Motor Speed Steering Control or Servo Steering Control?

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richardv2
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Motor Speed Steering Control or Servo Steering Control?

Post by richardv2 » Tue Jan 22, 2008 10:21 pm

Fast Line-Follower Steering? Motor Speed Steering Control or Servo Steering?

I want to build a fast line-follower. I've seen left/right motor only robots where all steering control is in the motors, and I've seen several with a steering servo and sensors out front and the hardware and motors in a trailer in back. My questions...

Is there advantage to either method? Seems like putting the sensors and steering out front would be better, but I don't know how to find out other than build both or ask here.

I'd like to hear your comments on which steering mode would be best. I will probably eventually try both, but for this attempt, I need to pick one.

hakbot
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Post by hakbot » Wed Jan 23, 2008 7:25 am

Seems to me that by using 2 motors for propulsion and steering would be the quickest and most simple way to create a line follower. I actually used 2 full rotation servos for my line bot. I used a camera and vision processing for feedback so it had to go a little slower, the servos suited it well.

richardv2
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Post by richardv2 » Thu Jan 24, 2008 7:27 pm

From what I've read, the main reasons for servos are:
Small package
Built in gear box
Good power/weight ratio
Built-in feedback

So for a small (light weight) robot, I would thing servos would be the way to go. I just have no idea at what weight it makes more sense to go with motor control.

Droidwerkz
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Post by Droidwerkz » Fri Jan 25, 2008 4:00 am

really what the debate is here is skid steer vs a tricycle type design right?

dc servo's come in many sizes all the way up to enormous 100 + volt servos used in large high precision machine tools. they can be cost prohibitive at that size, but they are out there. keep your eye out too, because sometimes flea markets/junk dealers will have them , and not know what the hell they are for, and you can get them for a steal!

I have built a few small robots using line following type- designs and you can go either way on this one

so heres an idea! ...i think the easiest way to have a machine follow a line is with a simple laser reflection /detection setup where a single steering motor (tricycle design) always runs in one direction or another and allows the motor to drift slightly in one direction and when the laser no longer sees the line it swithchs the directional control (h-bridge ) on the steering motor. so basically , your line is part of a closed loop feedback systems and you get a behavior like this from the steering motor:

steering motor direction= ccw, bot travels slightly left as it moves forward (the laser detector flips the h bridge when it no longer sees the line) so steering motor direction =cw(bot travels slightly right as it moves forward
(the laser detector flips the h bridge when it no longer sees the line)

you can make the "line drift" as wide or as narrow as you like depending on the thickness of the line. and the accuracy of the steering servo . this design can actually hold a pattern as tight as a few thousands of an inch and this design would also work well to track an embedded wire or a magnetic strip or even a light bulb and a photo detector (with either design i recommend you use reflective tape) with a bit of modification the same bot can search for a line to follow also.

the cool thing about using a steering servo is you can just run a single drive motor (for fwd/rvs) and run the hell out of it, or even use an engine of some type for forward propulsion

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