This is Duke:
A friend of ours adopted him a few months back. He had been shot twice and left for dead on the railroad tracks (some people suck.) He's fine now, but his back legs don't work. That doesn't seem to bother him though-he has a little chariot that he gets around in just fine.
Watching him move in this contraption gave me an idea for a kind of robot locomotion I hadn't seen yet, and I thought it was something I could do with the RocketBrand Studios 08M2 board. All it took was two servos and a Sharp IR (though as you can see in the video, I really need a longer distance sensor. This is the 10-80cm GP2Y0A21YK0F and it doesn't quite have the range once you get past the "shaky" zones those have, which isn't enough to give the tail a turning radius.)
It's pretty simple-the two servos lift each leg and push the one that's off the floor forward then drop it back down and start it over again on the other side. Other than the example of Duke, the closest analog I can think of to this kind of locomotion is a mudskipper.
If it wants to turn, it repeats the cycle on one side only five times and turns it in a semi circle (you can see it do this a few times in the video.)
The original program took distance readings at each step as the head/shoulder gimbal looked right, left and forward and then already had the decision making information for which way to turn in a very elegant (if I do say so myself) main programming loop. (For as many LMRians are now enthralled with Python, I would think that AxePad Basic would hold similar appeal.) However, the short-range sensor makes the beauty of the programing almost useless. If I had a job right now I might feel a little more inclined to buy another GP2YA02YK and take it to the next step, but I'm happy enough with the proof of concept and what I'm assuming is pioneering kinematics that this is probably going on the shelf.
The body is made from 3, 6 and 12mil PVC sheet and the casters are roller-balls from Harbor Freight-about $.90 compared to the $5.00 ones you can buy from robot specialty stores. The forelegs are made of coat hanger wire and have feet made of Oogoo for traction.
It's worth mentioning again that Chris the Carpenter gave me the last two RocketBrand Studios 08M2 boards and just made me promise to "...do something cool with them." I think this qualifies. These are amazing little boards and so easy to use! I think PicAxe is an under rated platform (!) for hobby robotics in light of the popularity of Arduino. It seems to me that for smaller robots-turtles, Boebots, even some hexapods-that Arduino is almost overkill. The comparable chip to the 08M2 in the ATMel line is the ATTiny25/45/85, and as noted elsewhere, the servo support and timing on one of these using Arduino as ISP is unsatisfactory. Also, I wouldn't have been able to make this happen without a surprise wedding gift from Ossipee, so thanks both of you guys!
Leave it to OddBot to come up with the solution. I was going to let it rest but I wanted to see if I could get it one step better (no pun intended) and implement the programming tricks I was so proud of (and of course move this post back to the top of the queue! ;-) I've attached both .bas files-the one it has now and the one I ran in the original video. I'll try to get more video up tonight or tomorrow. So far it has only proved itself on two rolls of tape stacked up on the bench, but it does what I expected it to in that situation. The real world is always a little more sketchy. On to the kitchen!
So as it turns out, I got the story of Duke all ass about face-or rather confused with another dog's story, that of Chance:
Chance was the one that was tied to a railroad track (apparently his previous owner was Snidely Whiplash) with the intention of having him killed by the next train but just lost the use of his hind quarters. Duke was shot twice as I mentioned but was thrown in a lake. I'm glad that I know the people who take dogs like this in and not the ones who do those horrible things to dogs. In any case, Chance is adorable (if incontinent.) He absolutely does not let it get him down. As an aside, the word "Cynic" originally referred to someone who thought the best way to live one's life was as a dog would (see Diogenes, the insane Plato.) He might have had something there...
Chance actually moves more like Dragin, given the lack of wheels. Also the color scheme is closer.
Anyway, I've added a third video that demonstrates the changes OddBot suggested and which shows everything working pretty well. It's a long one and it's pretty well commented. Dragin is starting to arc right a little in his motion-that could be any number of things, like servo wear or arm stress. Anyway, I'm officially checking the "Complete" box on this one (so I promise no more updates just to bump me up to the top of the page!) Also, this marks the point when I need to build a new shelf for these guys. I don't have room on, under or near the bench for all of them anymore.
Remember to scratch your dogs and cats behind the ear for me once, LMR. (And chinchillas if you have them.)
Update 19 June 2013
I couldn't resist adding this animated gif when I found it and saw that I'd mentioned chinchillas last time:
I believe that's a hedgepig. Bless his heart and his tiny little withered legs as he struggles valiantly against God's twisted designs...