ahmedragia21

Hi, i tried to follow a line , and used a motor with gear box , but i think its gear ratio is low , its a used one hence i couldnt read the excat gear ratio number , but when i rotate the motor using my hands i find no friction or hard move .. is it a must to use a high gear ratio motor for line followers ?

Hank Fletcher

That depends on the surface your robot will run on (smooth or rough?), the size of the wheels, the weight of your robot, and how fast you want your robot to go.

When you say it's easy to move the gearmotor, are you turning it at the axle? Can you post a photo, or explain where it was salvaged? Chances are, someone's used that motor before, and would be able to comment on its suitability.

Do the wheels run very fast when you lift the robot off the ground, but then the robot stops easily when it encounters any obstacle as it moves across the ground? If so, you're right: the gear ratio of your motor is too low, and you need to either make the wheels smaller or otherwise further gear the motor to get more torque vs. speed.

ahmedragia21

1. the surface is smooth
2. size of the wheel is 4CM diamater
3. weight of the robot approx 11kg
4. i wish the robot moves at 1meter / second
5.hmm , it turn the wheel by my hand i find its so easy to turn it (empty) or no much gears there ?
also i've heard that high gear ratio means high torque and hence u can control it better when u follow the line , is this correct ?

Hank Fletcher

Some answers to your questions:
1. That makes things easier!
2. The wheel size seems reasonable. What are the tires made from? Something with good grip will do a better job than something that spins due to a lack of friction between the tire and the surface.
3. That's heavy for a robot! What constitutes the majority of the weight? Is it the chassis, the batteries, or something else? Making your robot lighter is the easiest way to reduce the amount of power required to move it.
4. 1m/s is quite fast for a robot (it's a realistic walking pace), or even a basic R/C toy, especially one that weighs 11kg. Even 1/3 that speed is quite fast for a line follower. This just makes me more curious about how much power you're putting through your motors. What can you tell me about your batteries and how you're switching power to the motors? How many motors are you using?
5. The low torque you've described seems inadequate to move the mass of 11kg of your robot.

Yep, you've got that right. Bear in mind that, for a given power in watts, there is a trade off between torque and speed. A higher torque motor will move a heavy robot, but if you use the same power as you're using at the moment with your present motors, the robot will move slower. If you want more torque and the greater speed you've described, you're going to need bigger motors. If I had a better sense of what you're using already, I'd be better able to suggest something else. If there's no way to avoid the weight and speed requirements you've mentioned, something along the lines of power window motors are in order.

ahmedragia21

yea, the robot is heavy cuz it has gribbers and batteries ... the robot uses only two motors for driving the robot , but can i achieve a 1m/s for a line follower ?
i use an L298 for switiching the power ( 4 A ) , i use 24V two series Nicads .

Hank Fletcher

What do you mean by "gribbers"? Do you mean grabbers, as in, robot hands? If so, what are you using to power those? Or do you mean girders, as is in some kind of frame or chassis for the robot? I'm really curious about what motors you have already. If the gear ratio is low as you claim, the wheels must be moving really fast with 24V.

The easiest modification for you at this point would be to get really small wheels. With the power you have, you could also do okay with two power window motors. Presuming a 120rpm on the power window motors, your wheels would have to be about 20cm in diameter for a speed of 1m/s.

You can have a 1m/s line follower, but what's the criteria for your line? Are you designing the line course yourself, too? The faster your robot, the more inertia it will have, so the longer it will take to slow down, and it will be more prone to wide turns. Given the speed and and weight of your robot, thick wheels with a lot of grip would be a good idea.

ahmedragia21

Yea, i mean grabbers and i use small motors for them but with high torque ,
yes the robot is so fast at 24V , the line is a straight white line with white crossections on a green floor , yea the robot has a very high inertia , i tried to pass 3 horizontal lines and stop at the 3rd , it really stops at the 5th line ..