It has been a while since my last post, actually one year! Ouch..
The reason is that I've been occupied with many other projects and family life.
But I've got some free time now and then in the last couple of months. So I thought it was about time to make an update about the MorpHex robot. I'm calling the new version MorpHex Mark II (MKII). At first glance the MKII would probably look almost just the same:
As you can see, the sphere sections are reinforced using some T-shaped aluminium brackets for supporting and holding the plastic (PC) sphere sections. This made a huge difference when it comes to rigidity. On MKI I struggled with the fact that the plastic sphere section was to flexible and I had to reinforce the edges with ribs. The problem was the ribs kept getting loose (the PC glue wouldn't hold), so I had to do even more improvements. On MKII the ribs isn't really needed, simply because of the aluminium brackets that is shaped to match the inner part of each sphere section perfectly. I did spend some hours in the workshop fine-tuning the bending tool to make the bracket fit.
The main challenge with MKI was that it wasn't able to roll in a straight line of path, only in a curved direction. I believe the main reason was the constrained motion of the upper sphere sections. Having only one DOF (degree of freedom), or only one servo motor for each of the six upper sections made it very challenging. It might be possible to make a more complex linkage system that gave the upper sections a better motion when rolling. Not sure how though..
I therefore decided to use two servo motors on each of the six upper sections. Having 2 DOF would make it easier to control, so that the upper and lower sections move in a symmetric motion.
A picture of MorpHex MKII pushing out both (upper and lower) sections:
The challenge was to make the motors fit inside the upper section without getting in conflict with the electronics. A picture of the upper section before I monted the plastic sphere sections:
Compared to the leg section, the femur and tibia sections are mounted very different. One advantage is that the servos in the upper section draw very little energy when holding the ball shape. To make enough space for the upper sections I also had to make new leg sections.
All these hardware updates also made MKII a lot heavier. So I've had to upgrade the servos to 24x HSR-5990TG (all femur and tibias), 6x 5980-SG (coxa) and I'm still using the same HS-5645MG (inner body servo).
The code is still a WIP (work in progress), but I've done good progress lately. And this weekend I made MorpHex MKII roll again! I'm not 100% pleased with the result but it looks promising though.
Some new pictures:
As you see, the new upper section has a lot more freedom.
I'll probably make an optional rolling feature using this posture:
Hopefully I'll soon post some new videos..