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  • Author Author: dubbie
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A Black Line Following Mobile Robot : For Makevember

dubbie

I was asked at short notice to do an activity for a children's club I sometimes help at. It was supposed to be along a theme of knowing directions and compasses and stuff. I didn't think I could work out any compass stuff in time so decided to do what I knew something about, which was mobile robots. As it needed to have something to do with following directions I decided to use a black line following mobile robot. I initially decided to use a ready made black line following mobile robot but the ones I could obtain in time were rather puny and the better ones took too long to arrive, so I decided to make my own. I had just managed to get my 3D printer working again so it seem a good opportunity to make sure it was working properly.

 

I had some continuous rotation servo motors lying around waiting for a project, plus some LDRs left over from the LDR Camera Vision Thing Project14 activity, plus a Nano and some battery packs. What else do you need for a black line following mobile robot. All I did was to design a base plate for the 3D printer that held two servo motors and two battery packs, just push fit together. Unfortunately the battery packs wobbled about so nothing fitted tightly and I had to design a top plate to hold everything in place. I originally planned to redesign all the 3D printed parts to make amore coherent approach but time ran out. The Nano is plugged into a protoboard and then BlueTac-ed to the top. The sensor consists of a pair of white LEDs and associated LDR detectors. I spent a lot of time working out the correct height, spacing, brightness level and placement of the black line sensors and even on the evening before use I was still tweaking the hardware and software in order to get it to follow the black line reliably, see below.

 

 

It can still wander away from the black line on occasion, especially if there is a source of light shining in from the side and I wasn't able to make a compact and attractive design. But the idea was for the children to colour in a face for it and fold it into a box that just sits on top. Mostly they managed this and were quite excited when I got their parents to take a video of the mobile robot going round and round.

 

The code is fairly simple but getting the correct values for the motor speeds and delays took a lot of trial and error. I'm not a control engineer and I just didn't have the time to work out a mathematical solution to this so I tweaked values until I managed to arrive at a fairly stable and workable set of values.

 

 

 

So this is another contribution to the Makevember Idea.

 

Unfortunately due to redecorating the lounge (nearly finished!) and making this Black Line Following Mobile Robot I have rather neglected my LDR Camera and BeagleBone AI project. Still, there's still tomorrow, maybe it will all go together and work perfectly!

 

Dubbie

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  • in reply to 14rhb

    I must admit to not having used an LDR - LED combination before, I've always used specialised infrared LEDs and phototransistor detectors. It turned out a lot more difficult than I thought. The first problem was that the 3D printed holder just acted as alight diffuser for the LED and the LDR was constantly surrounded by bright light and didn't detect anything else!. I had to reduce the light output of the LED and put black marker on the sides of th eLED. Plus I moved the LDR from the top of the 3D part to the bottom, nearer the black line, to try and cut-out more of the sideways light from the LED. It could really have done with more experimentation to get the separation of the LDR from the LED (angle of incidence) right, as well as the spacing of the two detectors. I designed it based on a black line of 6 mm width and then realised I couldn't make a black line 6 mm wide! Fortunately, with a lot of physical and software tweaking I managed to get it to work but it was very much a last minute thing.

     

    Dubbie

  • in reply to dubbie

    Dubbie,

     

    What a great learning exercise.  It is easy to do something the same way that we have done it before, but you learn so much more by trying something new.

     

    Well done!

     

    Gene

  • in reply to dubbie

    Knowing this is your own bespoke sensor and you put lots of effort into the experimentation/design of that part makes it even better IMO.