My little rover Micro Sawppy Beta 2 (MSB2) has a mock RTG in the back, and in the front I installed a mockup for a rover robot arm. Even as a non-motorized mockup, it was more than Sawppy V1 ever got! A Sawppy arm was always on the to-do list but I never dedicated the time to make it happen. In the absence of my own efforts, I’m happy to see some other Sawppy builders have added robot arms to their rovers. Like CJ’s arm documented here on Hackaday.io and on YouTube.
And this rover flexing its arm on Twitter.
Both of these robot arm projects followed the mechanical geometry of real Mars rover arms, which makes me happy in a “These are my kind of people!” kind of way. I haven’t studied the arm as much as these other Sawppy builders had, so I decided to start simple and small with MSB2. I designed and printed a very simple arm as practice. I didn’t have any kind of actuators on hand that would work at such a small scale, so this arm is limited to manual articulation. (I could pose it like an action figure, but no remote control or autonomy.)
Still, it was instructive to see what kind of motion is possible with this mechanism. I knew two things from the start: it needed to go into the stowed position and it needed to extend out to act like it is retrieving a Mars sample. Once I started playing with it, though, I learned two other things.
The first lesson is that this draft had only a subset of range of motion as the real thing. I couldn’t replicate the sample storage movement sequence shown in a NASA tweet illustrating how Perseverance will transfer core samples to the carousel handling tools and sample tubes. The second lesson is that I had a vague idea to build a rover that can be friendly and wave “Hi” to people, but this arm could not bend the way I wanted because it would collide with the left front wheel steering servo. I’m glad I learned these lessons on a simple test arm, before I spent the effort to motorize my arm. What I could use for arm actuator is a problem itself, as I encountered a problem with the micro-servos I’ve been using.