I saw your question on the thread of someone else's, so I'm moving it to a question by itself
Hi,
My daughter selected this project for her science fair this year.
I have been working with her for a few days now but can simply not get the robot working. (https://www.sciencebuddies.org/science-f ... p021.shtml). I have bought the kit from Jameco Electronics and have assembled the robot as per the instructions. However, even after double checking the connections several times over the last 3 days - the robot simply does not move at all.
I have checked that the infra red LEDs on the optical sensor assembly are working (looking through my digital camera) and also verified the pinout of the transistor from this forum (Base, Collector, Emitter - with TIP102 printed side facing me).
Not sure about the sensor though - I am using the following config (holding it pin up and going clockwise from the blunt/flat corner - Collector (C), Emitter (E), Anode (A), Cathode (K).
Not sure on what's wrong with the circuit.
Is there any way to trouble shoot the individual components/pieces of circuit to narrow down the problem.
Prompt response will be greatly appreciated.
Thanks,
-Ashish
Some easy things to check would be connecting the motors directly to power to make sure they work. It's unlikely that both motors would be defective, so I expect that a motor check would show they both work.
If you have a multimeter, look at the emitter (E) output from the sensor (U1) with no reflective object nearby. It should be near 0V. Bring an object near and the voltage should increase. If not, you may have a bad sensor. They are easily damaged if you connected them incorrectly - if it happened that it was wired wrong and then you fixed it, you may have done damage.
Since the circuit is so simple there isn't a lot that can go wrong. From your description it sounds correct. Check that you don't have a bad connection to the reflective sensor [did you solder it or try using a jumper lead?] and double check that you're using the breadboard correctly. Another student ran into trouble when they thought they were making connections and ended up being off by one row.
I realized after I submitted that reply that I should comment on the diode. Technically, it's redundant since the TIP102 transistor has a diode inside the package. You can run without the external diode - but if you put the diode in backwards, the circuit won't work. Double check that you have the band oriented towards the red power bus, or try taking it out completely. If you build this circuit with another type of NPN transistor that doesn't have the built-in diode, the back EMF will likely kill the transistor. I recommend including it, especially since understanding why it's needed is rather critical to learning about controlling motors. But do check that it's not backwards.
Project Question: I am working on the "Line Following Robot" with my daughter using the kit from Jameco as suggested. Assembled the model and circuit as per the diagrams and instructuins online. The robot does not move at all when we connect the batteries.Tried moving the sensors close to the surface but to no avail. Any ideas on what could be wrong. Is there a way to trroubleshoot the components (transistor/sensor). We checked that the infra-red light on the sensor is lit (using a digital camera)
Thanks for the descriptive answer Howard.
To answer your questions
- I had soldered the sensor to a ribbon cable and connected it to the breadboard.
- the motors are working fine without the circuit (connected batteries directly to the motors) and the robot jumped into action straight away.
I have purchased a new set of components (transistors/sensors) and will try connecting these instead.
I will try checking the sensor as you mentioned and will update this thread on my findings (keeping my fingers crossed)
Project Question: I am working on the "Line Following Robot" with my daughter using the kit from Jameco as suggested. Assembled the model and circuit as per the diagrams and instructuins online. The robot does not move at all when we connect the batteries.Tried moving the sensors close to the surface but to no avail. Any ideas on what could be wrong. Is there a way to trroubleshoot the components (transistor/sensor). We checked that the infra-red light on the sensor is lit (using a digital camera)
Hi Howard, As per your suggestion - I went to Jameco and got a new set of sensors and some jumper wires and assembled the circuit afresh.
This time the motors started working, However, I ran into a couple of issues :
- one of the motors/wheels is running faster than the other one. I checked connecting the batteries directly and the motors work fine at the same speed.
- one of the sensors gets triggered much sooner than the other one (i.e. the motor starts turning when I bring a piece of paper even around 2 cm away, whereas I have to bring the paper fairly close to the other sensor to switch it on).
What can be wrong here?
I would expect a bit of mismatch between the two motors as they are made to rather toyetic quality standards. The design should compensate for minor differences. The fact that you're asking though, suggests that the difference is significant.
I'd first check that you wired it correctly. The two sides are completely independent of each other. They do use the same power rails from the same battery pack, but that's it. Make absolutely certain that you didn't plug anything from the slower of one side into any breadboard holes used by the other. The sensors and MOSFETs are totally independent on the two sides.
Are you sure you have the same resistance value on the IR sensor? If one is lower than the other and the LED is brighter, that could affect range. I'd suggest checking the resistors to see the colors codes are the same. If you have a meter, verify that the resistance of the two is pretty much the same as well.
I haven't heard reports of either of these issues before. If you figure out what the problem is, please report back so we can know for the next time. I appreciate your thorough bug reports and detective work.
Project Question: I am working on the "Line Following Robot" with my daughter using the kit from Jameco as suggested. Assembled the model and circuit as per the diagrams and instructuins online. The robot does not move at all when we connect the batteries.Tried moving the sensors close to the surface but to no avail. Any ideas on what could be wrong. Is there a way to trroubleshoot the components (transistor/sensor). We checked that the infra-red light on the sensor is lit (using a digital camera)
Hurray !! Got it Working !!
Tried replacing the sensors one at a time. This seems to have solved the problem.
Now the Robot 'sees' the line and follows it just fine (Had to tweak the distance of the sensors a bit to get it right).
Thanks for all the help and support Howard. Working on stabilizing the design a bit more (adding some support). Will post the links to Photos/Video once its all ready.
Must say - It's really fun to watch the robot move along the line. My kids cannot seem to get enough of it (already have burned a few sets of batteries just watching it go around in circles).
I'm so pleased for you and your daughter. Yes, the tweaking of the sensors is kind of critical to get it running well. I figured it had to be a minor wiring issues or an accidentally fried part - but that happens. If you have video of the line follower cruising around, we'd love it if you'd share a video with us. I had a hoot watching my development sample (the one in the project pics and video) cruising around too. It is mesmerizing somehow.
Hopefully your daughter does will with it and she'll also have stories of how perseverance pays off. Not all experiments work correctly the first time and you just have to stick with them.
Thank you for writing back and letting me know you fixed it.
Project Question: I am working on the "Line Following Robot" with my daughter using the kit from Jameco as suggested. Assembled the model and circuit as per the diagrams and instructuins online. The robot does not move at all when we connect the batteries.Tried moving the sensors close to the surface but to no avail. Any ideas on what could be wrong. Is there a way to trroubleshoot the components (transistor/sensor). We checked that the infra-red light on the sensor is lit (using a digital camera)
Just compiled a couple of videos of the robot and uploaded them to YouTube.
First version here http://youtu.be/i_dK79xCckA shows the first working model. There is not much structural integrity and this one is pretty crude looking with all the wires and connectors hanging around.
Second version here (http://youtu.be/WgaC8VdKrGI) is a significant upgrade to the original design (at least we like to think so). We wanted to add a bit of protection to the circuit and connectors as this model is going to the science fair where it may fall into some *NOT* so very gentle hands. Here are the changes we made:
- Added a protective cover made out of an empty 2 Litres soda bottle cut and glued over the breadboard.
- Installed a toggle switch on the cover to give the user the ability to turn it on or off.
- Added one yellow LED to the breadboard to indicate the power status.
- Added two green LEDs to the breadboard (along with the motor connections) to give a visual feedback of the wheels stopping and turning to the spectators (These look wonderful in the dark - check the second video to see them in action)
- Added a couple of strips to the front part of the foam board for extra support to the sensor arm making it more stable
- Changed the battery holder from 3 x AAA holder to a 2 x AA Battery Holder as we found that using three batteries was causing the robot to run very fast and frequently run astray - specially around the corners
- Reinforced the sensor arm with another layer of foam board (with slots cut for the sensors) and covered it with a strip of paper. You may have already noticed the Robot's 'googly eyes'
The exciting part was that the idea to put the LED eyes (the green LEDs) came from my daughter, who was also able to figure out the connections and place them on the breadboard. She is absolutely ecstatic about her creation and cannot stop talking about it. She also cannot wait till tomorrow when the display goes to the science fair for all to see.
Thanks so much for your help and support. Really appreciate it !!
The LEDs to show the motors turning on and off was a great idea and the video was really well shot. I would of course love to hear how your daughter does with the fair tomorrow.
I'm going to direct a link to this conversation to Amy Cowen who may want to talk with you about posting a success story. You can reach her through our scibuddy@sciencebuddies.org email. If you and your daughter would be willing to share your story, any pictures from the fair and your videos, please email her. We don't have your email here and it's better if you don't post it on the forum. It was awesome to see how your daughter embraced the project, worked with you to debug it and got it working so well. I think you'll find with some tweaking that it will run just fine (and a whole lot faster) with 3 batteries. You should have seen the first prototype that used roller skate wheels and a different motor. That little guy took off at over 15 miles per hour (I measured it), completely out of control and smashed into the garage door. It was a spectacular wreck - I may have to post the video.
Congratulations on your successful line follower! I am glad that Howard was available to provide some Expert assistance here in the forums, and I very much enjoyed watching your videos. You and your daughter did a great job with this robotics project!
I am contacting you separately via email to talk more with you about a possible story.
