Trackbot part 4

Side shot of Trackbot

With everything together the first test drive took place. As with Squarebot much time was spent on getting the emitter circuit at 38kz (one day I'll buy a multimeter that does decent frequency measurement). However I was finding exactly the same issues as I did with Squarebot. Low range on the emitters and lots of noise, false detects everytime the motors changed direction, etc. Going back to the breadboard of the design I moved around some of the filtering capacitors on the power supply. Totally different (better) behaviour. Based on this I added a nice big 470uF capacitor to the main board on the power input plug from the power board. Totally got rid of all the electrical noise from the emitter circuit. So even short cables like those on Trackbot still result in large amounts of EMF. I really need to learn how to make my own printed boards.

Once the new filtering capacitor was in Trackbot worked beautifully. He avoided things, the bump switch worked fine and he could climb over anything. I did a bit more work on the programming to add the functionality that if both detectors detected something then that should be considered the same as if the bump switch triggered. Ie full reverse then turn to get out of trouble. With this simple response Trackbot has rarely gotten stuck on anything.

A few times I have mentioned size/weight issues of Trackbot and my attempts to reduce them. In the end Trackbot came in at 430gm. Most of that is engines and batteries. Rechargeable batteries I found weigh two to three times more than standard batteries too.

So what lessons did I learn from this design? That cables are bad and just add issues into a design is one. I am really impressed with the Tamiya education range. Precision plastic components all designed to fit together. Perfect for building bots out of and quite cheap too. Something else I learnt was that rechargeable batteries don't hold their charge over time. I few times I have given Trackbot a run after a month or so only to find the rechargeable batteries are dead but the standard 9V battery is fine. For the next design I need to consider moving to a more modern battery technology which is lighter. Also I should have put the bump switch on an interrupt pin of the microcontroller so that I could have seperate behaviours for the bump switch and when both detectors detected an object.

What do I want to do after Trackbot? Make a mini-sumobot. I have purchased some engines from Solarbotics and am current in deep thought mode of a design. What is taking up a fair bit of my time is how to design/make a chassis for such a small bot. A 10cm square isn't much room to get two engines and wheels into. Originally I considered using a small box and wedging everything into it. I had machined in the engines so that was looking good. However I found that getting the rest of the bot into a fixed container (PC boards, batteries) just wasn't going to work. No room to work with and a real pain to get at components (like batteries). So my thoughts now are to use multiple boards and stack them. Easy to design each board (one for motors, one for battery, etc) and they just screw together. All of this is on a bit of the back burner now since Sonja has arrived. But it's nice to have dreams.