we purchased the Blue Bot 4-in-1 kit and have been trying to get at least one of the projects to work. In particular, we built the Line Following version of the robot and the problem is that one of the wheels spins much faster than the other. In addition, this fast spinning wheel spins on its own (i.e. without the sensor being exposed to white paper) if one toggles the MOSFET by touching it on the top. As a result when you put the robot on the path it just starts spinning without following the line. We checked the circuit a bunch of times and it seems to be correct, but the problems still persists. Any suggestions, recommendations will be highly appreciated cause the kid was very excited about this kit but is not getting really frustrated.
Hello,
Given the holidays, it might be several days before the expert sees your post. In the meantime, I (just a moderator, not an expert!) wonder if any of the discussion in this thread might help you?
Hi - glancing at your picture, the first thing I noticed is that one of your diodes is backwards. The diode at the top in your picture has the gray stripe facing toward the MOSFET. The gray stripe should be facing toward the power bus. Diodes act like one-way valves for electrical current, so if you put them in the circuit backwards, it can cause strange behavior (like one motor always running or never running).
I would flip the diode around and see if that fixes the problem. If not, please let us know and I'll take a closer look at the rest of your wiring.
Thanks for your help! We actually did find this error with the diode placement as well and fixed it. The wheels started working properly but we are still having problems with the line-following bot. Basically the challenge is that it's not following the line reliably. It's going too fast and going over the black line and starts wondering/spinning aimlessly. We have tried 4 and 2 and 3 battery powered circuits (1 battery wasn't enough) with different position of the resistors (more vs. less resistance) and the wheels still spin too fast which causes the line overshoot. We tried different width of the line, varied the height of the sensors from the floor and lighting as well and that didn't fully fix the problem either. Unfortunately the kid is getting very frustrated with this project, so if you have recommendations please let me know. Thanks.
Hi - unfortunately you have already tried much of what I would recommend - making the line wider and playing with the sensor spacing from the ground, but here are a few more things:
1) Test the robot in advance by holding it just above the ground so the wheels aren't touching (so you can tell when they're spinning but the robot won't drive anywhere). You can slide the robot back and forth over the line to make sure the wheels react appropriately.
2) Make sure your course has very GRADUAL turns. You can even start out by just trying to get it to follow a straight line instead of a loop. It won't do well with sharp turns or corners and will tend to overshoot.
3) Be careful with battery combinations and resistor values - the project FAQ should have recommended resistor values for the 3xAA battery pack. But if you use a resistor that's too big (specifically the current-limiting resistor for the infrared LED), then the LED won't emit as much light, meaning it's harder for the sensor to measure reflected light, and it will be harder to detect the line. If you use a resistor that's too small you risk burning out the LED. I'd generally recommend sticking with the resistor values in the project and not playing with those too much.
4) Have you tried different materials for the driving surface and/or line to see if they give more contrast? What are you currently using? In the past I've found that black electrical tape on white posterboard works well, with the line 2-3 pieces of tape wide. One piece is generally too narrow and the robot will overshoot.
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