Multi Drive Fun...

[FotoPlasma]

First of all, I'd like to commend you for the amount of work and thought you've put into this topic. It's great to see people going through this process of recognizing and defining a problem, and going through the process of generating a solution. Lately, the amount of purely technical (as opposed to speculative (the new control system) and argument-based (the etymology of drivetrain terminology)) discussion on ChiefDelphi has been declining, and this is a very refreshing. But I digress. This isn't what the thread's about.

Your method of converting the joystick position to a polar coordinate system (from (x,y) to (r,theta), that is) seems to be a very effective method for determining the intended orientation of the modules, but I think there are simpler methods (which don't produce the same results, but which are comparably powerful). One of these methods is to map an arbitrary analog value (the X-axis of one of the joysticks, in our situation) to the orientation of the modules. Concerning this, you'd want to shrink the value of the intended orientation (the X-axis value) by a factor of 2, based at 127. Hrm. Getting into tangents seems to be a forté of mine.

One of the most involved processes you'll probably get into is perfecting the algorithm for powering the motor which controls the orientation of the modules. Driving the motor at full speed has the chance of "over shooting", and causing the system to abruptly and violently reverse direction, while, if you don't give it enough juice, you'll wind up (essentially) stalling the motor (I'm not absolutely certain that this is technically correct terminology), when it can't overcome resistance to motion in the steering mechanism, and converting electrical energy almost entirely to heat, instead of mechanical energy (I could be wrong about this process, as well, though). So, you'll wind up wanting to move the motor faster when the difference between the actual orientation and intended orientation is above a certain threshold, and stepping the speed down as it approaches the intended orientation. And again with the tangents...

Speaking of tangents, one thing you might consider, instead of using a mathematical function to determine the arcsin, is using a lookup table, given input values mapped directly to output values. I believe it'd only really be space-wise and speed-wise effective if you're dealing with integer values, but that should be fine. Space and speed permitting (declaring and defining 255 or 360 bytes and spending instruction cycles reading these values, as opposed to performing mathematical operations on any given input value, which would probably take considerably more in the way of instructions), a lookup table implementation of arcsin might be the optimal route.

Oh, also, what you're calling "angle" steering is also referred to as "complementary" or "monster truck" (thanks, Mike ) steering.

And a question. What do you mean by "[the] motors aren't connected to the wheel assemblies"? I'm thinking of a coaxial system, such as 217's 2003 drivetrain (pictures are available online).

Just throwing a little kindling on the fire. I'll probably have more to say, tomorrow. Staying up until 3am the day before a midterm isn't good planning, on my part.