D2-1 Linefollowing Robot Assembly Guide - Ultra Cheap Robot Kit

Technology is amazing, and so are prices on electronics from china!

You can get these line-following robot kits for about $4.50 a piece on eBay, with free shipping. The only downside is that they only come with Chinese instructions- Not much use to most of us English speaking types! In this instructable, I'll banish that problem.

Step 1: Get Yourself a Kit, and Some Tools

You can find the kit on eBay, or AliExpress.

Shipping is from China, so it'll take about a month to get to you. If you're planning this for a present, order it well in advance!

eBay Link ($4.49, free 1-month shipping from China)
AliExpress Link ($4.25, and you know it, free 1-month shipping from China)

(If the links go bad, searching for "D2-1 kit" seems to work)

The next thing you'll need are the right tools. Many people will have some of these things already, but I'll list them all here with links to amazon.

Soldering Iron (Delcast 30W, $7 on amazon, and it actually works really well! Comes with solder)
Brass wool and holder (For cleaning the iron, if you want your iron to last, this is a must. A damp sponge or paper towel works too, but this works better)
Soldering iron stand (Not essential, but really nice if you plan to do more than this one kit)
Wire clippers (Not a combo stripper/clipper)
Wire strippers
Painter's tape (Very useful for holding components in place. Buying it at the store may be cheaper)

Together, everything here costs about $36, but it will all last you for ages if properly taken care of (Besides the solder and tape).

Step 2: How to Solder...

Have you ever soldered before? If you've an old hand at soldering, feel free to skip this step. Otherwise, read on!

Soldering is a super cool process, where you use a soldering iron, heated to over 600 degrees (Fahrenheit, for Celsius people that's about 350 degrees), to melt a soft metal and create a metallurgic bond between a metal pad on the circuit board, and a component lead. Soldering is not the same as gluing two things together, but more akin to welding two pieces of metal.

How to Solder:

The best video I've found so far is this ancient video on Youtube. You can ignore the parts about cleaning the leads and pads, since yours should be fine. (The link should skip that part.) Once you've watched that, take a look at my additional tips down below.

That will show you most of the important parts, but I'll add a few here.

CLEAN YOUR IRON! In my experience, most of the trouble beginning solderers have is because their iron's tip is too dirty. I like to clean my iron each time I pause from soldering, and then clean it again before I use it. Don't be afraid to clean it too hard! When the tip is shiny and silver, you know it's clean.
Tin the iron. Tinning is basically adding a small amount of solder to the iron before you use it. You don't want to add too much, since we're not painting the solder on with the iron- a small blob acts as a heat bridge, to help transfer heat between the iron and the component/pad.
Did you mess a joint up? Add too much solder? Just tin your iron, then re-apply it. On a cold or insufficiently wetted joint, often re-applying heat will help to reflow the solder. If there's too much, use the iron to melt the solder, then drag the excess away.

I plan to make an instructable and video on soldering through-hole components like are used in this kit. Once I do, it will be linked here!

Step 3: Soldering: IC Socket, Potentiometers

We'll begin with soldering some of the bigger pieces.

Find the IC socket, and insert it into the spot marked "IC1", as shown. Make sure the notched end lines up with the notch in the graphic, as shown.
Flip the PCB over, then solder each of the pins. You can use a bit of painter's tape to hold it in place.
Find the two 10K adjustable potentiometers, and insert them into the spots marked "R1" and "R2", as shown.
Flip the PCB over, and solder them in. You don't need tape to hold these in place.
Find the on/off switch.
Insert it into the spot marked "S1 SEITCH". (Yes, it's spelled that way, on the board!) You may need tape.
Solder the switch into place.

Now that you've soldered this end of the board, go ahead an insert the IC. Notice the little notch at one end? That needs to line up as shown, with the notch on the graphic on the board.

Step 4: Soldering: Red LEDs

Let's move on to the front of the PCB.

Find your two red LEDs.
They'll go into the spots on the boards marked "D1" and "D2", as shown. You'll notice a flat spot on the graphic on the PCB, and a flat side on the LED's bases. These need to be aligned for the LEDs to work.
Put a small piece of tape over each LED to hold it in place.
Flip the PCB over, and clip most of the wire leads off the LEDs, leaving about 1/4" or 5MM.
Solder each lead into place.
Remove the tape, and you're done with them!

Step 5: Soldering: Capacitors

Find your 100uF capacitors.
They go in the spots marked "C1" and "C2". Notice the white line on one side? That needs to be on the same side as the white half of the graphic on the board.
Once you've put them in, tape them in place, then flip the PCB over.
As with the LEDs, clip off most of the leads, leaving about 1/4" or 5MM leftover.
Solder them in place, then remove the tape.

Step 6: Soldering: Transistors

Find your transistors. They'll go in the spots marked "Q1" and "Q2".
Notice that they have a flat spot, as well as the graphic having a matching flat spot. Like the others, these need to be aligned. Go ahead and insert them into the PCB. You won't need tape here.
Flip the PCB over, and clip off the extra leads, leaving the same amount as with the LEDs and capacitors.
Solder the transistors in place.

Step 7: Soldering: Clear LEDs

Now we'll solder the LEDs that make up part of the line sensor. They emit red light, but they're clear, so I'll refer to them as clear.

Find the clear LEDs.
Insert the large bolt into the hole in the front of the PCB, then add the nut with the smooth rounded end, so you can tell how far you want the LEDs to extend down. You'll want them pretty close to the ground when the robot is turned upright, with maybe 1/2" or 1CM of free space between the LEDs and the ground.
Once you've figured out how you want to position the LEDs, hold it in place, then bend the leads over on the top side.
On the top side of the PCB, tape the leads in place.
Flip the PCB over again, and solder the LEDs in place.
Remove the tape, then bend the leads back up.
Clip them off carefully, leaving a small amount, in case you want to add some glue to reinforce them later.

Step 8: Soldering: Photoresistors

Find your photoresistors. It doesn't matter how these are placed, so you get a break!
They go in the spots marked "R13" and "R14", marked on the bottom of the PCB.
Make sure they stick out of the PCB to about the same level as the LEDs, then bend the leads over.
Add a bit of tape to the leads on the top side of the PCB.
Flip the PCB over, then solder the photoresistors in place.
As with the LEDs, remove the tape, bend the leads back up, and clip off the excess.

Step 9: Sort Resistors

Find all your resistors, and sort them into piles of each kind. It works well to label them, too.

Normally, you'd have to look up each one, but I've created handy little pictures to help you out.

Step 10: Soldering: Resistors

1K Resistors:

Take your 1K resistors, and bend the leads down at a 90 degree angle, as close to the resistor as possible.
Insert them into the spots marked "R7" and "R8". They will also say "1K". Polarity (which direction they face) does not matter with resistors. Hurrah!
Tape them in place, then flip the PCB over.
As with the other components, clip off the extra leads, leaving about 1/4" or 5MM.
Solder the resistors in place, then remove the tape.

3.3K Resistors:

As with the 1K resistors, bend the leads at a 90 degree angle.
Insert them into the spots marked "R4" and "R3", also marked "3.3K".
Reuse the tape you used for the 1K resistors, and tape them in place.
Flip the PCB over, then clip off the extra leads.
Solder them into place, then remove the tape.

10 Ohm resistors:

Bend the leads at a 90 degree angle.
Insert them into the spots marked "R9" and "R10", also marked "10".
Tape them in place, then flip the PCB over.
Remove the extra leads.
Solder them in place, remove the tape.

51 Ohm resistors

Bend the leads at a 90 degree angle.
Insert them into the spots marked "R5", "R6", "R11", and "R12". They'll also say "51" on them.
Tape them in place, then flip the PCB over.
Remove the extra leads.
Solder them in place, remove the tape.

Congratulations! You've finished soldering all the components. Now might be a good time to take a break, if you're feeling a bit sore in the neck muscles.

Step 11: Battery Box- and Some More Soldering!

Hahaha, you thought you were done soldering? Believe it or not, the work of assembling this kit is almost entirely soldering... But the good news? You're almost to the not-soldering part!

Grab your battery box, and feed the wires through the little hole on one side of the PCB, as shown.
Notice the pads on the PCB marked "3V" and "BT1"? That's where we need to connect the wires.
First of all, tin the pads, by adding a bit of solder to your iron, then soldering the pads just like you would when soldering a lead to a pad. You should end up with a little round blob of solder on the pad.
Now, solder the wires to the pads. Red goes to the one marked "+", and black to the other one.
Solder them by holding the wire in place over the pad, then applying your tinned iron.
Remove the iron, while holding the wire in place until the solder solidifies.

Once you've finished soldering the wires, you can attach the battery box to the PCB.

Remove the backing on the double sided tape, then press the battery box into place. The graphic outline on the top side of the PCB shows exactly where to place it.

Step 12: Prepare Wires

Find the set of wires that came in the kit. You should have a set of 4 wires.
Separate the wires into 2 sets of 2.
Using your wire strippers, strip about 1/4" or 5MM of insulation off both ends of each set. If you have a different kind of stripper than me, you may need to separate the ends a bit.
Tin the wire ends, by holding them on top of the end of your solder, then applying your tinned iron. This will make them much easier to solder to later on.
If you haven't already, separate the ends of the wires by about 1", or 25MM.

They're now ready to be used on the motors!

Step 13: Assemble Sliding Point

Since this is a 2WD robot, the front needs something to slide on.

Find your large bolt, and the two nuts that go with it.
Slide the bolt through the hole in the front of the PCB, from the top of the PCB.
Thread the flat nut on, and snug it into place.
Add the cap nut to the end.

Finished!

Step 14: Wire Motors

Now we're ready to connect the motors to the robot. This is the last soldering you'll have to do!

Take the wires you prepared in the last step, and insert the ends of each into the metal connection tabs on the motors, as shown.
Solder the wires to the connection tabs.
Now, tin the motor connection pads on the underside of the board, as we did with the battery connection tabs. They'll be marked "M1" and "M2".
Once you're done, take a look at the diagram I drew that illustrates the correct polarity for the motor. The "axle" on the motor needs to be facing down.
Before you solder the motors on, make sure the sticky tape is on the correct side for when you attach it! It should be facing towards you, assuming the front of the board is furthest from you.
Now that you're sure everything is correct, go ahead and solder the wires to the pads, like we did with the battery wires.
Repeat for the other side, and then you're finished soldering!

Step 15: Attach Motors

Let's attach the motors. Your robot is quickly coming together!

Peel the backing off the sticky tape on the motors, then press them into place as shown. Try to line them up as closely as possible to the outline graphic on the PCB.

Step 16: Attach Wheels

Find your wheels. They are big, round, and yellow.
The wheels have a small hole on one side, that fit the axles from the motors perfectly.
Once they're fitted, you'll need to hold them in place with the little screws that come with the kit. Don't over-tighten them, since they're just threading into plastic.

Step 17: Finished, & How to Use

Your robot is finished! Stick some AA batteries in it, and see what happens.

If it doesn't immediately follow the line, have no fears! Remember the potentiometers in the back? They adjust the sensitivity of each sensor/side.

Place your robot on the testing mat, with one of the sensors (clear LEDs and photoresistors).
Use a screwdriver to adjust one of the 10K potentiometers until the motor on that side turns on. (If it was already on, adjust it until it turns off, then turn it back just until the motor turns on) Repeat for the other side.
Continue until the robot follows a line well.

One more tip:

Be careful not to let the robot fall off a table, or get dropped. The LEDs on the front are susceptible to breaking the solder joint on the board if hit too hard. You may want to add a dab of glue to the top and bottom of the leads where they connect to the board, to help reinforce them.

And now, you're finished! Have fun with the provided mat, then try drawing your own! Experiment with tight corners and overlapping lines to see how the robot responds.