Two days ago I did a second attempt to make a new video of MorpHex outdoor. This time I wanted to see MorpHex rolling down a short slope. I think this is the first time I've ever seen a hexapod robot rolling downhill. The outer sphere sections protects the inner parts of the robot very well.
To be honest, not everything went ok during the filming. 5 seconds after 3:31 on the video the inner body servo broke down!
I've had a bad feeling for this servo for a long time now. I did think of replacing it when I made the MKII version, but for saving time I didn't.. sigh..
This was a major set-back since my plan was to demonstrate some other features as well. Currently I'm home alone, because my wife and our 3 kids has already left for Easter holidays. I'm going to join them tomorrow though. This meant I got much free time for playing around with the new Teensy3.1 on a breakout board designed by Kurt Eckhardt. I'm thinking of using this board on several of my robots in the future. The Teensy3.1 feature the latest ARM Cortex M4 processor. Also having connectors for the Robotis servos, a holder for XBee RF communication and a speaker make this board just perfect. Thanks Kurt! You can read more about Kurt's Teensy 3.1 breakout board on the Trossen Robotics Forum.
But instead I had to spend about 10 hours in my workshop for resurrecting MorpHex.
On this picture (from the bottom side of the body) I've removed the LiPo battery holder and marked the white Nylon gears just to be sure..:
Removed the "body-arms". As you can see, the screws that hold the Hitec HS-5645MG servo is a real pain to reach:
After removing the servo I opened the servo case just to confirm that one of the brass gears was broken:
Luckily I have several spare Hitec HSR-5990TG servos. They are much stronger and feature gears of titanium. FIY, the Hitec HSR-5990TG servo are discontinued. Some years ago I bought about 40 of them, used but in good shape and for a very good price.
The new servo in place!:
So far so good.? But no. At this point I found another problem. You see, the main reason for why the servo broke down was that one of the screws that hold the pairs of "body-arms" loosened after a while. To improve this I had to remove all the arms again and also remove the upper sphere section and the ARC-32 mcu board. Believe me, this made me pretty frustrated. What a mess!
As you can see from the picture below, the screw marked with a red circle became loose and came in direct conflict with a fixed part of the inner body. On the head of the screw you can see some scratches, actually this was more visible on the fixed body part of aluminium (no pictures of that). The solution was to use inset screw (the red arrow) and using locktite this time:
I don't think I've explained this before. The upper section are mounted to the inner body part using only three 4M screws (marked with arrows and a circle on the next picture). All in all, its a pretty simple task to mount.
After assembling everything together and recalibrating the inner body servo, I only had to do some minor changes to the code and MorpHex was working fine again!
My next upgrade might be the new Teensy3.1 board. But that require a lot of work on the code, not sure if that is my priority #1. I've some plans for a new robot too..
I wish you all a great Easter holiday!