Robotic lawn mower :


In the summer of 2015 I decided I wanted to free up more spare time to commit to other projects,
so a decision was made to purchase a robotic lawn mower.

After some advice I bought a Robomow RC304, which they claim can handle a lawn of up to 400m².

As it turns out, these claims need to be taken with lots of grains of salt.
More importantly, almost immediately the abundance of mechanical and software related shortcomings became apparent.
I'll devote another page ranting about this piece of #$^&@*, suffice it to say, I soon recognized the need to improve this device, which was easy enough: even if you tried, you would be hard pressed to come up with something even worse than this machine.
The device relies on the friction of its wheels on the grass for changing direction whereby a caster wheel up front makes sure direction changes are smooth.
Well, the grip of these factory wheels is very poor, and the caster wheels spends most of its time sticking to any position but the intended course.
So my first 'point of attack' were the factory wheels.

I decided tank-like tracks should be a reliable means of propulsion, and so I designed a lot of parts and started printing on my 3D-printer:

Robomow trax
I started printing all the tracks' shoes, I needed 52 in all !

Here's a time-lapse of printing one batch of 15 shoes:

Up till now I printed about 48 of them.
But then I got concerned about the tracks' grip on the grass and the mowers' resulting ability to rotate about its axis.
I then changed my plans and decided to print regular rims and glue/screw pieces of mountain bike tire to it.

I purchased 1 mountain bike tire (size 26x1.90) with
coarse studs,which I hoped would provide lots of grip.
Robomow Mountain Bike Tire

The tire has a pitch length of about 20.4mm, and I chose a pitch number of 28, which led to a base-diameter of about ø182mm.
But with studs of about 5mm high, this led to a final outer diameter of about ø191mm.
The factory wheel had an outer diameter of about ø184mm, still I felt this should work.

I cut the tires' sides off, leaving me with a strip of rubber roughly 55mm wide.
Based on that I modelled my rims, which led to wheels a great deal wider than the 38mm-wide factory wheels.

Here's printing one of the rims. Printing one took almost exactly 15 hours.
Of course I printed two :

After printing the rims, the pieces of tire were glued to the circumference, which went something like this :

The rims needed hubs with spokes to attach to the Robomow centre (plastic !) axles.
Here's printing one of them :

The rims were mounted to the hubs using 6 M3 bolts with washers and lock-nuts each. This should make for a secure connection.

Finally, the rim/hub assies needed a secure(-d) mounting on the Robomow (plastic !) axles, for which I desisgned a clamping ring.
Here's printing two of them :

After glueing I compared the factory-wheel with my newly fabricated wheel:
My expectations were high !

Here's the two mounted rim-hub-tire combinations with the two clamp-disks:

Here are 'before and after' shots with the factory wheels and my own 'designer'-wheels mounted on the mower.


...and after :

And here's a shot of the mower on my garage floor with its new wheels mounted :

Finally, I took to the garden, where the grass had grown significantly during my endeavours, so the new wheels soon were covered in grass.
I must say, grip has definitely improved, but the software is just as poopy as before, so improvement of the general operation is marginal.
It's still a pain in the neck.

Anyway, here's the mower running on its new tires:

After running the new wheels for about a week I conclude the improvement is insufficient, so only two options remain: Tracks, and replacing the robomow with a superior robotic mower, which shouldn't be too hard, Robomow is an all-round inferior design.

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On a side note, Robomow, like almost all other manufacturers uses a perimeter-wire to mark the outer edge of the garden.
This wire is secured to the ground using pegs, which come with the mower, but 'only' about 200, which, frankly, is far too few.
So, I printed a bunch of my own.
Here's printing one batch of 14 :

I modelled it after the factory supplied peg, but compensated for 3D printing.
I rounded 1 or 2 corners to prevent the wire from being cut, as happened with 2 of the original pegs.
I soldered the broken wire, and up till now its held OK.
Also, my Robomow mower managed to cut ('mow') through the wire one of the first times of mowing.
It's really an all-around stupid design.

Here's a link to a 3D model of one such peg, for wire up to ø4mm :

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