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1 High Tech High Top Hat Technicians Electricity/Electronics Introduction for FIRST Robotics Competition Part 2 P. Rada, Oct/Nov 2015
2 Summary of what we learned last week What? Unit Typical Examples Mech. Analogy Hydraulic Ana. Range R, 1m CIM motor: 0.15 Friction = Valve (heat) resistance 10M Loudspeaker: 4-8 break or Antenna: 50 damper (heat) Logic gate input: 10M U, voltage V 1uV- CIM motor: 0-12V Force Water or difference 10MV Electronic power supply: Pressure (or of potential, 15V height) (or electrical Sensor: 1mV pressure) HV AC line: 1MVAC I, current A 1nA- CIM motor: 0-80A Velocity (linear Water flow 1MA Red LED: 1mA or angular) rate Sensor: 1uA Homopolar motor: 1MA P, power W 0.1pW- CIM motor: 0-960W Work (horse Water flow * 10GW 11g router RF RXsens: 0.32pW power) height Red LED: 2mW Nuclear plant: 5000MW
3 Summary of what we learned last week 2 What? Unit Typical Examples Mech. Hydraulic Range Analogy Ana. E, energy Wh 1uWs CIM motor at 3000rpm, torque Work Water consumed 100TWh 0.7Nm, 1 min: 3.7Wh during flow * RF u-receiver for 1h: 3.6mWh length of height * 2011 elec. cons. in USA: time time 4,127,000,000 MWh Wire AWG & AWG FIRST: IC wire bonding: 15um ? pipeline Colors: AWG12- AWG-28: 0.32mm / 1.4Amax R,Y,W,BR = + 28 AWG-12: 2mm / 41Amax BLK,BLU = 0, -- 1000A/500KV cable: 56mm C, capacitor F 0.1pF- Optional cap for CIM:
4 Summary of what we learned last week 3 Battery PWM CIM motor model Use the multimeter
5 Complete model of the PMDC motor (CIM) = + + = Electrical section Mechanical equivalent circuit
6 Content Part 2 How to Switch power Selecting the motor driver PWM linearity JAGUAR motor driver, details & model TALION SRX Motor driver details & model What is a CAN bus? 5 min break In-wire connectors Complete electrical drive model and analysis Conclusion Q/As Practice session: Introduction to the oscilloscope
7 CIM Motor Driving Circuit with PWM Motor Driver(s) Power Distribution e.g. Victor-888 12VDC Wires Motor(s) e.g. CIM-217 Motor 12VDC 12VDC 12V/18Ah Wires Wires Wires battery PWM wires 0-5V RoboRIO (uC board with IOs)
8 Switching Power, Varying speed, and Direction: How? Requirements 1. Vary speed from zero to max Vary 12V voltage or what? 2. Forward or backward How to connect motor or +12V and - 12V batteries? 3. Very efficient and fast driver Else a lot of power in heat 40A on 0.1 Ohm, P = R * I2 = ? How? Relay? How to vary speed? Bipolar or MOSFET transistor in linear mode? Varies speed but Pact-switch = U*I = e.g. 6V*40A at 3000rpm = 240W = crazy! Bipolar Transistor in switching mode? VCEsat = 0.3V, so P = U*I = 0.3V*80Amax = 24W!! Need also diode(s) for current discharge BIG heatsink per each transistor + diode = lot of Pwaste & heat!
9 Switching Power & Vary Speed: How? RE: Variable speed Forward/Backward Very efficient How? Active switches? Maybe but: How to vary speed? How forward or backward speed? High efficiency?
10 Switching Power & Vary Speed: How? RE: Variable speed Forward/Backward Very efficient How? Active switches? Maybe but: How to vary speed? Need PWM How forward or backward speed? High efficiency?
11 Switching Power & Vary Speed: How? RE: Variable speed Forward/Backward Very efficient How? Active switches? Maybe but: How to vary speed? Need PWM How forward or backward speed? High efficiency?
12 Switching Power & Vary Speed: How? RE: Variable speed Forward/Backward Very efficient How? Active switches? Maybe but: How to vary speed? Need PWM How forward or backward speed? Topology High efficiency?
13 Switching Power & Vary Speed: How? RE: Variable speed Forward/Backward Very efficient How? Active switches? Maybe but: How to vary speed? Need PWM How forward or backward speed? Topology High efficiency?
14 Switching Power & Vary Speed: How? RE: Variable speed Forward/Backward Very efficient How? Active switches? Maybe but: How to vary speed? Need PWM How forward or backward speed? Topology High efficiency? Active switches are completely ON or OFF (no PCONS)
15 Switching Power & Vary Speed: How? RE: Variable speed Forward/Backward Very efficient How? Active switches? Maybe but: How to vary speed? Need PWM How forward or backward speed? Topology High efficiency? Active switches are completely ON or OFF (no PCONS) MOSFETs with very low RON Remember: P = R * 40A2 = If RON = 10m -> PMOSFET = 16W!, still too much
16 Topology 0: Push active switch + NO diode Destructive over-voltage spikes! Current abruptly cut in the motor inductors path (no diode connected)
17 Topology 1: Push active switch + diode Diode connected to avoid currents cut fly-wheel diode Diode current when OFF No more over-voltage spikes!
18 Topology 2: Push-pull with 2 active switches + diode Motor current good fly-wheel current good
19 Motor driver H-bridge concept Question: How can we run the motor backward?
20 Topology 3: H-bridge with 4 active switches + 2 diodes H-bridge for forward Switching OFF & backward speed Switching ON
21 Motor driver H-bridge concept Question: Why a dead time of 2us?
22 Dead time PWM ON & OFF NEVER active Simultaneously (no short-circuit) PWM ON PWM OFF Dead Time Dead Time Dead Time PWM OFF PWM ON PWM ON
23 Selecting the motor driver: PWM Linearity! Victor 888: Linearity? Victor888: linearity vs. temp.? CAREFUL!
24 PWM with Jaguar
25 PWM with motor driver Jaguar
26 PWM with motor driver Jaguar
27 Jaguar Specifications TI name: Stellaris (ref. design kit) RDK-BDC24 12V and 24V brushed DC motors 40A max. continuous Speed control CAN 1Mbps RS232 serial interface 15kHz PWM (motor run smooth) RON = ROFF = 2.5m Dead time = 2us Differential motor output VM+ and VM- Screw terminals for all power wiring Powerful 32-bit Stellaris LM3S2616 uController (ARM Cortex M3) Rich set of control options and sensor interfaces Open-loop speed control or closed-loop control of x(t), (t) or i(t)MOTOR Quadrature encoder input
28 PWM with motor driver Jaguar, more Use this one! Black MDL-BDC24
29 PWM with motor driver Talon SRX
30 PWM with motor driver Talon SRX FCK
31 PWM with Talon SRX, Simulation model 1 10ms Digital selector for Clock pulse width PWM_IN = 10ms period PWM Clock with 61us pulse width PWM Clock with 2.6us Internal PWM Clock = pulse width 15.625KHz -> 64us cycle PWM Output Min Throttle = 4% = min. pulses of 2.6us Max pulse = 95% (?) = 61us
32 PWM with Talon SRX, Simulation model 2 Add power switches with real components (MOSFETs with very low R_ON resistance) PWM Output
33 PWM with Talon SRX, Simulation Model 3 (real components) Add real components driver stage
34 PWM with Talon SRX, Simulation Model 4 (optimized) Add real components driver stage Optimized output stage Example of modern MOSFET: 60A cont 40V RDSON = 4.8m
35 Talon SRX vs. Jaguar Talon SRX Jaguar In your 2015 robot Yes to be confirmed No, to be confirmed Cost per driver $15 at Vex Robotics $80 Continuous current 60A / 100A-surge 40A / 60A-surge Issue date, availability Very recent, early 2015 Discontinued (Vex Robotic) in stock at Vex R. as of 11/13 Available somewhere? Size much smaller = 2.75" x 1.185" x 0.96 much bigger = 2.85" x 4.25" x 2.00 Extra heat sink required? No, has a integral heatsink No, has an internal fan Wiring Less easy (need to solder wire on wire Easy, 4 wire screw terminals and add heat shrink tube for isolation) Software API avail. for RoboRio ? ? Support CAN-bus & PWM Yes, plus SPI & USART (serial) Yes plus RS232 (serial) Recommendation for robot 2016 Advise to use only Talon SRX Advise to use only Talon SRX
36 What is a CAN bus? A controller area network (CAN bus) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other in applications without a host computer. It is a message-based protocol, designed originally for multiplex electrical wiring within automobiles, but is also used in many other contexts (e.g. fieldbus). Dev. started in 1983 at Robert Bosch GmbH and released in 1986 1st CAN controller chips came in 1987 (Intel & Philips) 1988 BMW 8 Series = 1st vehicle with CAN-bus CAN is a multi-master serial bus standard for connecting nodes Up to 1 Mbit/s for < 40 m 4 pins bus (CAN-, Ground, CAN+, V+) App: Car bus or fieldbus CAN network is synchronized but no CK transmitted (Shielded) twisted pair for more noise immunity
37 CAN Physical Layer v_CAN+ = v_CAN- = v_CAN+ = 3.5V CAN-TRX1 CAN-TRX2 2.5V (active) (passive) Dominant bit 0 Recessive bit 1 v_CAN- = 1.5V (passive) i_CAN+ = 20mA i_CAN+ = 0 i_CAN- = 0 i_CAN- = -20mA
38 CAN Physical Layer CAN-TRX1 CAN-TRX2 (active) (passive) Dominant bit 0 Recessive bit 1 (passive) What happen is the two 120 resistors are omitted?
39 Lossless bit-wise arbitration method of contention resolution Dominant bits = logical 0 -> Real time Recessive bits = 1 (passively to 1)
40 CAN bus data frame identifier Data Data Check Data length
41 CAN bus 70 electronic control units per car typically!
42 Robot: CAN-bus vs. PWM CAN-bus PWM wires Your 2015 robot USED for the conveyer motor USED for the 4 wheel motors Connectivity 1 series 2-wires from RoboRio 3 wires (PWM, Ground, rotation connected to motor drivers 1 to 6 direction) connected to every (2 daisy chain wires total) controller = 18 wires total Bus termination 120 Ohm resistor on each side none Driver output motor signal PWM modulated PWM modulated Linearity Depends on PWM frequency, Depends on PWM frequency, advised 15KHz advised 15KHz Software coding simplicity Similar if having/using API Similar if using API, *API = application program interface, is a set of Much simpler if no API for CAN-bus routines, protocols, and tools for building software applications Overall performance Similar to PWM wires Similar to CAN-bus Cost Similar to PWM wires Similar to CAN-bus Data conveyed on wires Can pass several signals PWM control & rotation direction Recommendation for robot 2016 Consider to use CAN-bus to OK as well connect to EVERY motor driver
43 In-Wire Connectors RS-232 MOLEX
44 In-Wire Connectors Max. current? Max. voltage? In-wire m & f? # of conductors? Amphenol Clamp/not? Easy conn./disc.? BNC Toolkit/wrench? Cost? PS-2
45 CIM Motor Driving Circuit with PWM Power Distribution Motor Driver(s) e.g. Victor-888 12VDC Wires Motor(s) e.g. CIM-217 12VDC 12VDC Wires Wires 12VDC 12V/18Ah Wires battery PWM wires 0-5V RoboRIO (uC board with IOs)
46 PWM with Motor Driver Talon SRX, maximum speed With PWM: ImaxPWM = U*0.96/Rtot = = 12*0.96/(11m+38m+13m+140m) = 11.52V/202m = 57.0A Without PWM: ImaxDC = U/Rtot2 = = 12V/(11m+13m+140m) = 12V/164m = 73.2A but how do you adjust the motor voltage?
47 Complete Motor System with PWM & C: Various scenarios IINPUT PWNOUT PWNIN Zooms for the next time responses
48 Complete Motor System with PWM & C: Various scenarios IINPUT 1) No C 3) C = 1uF, Rc = 1 (Hypothetic) PWNOUT 4) C = 1uF, 2) C = 1uF, Rc = 0.1 Rc = 13m Conclusion: No significant difference with this model.
49 CIM Motor Driving Circuit with PWM Power Distribution Motor Driver(s) e.g. Victor-888 12VDC Wires Motor(s) e.g. CIM-217 12VDC 12VDC Wires Wires 12VDC 12V/18Ah Wires battery PWM wires 0-5V RoboRIO (uC board with IOs)
50 PWM with Motor Driver Talon SRX, C & L_wires
51 PWM with Motor Driver Talon SRX, C & R,L_wires Battery motor PWM driver Warning: Oscillations!
52 PWM with Motor Driver Talon SRX, C & R, L_wires Warning: 1uF may cause C removed -> no oscillation! oscillation when inductance in the wires. Here using a better model for battery and Corrective action: Add motor wires. damping effect with the cap C -> add series resistor
53 PWM with Motor Driver Talon SRX, C & R,L_wires & Rs Can we reduce the batterys wire length? Can we reduce the motors wire length? Adding series resistor
54 PWM with Motor Driver Talon SRX, C & R,L_wires & Rs Oscillations removed with Rs! Rs = 2 Rs = 10
55 Conclusion PWM creates high frequency power signals with high I/ t Conducted & Electro-magnetic Noise! Be careful with adding the capacitor Cf of 1uF (verify no oscillation at motor input with oscilloscope) Value of Cf and series resistance Rs determine filtering Motor drivers: Advise to use Talion SRX vs. Jaguar cheaper, available, latest generation Use thick and short wires (AWG-12) for motor drivers and motors as possible Talion SRX: Connect with same or thicker wire (not done on robot 2015) CIM motor uses a lot of power (up to 1000W input) Use Heatsink + use for limited time e.g. < 5 min (and/or verify temp.) Use all the same motor drivers and same motors!! (no diversity) Model a circuit/system is fun and permits to understand what is going on! You can contact me anytime for questions!
56 Questions
57 Basic use of an oscilloscope
58 References Various articles from www.Wikipedia.com 2015 FIRST Robotics Competition (FRC) Game Manual Marc Posts presentation on PMDC motors http://www.eeweb.com/toolbox/parallel-wire-inductance http://content.vexrobotics.com/docs/217-3367- VEXpro_Jaguar_GettingStartedGuide.pdf Stellaris RDK-BDC24 Brushed DC Motor Control Module, Users Manual, TI Analogous Electrical and Mechanical Systems http://lpsa.swarthmore.edu/Analogs/ElectricalMechanicalAnalogs.h tml CAN Bus: Taking a Larger Role in EVs and PHEVs http://www.digikey.com/en/articles/techzone/2012/aug/can-bus- taking-a-larger-role-in-evs-and-phevs All simulations done with SPICE TINA v9.0 from DesignSoft see http://www.tina.com/spice_simulation
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