Rero robot kit - The review. Second part: ultrasonic obstacle avoidance 4 wheel car

rero_robot_kit_-_The_review._Second_part_ultrasonic_obstacle_avoidance_4_wheel_car.jpg (311481Bytes)

After my first review and robot done by the start guide, I tried something a bit more complex: an autonomous robot, which can find its way out from a room.

There are two basic ways or strategies of doing so:

  • the robot has basic sensing and computing, for example detecting obstacles and avoid them. On this way, if the robot checks all the path to one side, it always will find its way out. It's time consuming but easy with a basic robot.
  • the robot has advanced sensing for example artificial vision and powerful computing, then the robot can check its environment and calculate the shortest way out.

As this robot has in this box ultrasonic and infrared sensor and basic calculation, I will go for the first approach.

But to understand this development, let's first review in more detail the...

Hardware of rero robot kit

This kit as all most robot kits, has all the pieces you need to build not one but several types of robots.




I'm not going to describe all the parts, just the critical parts:

rero Controller: it's the brain of the robot, but also the mechanical base for (nearly) any robot you build with this kit. It's powerful enough to manage all the other parts at a fine speed:




  • PIC32MX575F512L 32-Bit MCU
  • Support up to 10 Cube Servos per port (come with 6 ports): that adds up to 60 servos! I mean, is the battery powerful enough to run 10 minutes those 60 servos? I would like to test it.
  • 3.2" TFT color LCS with touch screen: very, very useful!
  • Audio playback
  • Bluetooth 2.0: very useful to command your robot as you want
  • USB 2.0 interface
  • 11.1V Lithium Polymer rechargeable battery (come with charger). Yes, battery is inside this box, safe but easy to open in case you need it.




Cube Servo



  • Digital servo: for more precision and functionalities
  • Voltage: 6.5 - 17.8VDC
  • Rated Torque: (at 12V). Powerful enough!
  • Speed: 63RPM (no load at 12V). Fast enough for most robot projects.
  • Gear ratio: 194:1
  • Current: 1.5A (max at 12V)
  • Weight: 63g
  • Degree of rotation: 360 continuous. This is very useful, as you have great precision within all 360º, using as a full articulated joint, or driving a wheel. It is just great!
  • Communication: Half Duplex Serial. See more at the next point.
  • Daisy chain connection: means you can connect a servo to the other (serial concept), up to ten of them per port as stated above on controller info. So instead of a "star" configuration of conneting all servos to a main controller, here servos are connected in serial, up to ten, but also as star to the controller. More flexibility and fast of development.

Creating the second robot: an abstacle avoidance car with ultrasonic sensor

So when you start with this kit, I recommend you to do as the first robot the one explained in the "Quick start guide", you can see the video here, where you will learn all the basics on the hardware and mechanics of this robot, also the programming.

Then I just added the ultrasound sensor, on this way:



With the ultrasound sensor at front, and a servo that turns it from left to centre and right, this robot can check any obstacle at the front at 14 cm (I adjusted that distance so it can run enough between each measurement). To make it clear, this robot works in this way (this is also described in the next figure: it's a screen capture from the own rero planner software to program your robots):

  1. Robot centres front wheels (just in case they are turned from last movement).
  2. Robot checks for obstacles at less than 14 cm (140 mm).
  3. If there is not obstacle at the front, go stright.
  4. If there is an obstacle at less than 14 cm, check obstacle at the left at less than 14 cm.
  5. If there is not obstacle at the left, turn wheels to the left.
  6. Go stright (as front wheels are turned left car goes left, then go to point 1 (to keep stright as the obstacle has been avoided).
  7. If there is obstacle at the left, moves ultrasound servo to the right and measures distance at the right.
  8. If there is not obstacle at the right, turn wheels to the right.
  9. Go stright (as front wheels are turned right car goes right , then go to point 1 (to keep stright as the obstacle has been avoided).
  10. As there is obstacle at the front, left and right, turn wheels to the left and go back, so the car goes back to the left.
  11. Then go to the point 1.

You can see the whole operation in practice in the video I uploaded in Youtube.



This is the way you see the program that makes run this robot by itself as explained just above



If you follow the same hardware configuration as here, you can use my attached program

so you robot will do the same as mine


On this way, this car can go out from any room which has obstacles big enough. Some small obstacles like chairs or tables can be a problem, as the ultrasound sensor could no detect some parts, but those parts can hold the car to go forward. To avoid that, more sensors should be added but then the whole running will be slowler. Many similar kit robots have the same issue. However in this way this robot is good enough for most educational and hobby applications.

My robot is running now automosly quite fast by itself. It was not the same at the begining, until I realized I could reduce to the minimum the running time for servos and sensor, so they operate as fast as possible. That's the way it's now. I have uploaded this configuration in this review, you have it in the attachments section, also here.

The other way of operation for this robot is by mobile via Bluetooth. On this way the robot goes as fast as servos can drive, which is quite fast. Maybe not as fast as DC motors with some gear reduction, but these servos are multipurpose and with more precision.

As a recap for this second review, I have to say this kit invites to modify (tunning) any standard robot and create new functions in a very easy way. This is great, as robotics is not only electronics or programming, but at the top are the concepts of service: what is the service or services the robot has to fulfill? Depending how easy is for us to pass from that needs to testing solutions, we can achieve robots in a fastest and convenient way. There are also other important considerations when designing a robot, like cost, speed or ergonomy. All these features are important too, but with these kind of robot kits is exploring robotics concepts what we look for. And this rero robot kit helps a lot.

Please note: I'm finishing more details and interesting complex robots for this kit, so don't miss anything subscribing here, in Twitter and our Facebook group.

Very Nice

I really like the modular design as I have said before. The company seems to be putting a lot of thought into being able to expand the project. They have put some time into this and how it can be expanded or turned into another bot. How does one go about receiving one of these to review. These are great bots and would love to have the chance to disect one and see what all it can do.