I spent today working on my robot (apart from the necessary hours spent trying to extricate the kids’ christmas presents from their fiendish wrapping). I got the grass cutting blade working.
For back story, I’m trying to build a robot which will do various things for me. For example, grass-cutting. I’m not trying to build a replacement for one of those 2000 euro robomower things. Instead, it’s a very small bot which will eventually do quite a few things.
Anyway – one thing I wanted was to have it take great care in what it does, and that means cutting each blade individually, mad as that may seem. It will eventually be able to decide whether a blade should be cut or not, for example I may give it an instruction “cut the marsh grass, but leave the ordinary stuff alone”.
So – today’s task was to build a blade that can grab a single blade and then cut it. I chose to build it as a kind of guillotine, instead of a scissors, which had been my plan before. I may change this at some time, but it works at the moment.
The guillotine was built with some wood, Meccano, elastics, and a blade taken from a craft knife. First, a hook was built by hacksawing into a Meccano spar such that it could be used to “catch” a blade of grass when turned just so. The blade was glued to a second Meccano piece and they were both placed in some wood such that a channel allowed the blade to slide forwards and back.
The blade is pulled back by an elastic, and forward by a wire which is controlled by a servo (ultimately controlled by an SD-21). The screw that you see there is for helping to push the blade down, so it doesn’t just wave about but actually slices the grass.
It took a while to get the right angle for the blade to slide along the bottom Meccano “hook” such that it was flush with the hook. If the blade is not flush, then the grass would just bend under the blade, and not get cut (an advantage for the scissors idea…). I ended up having to bend the hook itself, and it’s still not perfect.
After that was all set up, a servo was glued to the board and an electrical wire (*shrug*) tied to the blade. That screw you see on the servo’s turny thing is just so the wire can be pulled a bit further than the diameter of the turny thing.