself a couple of Lego Mindstorms kits (so you have all the motors ans sensors you might require), and work up a useful collision-avoidin/path-cutting bot in your living room. maybe put it on a big sheet of paper, arm it with a felt-tip-pen, and tweak it's path-cutting algorithms like that.

Then, if you want to do more complex things - IR rangefinding, ultrasonics etc. strap a PalmPilot, Zaurus or some other PDS with IR on it and feed the midstorms controller unit with instructions from that.

Once you have it more-or-less foolproof (and you will probably want to run a wire round the maximum extents of your lawn and have a hall-effect or similar sensor pick up on it and kill the mower if it breaches that boundary) - then you can think about attaching a proper mower body and blade to it.

Then you'll probably want to port the whole thing to an embedded Linux u-Controller, and sell it for enormous profits.

Re:Well..

[drinkypoo]

Ripping apart radio controlled cars to get pieces for a lawn mower is like ripping apart go-karts to get pieces for a dump truck. Only the largest radio controlled cars are at all along the right scale and those things cost as much as a robotic lawn mower, no joke - I'm talking 1/4 scale here. Even 1/8 scale is pretty small, it's about the size of a lawn mower but designed for low weight and usually equipped with a 0.15 or 0.21 cubic inch nitroethylene motor. Those little .15ci two strokes can put out a horsepower or more but they have very little rotating mass and as such won't do you any good; the ones you want to use for mowing lawns are an order of magnitude larger and heavier.

That said, oversized radio controlled car servos can become the basis of your control mechanism - but there's no point in ripping up a radio-controlled car. The best thing to do is to get a self-propelled mower and a three channel radio and rig the thing up with some sort of system to make it drive in both forward and reverse. This could probably be done with a planetary gear arrangement, some sort of clutches, and a servo to flop it back and forth. Some (most?) self-propelled mowers are powered by a shaft which sticks upright, along the same axis as that of the motor, so designing something to fit on there should be fairly simple. However, I suggest something beefier than just connecting a servo to a linkage with a horn for your steering, perhaps rack and pinion. It's a big steering job even for an oversized servo.

Throttle control, of course, can be handled by any dinky little servo, if you just remove the return spring.

You can probably get an adequate ground-use-only radio system with three servos for a hundred dollars or less, but what you really want is to buy a three channel transmitter, a compatible receiver that will conveniently run off whatever power source you will choose to use (they would usually prefer to have five to six volts) and then go buy servos that fit your application. You'll probably end up dropping a couple hundred bucks on this stuff. And then you get to design the hardware to make the thing turn! Truly your cup runneth over.

Ask the USAF

[john_smith_45678]

Maybe you could attach a mower to one of these [yahoo.com].

Use a weed whacker.

[Darth Muffin]

Seriously, if you go ahead with this, don't use a regular metal mower blade. Use something like a weed whacker--a nylon string. Coverage is far less and speed is less, but speed shouldn't matter in this application. So what if it has to make 4x as many passes...

Simulated Prototype as a 4th year project

[Roger_Wilco]

I made a simulated prototype of a fast/simple algorithm, which was 100x (IIRC) faster than random wandering in my tests. A bit of information is here [bu.edu].

It requires that the robot know its position rather accurately, but if it's a hobby you could use differential GPS (which would add too much to the cost of a low-end commercial robot). You might look into localisation via wifi [usc.edu].

Re:Search the library

[sakusha]

Yeah, I remember an even simpler Pop Mech story. The guy started with a self-powered gas mower. He attached a rope between a drum and the mower. It ran in a spiral around the drum, the diameter of the drum was arranged so it shortened the rope 1 mower-width per revolution. Just jab the drum in teh center of your lawn, start up the mower and it mowed a nice clean circular area. Then you just clean up the corners of the yard manually, the big areas are already done.

Simple, effective, and does 80% of the job without any complex computer crap. You can do the last 20% yourself.

Re:Good Idea, But No.

[Eideewt]

It's odd that some people reflexively post anonymously, even when they're being genuinely funny or interesting. It's also odd that I don't have the sense to post AC, even though I'm not at all funny or interesting.

Re:Uhhhh

[magefile]

Also from "The Robots of Dawn". Which is related to the Foundation series, in a way. Very pre-historic, from the Foundation's point of view, but Dr. Hans Fastolfe was the guy who originally came up with the idea (although he couldn't implement it) of psychohistory. At Giskard's suggestion. That was why he was so interested in robots; he wondered if the 3 laws had equivalents in humans.

Anyone consider...

[mikeb39]

That perhaps leaving a small and valuble robot on your front lawn all day where less-then-respectable people can just grab it and walk away might be a poor idea?

I suppose you would build a larger version with the blades on the front to guard the smaller robot from would-be thieves though...

But that probably reintroduces the problem of it killing curious kids by mistake.

Re:Just for you?

[MrNonchalant]

On this same note I'd reccomend you check out this project [cmu.edu]. Video of it in action towrards the bottom. I've seen it working in the park nearby CMU, neato stuff. A little out of your league I'd think, but still worth a look.

Re:On second thought...

[BuckaBooBob]

No but one could upload some cool images to be cut into your lawn... Think Lawn Circles :) Hey if you can make it detailed enough.. You might even be able to make a good buck Mowing Things into peoples Lawns liek Happy Birthday ect.. or pictures (if you can get decent shading down pat...

Could take on a whole new idea.. :) could pay for itself in no time....

Hmm... I better run to the patent office here :)

Re:Electric sheep

[Tatarize]

Yeah, I'd say slow would be the best way to go. Primary because it opens the door to photovoltonics. You don't want to labor in the hot sun... but for the robot that could be food. I don't think having any grass in the robot is a good idea. It'll clog. But, then a swinging blade out in the open might not go over very well with the laws of robotics. Then there is the issue of transport. I suppose wheels.

Then again you could always plant a strong spinning laser in the middle of your yard. No moving parts. You could solar charge it. And best of all the fire department is usually pretty nice.

Mine

[EvilMidnightBomber]

Pic [earthlink.net] Started mine about 11 years ago. The mechanical platform was a roboticized Toro 4hp mulcher using a permanent magnet motor driven backwards to generate power for two beefy wheel drive servos and the electronics. Fully autonomous. Narrow beam ultrasound sweeping the forward path for semi-coherent vision. No external environment markers used except where there aren't any objects to range off of for 20 odd feet. You walk it through the lawn once and it makes an internal map of the environment and the path you chose it to follow. Then, just plop it down and hit the start button next time. Works infinitely more efficiently than the commercial attempts at *cough* autonomous algorithms the crux of which is which way to turn after boffing into the perimeter wire or an obstacle. Rev. 2 is going to go battery-powered for safety and you'll have to "show' it where the charging station is. Wish I'd had money to take it commercial.

Re:Electric sheep

[zuzulo]

As you say, this looks like a great candidate for simple robotics and emergent behavior. Instead of a 'flock of sheep', however, imagine a 'colony' of robotic 'ants' that simply wander around the yard snipping grass blades one at a time to specified height and carrying the cut remnants to the 'ant hill' where a human empties the hopper every so often and the ants recharge themselves.

Might make a good thesis or senior project for someone.

Re:Electric sheep

[peacefinder]

Seven years ago, I was sitting on a train, on vacation, watching the rolling plains of eastern Germany go by the window, when I thought of something like this.

What I envisioned then is a little beetle-like walking robot. It would move very slowly, but very persistently. It would have something very like mandibles with something very like a sense of taste, and would keep track where it is by means of a combination of GPS and a mesh network between dozens of them. There were other little details, like a milch-bug with a substantial power plant that the others could "nurse" power from, supplemental solar arrays on their backs, that sort of thing.

But they weren't for cutting grass... they're for cutting weeds.

Currently, people plow fields, plant a monoculture, and then use herbicides to selectively kill the non-crop plants. They do this not because it's the best way to grow things, necessarily, but because that's what our technology has supported and made efficient since the invention of the plow.

But what if a swarm of little robots could sow and tend a field without plowing? They could walk among the crop, taste every plant that they come across, and chop off the ones that don't taste like the crop. Even chew them up into mulch. Gently, persistently, precisely. No soil compaction from heavy tractors. No herbicides, no resistant strains of weeds.

I thought it was a great little vision. I never have had the gumption to try carrying it off, though, so here it is for anyone who wants it. Just don't patent it, or I'll fish out this comment as prior art. :-)

SOLAR POWER

[Anonymous Coward]

Hi Dude,

Solar Power. Slow Moving. Goat Like. Hey if it is Goat Like, you can call is a GNU-mower. heh.

What you need:

A way for it to know where it is relative to the garden

OR a way for it to find out where it is relative to where it has been, and correct mistakes.

Either it should know preceisely where it is, or just remember how far it has gone, if it hits something, write it to a non-volitile memory.

if you garden has some GNOMES :-) then you should end up with a hazy circle defining the obstacle after a while.

You should plot all this in an appropriatle resolution, so 4 pixels is about the size of the mowers cutting region.

You should then make each pixel to about 8bits, and set a value for how long it has been since it went there.

You shoudl then process the bytes in a FOFI (yes FOFI) method, so it would contiuously loop.

Now to get stripes, just preset the grid with:

09a.
18bc
27ct
36de
45ef

It will process them as 0 1 2 3 4 5 6 7 8 9 0 a b c d e f etc.

thus going up and down.

it will write each area it goes through as it goes through that area. of cours eyou need enogh bits for the resolution syou are looking to for the lawn.

Solar Power!

Else pay a college student to mow your lawn, and wash you car, and get off on her 20 yo bod, whilst helping her education! That help one of your drives, and let me tell you, your pocket will feel kinda full! :-)

You didn't hear that from me.

Re:Well..

[Ignignot]

That is a very limited and poor approach to the problem. I don't see what relays are going to do other than turn the motor on or off - what we're dealing with is a power problem. A series of relays makes even less sense, they don't help at all and will drain some amount of power and add to the weight. The thing is, smaller electric motors just aren't as effecient as bigger ones. To get more power to them you need a bigger battery. Bigger batteries weigh more. To lug around the big battery you need stronger motors... you see the problem? I think the answer is instead of taking the parts of a radio controlled car and putting them in a lawnmower, take the weedwacker spinny fishing line thing and stick it on a big rc car. Gear down the motors so that they'll move slowly and powerfully instead of fast and weak. Then you might have a viable cheapish solution. (both time and money)

1960's Solution..

[adeyadey]

I remember reading an old magazine 60's("Radio Constructor") that featured a solution to this- a guy had a circular lawn & wanted to automatically mow it - how did he do it? Complex electronics? no. He put a large oil drum in the center, and attatched the petrol mower by a long rope with a lenth the radius of the circle, wound around the drum. The mower is started, and as it unwinds mows a spiral pattern - then mows another spiral coming in! Bloke goes and has beer, and comes back just in time to switch the mower off as it hits the center.

The diameter of the drum should be a bit less than the width of the mowers rotors..

Or, just buy a goat.. :-)