BRiCS IIT Kanpur: Wall Following robot Kit

Build Robots Create Science (BRiCS): A hands-on learning initiative from IIT Kanpur

Wall Following Robot Kit

Assembled wall-following robot. Two motors with worm gears drive two wheels. A two-way switch (bottom left, whisker coming out of it), connects either the left motor (whisker pressed) or the right (whisker released).

Description

This is a low cost educational robot kit that can follow a wall to its left. If the wall turns left, the robot will turn and keep following it.

Robot at work videos:

video1 [AVI 1.3MB]

video2 [MOV 2.6MB]

It is made out of commonly available electronic components, tape-deck parts, and raw materials such as plastic sheets.

Components Needed

The set of parts (base etc. made by workshop students)

The kit consists of the following components. You can also find these in most electronics markets and build your own robot!

Base (the large plastic piece)
Small DC Motors - 2 nos (1.5V DC - we prefer the small tape-deck motors)
Plastic Worm Gears - 2 nos (small pieces that look like screws).
Plastic Round Gears - 2 nos (circular white pieces with teeth)
Wheels - 2 nos (we use tape deck pulleys)
Spring-loaded Two Way Switch - (This you will know by the springy action)
On/ Off Switch
Connecting Wires
Motor Holding plate (flat plate with central hole for heavy screw)
Wheel shaft holder (Aluminium channel without slots) - 2 nos
Battery Holder
Long steel wire for whisker
1.5v battery AA

In addition to the above, you will also need some glue for fixing the battery holder. You will need a cutting tool (e.g. a sharp knife or a hacksaw) and drilling tools (hand drill with some small drillbits), file, sandpaper, etc. if you want to work on the perspex base and change its shape, or add other functionalities.

Circuit Diagram

Can you see in the circuit diagram that only one motor turns at a time? The two-way switch connects either the upper blue dot ( right motor ) or the lower dot (left motor). It's a spring-loaded switch, and when the whisker doesn't press on the spring, only the right motor is on.

How the circuit works

Student's sketch of the circuit (Goa Science Center workshop)

The whisker extending out of the two-way switch acts as a Sensor for the robot. In the circuit diagram this is the box with the arrow going to either A or B. This part is called a "two-way-switch". It tells the robot when it is near the wall - such sensors are also known as touch sensors.

Since your whisker is on the Left side, it gets pressed when the robot moves close to the left wall. Then the switch moves from the upper blue dot to the lower one. This disconnects the right motor, which stops, and it completes the circuit for the left motor which starts.

This turns the robot to the right. After some time, the whisker is no longer in contact with the wall and so it is released. Then again the right motor turns on and the left motor stops, turning the robot to the left.

In this way the robot tracks the wall in a zig-zag manner.

Assembling your robot

Cut the perspex base to the shape you want, e.g. the figure shows the base for a mouse-like shape.
Make big square holes for the Gears in the middle and the wheels at the side as shown. You will need to mark out the size of these holes based on the gears you have.
Drill out holes to fix the motor holder and and switches. These must be at the right positions to match the holes already on the switches.
Fix the wheel
Connect the wheels to the shaft and mount a round Gear at the inside end of each shaft.
Fix the motors in the motor clamps, mount the worm gear at the end of the shaft, and then make sure that the worm is rotating the big gear on the wheel shaft.
[ Note: This is the most critical step. If the motor is not aligned so that it drives the wheel-shaft gear, then your robot will not work!]
Wind one end of the stiff wire tightly around a thin nail several times. This will be your whisker.
Fix the whisker on the shaft of the spring on the two-way switch, so that pressing the whisker operates the switch. Adjust the radius of the whisker so it applies the right amount of pressure on the switch.
Fix the battery holder on the base using glue.
Mount the on-off switch and make the connections using wires according to the circuit diagram. The wires will need to be twisted into the holes on the motors and the switches. (If you have someone who can solder these, it makes a better connection, but soldering is not necessary, just make sure the ends are twisted tightly in the holes).
Take some scrap piece of plastic or an aluminium strip, and bend it over the front of the base so that the robot is scraping along on this point.
Insert a 1.5v dc battery in the case and the robot is ready to move !!!!

Debug

Rarely will your robot work at one go. Debug it as you build it.

For example, after step 5, turn the axle to make sure the wheel turns. Aftr step 6, take two wires, and remove the insulation from the ends. Now connect the battery to the two motor terminals, and see if the wheel turns. Do it for both motors. Often, the gear may not sit properly below the worm, or the axle shaft may need to be aligned a bit.

Similarly, after putting the whisker, press it and check for the click sound of the switch. After step 10, run the motors to make sure the 3-way switch is working properly. Often, you may find a wire is reversed, or some other connection is loose.

Remember, perhaps the most important thing you will learn in building this is not how current flows or how worm-gears work, but that in life, almost everything needs to be debugged before it works!! It may take a bit of tweaking, but don't give up, you can do it!

Conducting workshops with the Wall-Following Robot

The wall-following robot kit is appropriate to school children from class eight on, though we have also used them with younger children. It is a mistake however to think that they will be able to finish the robot in an hour or two. Most children in the Indian context are very hesitant to start playing with wires and motors and batteries, and typically it takes about 4-6 hours to get most groups to build the complete kit. Typically the first prototypes are ready within an hour, but that's when the debugging starts!

If you want to have a more intensive experience, they can also make the body of the robot, including the base, the motor mounts, the axle mounts, etc. This would make it a two-day process, and it gives them more confidence to build their own units later.

Here are some images to show what to expect in workshops.

Workshops with the wall-following robot a) Vasant Valley, Delhi; sawing the base (2-day workshop). b) Girl building robot at Goa Science center. c) Groups building robot at Navodaya Vidyalaya, Sirsaul. [click to enlarge images]

Workshop at Jaipuria, Kanpur, 2006, with parents. Students filing for better fit, Nehru Science center, Bombay (2 day workshop).

Once the basic robot is working... Give it character!

Once your basic robot is working, you can try making it more lively.

Decorate your robot by giving it a cover (cut paper and glue it) - and paint it in the colours of your favourite animal. If you want you can also add another shaft on the front which can bob up and down as the robot moves or you can make many other changes (see elephant idea below).

Idea: Elephant

Cut out two side views of an elephant on thin card paper. Cut off their trunks, but keep the long teeth. Paint the sheets grey and black and give him two nice eyes
Make a separate piece for the trunk, give it a small hole at the base. Fix the trunk between the two sheets, with a pin which will act as a hinge (you can also staple it, and cut off half the staple).
Cut a small groove in front of the perspex base and put an extra wheel (or any cylinder) in it. Don't put a rubber rim so it is low-friction (it will need to slip sideways when you turn).
Make the axle a bit long (you can use a gems clip), and put a U-bend in it (this is a crankshaft). Support the other end of the axle on a little raised cardboard, so the middle can go up and down as it rotates.
Now connect the middle part of the "U" to the trunk of your elephant by a thread. Connect it to a point behind the hinge, so the weight always pulls up your thread.
Note: The nearer you connect the string to the hinge on the trunk, the more pronounced the motion. The tradeoff is that the forces are higher and it may cut through the cardboard.
Now as you run the robot, the trunk of the elephant goes up an down!!

Can you make a Giraffe that nods its head? How about a space alien with antennae? You are limited only by your imagination!

[BRiCS home @ iitk/robotics/] [BRiCS page at iitk.cse/]

Sarala Verma and Amitabha Mukerjee, Center for Robotics and Mechatronics, IIT Kanpur, 2003/2008.