Week 4: Actuation

Overview

How do our robots move?  We will talk about actuation, bearings, and supports.

 

Bot of the Week

Machines That Make: Hot Wire Cutter

 

Bot of the Week in Action

Bantam Tools Desktop PCB Milling Machine (Othermill) – The carriage is actuated along the X axis, the Table is actuated along the Y.  Why are the X and Y controlled the way they are?  Why lead screws?  Why Steppers?

 

Actuation, Making it Move

Steppers, timing pulleys, timing belts

For your X-carve builds you all used steppers (NEMA 23), timing pulleys (GT2), and timing belts (GT2).

Pros – You have it already.  Can scale very easily.  Can travel long distances.

Cons – Keeping tension, dust/debris can get in it.  Belts can stretch over time.

 

Stepper Motor Lead Screw

Pololu
Amazon

Lead Screws – Acme thread.  Amazon

Lead Screw, Nut, Coupler, Pillow BLock Assembly

 

DC 4-9V Drive Stepper Motor Screw With Nut Slider 2 Phase 4 Wire

 

Pros – Won’t move when unpowered.  Don’t typically get jammed.  Can handle high torque.

Cons – Expensive, distance is relatively short.

 

Rack and Pinon

CNC Router Parts

Pros – Straight forward, stable.  Can handle high torque.

Cons – Gears are conceptually easy, but difficult to work with in practice.  Expensive.  Debris can get caught in teeth.

Servo Rack and Pinon

 

String and Cables

Water Color Bot

Pros – Affordable.  Light.

Cons – Keeping tension, only capable to carry small loads can slip.  Slips off track easily.

 

Servos

Egg botplotclock

Pros – Affordable and easy to control and power, possibly just with an Arduino.

Cons – Usually, very under powered.

 

Other Actuation Options

Linear Actuators

Linear Servos

 

Motorized Slide Pot – Pong Game

 

Gantries and Support

The Makeblock kits came with rods and linear bearings.  They reduce friction and add stability.  If you plan on going with a different system, remember you want to eliminate as much friction as possible.

Using rods and linear bearings (adafruitAmazon) can make for easy movements.

 

Awww Snap!

 

Slide Rail and Linear Bearing Pillow Block

 

A more affordable, and less robust, option are drawer slide hardware.  Can support heacy loads.

Channel Sliders – Come in various profiles, ride a specific channel system.

 

Tube Rollers – Gravity keeps these bearings in contact with rails or tubes.

 

Other Things to Think About

Shocks – For short distances in the Z axis.  Perfect for keeping tension on a pen or scribe.

 

 

 

 

 

Counter Balance – If your machine is having trouble moving up and down, you may need to add counter balance (a weight).   This is often used when machines go vertical.

Polargraph

 

In Class

We are going to build a one axis gantry out of cardboard.  Based on the work of Nadya Peek and James Coleman from MIT.

 

Assignment

Watch:
Adam Savage’s Maker Tour: MIT’s Center for Bits and Atoms (Part 1)
Adam Savage’s Maker Tour: MIT’s Center for Bits and Atoms (Part 2)
Adam Savage’s Maker Tour: MIT’s Center for Bits and Atoms (Part 3)
Adam Savage’s Maker Tour: MIT’s Center for Bits and Atoms (Part 4)

 


Related Reading/Viewing

Linear Motion Drive Mechanisms 

Servo City – Linear Motion

How to Make (Almost) Anything

Modular Machines that Make : Cardboard CNC

Adam Savage’s Maker Tour: MIT’s Center for Bits and Atoms (Part 3)

Machines that Make: Reconfigurable Stages

Motorized Camera Slider

Comparing Linear Servos and Linear Actuators