View Full Version : [Question(s)] need help with steering for a 3 wheel robot

01-24-2009, 10:17 AM
hi.this is my first robot project.i am trying to build a three wheeled robot which will have the front wheel attached to a servo/steppr motor for steering and the rear wheels will have dc motors.but i am very confused about the steering method.from what i have gathered is that the robot is supposed to turn in one direction [say left] when the servo/stepper turns in one direction and when the servo/stepper will turn in opposite direction the robot will turn right. can anyone explain this because i am very confused with my idea of it and cant figure how the front wheel will go left or right because isnt it turning in the same direction as the rear wheels (that is in forward or in reverse)? :confused:

and also

1.will the rear dc motor(s) will be running all the time during this turning process?
2.can anyone please tell me how to mount the front or steering wheel of the robot on the servo/stepper and the way it should be fitted with the robot chasis? pictures will help a lot.


01-24-2009, 11:12 AM
If you're turning a servo to turn a wheel, the robot is going to turn just exactly the same way a car or motorcycle or any other vehicle following the laws of physics would. ;)

1. Well, yeah, they're gonna have to push the robot. The servo is just turning a steering wheel left or right.

Welcome to the forum!

[I'm going to move this over to "Mechanics" pretty soon, I think...]

01-24-2009, 11:38 AM
Ok...couple of questions...and maybe some answers.

A...how big are you planning to go with this robot?
2) Were you planning on driving the two back wheels with just one DC motor?

I guess the how big is not that important. If you are planning to control the two back wheels with just one motor, then you're looking at a robot that will stear like a car. The robot will turn in a curve...based on the turn of the front center wheel.

If you are using two DC motors for the back wheels, then you may want to consider using a passive caster wheel fro the front wheel. Using a powered wheel and steering it means that your robot will still have to turn like a car...following a curve...or you could turn in place, by having one back wheel go forward, the other backwards, and the front wheel turned 90 degrees and powered in the desired direction of travel.

Another idea would be to use omnidirectional wheels. (http://www.robotmarketplace.com/products/0-276-2165.html)..and simply use a DC motor to power each wheel.

Again...I guess more information would help.

Good luck


01-24-2009, 12:45 PM
thanks for replying people :]

darkbak2: i guess this is a medium sized robot.im planning to take the body of a toy car and use it as the mechanical platform.also im planning to use its wheels.

as i said i havent built a robot before.so i dont know if using one motor for two rear wheels or two motors for two is better.but initially i thought about two motors.

what you said about turning in place by turning the two motors in diff.directions/omnidirectional wheels, but if i use dc motors for the rear wheels then i guess i wont be able to turn them as precisely as i would like to and specially if i am trying to build a line following/obstacle avoiding robot.right? i wanna use servos/stepper just because they'll make the turns accurate.also may be i'll need to know how much the car has turned.so dc motors dont help :(

p.s: as far as i know turning a four wheeler robot is more difficult than doing it in 3 wheels.that's why i wanna build a 3 wheeler.

01-24-2009, 01:23 PM
You can do it just fine with a servo actuating the steering on the front wheel and a single driven rear wheel. It's just a tricycle. Or you could both drive and steer the front wheel - that's like a little kid's tricycle. Either will work fine.