[mowbot] RFD: Define reference 'grassbox' for mowbot development.

Byron A Jeff (byron nospam at cc.gatech.edu)
Tue, 12 May 1998 16:04:49 -0400 (EDT)

I've been on the list for three years. It has had some interesting information.

However after all this time I still feel like I'm lacking to knowhow, skills,
and equipment to develop a working mowbot.

Early on in the list development, there were raging arguments about how
to develop such a beast. Personally I think that was much more informative
and productive than what followed, very few people discussing their own
personal development.

After sweating in my back yard cutting high grass for 2.5 hours over the
weekend, I'm now motivated to do mowbot development again.

IMHO we really should consider having a reference platform. While much of
the discussion has centered around sensors, mapping, and boundary detection
(Which I believe are solvable problems) where I'm confused is the pure basics:
How to get a mobile platform that cuts grass.

I see that modifying electric lawnmowers seems to be the new turn. I'm just
wondering what the diffculty is in developing a easy, inexpensive, platform
that moves about as an alternative.

Secondly what about actual grass cutting? My last foray into this field
(pun intended) was last spring. Someone on the list has experimented
successfully with attaching Exacto Knife Blades to the end of a motor
driven platform. I repeated the experiment, using a round plastic J-box
cover with the attached blades. I found that if driven by a electric drill
it was fairly effective. The only other addition it needed was some type
of protection above the disk because the cut grass kept wrapping around
the spindle. I envision something like an oil funnel. Cheesy ASCII graphics:

| |
| Motor | <- This needs to be about the same power as a
| | <- Home power drill. Any ideas?
=======||============= Base of Mowbot. Drive shaft passes through a bearing
/ \ mounted on the platform.
/ \
/ \ <---- This is the funnel I was speaking of...

^ ^ ^
| | |
Blade disk Blade

Of course finding a powerful enough motor is another problem. I want to
thank Paul for posting that motor driver board a while back. BTW is that
a kit or is it fully assembled?

Can anyone talk about motors, drivers, gears, pulleys, bearings, and other
mechanically oriented stuff required to get a platform going? The drive
electronics and sensors are rather ineffectual without a platform to
carry it on.

Sorry to ramble. If you're still here you're as interested as I am. What I
thought about while mowing over the weekend was how to define a reference
point to mowbot development. I finally hit upon the idea of the reference
grassbox. The grassbox has these parameters:

1) 20 foot square
2) Bounded by 6 in high boundaries
3) Sloped at a 40 degree angle.
4) Contains grass 1 ft high

The numbers are arbitrary. I just thought that numbers like these can give
us a target.

Given the grassbox here are some performance parameters for a mowbot:

1) MB can cut the given area to a 2 inches.
2) MB must not tip over.
3) MB must cut all grass to within 4 inches of all boundaries
4) MB must perform given task on a single charge.
5) MB must be buildable using hobby available components.
6) MB total cost must not exceed $X (not sure what X is. Subject to discussion.
Probably would be nice if it were in the ballpark of a good power mower, say
$300 to $400 US.)

Note that the performance parameters only define the powerplant (body, drive
and cut motors, batteries) and not the electronics, which can be added later.
If anyone can tell me how I can buy/salvage electric motors and connect
them to lawm mower wheels, I'd be eternally grateful.

I guess I just feel that too much of the focus is on the automation part of
the project. I'm still struggling with the fact that the typical lawnmower
(both gas and electric) were designed with a human operator in mind. How
does one build an autonomous platform that cuts grass?

BTW the last post pointed out using a 500 oz-in ($250! Ouch!) servo. It seems
to be a round hole (electric lawnmower designed for human operation) square
peg (making it autonomous) problem. Can't steering simply be done by having
centered, bi-directional drive motors? That's why I think building a platform
from scratch is such an excellent idea.

Hope this stirs up some discussion. I'm itching (literally ;-) to get
started again.