Basic Fursuit Electronics Motors v2.0 Flfgf 21/11/2019 Floere T. - - PowerPoint PPT Presentation

Basic Fursuit Electronics Motors v2.0

Flüüfgf – 21/11/2019

Floere T. Pillowbeaver, Devourer of Nuclear Submarines fmoere@robocow.be

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Disclaimer

This presentation is intended for educational purposes only and does not replace independent professional judgement. The presenter, nor the convention, nor RoboCow Industries assume any responsibility for the content, accuracy or completeness of the information presented.

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What is this Talk About?

• A basic introduction to:

– Small motors, RC servos, and how to drive them – Transmissions and mechanisms – Power solutions

• The focus is on the WHAT and WHY, rather than on

the HOW

• These slides can be downloaded after the talk:

– https://www.robocow.be/events/

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Let’s Watch Some Videos...

• WMW66 Costumes – Animatronic Fursuit Head

https://www.youtube.com/watch?v=eEEZLMv56xQ

• Hemms Fox – Coolest Fursuit Ever

https://www.youtube.com/watch?v=_stG5w_ExAs

• ElminsCosplay – My Giant Motorized Aether Wing Kayle Cosplay

https://www.youtube.com/watch?v=BT5mDQA6gnY

• mostudio – Animatronic Lion Full-Head Mask

https://www.youtube.com/watch?v=evcbnY3Cl90

• Control is clearly the issue, but that’s for my other talk!
• The good news: we don’t need Hollywood budgets

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The Electric Motion System

Energy Source Moving Field Generator Electrical to Mechanical Energy Conversion Transmission Or Output Feed-Back Control Input

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Content

• Motion

T ypes of motors and how to control them

• Transmission

Selection of mechanisms

• Power

Power sources and stability

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Content

• Motion

Types of motors and how to control them

• Transmission

Selection of mechanisms

• Power

Power sources and stability

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Types of (Geared) DC Motors

Plain motor

• High speed
• Low torque

Geared motor

• Low speed
• High torque

Linear actuator

• Low speed
• High force
• Linear motion

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Anatomy of a DC Motor

https://learn.sparkfun.com/tutorials/motors-and-selecting-the-right-one/dc-brush-motors---the-classic

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Anatomy of a DC Motor

• Advantages:

– Simple and generally “inexpensive” – Good starting torque – Geared versions readily available – Easy to drive

• Disadvantages:

– Brushes wear out – Sparking causes interference – High stall current can cause issues

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DC Motor Stall Current

• When the motor can’t

turn, the current becomes very high

– Only limited by the

resistance of the winding and brushes

• When the motor runs,

the current is lower

– Given by the

resistance of the winding + brushes and the back-EMF

https://www.pololu.com/product/1117/faqs

Current S p e e d

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DC Motor Stall Current

• Rule of thumb: limit the continuous operation of

small motors to 20-30% of the stall current

– Unless the manufacturer data says otherwise

• Gear boxes can be damaged at stall torque
• Motor windings and brushes can overheat
• Mind your electronics!

– Fuses will be too slow to protect the power

drivers, they may need active current limiting

• Fuse and wire gauge selection is important with

high-current capable batteries

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Protecting (Geared) Motors

• Mechanical: gear boxes

– Limit torque using a

slip clutch, spring, shear pin, etc…

– Magnetic torque

limiters are nice! → Simple to make yourself and re-setable

• Electrical: over-heating

– Consider a PolyFuse to

protect against prolonged over-load

• All of this also applies to

RC servo motors (later)

MCD Pro-Bite DAGU RS022

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Types of BLDC Motors

All images: HobbyKing

Inrunner BLDC Outrunner BLDC Ducted Fan (with BLDC motor)

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Anatomy of a BLDC Motor

• Not actually DC

– 3-phase synchronous

permanent-magnet machine with internal star point

– Rotating fjeld

generated electronically

• Requires an ESC

(Electronic Speed Controller)

• Can be quiet with a

vector control ESC

Dave Wilson – Texas Instruments

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Anatomy of a BLDC Motor

• Advantages:

– High effjciency with high power density – Good starting torque – No brushes to wear – ESC often has various types of protection

• Disadvantages:

– Higher system cost (not always!) – ESC + PWM control source needed – Regenerative breaking can cause issues – External cooling may be required

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BLDC Fast Speed Reduction

• Be careful with fast

speed reductions!

• Kinetic energy is

converted back to the power supply (regenerative braking)

– Can cause the DC

bus voltage to rise

– May destroy the

ESC and/or other components!

• The power system must

absorb the BEMF energy

– Not possible with:

• Most benchtop

power supplies

• Polarity protection

diode

– Use a brake chopper

if needed!

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External Cooling

• Many cheap motors

are desigend for RC aircraft and drones:

– External cooling

from the propeller air stream

• Other cooling methods:

– Internal cooling fan

(at reasonable RPM)

– Conduction cooling

Kenzi Mudge

• Many cheap motors are

hugely over-rated!

• Risk of overheating in

many costume applications

– Beware of high

torque operation!

– Still fjne for low duty-

cycles

• Use an external fan if

the motor runs too hot!

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Types of RC Servo Motors

Regular servo

• Rotation
• < 10 ms for

60° exists! Linear servo

• Push-pull
• ~20 mm/s

max speed Control boards

• For generic

actuators with feed- back pots

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Anatomy of a RC Servo

http://www.robotpark.com/academy/servo-motors-51057/

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Protecting the Gear Train

• The gear train has

some fragility

– Forcing it can strip

gear teeth

• Protect gears from

excessive force

– Servo saver – Spring linkage

• Consider a re-

settable torque limiter (slip clutch)

Traxxas Kimbrough

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Content

• Motion

T ypes of motors and how to control them

• Transmission

Selection of mechanisms

• Power

Power sources and stability

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Driving RC Servos and BLDC ESCs

• Pulse-Width Modulation

–

The ratio between on and

• fg is changed (modulated)

–

Expressed in % duty cycle

• With RC servo/ESC: timing

defjnes the set-point (= desired position/speed)

–

Eg: 1.5 ms → 90° centre 1 ms – 2 ms → 0° - 180°

–

Usually updated every 20 ms (= 50 Hz)

• Control sources:

–

MCU (eg: Arduino)

–

RC remote control Word of Warning

• RC servos/ESCs are open-loop

with respect to the controller

• There is no feed-back if the set-

point is not actually reached!

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Servo Tester and BEC

• Adjustable PWM source
• Cheap and very handy

when installing a servo

• Mind the supply range!

(eg: 4.8 – 6V)

– Higher voltages

common with HV servos and BLDC

– Use a BEC or other

5V source (BEC = Battery Eliminator Circuit)

Images: HobbyKing

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Driving DC Motors: Switches

• NC limit switches + diodes

+ DPDT switch

– Control direction and

travel

– Use relays for:

• Bigger motors
• MCU control
• Switch variations

– on – on – on – ofg – on – (on) – ofg – (on)

• DPDT = double-pole

double-throw

• NC = normally-closed

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Driving DC Motors: PWM

• H-Bridge using PWM

– Control speed and

direction

– Replaces DPDT switch

• Position / travel control

– Use electronic position

feed-back (eg: pot)

– Keep the limit switches!

• Protection is important

– Back-EMF (FWD) diodes – Over-current – Overheating

• Best use COTS modules!

Word of Warning: avoid the old L298

• No real over-current protection
• High voltage drop (~4V @ 2A)

–

Lots of heat

–

Limited use with 1S, 2S LiPo

–

Acts as a current limiter...

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Content

• Motion

T ypes of motors and how to control them

• Transmission

Selection of mechanisms

• Power

Power sources and stability

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Torque

• Power = rotational

speed * torque

• T
• rque usually the

driving design factor in costumes

• Expressed in:

– N.m

(Newton meter)

– Lb.ft

(pound foot)

– Force @ distance

• It measures how hard

we twist on an axle

– 5 N.m= 0.5 kg @ 1 m

= 50 kg @ 1 cm

– Gets easier with a longer

lever, but we have to twist it further (slower)

• How to measure?

– T

• rque wrench

– Kitchen scale

• Use a known lever
• 1 N ~ 100g

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Reduction Gears

• Small motors are very

high speed, low torque

– We need high torque

at a useful speed

– Gears can do that

• Silent gear trains are

expensive!

– Precision cut – Gradual meshing

(helical, herringbone)

• Many confjgurations!

Epicyclic Gear - Wapcaplet Cycloidal Gear - Mattmoses

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Belts and Pulleys

• Much more quiet

than gears, and more forgiving

• But:

– Wear & tear – T

• rque limits

– T

• othed (timing)

belts make noise

• Much larger system

for same reduction ratio as gears

Sumray ServoCity

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Rotation ↔ Linear Motion

Slider-Crank Mechanism Quite easy to do with hobby means. Consider using PTFE to line the slider for low friction and low noise. Ballscrew Note: this is NOT just a piece of threaded rod from the hardware store. The thread is special, and the screw has ball bearings in it for low friction. A nylon screw with the proper thread is an affordable option.

Hiwin Roscrew

Rack and Pinion Classic mechanism, used often for steering in cars.

14Core

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Bowden Cables

• Inexpensive and

fmexible way to transfer linear motion from one place to another

• Friction and slop

limits the range

• Minimize any bends
• Minimize chafjng at

the case terminations

• Cheap casing:

– 4 mm PTFE tube – Bicycle gear shift

casing

• Cheap cable:

– Nylon fjlament – Dyneema or

Spectra braided fjshing line

– Bicycle gear shift

wire

Baran Ivo

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Bowden Cables - Examples

Animatronic . Robotic ADI zivvea

“Face Hugger” – 30 Axis of Motion!

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Animatronics

• Huge subject in itself, and for another time…

...such as my talk on animatronic jaws tomorrow!

• That said, let’s quickly look at some cool

techniques

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Compliant Mechanisms

• Soft robotics and

compliant mechanisms are interesting!

– Silent, soft, fmexible

→ hard to break!

– Many work well,

even when made inaccurately!

– Often 3D printable – Often well suited to

bowden cables

CarlTronic – Jakob Welner

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Tails and Tentacles

• Combines Bowden cables

and fmexible mechanisms

• Usually: cable guiding disks

spaced on a fmexible, non- compressable, non-twisting core (eg: speedometer cable casing → double-wound)

• Many good tutorials on-line.

–

Eg: “Cable Mechanism Basics – T entacles,” Richard Landon, Stan Winston School of Character Arts (Not free, but very good)

• 3D printable version on

Thingiverse and others

Mark Valentijn Tail for “Where the Wild Things Are” - Adam Keenan

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Content

• Motion

T ypes of motors and how to control them

• Transmission

Selection of mechanisms

• Power

Power sources and stability

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Danger Will Robinson!

• There are many things that can go wrong

when adding electricity, electronics and mechanisms to a costume.

• A non-exhaustive discussion can be found in

my earlier talks:

– “Fur in Motion v1.1” – “Silly Electronics for Fun and Absolutely no Profjt”

Both the V1 and V2 series of talks

– “Paws-On Basic Fursuit Electronics Workshop WIP”

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Power System Stability

• Battery and wiring

have resistance

• High motor start

current will cause bus voltage to drop

– Deeper, partial dips

are “brown-outs”

– This has an adverse

impact on the other system components

• Impact of voltage

fmuctuations:

– MCUs can crash – Analog circuits

can have their

• perating points

disturbed

– General undefjned

and unexpected behaviours and interactions

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Basic Suit Power Bus Design

• Star Ground
• Bufger capacitors
• Isolate sections

(diode + capacitor)

• Suffjcient source performance

(low impedance, higer voltage)

• Suffjcient wire gauge
• POL DC/DC converters

– Eg: buck-boost

• Multiple power sources

(method of last resort)

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Stupidity Diode

• If your batteries are:

– Loose cells – Can be connected

in reverse

• Put a Schottky diode

in series! (After the battery fuse)

• Not always practical

– Voltage drop

(0.2 V – 2 V)

• Consider P-MOS

protection circuit

– Use FET with low

enough Vth!

Infineon: “Automotive MOSFETs – Reverse Battery Protection” June 2009

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Sources of Energy

• Batteries for now…

...which are a mess

• Motors require:

– Signifjcant energy

→ Watt-hours

– High peak current

→ Amps or xxC

• Fuses require high

short-circuit currents

• Most costumes need

small power packs

• Usable battery types

– NiMH – LiFePO4 – LiPo – Alcaline + supercap – Pb gell cell / AGM

• Usable ≠ safe!
• Air travel restrictions

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Sources of Energy

• In practice:

– NiMH – LiFePO4 – LiPo

• First two are much

safer than LiPo

• Last has ~double

the energy density

• All exist in versions

that can source high (peak) currents

• Battery internal

resistance is key

– Cell voltage drops

when loaded

– Udrop = Rcell x Iload

• Maximum discharge

current is important

– In Amps or xxC

• Read the battery

data sheet!

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Panasonic

Charge Time (min.)

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Enix Energies

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Enix Energies

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Battery Selection

• NiMH

– Restrained failure

modes

– Resistant to much

abuse

– Energy density ½ LiPO – Weight at least 2x LiPO – Lower discharge

current vs LiPO

– Long life (1000 cycles) – Caution: may still vent,

explode, etc…

• LiPo

– Vigorous failure

modes

– Highly sensitive to

abuse

– High energy density – Light-weight – 50C and up discharge

current

– Short life (few 100 cycles)

https://rogershobbycenter.com/lipoguide/

Consider LiFePO4as a safer middle-ground

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Batteries - SSDD

• Consider them all as dangerous and follow LiPo

handling safety recommendations

• Isolate them from your body and by-standers

– Mechanically

going in → impacts, deformation going out → shrapnel, fmames, smoke, fumes

– Thermally

• Implement a safety “pack eject” procedure
• Store and charge them in a suitable, fjre-proof

container

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LiPo Battery Fire

• Do not abuse
• DO NOT ABUSE!
• FOR THE LOVE OF ALL

THAT IS DEAR, DO NOT ABUSE A LiPo!!!

• Use protected cells if at

all possible

– Usually limited to 2C

and much less…

• But, really, just DO NOT

use LiPo in a costume!

https://www.youtube.com/watch?v=gisdMQbtJqk Also, have a good look at the link below. It is a series of test of various, common LiPO storage options: https://www.youtube.com/watch?v=CnNId0mDnBo https://www.youtube.com/watch?v=gz3hCqjk4yc Adafruit Industries

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LiPo (and others) Safety

• Insure mechanical +

thermal protection

• Always use a LiPo bag
• Use the smallest

possible battery

• Use a battery fuse
• Use an under-voltage

detector (+ cut-out)

• Keep the pack external

to your suit

• Have a quick-eject for

the pack (and use a separable connector)

HobbyKing

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Power Distribution Fusing

• Battery fuse protects the

battery and main bus wire

– It does usually not

protect the various loads, (if more than

• ne)
• You need a fused power

distribution box!

– Ofgers selectivity!

→ a section can fail without taking-down the rest of the system

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Basic Fuse Selection

• Automotive ATO blade

fuses are convenient

– Up to 30 A (40 A) – Fairly slow-blow

• Some voltage drop is

inevitable

• Understand I²t curves!

LittleFuse

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Safety: Sources of Fire

• Batteries
• Wiring
• Electronics
• Electro-mechanical

components

• Root Causes:

– Joule heating

P = R x I²

– Chemical

• Thermal

runaway

• Ignition of H2
• Ignition of Li

– Arcing

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Safety: Mechanical Risks

• Mechanism

– Guard against the

intrusion of body parts (yours + others)

– Beware of long hair – Parts can break and

shatter → shrapnel

– Limit maximum force

and speed

– If, say, a wing hinge

pivot breaks, do you end-up with a rapier going into your body?

• System Build: what if you

fall or others fall on you?

– Sharp edges – Long, narrow

structures can impale you + others

• Screws, horns, etc...
• Trim, cap, or mount

so they collapse or easily detach

– Padding compresses

when you fall on it!

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Questions? Ideas? Let’s Talk!