GRZR Robotic Lawnmower is Mobile

For the first time, our robotic lawnmower project has mobility and a modicum of intelligence. Two bump sensors dictate which way the robot should turn on impact with an obstacle. It's still early days.



The robot is powered by 4 AA cells via a boost regulator that gives us a constant 5V.  An Arduino does the thinking and drives 2 continuous rotation servos.

We also did a test today on the blades and motor.  Bottom line - it works well when there's not much grass to cut but the tiny motor soon gets bogged down and the blades lose speed.  We're going to need a MUCH more powerful motor and that will mean we need to re-think the power source for the whole robot.

DC Motor Driven by Arduino

At last, I've mustered up the courage to hook up a DC motor to the Arduino!

The reason that it's a big deal is that you can't connect a DC motor directly to the output pins on the Arduino - it'll draw too much current and fry the Arduino chip.  This method uses a transistor to switch the large amount of motor current with a small amount of 'control' current.  As an added level of safety for the Arduino, I've also use an Opto-Isolator which a means of completely separating the two circuits - control and output.  Unless I do something silly (!), the Arduino should be safe.  (I already fried one transistor in testing because I'd forgotten to put a diode across the back end of the motor!)

BIG respect and thanks to Mike Cook for his excellent article on hooking up motors.

My circuit diagram is a hacked together version of a couple of his diagrams.

(used with permission - thanks Mike)

The immediate application is for driving the blades on our learning project GRZR - the robot mower!

Grazing Mower - blade test 1

CAUTION:  wear safety goggles to watch this video.



It may seem nuts but this is a similar blade setup to the Husqvarna Automowers ie. multiple swiveling 'razor' blades around a large spinning disc.  I'm just running a little smaller at the moment.

When the drill had a charge (!) it was very effective at nibbling the grass down.  It's easy to see how this can work very well as the 'bot passes by repeatedly.

Like.


What do you reckon the chances are of the robot being able to identify weeds then stop over the top of them and say: zap them with a laser beam!  ?  — that's one for the boys  ;)

Robot Lawnmower takes first steps as an ArtBot

I have a dream...

Mowing the lawn seems like a huge waste of time and energy to me. So, if I can build a machine to cut the grass for me then I'm a happy chappy!

I'm not the first to feel this way. A number of companies have done it already, such as Husqvarna. The problem is, their machines start at about £1,500! They are indeed splendid machines and I'm told that the people who own them would never go back to regular manual mowers.

Such a project is a great opportunity for learning electronics and mechanics and more, so I'm teaching a couple of lads on the back of it. Our first goal has been to make something move under it's own
steam.

The 'brain' is a Seeeduino board (an Arduino clone). We programmed it with some simple moves and powered it with a 9V battery. Two continuous rotation servos do the moving. The whole thing was bodged er.. built on an old CD and held together with blueTack. The fun of prototyping!!

It has no sensing capability at the moment so when it bumps into an obstacle... it.. er.. carries on regardless. The basic moves programmed were: drive forwards, turn ≈90° Left, drive forwards, turn ≈90° Right.  Rinse and Repeat.

The nest of wires on the breadboard was for a 5V regulator (thanks Oomlout!) and distributing the power to the servos and the Arduino.  This first pic is my trial build the night before. I needed to prove to myself (!) that it would all hang together nicely and actually work.  I went to bed with a big smile on my face! :D

Meet John and Harvey, our illustrious team...

And then for fun we strapped ever increasing numbers of felt tip pens to the back and turned it into an ArtBot!  The pre-schoolers thought it was marvelous - especially when it ran off the edge of the paper and started drawing on the floor!

 

See the video... :D

PS. We will consider offers for the final piece of art.  Proceeds will go towards our ongoing project.

Addendum
I've just had a fiddle about in the shed with two Stanley blades mounted on a mini CD.  The blades are bolted near the edge of the disc and are able to pivot.  This is the same approach at the Husqvarna machines - only much smaller.   Centrifugal force keeps the blades pointing out while hitting a tough bit of grass or twig flicks them in out of the way.   (see subsequent post for video)

I popped a big fat bolt through the centre of the disc and stuck the bolt shaft into my battery drill.   !!
Wearing safety glasses (!) and armed with the drill I ran some experiments on the lawn.

Yahoo!!  It works.  It seems that spinning it faster makes it more resilient to getting bogged down by too much grass.  Slower movement across the lawn helps too.  Very quickly you can see how the 'grazing' aspect - nibbling the tops off the blades of grass - can achieve a great result.  Next step... fit the spinner to a beefed up version of our 'artBot'.