Your Robot's Arm

Try It — A Different Kind of Job

Your arm motor is the exact same kind of motor as your wheels. What changes today is not the motor — it is the job.

Remember the number from Project 3 — the one that changed when you turned a wheel by hand? The brick is counting how far every motor has turned, all the time. Today that counting stops being a curiosity and becomes the whole point: “up” is a place — a number of degrees from home — not a push.

Feel the places

Arm motor in port A. On the brick, open Port View (the same screen you used in Project 3) and arrow over to port A, so you can see the arm motor’s live number.

First put the arm all the way down — resting at the bottom of its swing. Note the number Port View shows there. Now move the arm gently with your hand, from the bottom of its swing to the top, and watch the number climb away from where it started.

• My arm motor is in port A and Port View shows its number
• I moved the arm by hand and watched its number change

In your own words: what is the difference between telling a motor how far to roll and telling it where to be?

Learn It — Positions, Not Spins

One block does today’s job. It needs four pieces of information: which motor, which way, how far, and the unit — degrees.

The count starts where you start

Here is the one thing you must never forget about this brick: when a program starts, every motor’s count starts at 0 right where the motor happens to be. The brick does not know where “down” is. It only knows how far things have turned since the start.

This block finishes the trip

A run for degrees block does not start the arm and let go. It swings the arm the whole distance you asked for, and only then does the next block run — just like your move-for blocks on the wheels.

Where you are headed

Seven points for one touch. It is the best points-per-effort deal on the field — as long as you actually make contact.

Do It — Reach and Touch

Step 1 — Set your arm’s home

New project called Arm — names in the project name. But before any blocks: with your hand, set the arm all the way down, resting at the bottom of its swing. That pose is home. Every program from now on begins with the arm here, and every number you write down today is measured from here.

Say it out loud as a team, because it is the Start Pose Rule and it runs your whole season: arm down by hand, then press run.

Step 2 — Find your three positions

With the arm at home, open Port View on port A and note the number it shows. Now move the arm by hand, slowly, up to each pose — and write down how far the number moved from home. These three numbers are about to run your whole season.

Step 3 — The Wave

Make the arm visit all three positions, holding each one long enough to see. One new idea first: a run-for block moves the arm from wherever it is — so each trip is the difference between where you are and where you are going. Work out your two trip numbers before you build:

Now plan it as pseudocode — speed, then up, pause, horizontal, pause, down, pause, back up — then build it. Arm at home first, always:

• My arm moves to all three positions with a pause between each

The run-for block already finishes its trip before the next block runs. So what are the wait blocks for?

Step 4 — Prove the speed matters

Change the set speed block to 100% and run the Wave again. Stand back a little.

Put it back to a gentle number. That is the arm’s speed from now on.

• The speed is back to gentle

Step 5 — Prove the direction matters

Pick one arm block and flip its arrow the wrong way. Run it — with your hand ready near the stop button.

What happened, and what could that do on a real field?

Set it back. From now on, the direction dropdown is a decision, not a default.

• Every arm block’s arrow is back to a direction I chose on purpose

Step 6 — Drive and touch

New project called Reach. Practice away from the field first: put any object a short drive away, then drive to it and touch it with the arm.

Two rules, borrowed from how the mission works:

• The arm must start up and move down to touch. No driving around with the arm already out front.
• Touch it with the arm only — not with the robot’s body.

• I can drive to an object and touch it with the arm

Step 7 — Mission 9 — touch Botguy7 pts

Onto the field. New project called Botguy.

Botguy is inside the enclosure. Your robot has to reach in and make contact — direct contact, arm to Botguy.

• My arm makes direct contact with Botguy
• I did not knock the enclosure out of place getting there

Step 8 — Run it five times

Score It — Checkpoint

My score

My arm card

Keep these next to your driving numbers. Everything from here uses them.

Can you do it again?

• I set the arm to its home pose by hand before every run — the Start Pose Rule
• I know which port my arm is in, and my blocks all say the same port
• I know my arm’s real ends and never command a swing past them
• I can build a run-for-degrees block with the right port, direction, and degrees
• I set a gentle speed before the first arm move, so the arm never slams
• A teammate could set my arm’s home pose from my description alone
• I can combine driving and arm movement in one run

Think about it

The wheels never need a start pose — the arm always does. What is different about an arm’s job that makes home matter so much?

Your degree numbers are scattered through your program as bare numbers. If you rebuilt your arm slightly differently tomorrow, how many places would you have to change?

You can touch Botguy but you cannot get him out of the enclosure. What exactly can a claw do that a single arm cannot?

Next

In Project 8 — Arm and Claw Together, a second motor joins the first. Two motors working as one system means you can finally grab, carry, and release — and a whole set of missions opens up at once.