Let's Make Robots!

cr2cX

Navigate and avoids obstacles
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cr2c2_Schematic.png205.07 KB

A robotic platform far various experiments related to this field and to teach my kid some things about robotics. It's 16 years since I have build my first robot and now I want to do it again.

I have decided to buld all modules "from scratch" by using my own designs and home made boards and sensors. I've took the hard way, I know. I have build and test (and sometimes modifed) the boards one by one that is why there are some things that could have been removed and/or improved.

Current version is named cr2c2 and others will come.

Obstacle detection is done using 4 custom build IR sensors each composed, basically, from a L53F3BT IR LED Emitter and a L932P3BT phototransistor. I have build 2 sensors but I did not like their limited detection capabilities so I have added another two. More details about this sensor configuration are in the blog.

A front picture is at the top of the page. Here are the back and top pictures of the current version:

In current version the obstacle avoidance worked good, mainly because of the software. The test was made by running the robot, with half speed, through a labyrinth made by CD's, furniture and room's walls - first video.

Short term plans: find his base and recharge itself when needed.

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Bravo Calin, bun venit pe LMR!

Your robot looks nice and the self built modules are great! Looking at your schematic I see you used pull up resistors for the motor drivers lines, so by default the motors are braked. I also see that you're also using Timer0 for PWM, which leaves Timer1 available for the Servo library and Timer2 for the Tone library (or other purposes). To avoid the need of setting the drivers in parallel, I use the SN754410 chip, but that isn't available in Romania. Perhaps I'll ask Viorel (from robofun.ro) to bring some. I also like your sensors, I am considering making little boards like that but I want the sensors to be active low. Nice job and I'm looking forward to see more!

Cheers!

Gabriel.

Multumesc! I am glad to be a member here!

Yes, I have used pull-up resistors for motor driver to keep the motors braked until the microcontroller starts controlling them. I have used Timer0 because I wanted to use only 4 pins for motor control (starting the test/learning without PWM then upgrade to PWM like it is now) and still be able to use PWM, beside D4-D7 was a good choice for software and hardware board. SN754410 + 4 schottky diodes is a good alternative (I have L293E which can use simillar currents) but I really want to use MOSFET transistors or something like IRF7307 for the next motor drivers and/or controllers.

The IR sensors works but I consider them a pain in the a55 for object detection, altough cheap and usable as you have seen in the video, but low angle and highly dependent on the reflecting material. They may work better as replacement for touch sensors, for sensing table margins, stairs and "holes in the ground".

I know about the simple IR reflection sensors disadvantages, but like you say, they are good enough for bumper sensors. Of course, when you need distance you use proper sensors. About the motor driver, I liked that someone came to use the same setup I used when I designed the Robot Builder's Shield for Arduino and the µBotino board. The SN754410 is a nice driver, has the protection diodes integrated and I never burned one and used many. Of course, I don't use motors with stall current greater than 1A. For more current different driver is needed. Making your own driver is a nice thing to do, but for me it's not worth the effort. I will always get a ready built driver chip or board. I'm sure you can do it and it will be nice to see it working.

Spor la treaba! Good luck!

Gabriel.

Your robot is brilliant! I really like the way you've made all of your modules from scratch, I might give that a try one day, except mine would never be as neat as yours....

Thank you! If you do not want to use modules, it may be better and faster to build everything in only one board. Also, the sensors could have been better aligned and 6 might had better results - however I think I will use ultrasonic or IR Sharp sensors for future robots.