Robot kit

[deleted-333603]

Hi experts! Im trying to make robots with the kit my mom got and Im hoping to put one in the science fair. Ive tried two so far. The one that avoids objects goes forwards, hits something and then goes backwards without stopping. I tried wiring the motors the other way and I can make it go backwards or spin, but not work right. I also tried the line robot. At first it didn't go at all. I saw your advice that kids usually make it wrong so I had my science teacher help me. She said it was right. One of the motors started working but it doesn't follow lines. Also the metal wheel doesn't turn. Is it supposed to?

Thanks for your help. I have science class in the afternoon and maybe my teacher can help me fix it with your advice.

Niki

[norman40]

Hi sciencenic,

The obstacle-avoiding robot project is described at this link:

https://www.sciencebuddies.org/science- ... background

As I understand it, this robot turns right or left if one of the “whiskers” touch an obstacle. If both “whiskers” hit an obstacle the robot goes backwards. But I don’t think there’s any switch mechanism to make the robot stop. This seems to be the same as the behavior you described for your robot so I think it may be working as designed. Take a look at the video in the background section of the project and try your robot with obstacles laid out as shown in the video to confirm its operation.

The line-following robot project is described at this link:

https://www.sciencebuddies.org/science- ... p023.shtml

In this design the speeds of the left and right wheels are controlled by sensors at the front of the robot. The wheels turn fast when the sensors “see” a white surface and the wheels turn slowly when the sensors “see” a dark surface. This enables the robot to follow a dark line drawn on a white surface.

If the wheels turn but the robot won’t follow a line, you may need to adjust your line width as outlined in the project procedure. Also, you might want to step through the robot test steps in the procedure.

I hope this helps. Please ask again if you have more questions.

A. Norman

[deleted-333603]

Thank you for answering, Mr. Norman. When the robot hits an object it goes backwards and doesn't stop going backwards. It hits stuff that was behind it and never goes forwards again. That doesn't make sense. The video shows it sort of turning when one side goes backwards just a little bit. How do I make that happen? Do I have to reprogram the chip?

My science teacher loaned me a meter that measures voltages and showed me how to look at voltages on the circuit board. She looked at the instructions and wasn't sure how it was supposed to work. I told her I asked here. She said to ask you what voltages I should be seeing on different rows of my circuits and if you had a wiring diagram. What am I looking for with the meter? We tried the steps in the procedure. The motors both work if you connect them to the battery.

Niki

[bfinio]

Hi Niki,

Could you clarify something - when you say "When the robot hits an object it goes backwards and doesn't stop going backwards." - do you mean that when one of the bump sensors hits something, then both wheels start spinning backwards? Or that when both bump sensors hit something, then both wheels start spinning backwards? Each bump sensor should only control one wheel, so if both wheels change direction when just one sensor hits something, then something is wrong with your circuit. Especially if you are new to using a breadboard, it is pretty easy to misplace just one or two wires in the circuit, which can cause the whole robot to behave strangely or stop working altogether. I would suggest that you very carefully double and triple-check your robot against the wiring diagrams in the project's procedure.

There is also a chance that your bump sensors are getting "stuck," causing the robot to get stuck in reverse. This could happen, for example, if you use too much glue or tape to attach popsicle sticks to them. Try pressing on the bump sensors with your hand. You should hear them "click" once when you press on them, then "click" again as they spring back into place when you let go. If you don't hear the second click, it means they are getting stuck.

Finally, there is no programming involved in these projects, so you do not have to reprogram the chip. Let us know if the steps I suggested work. Also, I think sometimes people have trouble uploading attachments, but if you can take some pictures of your breadboard and upload them, I can check your wiring.

Thanks,

Ben

[deleted-249560]

Hi Niki-

I think it's great that you want to debug your circuit. Since you said that you had double checked your wiring and your teacher did too, then seeing how to check something with a meter is a good experience. If you didn't find it already, the Help tab of the project (https://www.sciencebuddies.org/science- ... shtml#help) has the wiring diagram your teacher asked you to ask about - what engineers call a schematic.

The obstacle avoiding robot is the easiest to check with a meter. First, you have to make sure that your batteries are putting out least 4.5 volts. Set the multimeter to DC volts and a 20 volt range if it has manual settings. If it's 'autoranging' then don't worry about that. Connect the black lead of the meter to the boar where the black wire of your battery pack connects. Connect the red lead of the meter to where the red battery lead connects. The meter should display a number between 4.5 and 6 volts, depending on the size of your battery pack and how good your batteries are.

When you look at the chip, you'll see a dent at one end. If you followed the pictured procedure that end should be plugged into E15 and F15. With the dent pointing up, pin 1 of the chip is in the upper left corner. You count from 1 to 8 going down on the left side, then 9 through 16 going back up the right side.

Leave the black lead connected as it was and make sure the battery switch is on. We're going to call whatever the battery voltage you read as 'High' and 0 volts will be 'Low'. Start by seeing that pins 1 and 8 are 'High'. Pins 4 and 5 will be 'Low'. On the other side of the chip, see that pins 12 and 13 are 'Low' and pins 9 and 16 are 'High'. Those pins are the ones that always stay the same and give the chip power for the motors and tell the chip to operate.

One of the switches has connections to pins 2 and 7. Check those with the meter. One will be High and the other Low. Then push the switch and hold it. Check again the voltages will be reversed - the Low one became High and the High one became Low. Let go of the switch and it will go back. Do the same test with the other switch, looking at pins 10 and 15. If this doesn't look right, make sure the resistors are plugged in correctly.

Assuming that everything looks right so far, connect the black lead of the meter to pin 3 and the red lead to pin 6. You should see your battery voltage. The meter might say +4.5 volts (or whatever 'High' is) or it might say -4.5 volts. As long as it doesn't say 0 volts that's a good start. Then press the switch on that side and it will change from +4.5 volts to -4.5 volts or vice versa. On the other side of the chip, connect the meter to pins 11 and 14 and do that same test.

If you got this far, your wiring is certainly fine and the chip is working correctly. The only other possibility is that you have a problem with the motor which is highly unlikely given the description of your problem.

Give that a try and see if you can figure out what might have gone wrong with this robot. The line follower is a little harder to work through but the procedure is pretty much the same.

Howard

[deleted-333603]

Thanks Mr. Howard. I gave your suggestion to my science teacher and she helped me check that during lunch. She said the switches worked but the chip didnt. She wired the line follower and checked that and said the transistors were broken. My dad was going to look for a new metal wheel but now my mom just wants to return the kit since its so broken. How does she do that?

I'm greatful for the help and my mom says thanks too!

Niki

[deleted-249560]

Hi Niki-

Debugging your designs is part of the fun. I'm sorry that you had trouble but I hope you learned something from trying to fix it. Your mom can talk to Science Buddies' customer service and talk to them about it.

Howard