Fur in Motion v1.1 Nordic Fuzzcon – 28/02/2019 Floere T. Pillowcase, Devourer of Automobiles (fmoere@robocow.be)
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. 2 / 62
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 on the HOW ● These slides can be downloaded after the talk: – https://www.robocow.be/events/ 3 / 62
● 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/ 4 / 62 * Survival with all body parts intact is not guaranteed. Hugs at your own risk.
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 5 / 62
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 6 / 62
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 ● 7 / 62
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 or 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 8 / 62
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 9 / 62
Types of (Geared) DC Motors Plain motor Geared motor Linear actuator ● High speed ● Low speed ● Low speed ● Low torque ● High torque ● High force ● Linear motion 10 / 62
Anatomy of a DC Motor 11 / 62 https://learn.sparkfun.com/tutorials/motors-and-selecting-the-right-one/dc-brush-motors---the-classic
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 12 / 62
DC Motor Stall Current ● When the motor can’t turn, the current becomes very high – Only limited by the Current d e resistance of the e p S winding and brushes ● When the motor runs, the current is lower – Given by the https://www.pololu.com/product/1117/faqs resistance of the winding + brushes and the back-EMF 13 / 62
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 14 / 62
Types of RC Servo Motors Regular servo Linear servo Control boards ● Rotation ● Push-pull ● For generic actuators ● < 10 ms for ● ~20 mm/s with feed- 60° exists! max speed back pots 15 / 62
Anatomy of a RC Servo 16 / 62 http://www.robotpark.com/academy/servo-motors-51057/
Driving RC Servo Motors Pulse-Width Modulation ● The ratio between on and – ofg 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° – Word of Warning Usually updated every – RC servos are open-loop with 20 ms (= 50 Hz) ● respect to the driving controller Control sources: ● There is no feed-back if the set- ● MCU (eg: Arduino) – point is not actually reached! Dedicated controller – 17 / 62 RC remote control –
Protecting RC Servo Motors ● The gear train has some fragility – Forcing it can strip gear teeth ● Protect gears from Kimbrough excessive force – Servo saver – Spring linkage ● Cheap servos can over-heat due the Traxxas 18 / 62 motor stall current
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 19 / 62 NC = normally-closed ●
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) Word of Warning: avoid the old L298 – Keep the limit switches! No real over-current protection ● Protection is important High voltage drop (~4V @ 2A) ● ● – Back-EMF (FWD) diodes Lots of heat – – Over-current Limited use with 1S, 2S LiPo – – Overheating Acts as a current limiter... – 20 / 62 Best use COTS modules! ●
Protecting DC Motors Gear boxes can break ● – Limit torque using a slip clutch, spring, shear pin, etc... Consider a PolyFuse to ● protect against prolonged MCD Pro-Bite over-loads Motor electronics: ● – Able to accommodate the stall current – Protected against back-EMF, U, I, T Observe the section on ● fjre safety! 21 / 62 DAGU RS022
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 22 / 62
Sources of Energy ● Batteries for now… ● Usable battery types ...which are a mess – NiMH ● Motors require: – LiFePO 4 – Signifjcant energy – LiPo → Watt-hours – Alcaline + supercap – High peak current – Pb gell cell / AGM → Amps or xxC ● Usable ≠ safe! ● Fuses require high short-circuit currents ● Air travel restrictions ● Most costumes need small power packs 23 / 62
Sources of Energy ● In practice: ● Battery internal resistance is key – NiMH – Cell voltage drops – LiFePO 4 when loaded – LiPo – U drop = R cell x I load ● First two are much ● Maximum discharge safer than LiPo current is important ● Last has ~double – In Amps or xxC the energy density ● Read the battery ● All exist in versions data sheet! that can source high (peak) currents 24 / 62
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Charge Time (min.) 27 / 62 Panasonic
Enix Energies 28 / 62
Enix Energies 29 / 62
Power System Stability ● Battery and wiring ● Impact of voltage have resistance fmuctuations: ● High motor start – MCUs can crash current will cause – Analog circuits bus voltage to drop can have their – Deeper, partial dips operating points disturbed are “brown-outs” – General undefjned – This has an adverse and unexpected impact on the other behaviours and system components interactions 30 / 62
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) 31 / 62
Stupidity Diode ● If your batteries are: ● Not always practical – Loose cells – Voltage drop (0.2 V – 2 V) – Can be connected ● Consider P-MOS in reverse protection circuit ● Put a Schottky diode – Use FET with low in series! (After the battery fuse.) enough V th ! 32 / 62 Infineon: “Automotive MOSFETs – Reverse Battery Protection” June 2009
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 33 / 62
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. 34 / 62
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