How does the Ladybug Robot circuit work?

[briggy]

i'm doing a year 12 physics project where the focus is on electronics, and, stupidly, i decided to pick a ladybug robot kit which, with no prior electronics experience, i am finding impossible to explain. i need to stay top of my class at physics and this will be the decider!

The Ladybug Robot moves with its six legs and makes use of infrared emitting diodes as its eyes to avoid obstacles along its path. Ladybug automatially makes a left turn the moment it detects an object in its path. It continues to move forward again when no obstical is in the way.

could somebody please take me through a step-by-step of how it works? i understand each of the individual components to an extent, but just can't figure out how they relate and i just don't known where to start.

p.s. my robot didn't actually work - the right set of legs move forward all the time, but the left set don't move at all, regardless of obstacles. i need to be able to explain what i've done wrong also.

 

[Resqueline]

The IR-LED is driven by Q8 & Q7 that are configured as an oscillator. This makes the LED blink very fast. Any reflected light pulses are detected by the photo-diode and passed through C1. This stops any ambient light conditions from affecting obstacle detection. The pulses are then amplified by the first two amplifiers of IC1 and rectified by D1. The resulting DC voltage (at pin 12) now represents obstacle proximity. If this voltage rises above half of the battery voltage - the second two amplifiers (that are configured as voltage comparators) will switch state and make M2 reverse direction (by means of Q1-Q6 that are configured as a full (H)-bridge driver). Pin 1 & 14 of IC1 are always in opposite states (one high, the other low), commanding M2 to run in the same direction as M1 when there is no obstacle and in the opposite direction when there is an obstacle.
The only thing that works (for certain) in your robot is M1, that is connected directly to the batteries. The problem with the other motor not running at all could be with just about anything in the diagram, from the oscillator & LED to the photodiode-amplifier-rectifier-comparator & H-bridge.
You'd have to measure some voltages around the circuit in order to get an idea about where the fault could be.

 

[briggy]

Thanks so much for your help!
Your response has given me a much clearer understanding of the circuit, and I finally feel that I can explain it with some confidence in my assignment XD
Thankyou!!

 

[flyingmelon]

Thanks so much for your help!
Your response has given me a much clearer understanding of the circuit, and I finally feel that I can explain it with some confidence in my assignment XD
Thankyou!!

nice work, good help

 

[kadafi23]

i also have a ladybug robot and it worked. i was just curious about the ceramic capacitor on the two shaft motors. what's that for?

i hope you reply as soon as possible cause i need the answer for my project on my course circuit analysis. by the way, your post on how the circuit works, i think it will help a lot for my project. thanks for that!

 

[Resqueline]

Ceramic caps on brushed DC motors are there to suppress RF noise from the commutating sparks.

 

[petergreenpeace]

Hi,
I also have bought the Ladybug robot and i put the electronic circuit in a RC car because i want to make an obstacle avoiding robot.What do i have to modify on the circuit cause the M2 motor turns in both direction when the sensor detects an obstacle and i want to make it turn on one direction for the steering of the RC car.(so when the sensor detects an obstacle it turrns the M2 motor only to the left for example.)

Thanks,
Peter