Basic Fursuit Electronics Motors v2.0 Flüüfgf – 21/11/2019 Floere T. Pillowbeaver, Devourer of Nuclear Submarines 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 / 58
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/ 3 / 58
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 ● 4 / 58
The Electric Motion System Control Input Output Moving Energy Electrical to Mechanical Field Transmission Source Energy Conversion Generator Or Feed-Back 5 / 58
Content ● Motion T ypes of motors and how to control them ● Transmission Selection of mechanisms ● Power Power sources and stability 6 / 58
Content ● Motion Types of motors and how to control them ● Transmission Selection of mechanisms ● Power Power sources and stability 7 / 58
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 8 / 58
Anatomy of a DC Motor 9 / 58 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 10 / 58
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 11 / 58
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 12 / 58
Protecting (Geared) Motors Mechanical: gear boxes ● – Limit torque using a slip clutch, spring, shear pin, etc… – Magnetic torque limiters are nice! MCD Pro-Bite → 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) 13 / 58 DAGU RS022
Types of BLDC Motors All images: HobbyKing Ducted Fan Inrunner BLDC Outrunner BLDC (with BLDC motor) 14 / 58
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 15 / 58 Dave Wilson – Texas Instruments
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 16 / 58
BLDC Fast Speed Reduction ● Be careful with fast ● The power system must speed reductions! absorb the BEMF energy ● Kinetic energy is – Not possible with: converted back to the ● Most benchtop power supply power supplies (regenerative braking) ● Polarity protection – Can cause the DC diode bus voltage to rise – Use a brake chopper – May destroy the if needed! ESC and/or other components! 17 / 58
External Cooling Kenzi Mudge ● Many cheap motors are ● Many cheap motors hugely over-rated! are desigend for RC aircraft and drones: ● Risk of overheating in – External cooling many costume applications from the propeller air stream – Beware of high ● Other cooling methods: torque operation! – Still fjne for low duty- – Internal cooling fan cycles (at reasonable RPM) ● Use an external fan if – Conduction cooling the motor runs too hot! 18 / 58
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 19 / 58
Anatomy of a RC Servo 20 / 58 http://www.robotpark.com/academy/servo-motors-51057/
Protecting the Gear Train ● The gear train has some fragility – Forcing it can strip gear teeth ● Protect gears from Kimbrough excessive force – Servo saver – Spring linkage ● Consider a re- settable torque Traxxas limiter (slip clutch) 21 / 58
Content ● Motion T ypes of motors and how to control them ● Transmission Selection of mechanisms ● Power Power sources and stability 22 / 58
Driving RC Servos and BLDC ESCs Pulse-Width Modulation ● The ratio between on and – ofg 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° Word of Warning Usually updated every – RC servos/ESCs are open-loop ● 20 ms (= 50 Hz) with respect to the controller Control sources: ● There is no feed-back if the set- ● point is not actually reached! MCU (eg: Arduino) – RC remote control – 23 / 58
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 24 / 58 Eliminator Circuit) Images: HobbyKing
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 25 / 58 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... – 26 / 58 Best use COTS modules! ●
Content ● Motion T ypes of motors and how to control them ● Transmission Selection of mechanisms ● Power Power sources and stability 27 / 58
Torque ● Power = rotational ● It measures how hard speed * torque we twist on an axle ● T – 5 N.m= 0.5 kg @ 1 m orque usually the = 50 kg @ 1 cm driving design factor – Gets easier with a longer in costumes lever, but we have to ● Expressed in: twist it further (slower) – N.m ● How to measure? (Newton meter) – T orque wrench – Lb.ft – Kitchen scale (pound foot) ● Use a known lever – Force @ distance ● 1 N ~ 100g 28 / 58
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 29 / 58
Belts and Pulleys ● Much more quiet than gears, and more forgiving ● But: Sumray – Wear & tear – T orque limits – T oothed (timing) belts make noise ● Much larger system ServoCity for same reduction ratio as gears 30 / 58
Rotation ↔ Linear Motion 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. Slider-Crank Mechanism 14Core Quite easy to do with hobby means. Consider using PTFE to line the slider for low friction and low noise. 31 / 58
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