Fur in Motion v1.1 Nordic Fuzzcon 28/02/2019 Floere T. - - PowerPoint PPT Presentation

Fur in Motion

v1.1

Nordic Fuzzcon – 28/02/2019

Floere T. Pillowcase, Devourer of Automobiles (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 on:

– How to drive DC motors and RC servos – Power solutions – Safety

• The focus is on the WHAT and WHY, rather than
• n the HOW
• These slides can be downloaded after the talk:

– https://www.robocow.be/events/

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• Celebrate the craftmanship in our community!

– I’ll be there with my fjrst animatronics WIP – There’s beer brewing, waffme nomming and a

variety of untimely-yet-hilarious demises

• Bring safety goggles and a hard hat *
• Don’t forget to pay-up your insurance!
• Re-load the website. Catch them all…

https://fmuufgf.org/

* Survival with all body parts intact is not guaranteed. Hugs at your own risk.

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Content

• Motion

T ypes of motors and how to drive them

• Power

Power sources and stability

• No Fire

How to stay alive to tell the story

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Content

• Motion

T ypes of motors and how to drive them

• Power

Power sources and stability

• No Fire

How to stay alive to tell the story

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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 next year’s subject!
• The good news: we don’t need Hollywood budgets

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Motors for Fursuits

• General Input/Output T

axonomy:

– Input power: AC or DC

• All motors are AC on the inside
• Alternating fjelds are generated using an AC supply or

made from a DC supply (using brushes and a commutator

• r electronically)

– Output shaft: geared or direct – Output motion: rotation or linear

• Control: open-loop or closed-loop (e.g.: servos)
• Drive circuit: highly motor dependent

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Motors for Fursuits

• Costume applications will generally use:

– DC motors with a gear box – RC servo motors (= small DC motor + gear

box + motor driver + feed-back control)

• Easy to get, easy to drive and cost-efgective
• Low operating voltages handy with batteries
• Integrated gearboxes yield high torque (N/m)
• Rotational and linear motion available

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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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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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Driving RC Servo Motors

• Pulse-Width Modulation

–

The ratio between on and

• fg is changed (modulated)

–

Expressed in % duty cycle

• With RC servos: timing defjnes

the set-point (= desired position)

–

Eg: 1.5 ms = 90° centre

–

1 ms – 2 ms → 0° - 180°

–

Usually updated every 20 ms (= 50 Hz)

• Control sources:

–

MCU (eg: Arduino)

–

Dedicated controller

–

RC remote control Word of Warning

• RC servos are open-loop with

respect to the driving controller

• There is no feed-back if the set-

point is not actually reached!

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Protecting RC Servo Motors

• The gear train has

some fragility

– Forcing it can strip

gear teeth

• Protect gears from

excessive force

– Servo saver – Spring linkage

• Cheap servos can
• ver-heat due the

motor stall current

Traxxas Kimbrough

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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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Protecting DC Motors

• Gear boxes can break

– Limit torque using a

slip clutch, spring, shear pin, etc...

• Consider a PolyFuse to

protect against prolonged

• ver-loads
• Motor electronics:

– Able to accommodate

the stall current

– Protected against

back-EMF, U, I, T

• Observe the section on

fjre safety!

MCD Pro-Bite DAGU RS022

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Content

• Motion

T ypes of motors and how to drive them

• Power

Power sources and stability

• No Fire

How to stay alive to tell the story

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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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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
• Isolate sections
• Bufger capacitors
• Suffjcient wire gauge
• DC/DC converters

– Eg: buck-boost

• Multiple power

sources (avoid, 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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Content

• Motion

T ypes of motors and how to drive them

• Power

Power sources and stability

• No Fire

How to stay alive to tell the story

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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 more extensive, but certainly non-

exhaustive, discussion can be found in:

– “Silly Electronics for Fun and Absolutely no Profjt”

Both the V1 and V2 series of talks

– “Paws-On Basic Fursuit Electronics Workshop WIP”

• Here, only some highlights regarding fjre

prevention when using high-current loads and high-capacity batteries are discussed.

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Common 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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LiPo Battery Fire

• LiPo batteries are VERY

sensitive

• 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 DON’T

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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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 (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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Battery Connectors

• The RC people have this

fjgured-out

– Several options – High-current types

must be soldered

• Solder them properly

– Safety-critical! – Tinning thick wires

takes special care

– Follow a tutorial!

• Or buy pre-assembled
• Don’t cheap-out!

https://www.rchelicopterfun.com/rc-lipo-battery-connector.html Traxxas Deans EC3 Amass XT-30 https://rogershobbycenter.com/lipoguide/

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Wire Selection

• Main battery wiring → high-fmex silicone
• Use suffjcient gauge

–

Allows fuse to blow

–

Prevents wire from over-heating and the isolation from catching fjre

• Max. current limit set by fuse

→ for the portion AFTER the fuse

• Max. current limit set by battery

→ for the portion BEFORE the fuse

• Conservative rule-of-thumb:

700 circular mil / A = 0.35 mm² / A

• T

emperature coeffjcients

–

Cu: ~0.00386 per °C

–

Al : ~0.00429 per °C

• (Ohms @ T) = (Ohms @ 20 °C) x

[1 + (T – 20 °C) x coefg]

AWG Ohms per km 0000 0.46 11.684 107 0.049 0.16072 000 0.4096 10.40384 84.9 0.0618 0.202704 00 0.3648 9.26592 67.4 0.0779 0.255512 0.3249 8.25246 53.5 0.0983 0.322424 1 0.2893 7.34822 42.4 0.1239 0.406392 2 0.2576 6.54304 33.6 0.1563 0.512664 3 0.2294 5.82676 26.7 0.197 0.64616 4 0.2043 5.18922 21.1 0.2485 0.81508 5 0.1819 4.62026 16.8 0.3133 1.027624 6 0.162 4.1148 13.3 0.3951 1.295928 7 0.1443 3.66522 10.6 0.4982 1.634096 8 0.1285 3.2639 8.37 0.6282 2.060496 9 0.1144 2.90576 6.63 0.7921 2.598088 10 0.1019 2.58826 5.26 0.9989 3.276392 11 0.0907 2.30378 4.17 1.26 4.1328 12 0.0808 2.05232 3.31 1.588 5.20864 13 0.072 1.8288 2.63 2.003 6.56984 14 0.0641 1.62814 2.08 2.525 8.282 15 0.0571 1.45034 1.65 3.184 10.44352 16 0.0508 1.29032 1.31 4.016 13.17248 17 0.0453 1.15062 1.04 5.064 16.60992 18 0.0403 1.02362 0.823 6.385 20.9428 19 0.0359 0.91186 0.653 8.051 26.40728 20 0.032 0.8128 0.519 10.15 33.292 21 0.0285 0.7239 0.412 12.8 41.984 22 0.0253 0.64516 0.327 16.14 52.9392 23 0.0226 0.57404 0.259 20.36 66.7808 24 0.0201 0.51054 0.205 25.67 84.1976 25 0.0179 0.45466 0.162 32.37 106.1736 26 0.0159 0.40386 0.128 40.81 133.8568 27 0.0142 0.36068 0.102 51.47 168.8216 28 0.0126 0.32004 0.08 64.9 212.872 29 0.0113 0.28702 0.0647 81.83 268.4024 30 0.01 0.254 0.0507 103.2 338.496 31 0.0089 0.22606 0.0401 130.1 426.728 32 0.008 0.2032 0.0324 164.1 538.248 33 0.0071 0.18034 0.0255 206.9 678.632 34 0.0063 0.16002 0.0201 260.9 855.752 35 0.0056 0.14224 0.0159 329 1079.12 36 0.005 0.127 0.0127 414.8 1360 37 0.0045 0.1143 0.0103 523.1 1715 38 0.004 0.1016 0.00811 659.6 2163 39 0.0035 0.0889 0.00621 831.8 2728 40 0.0031 0.07874 0.00487 1049 3440 Conductor diameter inch Conductor diameter mm Conductor cross-section mm² Ohms per 1000 ft.

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Switch / Relay Selection

• Usually rated for AC + DC

–

DC rating is relevant, at the system voltage

–

Inductive loads (motors) reduce the rating

–

(T ungsten) lamp loads are worst → near-short when cold (like a capacitor)

• Do not cheap-out!

–

Contacts spot-weld on

–

Burned-in contacts

• verheat

–

DC switching is much harder than AC as there are no zero-crossings to extinguish the arc

www.nkkswitches.com/pdf/electricalratings.pdf Apem

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Switch / Relay Selection

• Select the right contact

plating material!

• Silver for high currents

– Ag contacts oxidise – Arcing cleans the

contact plating

– No arc = problems

• Gold for low currents

– Au does not oxidise – Arcing destroys the

contact plating

www.nkkswitches.com/pdf/electricalratings.pdf

NKK - Small Toggle Switches

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DC Arc Demo Video

• Partial, slow opening of a knife switch

– Contact distance ~representative of a

typical, compact AC switch

• 150 V DC, 10-20 A
• Resistive + inductive load (15 mH + 8 Ohm)

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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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Fuse Holder Selection

• Make sure it is rated for

the nominal DC current

• Buy in-line fuse holder

with factory-crimped wires if possible

– You need a special

tool to do this well!

• The holder has some

contact resistance

– Do they mean in total

• r per contact?

– Probably excludes

the wire

Multicomp

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The PolyFuse

• Not your main battery fuse
• Good to protect motors, etc...
• Self-resetting
• Gets hot during fault

→ enclose in a box!

• Mind the Ron!

Littlefuse

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Short-Circuit Current

• Must be able to blow the

fuse when a short occurs

– Need suffjcient current

to do this!

• Ishort = Ubat / Rsum, where:

– Ubat = battery voltage – Rsum= sum of all

resistances

• Calculate at lowest Ubat

and highest Twire

• Caution: partial short may

not blow fuse!

• Say: 1S LiPo = 2.0 V min.

– Rbat

= 20 mΩ

– Rfuse = 10 mΩ – Rholder = 10 mΩ – Rswitch = 10 mΩ – Rwire = 2X 20 mΩ

• Ishort

= 2.0 V / 90 mΩ = 22 A

• Fuse of 10 A blows in 0.5s

→ OK

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Dynamic Impedance

• Semiconductors are

very non-linear!

• Diode voltage drop

depends on current

• MOSFET regions:

triode - saturation

– Can desaturate! – Limits current, but

lots of heat!

• Huge impact on fuse

calculation!

ON-Semi 1N400x Vishay IRF640 Saturation Saturation Triode Triode

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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 one)

• You need a fused power

distribution box!

–

Same process as main fuse selection, but computed for each load group individually

–

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

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Build Quality

Work Cleanly! Safety and Reliability utterly depend on it!

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Wiring Harnesses

• Bundle wires and use

connectors

– More reliable – Less restriction of

motion

– Easier for suiting-up

and down

– Easier for suit

cleaning

– Easier for testing

• Choose properly-rated

connectors, though!

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Wire Termination

• Use insulated crimp

terminals for fast-on and screw connectors

• Do not tin stranded wire for

use in screw connectors

–

Solder is not elastic and wires will work loose

–

Use wire-end ferrules!

• Do tin wires for soldering
• Use lots of heat shrink!
• Use a good crimp tool

–

Use the ratchet type!

–

The “pliers” type is unreliable

To solder To solder To screw To screw

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Strain Relief

• Soldered joints are stifg due to the

solder wicked into the wire strands

–

Stress fatigue will happen fast

• Thin wires have little pull strength

at the joint (thin conductor)

• T

ake the strain by clamping the wire some distance from this point

• Need to observe the wire minimal

bending radius as well!

• Relieve various pulling forces

through smart cable routing

–

Use ‘S’ or ‘U’ wire routing to add ‘stretch’ to the wires!

• Follow body plan (e.g.: spine) to

reduce motion

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Electronics Enclosures

• Things may get hot
• Parts can explode

– Shrapnel, nasty fumes – Electrolytic capacitors

are especially nasty

• You will sweat, bump into

things, spill drinks

– Partial shorts, corrosion

• Prevent fjre, burns, injuries

but also improve reliability → put it in a box!

• Good base to attach strain

relief, connectors, controls

Kaiborg Studios

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Dealing with Sweat

• It gets everywhere!

– Both conductive and

corrosive

– Leaves salt deposits

• Remediation

– Conformal coatings on

circuit boards

– Adhesive-lined heat

shrink (stronger splices!)

– Suitable, IP-rated

switches, enclosures, connectors, etc...

White = salt deposit White = salt deposit Tarnished copper in splice Tarnished copper in splice = = higher contact resistance! higher contact resistance!

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Brief - Chemical Risks

• Batteries

– Violent exothermic

reactions (esp. LiPo)

– Prolifjc quantities of

fjre and smoke

– Electrolytes vent

when overheating

– Caustic / acidic

spray + vapours

– Shrapnel may eject – Combustion products?

• Electrolytic capacitors

– Electrolyte vents

when overheating

– Caustic / acidic

spray + vapours

– Shrapnel may eject – Combustion products?

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Brief – 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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Always

• Keep your batteries

in a fjre-proof bag

• Use properly-rated

fuses, the main one right at the battery

• Use properly-rated

connectors and wires

• Enclose your

electronics

• Work cleanly
• And for all that is

good in this world:

– Respect batteries – Have a safety

STOP switch readily at hand

– Have a battery

safety cut-out + ejection solution

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So, We’re All Gonna Die?

• NO -

The risks can be largely mitigated. All it takes is to be aware of them, and to ask for / offer help where needed! We’re Furries! Let’s do what we do best: help each other and have fun! And do the Safety Prance

https://www.youtube.com/watch?v=5dIu8gHkzEs

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Questions? Ideas? Let’s Talk!