This is part two of my larger robot, it follows up what happens with the small rocks here: What kind of sensor do i need for knowing that something is placed at a position?

Now i am taking the rocks down a tube for placement. In the case they need to be altered so they always will stand up before they enter the tube. Obvioulsy a rectangular rock wont fit if it comes in sideways. The dimensions here are pretty small. The rocks are about 15 mm x 10 mm. The tube i use is actually a plastic drinking straw. And the material i use for the rest of the robot is Lego powered by step motors which draw the conveyor belts to move the rocks. The control is Arduino.

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(sorry for the lousy illustration, if you know a good paint program for mac like the one used to draw the picture in my other post, please tell me :-))

The rocks will always enter one at a time and have as much time they need to be adjusted to fit and enter the tube so the fall down. The question is, how to ensure all rocks are turned the right way when they get to the straw. Im not sure if using Lego when building the robot is off topic here, but a solution involving lego is preferable. And it has to be controlled by an Arduino.

General tips in how to split a complex task into subtasks robots can do is also good, is there any theory behind the most common sub tasks a job requires when designing multiple robots to do it?

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    $\begingroup$ I used inkscape to redraw the picture in the other post. It should be available for mac too. $\endgroup$
    – Shahbaz
    Commented Apr 23, 2013 at 15:05
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    $\begingroup$ What about some kind of vibrating funnel that would automaticaly put the rock in the right position? (You know, like the ones used for coins, when they have to enter a slot). $\endgroup$
    – mimipc
    Commented Apr 23, 2013 at 15:06

1 Answer 1


One way to do this is complicated, involving computer vision and a robot arm or other manipulator that can directly affect the orientation of each rock.

The low-tech way to do it would be to use a separate conveyor that gave you one rock at a time, and use walls to funnel it into a gate that matches the internal dimensions of the straw. You would then just detect when the rock begins to push on the funnel walls (instead of travelling through) and knock it backwards to try again. After a few tries, it should end up in the proper orientation (or you can give up and reject it at that point). An even simpler way would be to skip the detection and just oscillate the funnel continuously, which would be safe if you're assured that each rock is guaranteed to have a working orientation.

It's similar to this patent which suggests a single wall, with the other side being open for improperly-aligned objects to fall off the belt.


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