Victor 884

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The Control System Logic of a Control System Closed loop PID controller Open loop Parts of a Control System Computer Robot Controller 2009 RC 2006 RC 2004 RC 2003 RC 2000 RC 1996 RC 1993 RC Robovation Input Operator Interface Joystick Output Victor 884 Spike Sensors Encoder Accelerometer Light sensor IR sensor Gyro CMUcam2

The Victor 884 is a speed controller developed by Innovation FIRST as an improved version of the Victor 883. The Victor 884 works by reading a PWM signal from a robot controller, and adjusting the effective voltage supplied to the motors accordingly. The Victor 884 was the only FIRST legal speed controller allowed in the 2005 control system.

Contents 1 Technical 2 Connections 2.1 Data 2.2 Input 3 Programming

Technical

The Victor 884 is part of the FIRST control system. The Victor 884 works by recieving a PWM signal input from a robot controller, which may include the (full) Robot Controller, the Robovation controller or a Vex Controller. Depending on the range of the PWM signal - with 0 being full reverse, 127 being neutral, and 254 being full forward - the Victor 884 adjusts the output of the motor accordingly. This achieves a variable speed control for such applications as Drive trains, arms, or elevators.

The operating voltage of the Victor 884 ranges from 6V to 15V DC, with a maximum operating current of 40 amps. The variable output from the Victor 884 ranges from 3% to 100% of full throttle. A cooling fan operated by the input voltage of the speed controller insures that the Victor 884 is continously cooled.

Although some motors may be run on a Spike if desired, the CIM motors must use a Victor 884 speed controller. The Victor 884 Speed Controllers may be wired into either a 30 Amp or 40 Amp fuse on the breaker panel depending on the motor being used. Each additional motor on a FIRST Competition Robot needs to have a Victor 884 or Spike relay.

A small jumper on the Victor 884 determines whether the Victor will 'coast' or 'brake' when it stops recieving signal. In 'coast' mode, momentum of the spinning motor will enable the motor to coast to a stop when it stops recieving signal. In 'brake' mode, the Victor will short the output terminals together, providing a resistance to the momentum of the spinning motor. As such, the motor will come to a stop much more quickly.

Typically, a robot will use 'coast' mode on most drive motors, as abrupt stops can cause tipping issues. Turrets, arms, and other manipulators should usually use 'brake' mode, both to help hold a load at its desired position and to aid in controllability.

Connections

Data

A 3-pin PWM cable connects the Victor 884 to the robot controller. On the Robot Controller, the PWM cable destined for the Victor 884 speed controller should be connected to the "PWM output" set of ports. A Relay extension cable or a Y-cable may be used if the Victor is mounted far away from the Controller or if one wants a single PWM output port on the Controller to control multiple Victors.

Input

The two input terminals on the Victor supply the power needed to run the speed controller, the cooling fan, and the motor output. The cooling fan on the Victor 884 should be wired into the two input terminals. This insures that the speed controller stays cooled off whenever the Victor is on. If wired incorrectly to the output terminals, the cooling fan will only work when the output motor is being driven, which will lead to over heating and the possible release of Magic smoke.

The two input wires must be correctly wired to match their polarity. If the polarity of the input wires is switched, the speed controller may cease to function. Sparks, arcing, fire, burning smells, or magic smoke may indicate that a Victor 884 was wired incorrectly, and hence been destroyed.

Programming

The PWM outputs on the Robot Controller can be set across the normal hobby servo range, 1 to 2 ms. The 8-bit PWM channels used on the PIC microprocessor of the Robot Controller (and Vex controller) has a resolution of 256 values, which fit in an unsigned char. 0 commands full reverse, 127 commands stop, and 254 commands full forwards. 255 should be avoided on older RCs because it acts as a special signal command when transmitted between the Robot Controller and OI. Newer versions of the RC seem to have no issue with a 255 command. However, for code portability, 254 should be the maximum value used (besides, using 254 results in symmetric forward and reverse resolutions).

Note that a neutral PWM command to a (factory calibrated) Victor consists of a pulse of about 1.5 ms duration. As such, when no PWM input is applied, the Victor will detect this and flash it's yellow LEDs.