F. L. I. G. (Posts about dinky)

Arm Design

Pal Denes — Wed, 25 May 2022 11:00:00 GMT

At the start of this project, I decided to build a robot arm with a “classic”, articulated design: a rotating base, with “shoulder”, “elbow” and “wrist” joints. I wanted to make something that’s suitable for picking apples, but not specific to this task, something that could maybe even used or developed further in the future for other applications.

To be able to reach any point in any orientation of the end effector (or gripper), we need seven degrees of freedom: this means seven servos for joints + one more for operating the gripper. We don’t necessarily need that to be useful though. If we’re happy with limited orientations, we can get away with less.

Why ROS?

Pal Denes — Sat, 30 Apr 2022 11:00:00 GMT

If your day job title is some variation of “developer” (maybe as opposed to “programmer”!), chances are that you spend more time on figuring out how to use various libraries and frameworks and how to “glue” things together, rather than creating a lot of novel code from scratch or inventing things. Doing Pi Wars can be an escape from all this, with complete freedom to experiment – which also means that reinventing the wheel is perfectly fine! But the opposite can also be true: figuring out what existing building blocks you need and how to fit them together efficiently to achieve a goal can be an interesting puzzle in itself. And creating from scratch “yet another” variant of everything that’s been done by others before can also feel wasteful after a while.

Servos for Dinky

Pal Denes — Sat, 05 Feb 2022 12:00:00 GMT

Until now, I’ve only had some experience with simple hobby servos (the cheaper the better, I thought, never bothering with much research or trying to pick specific types/brands or looking at parameters like torque – just tried to use whatever I could get, hoping for the best). Hobby servos are of course well understood and work reasonably well for robots, but their control method is a bit crude (no position feedback) and not very accurate.

When looking around for various robot arm projects for inspiration, I frequently came across the Dynamixel servos from Robotis and was intrigued, wanting to try something “serious” this time.

Finding Apples with OpenCV

Pal Denes — Fri, 31 Dec 2021 12:00:00 GMT

When I first started to think about the Nature’s Bounty challenge, I decided to try and find a way to automatically detect apples using a camera and OpenCV. My thinking was roughly:

Apples are of a known size and colour (and there is nothing else around that’s round or red).
Apple detection should be relatively generic, in the sense that we shouldn’t rely too much on knowledge about their expected positions on the tree.
We’re only detecting apples, not tree branches (so apples are just “floating” in space, and we can grab them freely – but we might try to do this “cautiously”, expecting some invisible branches might be in the way).
Apple detection should be as simple and efficient as possible (better to refine readings continuously as we get closer than to try something “perfect” that might be too slow or resource-hungry).