Robotics & Motion Control

Welcome to the workshop. I'm Volt, your tutor. I've spent years with my hands inside motion systems — the kind that drive a cycleWASH Pro Platinum's brush carriage down a bicycle, that index a CyclePanel conveyor one slot at a time, that hold a robotic arm steady while it places a part to a tenth of a millimetre. This course is that experience, distilled.

Who this is for: Kaern founders building anything that moves — automation cells, machines, conveyors, robotic products. You don't need an engineering degree. You need curiosity and the willingness to get a little grease under your nails.

What you'll walk away able to do:

• Reason about motion the way an engineer does: position, velocity, acceleration, torque, and the tradeoffs between them.
• Choose the right motor, drive, and actuator for a job — and not overspend.
• Close the loop with sensors so your machine knows where it actually is, not where it hoped to be.
• Plan smooth, fast trajectories and command a controller to execute them.
• Design a robotic work cell and make it safe enough to put in front of a customer.

A note on how I teach: I ask questions. When I ask one at the end of a script, stop and answer it out loud before reading on. Motion control rewards people who think before they move. Let's go.

Module 1 — Motion Fundamentals & Kinematics

Learning objectives

• Define position, velocity, acceleration, and jerk, and explain how they relate.
• Convert between rotary and linear motion using pitch, gear ratio, and radius.
• Read and sketch a basic motion profile (trapezoidal and S-curve).
• Distinguish forward and inverse kinematics in plain language.

Lesson 1.1 — The four words that describe everything that moves

Teaching script (Volt): Pull up a chair. Watch the brush carriage on a Pro Platinum start from rest, glide down the length of a bicycle, and stop dead at the rear wheel. Four words describe that entire trip. Position — where it is. Velocity — how fast that position is changing. Acceleration — how fast the velocity is changing. And the sneaky fourth one, jerk — how fast the acceleration is changing.

Why do you care about jerk? Because jerk is what your customer feels. A machine that snaps from zero to full speed has infinite jerk for an instant, and that's the clunk, the spilled water, the bolt that rattles loose over six months. Think of driving a car: position is where you are on the road, velocity is the speedometer, acceleration is the pedal pressing you into the seat, and jerk is the whiplash when someone stamps the brake. Smooth drivers manage jerk without naming it.

Every motion controller you'll ever touch is, underneath, just a machine for shaping these four quantities over time. Master the vocabulary and the rest of the course is detail.

Here's my question: if a conveyor moves at constant velocity, what is its acceleration — and what is its jerk?

Lesson 1.2 — Turning circles into straight lines

Teaching script (Volt): Most of our motors spin. Most of our jobs are straight — a carriage sliding, a belt advancing, a panel indexing forward. So the daily work of motion control is translation: rotary into linear.

Two numbers do almost all of it. Pitch — how far a leadscrew or belt advances per revolution. And radius — for a pulley or wheel, how far the rim travels per radian turned. On a CyclePanel conveyor with a drive pulley, one motor revolution moves the belt by the pulley's circumference, π times its diameter. Want finer control? Smaller pulley, or add a gearbox. A 10:1 gearbox means the motor turns ten times for one output turn — you trade speed for resolution and torque, all at once.

This is the founder's lever. The same cheap motor can be precise-and-strong or fast-and-weak depending entirely on what you bolt to its shaft. You don't always buy a better motor. Often you buy a better ratio.

Question for you: a drive pulley is 50 mm in diameter. Roughly how far does the belt move for one full motor revolution — and would a 100 mm pulley make the motion finer or coarser?

Worked example

A leadscrew has a pitch of 5 mm/rev and is driven directly by a stepper with 200 steps/rev.

• Linear travel per revolution = 5 mm.
• Linear travel per step = 5 mm ÷ 200 = 0.025 mm/step (25 microns).
• To move the carriage 80 mm: 80 ÷ 0.025 = 3,200 steps.
• If the motor spins at 600 rev/min = 10 rev/s, linear speed = 10 × 5 = 50 mm/s, so the 80 mm move takes 80 ÷ 50 = 1.6 s (ignoring accel/decel).

Hands-on exercise

Take any rotary-to-linear system you can find (a 3D printer axis, a drill press, even a hand-cranked vice). Measure the pitch: mark the screw, turn it exactly 10 full turns, measure total linear travel, divide by 10. Then calculate how many turns you'd need to move it exactly 37 mm. Verify by doing it. Write down the error between your prediction and reality and propose one reason for the gap.

Common mistakes

1. Confusing speed limits with accel limits. A motor that can hit 50 mm/s can't necessarily get there instantly — acceleration is a separate constraint.
2. Forgetting the gearbox in the math. People compute steps-per-mm at the motor and forget the 10:1 reducer downstream, ending up 10× off.
3. Ignoring jerk entirely. Designing only for position and velocity, then wondering why the machine shakes.

Check for understanding

1. In your own words, how are acceleration and jerk different?
2. A pulley is 40 mm in diameter. How far does the belt travel per revolution?
3. Why might a founder add a gearbox instead of buying a more powerful motor?