Back in 2010 I thought that the birth of my first son, Scott, would be just a small blip in my journey into robotics but, looking back, it seems to have been the end of that chapter. Of course, raising children takes time, and Scott was just the first; he was followed shortly after by Max and if I thought assembly and robotics was complex to learn it’s nothing compared to raising kids!
I’ve been very busy with other things just recently and so I haven’t been able to spend much time on this project. Work has been busy as I’m working towards a new release of my code and my son Scott was born on 25th January. Right now I have very little spare time for my robotics but I’m sure that will change as things settle into a new routine.
Once the servo controller code was feature complete I switched to looking at the hardware side of things and thinking about the next stage, the servo sequencing.
From a hardware point of view I had several things to work on. Firstly I needed to get the servo controller and I/O multiplexor chips off of a breadboard and onto something a little more permanent. Since I still find building things with perfboard a little hard I decided to build the controller itself on one board and build separate daughter boards for the I/O multiplexing.
I decided to treat myself to an early christmas present and bought a 60W temperature controlled soldering station (a ZD-916 which I got from Maplin). All I can say is WOW. Suddenly I can solder neatly rather than making a smeary mess. The difference between this and my cheapo 12W soldering iron is just unbelievable. It just makes the whole process SO much easier. Where in the past when soldering something with a large heat sink or onto a large pad would be painful as both items would never seem to get up to temperature now I hear the iron click on as I touch the items to be soldered and the heat stays constant and it just works… Highly recommended.
For those of you interested in the kind of thing that this blog is about you might also find ChipHacker.com useful. It’s a ‘stackoverflow’ for embedded programming and electronics people. Hopefully it will become a useful resource!
I now have an easy to extend PWM servo controller and the next job on my list of things to do is extend it so that it supports the functionality that I feel I need for correct control of my hexapod’s legs. As I mentioned here, I’d like to be able to tell the servo controller to move a group of servos to a particular set of positions so that they all arrive at the same time and, the movement is incremental and the movement can be stopped at any point in case a leg sensor detects an obstruction.
Here are some links that may help once I move onto fabricating the various pieces required to build the hexapod’s body.
This is a simple 4 legged walking robot that was machined from an A4 piece of 4mm ply wood. This is the guy’s website, with more details of how he produced the robot. And this is the Dutch prototyping lab that he used to laser cut the pieces. Finally, this is an interesting link to David Buckley’s walking robots page.
A collection of links that I’ve been using recently for research.
Servos and robotics Hitec HS-422 Servo. The servos I currently have; likely not suitable for use as actual leg servos due to lack of torque. Useful link as www.superdroidrobots.com has links to the spec sheet for the servo and a selection of different spec servos with corresponding prices. More useful to me than the actual Hitec website as that doesn’t list relative prices.
My package from Cool Components arrived this morning. My choice of prototyping equipment was quickly validated when I plugged together the Arduino and the Pololu servo controller board, plugged in the servos and servo power supply, connected the lot to the pc via a usb cable and had three servos twitching back and forth under the control of the Arduino is no time. The idea is that I can now begin fabricating a leg, connect up the servos and then experiment with leg movement without needing to get the soldering iron out.
I saw these Dynamixel DX servos mentioned on Trossen Robotics this morning, see here. They’re interesting because they have a richer interface than the normal hobby servos that I’ve been looking at and they provide a multidrop RS485 interface so that you can chain multiple servos together and control them individually via a single line. You can get feedback on the angular position, velocity and torque and also alerts if temperature and voltage deviate from expected (user specified) ranges.