FIRST Electrical Design FIRST Robotics Championship Conference Steven Shade Team 1111 April 16, 2003

Overview Definitions Basic Layout of FIRST Electrical Systems Common Problems IFI’s Robot Controller Incorporation of Sensors on a FIRST Robot Questions

Electrical Definitions and Devices Voltage –Work done to move unit positive charge form point A to point B –Measured Between Points Current –Rate of change of charge through a surface –Measured Through Something Circuit –At least one complete loop of current “Ground” –Hesitant to use since our robots are not connected to the ground –For our purposes, has a value of 0V –Also going to use Common Resistor –Impedes Current Flow –Current has Linear Relationship with Voltage (Ohm’s Law) V = I*R Diode –Allows Current flow in only one direction –Current Modeled as Ideal Relationship with Voltage V = I –Special case: LED (Light Emitting Diode)

FIRST Electrical Layout 12V SLA Battery 40A Power Distribution Block 20A & 30A Circuit Breaker Panel 120A Circuit Breaker - + Ground Stud Robot Controller Victor 884 Speed Controller Spike Relay Victor 884 Speed Controller Backup Battery

Common Problems Why does my Robot Controller resets during the middle of a match? (Pre-2004) Why does my primary battery only last one match? Why does it always take so long to debug electrical problems?

Wire Selection and Layout Primary Batteries should last 2-4 matches There is resistance in every wire –.001 ohm/ft #10 wire –.0004 ohm/ft #6 wire There is resistance at every connection Resistance from wire and connections coupled with high current loads, places a voltage drop along circuit path

Example Drawing 116.4A (stall current of drill motors) over provided battery cables V = I*R V = 116.4A * (.0004 ohm/ft * 8 ft) V = 0.372V This does not include resistances from connections The total drop can be in excess of 0.5V!

Example Continued Still drawing 116.4A Now also adding the #10 wire Rtotal = (.0004 ohm/ft * 8 ft) + (.001 ohm/ft * 6 ft) Rtotal =.0092 Ohm V = I * Rtotal V = 1.07V

Reducing Resistance Check every crimp to make sure the wires do not move or turn when pulled Use the correct tool for the job Solder all critical joints Shorten the length of your wires (also helps in keeping things neat and traceable)

General Layout Tips Label Everything! Tie all wiring up Plan, create drawings just like mechanical systems Create a Test Bed When in doubt, insulate

Interfacing with the RC Robot controller Analog Inputs and Digital Inputs and Outputs Switches connect to the Digital Input and Common Sensors send a value between 0V and 5V to Analog Input

Battery Charging Replace the clips that come on the battery charger to a connector like the one on your battery