[dougwilliams]

As Alan pointed out, you can use encoders for more accurate speed control of individual wheels (which in itself may have utility). However, I think jtrv is probably really looking for the distance traveled function / odometer (as Alan pointed out).

That in itself you can do (easily?) - as you would need to mathematically combine the feedback from all four wheel sensors. I've been thinking about that the last few days, and in theory, it seems like you could do that and understand what is being driven to each wheel. If you mathematically reversed the trig functions from the software motor drive functions - you could effectively tell yourself what direction the robot is going, and for what amount of time.

The caveat is - what direction the robot "should" be going is different that actually going. You could spin a mecanum if you are stuck against something, and that problem is more prevalent in comparison to a traction wheel which might just stall. It wouldn't account for designed slip of mecanum rollers.

I'm curious if anyone has done that and what the utility of that wound up being (if so please send a link or reference).

And then as juchong pointed out, with a gyro/IMU you should also be able to take encoder inputs and couple that with accelerations and gyro spin feedback and predict better where you are on the field.

Has anyone ever seen that done - and again - if so, what was the overall effectivity of that for positional control? It's something I'd love to do - but don't have a good understanding of the resources needed and whether it's worth it. If anyone has any additional info I'd love to take a look.