I performed some experiments on the motors I have and came up with some interesting results. Instead of a stall torque of 50 lbs. at 12V 3.5 Amps, the stall is more like 100 lbs. at ~6 amps. This is good and bad. Good because my robot is going to have plenty o' power to move around (maybe even with a payload) bad because the L298 motor driver I was planning to use ain't enough. My solution is to make my own motor driver using FETs .
After blowing up a few "test units" (10 so far) learning to work with them properly, I learned two things - A.) You've gotta tie your gates down when you aren't using them. B.) Don't play around with blowing up FETs, get a FET driver with a high-side charge pump. I did some research and determined the HIP4081A fits my purposes well - I also found out (via the internet) that a few of my TCRG hommies have already gone down this path and are using the HIP4081As now. I just placed an order with Newark for a few drivers and I'm waiting for them now.
While playing the FET game, my supposedly good gel-cell 12V 17-AH batteries from Mendelson Electronics didn't perform very well - like at all. Maybe I didn't take proper care of them, maybe I got jacked, whatever. My next move was to stop playing around with gel cells and get a decent deep-cycle 12V marine battery. I found a swell battery that put out 105 amps and at 58 lbs would be a freakin' mongo lump in the middle of my `bot. I got 2 of them and I'm going to put them both in the frame - aesthetics be damned.
I put (mostly) together what amounts to the new proto-type leg and immediately determined I need bearings. I've been hunting for them all day and finally stumbled across a bearing source on the net - I order a couple pairs to play with. Along with the bearings I need to lathe a decent aluminum axle (here is my future aluminum source ) for each leg joint (I'm up to 5 per leg). There have been many little changes to this leg design along the way and I expect there will be many more.
I came up with this modular method of prototyping boards I was going to use across the board on my robot. I've decided that would be a bad idea, and will only be using prototype boards to figure out what the standard boards will be. When I get it right I'll make a more economical board to put in the robot.
This robot project is spinning off sub-projects out of necessity. One thing I want to do is automate Kenneth Maxon's oven-soldering method. Another thing I want to do is morph my Sherline lathe into a stand-alone lathe/mill (this is mandatory). I'm trying not to lose focus and get distracted by these sub-projects, but I might take a month and bang them out. Luckily the same technologies used in this robot project are easily morphed into these sub projects. (If I say this often enough I might start to believe it).
I hope you guys don't mind my embedding the links into this entry - I sometimes use these entries to figure out what the hell I was thinking when I did/bought whatever it was that is in question. Someday I'll actually sit down and do a web site -
you know, when I have time...