Escape Robot Kit - Need help troubleshooting...

[shifty_]

Hi all, I am brand new to the forum, and brand new to electronics. I have a really basic robotic kit that my son and I are having issues with. Hoping someone with more experience than I can help...

This was a gift for my son (13) and it is his (and my) first intro into electronics. He did a great job building and soldering (I thought) but when we turned it on we seem to have an issue. And I have troubleshot the problem to the extent of my knowledge - but don't know where to go from here.

Basically, the robot is a 6 wheeled skid steer vehicle controlled by an integrated circuit. The vehicle is supposed to drive around and emit infrared pulses via 3 IR transmitters and then sees which one it gets a bounce back from via an IR receiver - this forms a simple collision avoidance system. There are 2 motors, each one connects to the PCB via a pair of + and - terminals and each motor drives a set of 3 wheels. It skid-steers by getting a normal flow of power or a reversed flow depending on the input received from the IR receiver. I have figured out that everything works except for one aspect - Motor 1 never drives forward... It can only drive backwards when the receiver gets a bounce back from the appropriate transmitter.

So when you turn on the robot, after it initializes, both motors should drive forward the whole time until it's about to hit something then the IC puts the appropriate motor in reverse to steer it away. So if you hold your hand up to the transmitter on the same side of the vehicle as Motor 1, the robot emits a beep and the IC provides a reverse flow of power from the terminals on the PCB and drives Motor 1 backwards - take your hand away and it should start driving forwards - but it doesn't - the motor just stops.

The troubleshooting I have done so far is:

• Went right through and checked and re-soldered every component on the PCB (paying particular attention to the motor 1 circuit) - and everything to my untrained eye seems fine
  
• Swapped the motors around on the PCB (put motor 1 on the motor 2 circuit) - and motor 1 while connected to the motor 2 circuit then drives forwards and backwards - so there is no issue with the motor 1 gearbox or motor 1.
  
• Swapped motor 2 to the motor 1 circuit - then motor 2 behaved the way motor 1 behaved - i.e. won't drive forwards only backwards when it gets a bounce back signal via the receiver. So issue is definitely on the PCB somewhere

Any ideas on where I go from here? I can provide photos and also a copy of the circuit diagram.

Thanks in advance...

 

[shifty_]

Hi again... I went and bought a multimeter and have determined that voltage on the M1 terminal just sits on 0v and goes to -4.5v when the sensor is activated. Whereas the M2 terminal sits on +4.5v normally and goes to -4.5v when activated. So M1 terminals are definitely not receiving the positive voltage. I have attached the circuit diagram - maybe someone can help me figure out what I need to test to narrow down where the issue is?

 

[wingnut]

Hi Shifty

I am no expert, only a dabbler, so until you get some better advice, here is my twopenceworth...

You seem to have diagnosed the problem quite well, that M1 seems to lack a pullup resistor making it normally sit at +4.5V.

Many micros have internally set pullup resistances, which is set in the software program, usually only on input not output pins. Maybe your micro has pullup on output pins Otherwise one has to put a 20k resistor from the +4.5V rail (or VDD) to the M1 terminal. Your circuit does not show any external pullup resistor.

If this were my project I would try adding a 20kiloOhm resistor between +4.5V (or VDD) and M1. If you are a programmer, it could probably be added in the software something as follows... pinMode(9, INPUT_PULLUP);

 

[KTW]

Did you try interchanging the sensors to test them?Not saying this is the problem but I have heard of them failing on this same unit.