[ale] robots

[Jeff Hubbs]

> Well let's take them one at a time:
> 
> Walker: The only slightly new idea here. It requires an even more sophisticated 
> suspension system than what already is required for a rolling bot. To be stable
> it'll need a minimum of 6 legs. Also legs give much benefit on unstable, uneven 
> terrain. Though yards are sloped, they generally are graded to be pretty 
> smooth. So the perceived benefits are far outweighed by the added complexity.
> Walkers are cool technology, but extremely difficult to engineer and control
> the  knees, ankles, and feet required to make them usable.

Uh, who said anything about knees, ankles, feet, or difficult
engineering and control?  My walker's legs would probably becurvy pieces
of springy wire with one end attached to a slowly turning shaft. 
Opposing legs would probably share a common shaft.  Again, look at the
principles embodied in Mark Tilden's robots at
http://www.beam-online.com/Robots/Galleria_other/tilden.html.

> 
> Blade: Blades spin fast for a couple of reasons. First is so that the grass
> can be sheared cleanly. 

I can shear grass cleanly with a pair of scissors as s-l-o-w-l-y as I
feel like.  

Lawnmower blades spin fast because piston engines with no reduction
gearing spin fast.  Also, if you spin blades fast enough, you don't need
any kind of opposing anvil or bypass blade; you're relying on the
inertia and stiffness of the grass itself.   My mowing robots would use
a slow-moving bypass blade and so the blade need only turn fast enough
to get the job done

Ripped grass tends to get sick. The second reason is
> that rotary bladed mowers can handle grass that's several inches higher than
> the blade, while reel/scythe style mowers requires the grass to be near the
> height of the blade. Also they have serious issues with common items such as
> sticks.  

True, my mowers would clamber around and over sticks, doing the best
they could as they went.  

> So it would not be possible to just throw them out in the yard.

Sure it is; that's my up-front design goal.  The question is one of
doing what it would take to make the goal realizable.

> 
> Size: Limits both the surface area that can be cut and the speed at which
> it can be cut. And speed still is an element because the grass will look 
> uneven if the the mowers cannot keep up with the growth rate.

My mowbots rely on their number, their relentlessness, and the concept
of a random walk to arrive at a reasonably even cut.  

> 
> Solar: A catch 22. First is that you have to increase the size of the solar
> panel in order to gather enough energy for the bot to do its job. But 
> increasing the size increases the energy requirement. So solar bots spend
> a lot of time just sitting and gathering instead of working.

Heck, no!  My bots would run when they're in the sun and die a little
while after dusk when their leftover stored energy runs out.  They'll
sit in the yard overnight and they'll start moving again when the sun
hits them.  See, my design can work because I treat *energy*
requirements and *power* requirements as two different things.  You say
you have to engage 3-5hp for a few minutes to a couple hours every 7-14
days.  I say I can expend mW nearly every day for several hours a day
all summer long.


> Multiples: Electronic goats in a herd. Now they must be able to communicate
> with each other (or a centralized system that know all of their locations)

Why bother?

> so they won't get in each other's way. 

Who cares?  Certainly they don't - and as long as my bots have legs that
are too strong for the blades to cut and some means of detecting and
correcting a blade jam (sense blade motion; reverse blade motion if
blade is stuck), what do I care if they bump into each other?

> Or as you discussed having real dumb
> avoidance/collision behavior.

Well, like I said, no use in having them wander on down the road.

> 
> See current lawnmower technology isn't built in its current fashion simply
> to accomodate the human operator. Gas has very high power/weight ratio. 1 
> gallon can provide 500 watts of power for several hours. fast spinning blades 
> are very effective cutting technology. Wheels work the vast majority of the 
> the time. 
> 

See above.  I want robots that do the stuff I hate doing but have to do
regardless

> Then there's the issue of trying to get the project done in a timely and
> somewhat cost effective manner. Engineering from scratch is both cost and
> time prohibitive.
> 

Then don't engineer from scratch.  Use Tilden's designs or someone
else's.  Hack a Bio-Bug and fit a cutter onto the front.  

> That doesn't mean that I won't be look at alternative methods further down
> the line. I bought a reel mower and I do want to see how it does under power.
> In the end I'd like to see about moving to a battery only platform and having
> a battery tanker to shuttle batteries back and forth.
> 
> 
> >  I would consider
> > myself successful if I can drop these things in the yard in May and
> > gather them back up in November, having never had to actually go out and
> > mow the lawn in between.  
> 
> True. But it's a bar that'll be difficult to reach. One reason that I didn't
> limit my power budget is because tasks become very very difficult when power
> is limited. This isn't a project that'll be put on the ice sheets of the Artic.
> There's plenty of nearby power and spending 2 minutes filling a gas tank is
> trivial compared to a significant amount of time sweating out mowing the grass.

But you will have retained much of the hassle of using a gas lawnmower. 
You'll still have to go out in the heat and fuel it and (I presume)
start it.  Are you actually going to go inside and toss brewskis while
this thing wanders your yard, even though it has a blade tip speed of
several hundred miles an hour, contains highly flammable liquid fuel,
and operates at very high temperatures??

> 
> The bar you have set is like trying to pole vault over a 25 ft bar. Someday
> someone may get there, but it'll take a prohibitively extraordinary effort
> to do so.

Not at all.  The fundamental walker structure and behavior is already
well-trodden ground; this only refines the concept, adds grass-chopping,
and tries to solve a real-world problem (as opposed to just being a
photovore, etc.) and therefore requires some directed design work.

> 
> > 
> > Reference http://www.solarbotics.com/.
> 
> [ Solarbot behavior trimmed for brevity... ]
> 
> > I think if you go the high-speed whirling-blade route, you're going to
> > have more unintended consequences than you can stand (many being
> > safety-related) and you'll be spending all your time futzing about with
> > this thing instead of going about your other business while your yard is
> > slowly munched into submission all summer long.
> 
> As I stated, the primary safety mechanism is a secured, enclosed space. Fences
> and motion/gate sensors. 

Your safety measures fall into the category of prevention of very high
powers from being misdirected, whereas mine come from not having high
powers in the first place.  My mowbots can be safely investigated,
sniffed at, and even peed on by cats, dogs, and kids.  

> 
> My goal is to build with cheap well understood technology. The further afield
> one strays, the more difficult and costly it becomes to engineer. I have a
> platform that navigates the yard. I have cutting technology that cuts grass.
> I have a power plant that generates sufficient power. I have sufficient
> sensor and compute power to self actualize the platform. At long last I'm at
> the prototype integration phase.
> 
> Now is not the time to change horses. Doing so will simply guarantee not
> finishing the race.
> 
> Thanks for your thoughts.
> 
> BAJ
> 




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