Robots are cool, right? In this tutorial, we are going to make a small robot that can drive around and help us explore Mars!

You'll also need:

• 2 wheels and tires (and the little screw that comes with them)
• 3 wooden pieces
• 2 hook and loop squares
• 1 mini screwdriver

Did you know that Hook and Loop fasteners, often called Velcro™, are used by NASA because it works so well to temporarily hold things in place in zero-gravity?

We are going to use Hook and Loop squares to attach the Continuous Rotation Servos to our Mars Rover.

Hook and Loop fasteners are called that because one side has softer fabric loops, and the other side has scratchier plastic hooks that grab onto those loops.

The first thing we need to do is peel apart the squares:

Attach the soft square to one side of one of the servos:

Next, set the other servo next to the one you just placed the soft square on, and make sure it is facing the opposite direction. Then stick the other soft square to it:

Now, take out the wheels and tires. Pull a tire over the wheel - it might take a bit of effort:

Do that for both tires and wheels.

Then, find the side of the tire with the hole that fits onto the servo. Line the tire up and push it onto the servo's output shaft. It might push a bit hard, but it will fit on.

Do that for both servos as well.

Finally, use the screwdriver to install a screw to hold the wheel onto the servo. Do this for both servos, too:

Next, connect the jumper wires shown in black in the picture above to the breadboard row connected to the Pico's GROUND pin, and plug the other ends of the jumper wires into the socket of the servo motors' 3-pin cables that lines up with each connector's brown wire.

Place the two resistors in the breadboard like it shows in the picture above. Then, use the two shorter jumpers to connect one of the resistors to GP0 and the other resistor to GP1 on the Pico. Now, connect one of the long jumper wires to the other lead of the resistor connected to GP0 (one of the jumpers shown in yellow in the picture above). Plug the other end of the jumper wire into the last socket on one of the servo's cables. Connect the other long jumper wire from the other lead of the resistor connected to GP1 to the other servo's cable.

When your wiring is finished, click NEXT.

Before you attach your servos to the wood pieces to make the rover, we need to center the servos. This means that we are going to send the servos a "speed = zero" command that makes the servo stop moving.

To do this, grab a start block from the Chip menu and drag it into the workspace.

Grab a servo pin set speed block from the Actions menu and attach it to the start block. Then, grab a repeat forever block and attach it after the servo pin set speed block.

We aren't going to add anything in the repeat forever block, but we need it to make sure the Pico doesn't stop running our program.

Once you've built the program above, plug in your Pico to your computer's USB port, click CONNECT and select your Pico.

This next part is really important. Make sure you know which servo is connected to pin 0, and pick it up and hold onto it. When you start your program, the wheel will probably start turning!

If you don't pick up your servo, it may try to roll right off the table!

Once you are holding your servo, click START.

The wheel attached to your servo is probably spinning, and now you need to use the small screwdriver to adjust it until it stops:

You are trying to turn the adjustment screw to the "center" spot like it shows in the picture below. This center spot is not very big, so turn the screwdriver slowly. If you accidentally turn it to the transition zone, that's okay, it will just act "jittery" - just turn it to the other side:

Once your servo has stopped, you can set it down and click STOP to stop running your program.

Now, change the servo pin set speed block to pin 1.
You are going to repeat this process for your other servo.

Once both of your servos are centered, click NEXT.

Ready to build the rest of the Mars Rover? Let's go!

Attach the other two squares (these are the scratchy ones) to the spot on the bottom of the largest wood piece like it shows in the picture below:

Then, attach your servos to the squares like it shows in the picture below.

First, UNPLUG your PICO from your computer.

You are going to pull the wires through your Mars Rover, so you will need to unplug them. Make sure you reconnect them correctly. If you need to go back 2 steps to see how they are connected, that's okay!

Finally, pull the wires through the hole in the middle of the wood piece. Look carefully at the picture below. The wires on the servos should be coming out toward the back of the Mars Rover.

If the wires on your servos are coming out on the front side, simply pull the servos back off, and switch them around so that the wires come out toward the back of the Mars Rover:

Flip your Mars Rover over so that the servos are underneath. Then, slide one small wood piece into the other small wood piece as it shows in the picture below so that they fit together. Finally, slide both wood pieces into the "X" on the back of the Mars Rover:

Look carefully at the picture below. We are going to need to know which servo is the right servo, which one is the left servo, and which side of the Mars Rover is the front and which side is the back:

The right servo should be connected to GP0, and the left servo should be connected to GP1. If you need to, switch the jumper wires that are connected to GP0 and GP1 on your Pico.
Once you have finished building your Mars Rover and you've double-checked your wiring, click NEXT.

Before you plug in your Pico, connect it, and run your program make sure that you have enough room to let your Mars Rover roll around where it won't roll off your counter, desk, or table!

Plug your Pico into your computer. Click CONNECT, and then click START.

What happened? Why did the Mars Rover spin around?

Click NEXT.

Why did your Mars Rover just spin around? We set both servos to the same speed, but if you look carefully, one of them is facing the opposite direction. This means that if we want our rover to go forward, we need to spin one servo in one direction and spin the other servo in the other direction.

Change the value in the servo pin 0 set speed block to -30:

Go ahead and click START to test it out. Did it drive forward this time?

If everything worked correctly, your Mars Rover should have driven forward for 2 seconds. Unfortunately, there are usually going to be a few issues.

The first problem is that your Mars Rover might have veered a little bit to the left or a little bit to the right instead of going straight forward. Did that happen with your Mars Rover?

If you want to try and make your Mars Rover drive straighter, all you need to do is make some small adjustments to the values in the servo pin set speed blocks.

No two servos are exactly the same - so even if you send them the same signal, they probably won't go exactly the same speed. These small differences between the wheel speeds will cause the rover to veer off a straight path.

If your Mars Rover veered to the left, you can try making the left wheel (the one connected to pin 1 a little faster by changing the servo pin 1 set speed block to 31 or 32 or 33.

If it veered to the right, try setting the servo pin 0 set speed block to -31 or -32 or -33.

Experiment a little bit until you're happy with your Mars Rover's forward motion (it doesn't have to be perfect!), and then click NEXT.

Let's turn forward and backward motion into functions. That way, we can re-use them over and over again in our code!

First, delete the wait 2 seconds block by dragging it to the trash can.

Grab a to do something block from the Functions menu and drag it out to the workspace. Change the name of the block to "go forward". Then, drag the two servo pin set speed blocks away from the start block and place them in the to go forward block:

Right-click the to go forward block and select Duplicate. Change the name of the new block to "go backward".

Now, switch the values so that the servo pin 0 set speed block's value is 30 and the servo pin 1 set speed block's value is -30 (or whatever values your blocks had after you adjusted them):

Now that we have some functions, let's try making our Mars Rover move!

For our first test, let's make our Mars Rover wait 2 seconds, then go forward for 2 seconds, and then backward for 2 seconds. Grab a wait block from the Chip menu and connect it to the start block. Change wait time to 2 seconds.

Next, grab a go forward block from the Functions menu and connect it to the wait block. Right-click the wait block and select Duplicate. Connect the new block after the go forward block. Do this again with a go backward block and another wait block:

Now that we have forward, backward, and stop movements, let's add turns!

Remember when we first tried the Mars Rover out and it spun around? We can make the Mars Rover turn by setting the speed for both servos to the same value.

To turn left, we need to make the right wheel drive forward, and the left wheel drive backward. That means that to be able to turn left both values need to be -30.

Let's make a turn left function. Right-click the to go forward block and select Duplicate. Name the new block "turn left". Change the servo pin 1 set speed block to -30:

Let's add a left turn to the end of our program. Grab a turn left block from the Functions menu and connect it to the last wait block. Right click one of the wait blocks and select Duplicate. Connect the new block to the end of the program and change the time to 0.5 seconds:

Why 0.5? To make a turn, your Mars Rover won't have to spin it's motors for very long, so we are going to start with a really short time like 0.5 seconds.

Try it out by clicking START.

Your Mars Rover probably turned a lot - and it probably spent more than 0.5 seconds turning. The more time your rover spends turning, the more it will turn, so we actually need to use a stop moving block at the end of your program from now on.

Grab a stop moving block from the Functions menu and connect it at the end of your program. Then click START to try it again:

Did it turn straight to the left? Did it turn too much? If so, try an even smaller time like 0.45 or 0.40. If your rover didn't turn enough, try a little longer time like 0.55 or 0.60.

Experiment and tune your Mars Rover's left turn!

When you are ready, click NEXT.

A right turn is just like a left turn, except the motors need to go in the opposite direction.

Right-click the turn left block and select Duplicate. Name the new block "turn right". Change both servo pin set speed blocks to 30:

Let's add a right turn to the end of our program.

Grab a turn right block from the Functions menu and connect it right before the stop moving block. Right-click the last wait block and select Duplicate. Connect the new block right before the stop moving block:

Click START to try it out! Make adjustments to the new wait if you need to just like you did for the left turn.

Now that we have functions for each of the ways that our Mars Rover can move, let's get ready to build a program that moves our Mars Rover in a pattern.

We are about to delete some blocks, but before we do, it is a good idea to write down the wait times you used for the right and left turns.

Once you've written those times down, grab the first wait block below the start block and drag it (and all of the blocks below it) to the trash can to delete them:

Since we want the Mars Rover to move using a set of directions, we can use a list. By using a list, we can make our set of directions as long as we want.

We are actually going to need two different lists. The first list will hold the movements, and the second list will hold the wait times.

First, we need to create variables to hold each list. Click the Variables menu and then click Create variable... button. Name the new variable "movements". Drag the set movements to block out and connect it below the start block.

Next, click the Variables menu again and then click Create variable... button. Name the new variable "wait times". Drag the set wait times to block out and connect it below the set movements to block:

Grab a create list with block from the Lists menu and place it in the input of the set movements to block.

Click the blue gear icon on the create list with block. In the mini workspace, drag an item block into the list block. Do this again so that there are a total of 5 item blocks. Then, click the blue gear icon again to close the mini-workspace.

Right click the create list with block and select Duplicate. Move the new block into the input of the set wait times to block:

Now that we have our lists, let's add things to them. Grab a "_" block from the Values menu and place it into the first input of the first create list with block. Do this 4 more times to fill the list.

We are going to type 1 letter into each of the "_" blocks. Since we have 5 different movements (Forward, Backward, Left, Right, Stop), we will use the first letter to represent each one. Type 1 letter: F, B, L, R, or S into each of the "_" blocks:

Next, we need to add the wait times for each movement. Grab a 0 block from the Values menu and place it into the first input of the second create list with block. Do this 4 more times to fill the list.

Now we need to change the 0's to wait times. For forward, backward, and stop, use 2, and for turns, use 0.5 (or whatever adjusted number you came up with when you improved your turn movements):

Next, we need to loop through the list and do one of the movements based on that value in the list.

One of the cool things you can do with a list is get and remove an item in the list - so we can keep doing that to get the next movement, and stop when the list is empty!

Grab a repeat while block from the Loops menu and connect it below the set wait times block. Change the while to until. Then, grab a _ is empty block from the Lists menu and place it in the input of the repeat until block:

Grab the movements block from the Variables menu and place it into the _ is empty block. Then, grab an if _ = _ do block from the Logic menu and place it in the repeat until block. Grab an in list _ get # block from the Lists menu and place it into the left side of the _ = _ block. Change the # to first:

Since we are trying to get the first item in the movements list, grab a movements block from the Variables menu and place it into the first input of the in list _ get block.

Next, find the "F" block at the beginning of your program. Right-click and Duplicate it, and place the new block into the right side of the _ = _ block. Then, grab a go forward block from the Functions menu and place it into the if do block:

Now we have a way to take an item from the list and turn it into a movement!

Right-click the if do block and Duplicate it. Connect the new if do block right after the first if do block. Change the F in the "_" block to a B, and then delete the go forward block and replace it with a go backward block from the Functions menu:

Do this again for turn right (R), turn left (L), and stop moving (S):

Now that we are done with the first item in the movement, we need to remove it.

Right-click the last in list movements block and Duplicate it. The new block is greyed-out, but you can still change the values in the dropdown menus on the block.

Change get to remove. This will change the shape of the block. Now, connect it right after the last if do block:

Now that all of the movements are taken care of, we need to add code to wait.

Grab a wait block from the Chip menu and connect it after the in list movements remove block. Grab the 1 block inside of the wait block and drag it to the trash can to delete it.

Next, right-click one of the in list movements blocks inside of one of the if blocks and Duplicate it. Place the new block inside of the wait block. Change movements to wait times, and change get to get and remove:

Almost there! Remember that at the end of our program, we need to add a stop moving block. Grab a stop moving block from the Functions menu and place it at the end of your program: