What is Servo Controller?

koolitude

I am wondering if it is possible for a robot to move and turn simultaneously with just 1 pair of servo/wheels and a ball caster...

It seems that when I was trying to write a program to control the motion of the robot... the robot cannot move while it is trying to turn... i.e. it can only move forward again after turning...

Am I right to say it is because of the constraint of the mechanical design of the robot?

In order to move smoothly while it is turning, I need an extra pair of wheels for steering, right?

Besides, what is a servo controller? Do I need one for controlling the steering wheels?

Many Thanks!!!!!

Mike Green

A robot with two wheels and a caster can move and turn at the same time if the wheels are turning at different speeds. The greater the difference in speed, the faster the turn. For very fast turns, you can even reverse one wheel.

The Stamp is acting as the servo controller in the BOE-BOT. There is plenty of discussion of this and worked out examples in the various manuals and tutorials downloadable from the Parallax website. The reason for a separate servo controller is that the Stamp can only do one thing at a time. It's possible to combine some things by essentially "time sharing" the Stamp since servo control only requires a brief pulse (2ms) to be sent every so often (50/sec) and the Stamp can do a number of other things in between pulses. Once you get more than 2-3 servos and a couple of different sensors (PING + IR + contact switches, etc.) you start running out of available processing time. The easiest thing to offload is the servo control. Parallax has its own external servo controller and another device that can easily do servo control (PWMPAL). I wouldn't bother with an external servo controller for a BOE-BOT unless you're doing something very fancy. If you're going to do that, consider moving to a Propeller or the new BS2pe motherboard with its two peripheral processors.

allanlane5

Yes, the BOE-Bot can move forward and turn at the same time. The problem is, usually people want to have some control as to where their robot ends up. Thus it's easy to 'move forward 1/2 second, rotate right 90 degrees, and move forward another 1/2 second'. Much easier than it is to "Steer in an 18" radius curve for 1 second" and wind up in the same place.

So, especially for beginners, the "go straight then rotate then go straight some more" algorithm is much easier to learn, implement, and verify.

But you're perfectly welcome to experiment and find the PULSOUT settings that give you the "smooth curves" you're looking for.