Direct Drive Four Motor System

[Matt Adams]

Originally Posted by Jason Kixmiller

Actions speak louder than words (said or typed) and a winning season speaks for itself. Whether you custom built every piece or assembled from "the shelf," having a successful season allows your performance to speak for you. Many teams have great features/machines, but arguing about the best is in many ways missing the point.

Back to the true topic at hand, I have a question:

Is it feasible for the 4 independent motors to be electronically controlled/programmed to have the same output speed?

Absolutely, but it requires feedback, such as an encoder, resolver, tachometer, and a good controls algorithm, especially to control the speed of four different axis. However, I'll ask another question for you:

It is worthwhile to electronically control the speed of each individual tire in a closed loop fashion on FIRST robots?

This is an interesting question, and there are a few distinct and divided groups on these forums about drive wheel feedback / controls in general. There are some very adamant people who swear up and down that closed loop control (position and/or velocity feedback on the wheel) is critical, others who deem the resources / benefit are too small, and still others who ask, "Closed loop? What's that?" I consider myself to be in the 2nd group.

My thoughts are merely, "Can't a good driver with some practice on the robot before it is shipped 'aim' an open loop drive system 'straight enough'?" The advantage of a closed loop system is pretty nice if you have two pairs of motors controlling two wheels on each side - you can essentially ensure that when you push both joysticks full forward, that the robot will move straight and not veer off by say up to 10 degrees or so as it might in an open loop system. Driving is more intuitive, this is a very good thing.

Correct me if I'm wrong, but this thread has sort of now technically spun into a suggestion about a 4 wheel robot with independently driven wheels, each with an independent gear box, as well as a closed loop feedback setup on each axis to ensure that the wheels all spin at the same rate.

Others may disagree, but my opinion about this can be said in a single word: Overkill.

Matt