Re: [mowbot] Motors arrive

Byron A Jeff (byron nospam at
Wed, 5 Mar 1997 08:21:00 -0500 (EST)

> Byron A Jeff wrote:
> >
> > I was going to come in a post this morning too. It has been raining like
> > crazy here in Atlanta and there have been record highs (80 degrees!). Little
> > tuffs of grass are starting to pop up! Sigh!
> Hehe I know what you mean. We had a few days of rain and now the grass
> is about 1/3 up my shin.
> >
> > Anyway just to re-interate my agenda in priority order:
> >
> > 1) Mobile platform than can move in a straigt line at up to 25o incline.
> > 2) Cutting tool that reasonably cuts grass.
> > 3) Everything else (edge detection, low power go home and feed circuit, auto
> > grass cutting)
> >
> > A couple of weeks ago I was intently examining a childs 16 inch real bike
> > wheel. It seemd to be real easy to mount, uses a standard bike chain
> > (obviously) and seemed really sturdy. Does anyone have any comments on the
> > possibility of driving a pair of wheels with gearmotors such as above. Of
> > course the gearing for bike wheel are such that they only drive in one
> > direction, the other causes braking. However it seems to me that steering
> > can be accomplished by stopping one wheel and driving the other, which would
> > effectively spin the bot around the braked wheel.
> Yep, but how would you backup if you need to? I can imaging the mower
> going right up to a wall to mow and then not being able to turn because
> the front is right against the wall. 16inches sounds pretty big, I've
> been trying to keep the robot as small as possible to make it
> maneuverable as possible. The wheels I'm using are Rover lawnmower
> wheels, sealed plastic (so they don't fill with water), a good tread and
> about 175mm in diameter (7 inches). At 30rpm I get around 1km/hr while
> keeping the required torque down. 16 inch wheels will move faster with a
> slower motor, but they will increase the required torque.
> >
> > Here's a couple of really crufty ASCII pictures to illustrate:
> [..............]
> > You get the basic idea. I figure if the body is wide enough that it'll be
> > difficult to tip it. I have it low to the ground to keep the Center of
> > Gravity Low.
> This is fine on a flat surface, but what will happen when you encounter
> rough ground? It looks like the driven wheels could get lifted off the
> ground if the robot travsersed a small dip. I'll be using 2 driven
> wheels near the front with a single idler at the rear, this way all 3
> wheels should always be in contact with the ground.

OK. This is exactly the kind of critique I needed. How exactly are you
interfacing your motors and wheels?

> >
> > Any updates on cutting technology? Anyone consider simply using a real
> > lawn mower attached to a base such as above. Real lawn mowers definitely
> > have the correct cutting technology, they just don't have the correct
> > platform for autonomous (sp) motion.
> I've looked at using a standard mounting wheel from a mower with the
> swingout metal blades, but it just looked too heavy. The electric motor
> to drive it would be quite a drain on the power supply. I did find a
> light small plastic blade for cutting grass, when the parts come back
> from the engineer I'll be able to run some experiments with it. I'm
> getting him to put together a leadscrew lift system for the blade motor
> so I can vary the cut height.

Must be nice to actually have an engineer on the project! ;-) I have to
do everything on my own, and I have to do it cheap. That's why I continue
to look for cheap commonly available stuff to do the job.