Week 3: Wheel Based Mechanisms

Overview

Mechanisms can be a daunting subject matter.  We will try to keep things simple.  We will primarily, if not exclusively, be dealing with wheel based mechanisms.

 

Things that move are difficult to create.  Devices that involve precise movements and mechanism can be very challenging.  We will take some basic mechanisms and break them down into simple forms that we can create and work with.

 

Friction Wheels

Basically, a wheel rubbing up against another wheel.  Friction wheels might be the easiest mechanism for us to implement.

Tip: Use material that will make contact easier: rubber stoppers, O-Rings, even velcro.  Any material that ensures constant contact without slipping.

Gears are tough to work with, they require a high level of precision and deep understanding of mechanical engineering.  Whenever possible, replace gears with friction wheels.

Epitrochoid – An epitrochoid is a roulette traced by a point attached to a circle of radius r rolling around the outside of a fixed circle of radius R, where the point is a distance d from the center of the exterior circle.

Hypocycloid – An hypocycloid is a roulette traced by a point attached to a circle of radius r rolling around the inside of a fixed circle of radius R, where the point is a distance d from the center of the interior circle.

Laser Cut Spirograph Instructable

Astrograph

 

Velcro Wheel
Velcro Friction Wheels

 

O Ring Friction Wheel

Mounting plate from hardware store, 1/4″ bushings (3), shoulder screws (3), rollers (3), O-rings (3), washers (many)

 

Obviously friction wheels have a major flaw – friction.  But if it is a low load mechanism with only two or three wheels, friction wheels can be very handy.

 

Pulleys and Belt

Tightening Pulley

Vibratory Motion

Belt Drive

Belt Drive

Belt Drive

Belt Tensioner

Drive for Moveable Trivision Billboard

 

Timing Belt Pulleys

Timing belts and timing pulleys are typically used with stepper motors for precision devices (CNC’s, mechanisms, etc.).  The pulleys can mount directly onto the shaft of a stepper and the teeth of the pulley fit the teeth on the belt.  Belts and pulleys can be purchased at Adafruit.

 

Block and Tackle

The power obtained by this contrivance is calculated as follows: Divide the weight by double the number of pulleys in the lower block; the quotient is the power required to balance the weight. via

 

 

Crank Mechanism

Think a train wheel.  A wheel, a linkage, and a slider.  Converts rotational motion into linear motion.

 

Flapping Bird Mechanism

 

Controlled Output Escapement with Six Slots

 

Double Crank/Friction Wheel Mechanism

Vectorworks File

SVG File

 

Cams

A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice versa. via

Water Experiment No. 33

The Cache Machine

Disk Cam

Double Cam Mechanism

Cam Driven Scissors

Cam Mechanism

 

“Programmable” Cams

Cam Vectorworks FileSVG File

Mounting Plate Vectorworks File, SVG File

 

 

Mechanism Breadboarding

The goal is to prove out mechanical and electrical mechanisms, by fabricating a series of functional “quick and dirty” breadboard models. Such models can aid in tolerance/clearance issues, establish a proof of function, all while keeping the design intent in focus. Quick proof. via

A typical breadboard model is a quick and effective process to determine the function of mating parts, assemblies, or component configurations before the design CAD is developed for prototyping and/or manufacturing. Sometimes quick printed parts or rapid, laser cut, two-dimensional acrylic linkages are all that is needed to negate or prove a mechanical concept. And, if the model needs to survive more robust endurance tests, make parts out of real materials such as aluminum or delrin.

 

Hardware

I’ve been using some hardware that I have found incredibly useful when making mechanisms.

Idler Shaft

 

 

Tight Tolerance Shoulder Screw

 

Prime-Line Products D 1503 Steel Ball Bearing Sliding Door Roller, 1-1/2-Inch, 2-Pack

1-1/2 Inch Steel Rollers

Lubrication – WD-40, 3 in 1 oil

 

Loctite Red 271

 

Standoffs, spacers

 

Assignment

Building a mechanism, two week assignment.  First week complete semi-working, proof of concept, breadboarded mechanism.  Week two, have complete, robust mechanism.

 


Related Reading/Viewing

507 Mechanical Movements

Mekanizmalar.com

Mekanizmalar YouTube Channel

Nguyen Duc Thang’s Animated Mechanical Models

Computational Design of Mechanical Characters

Friction Oscillator

Radial Solenoid Engine