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Mobile robot convoying

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New Member
Hi, all!

I am triing to build a mobile robot that would be able to follow another mobile robot withouth any communication between the two of them.

The general idea was to use a pic micro and two analog IR sensors facing forward in the back robot. However, the following isn't going smoothly and the back robot gets lost very easily (especially when one of the sensors looses sight of the front robot). Do I need extra sensors? Is my design to simple?

I am interested whether anyone has any experience and all help would be greatly appreciated.



New Member
That is a good idea on the 2 IR sensors... but make sure that both of the sensors see the bot at the same time... so that when one of them looses track the other one still sees the robot and tells you what way to turn. It would be a good idea if the back of the "FRONT" robot was a white "wall" so that it is easier to track.

You could also have the "FRONT" robot shine a bright light, and have some LDR cells follow the brightest point. The problem here is that if there is a window near by during a sunny day, chances are that your light won't be stronger than the sun :lol:



New Member
You should use an ultrasonic sensor to keep the fixed distance between the 2 robots. And add 2 IR sensors on the 2 side of the following robot.

As the real distance is longer than the fixed one, you may accelerate the following robot, and if the front robot turn, the 2 IR sensor will "see" and make the following robot turn. If the front robot stop, or go back, the following do the same.

You should keep the fixed distance in effective IR range, and it works. You may use SRF04 at fixed distance about 0.2 to 1m. If you get enough money, you may use 2 SRF04 (about 20 USD each), and it gives a perfect result. The fixed distance, as in this case, can be upto 2 or 3 m.

Also in this case, if you don't wanna use fixed distance, you may use normal measuring distance of ultrasonic ranging device, and you can drive the following robot with ease.


New Member
Thanks a lot for the info... Judging by your reply you have hands on experience with this kind of project?You wouldn't know a web site with some more info, would you?

If I understand you correctly you would use on analog distance sensor in the middle and two digital (he is there/not there) on the sides...?

I am using two analog GP2D120 sensors on the sides though I get quite a lot of interference when reading the value (window averaging the values provides me with kind of sinus value at constant distance). Maybe my power source is creating the interferance... :?

Best regards,


New Member
No, I meant there were 2 designs you can use.

1) You use one SRF in the middle, and 2 IR on 2 sides. You set a fixed distance to SRF, it's not a digital. If the real distance is longer than the fixed distance (in your program), you accelerate you robot, if shorter, you deccelerate.

The 2 IR is used to turn the robot, if the left IR is ON, turn the robot to left, because the object is on the left of your robot, and you have to follow it.

2) If you got 2 SRF, you put it on 2 sides, and no need the middle one. You do the same as in the first case. But you now get clearer information about the object that you have to follow. You may keep the fixed distance to follow the robot or a range distance as you want to.

|_______| |____3_|
|____| |____|
|__| |__|

The 2 SRF will be showed like this. If the object is some where in this range, you may control your robot with ease to follow.

IF the object is at 1 (the SRF1 detect the object, the SRF2 doesn't, and you know the distance), you turn the robot to left and move forward quickly. But if it is at 2, and the distance is good enough (in the range you wanna), slowly move forward to the robot until it is close enough to the object. If the object is at 3, it means the object is so close to the robot, and it's in the right. So, slowly, move back and turn right.

I give here an example, you may creat your control rules as complex as you want, because to this 2 SRF, you get more information than the first case.

You may use GP2D12 in stead of SRF, but GP2D12 give you a shorter range (20 - 80cm). SRF give you 3cm - 3m range of detection.


New Member
Hello falleafd ,I saw you in forum **broken link removed**
I read your post about ultrasonic sensor in this forum
I really excited .You can told me more detail about ultrasonic sensor .
I want to program robot to detect obstacle using ultrasonic sensor
you can explain me ,can't you ?
To dectect obstacle , which another sensor can we use ?
thanks for your comment
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