Changes between Version 14 and Version 15 of ElectricalFrcIntroduction

Timestamp:

Sep 10, 2017, 12:25:18 AM (8 years ago)

Author:

David Albert

Comment:

--

ElectricalFrcIntroduction

@@ -141 +141 @@
 
 == Power Distribution ==
-[[Image(http://cdn3.volusion.com/vyfsn.knvgw/v/vspfiles/photos/am-2856-2.jpg?1442240393, 25%, right)]] Power from the battery goes through the master breaker and into a Power Distribution Panel (PDP).  The PDP distributes the battery power to the various circuits in the robot.  The PDP monitors the current flowing through it so the robot computer can monitor the current drawn by each circuit.
+[[Image(http://cdn3.volusion.com/vyfsn.knvgw/v/vspfiles/photos/am-2856-2.jpg?1442240393, 15%, right)]] Power from the battery goes through the master breaker and into a Power Distribution Panel (PDP).  The PDP distributes the battery power to the various circuits in the robot.  The PDP monitors the current flowing through it so the robot computer can monitor the current drawn by each circuit.
 
 Each circuit leading from the PDP to the robot loads should be provided with a [https://www.andymark.com/40-Amp-Snap-Action-Breaker-p/am-0288.htm snap breaker] that is  appropriately sized (5, 10, 20, 30, or 40A) for protecting the circuit it will be  powering.  For example, FRC rules specify that the smallest gauge (thinnest) wire you can use for powering motors is 12AWG which is limited to 41A so a 40A breaker might be used to protect it (you should also probably use thicker wire to provide some margin for error).  Snap breakers use two metals that bend at different rates when heated; the metals are arranged to touch securely and conduct electricity when cool, but when heated, will deform and snap apart, opening the circuit and protecting the wiring from overheating.
 
-The PDP uses two types of connectors:
+The PDP uses several types of connectors including:
 
- * WAGO connectors for wiring to high current loads (motors)
- * Weidmuller connectors for wiring low-current signals (e.g. to the roboRIO)
+ * WAGO connectors for wiring to high current loads (motors).  These connectors are opened to insert wire using a small flat-head screwdriver.
+ * Weidmuller connectors for wiring low-current signals (e.g. to the roboRIO).  These connectors are opened to insert wire using a pen or fingertip.
 
-Consult the [http://ctr-electronics.com/PDP%20User's%20Guide.pdf PDP user manual] for information on how to insert and remove wires from the connectors.
+Consult the [http://ctr-electronics.com/PDP%20User's%20Guide.pdf PDP user manual] for more information.
+
+Note: the connectors on the PDP aren't the best choice for robots: they aren't locking connectors and so wires can work their way loose with vibration.  The connections are also close together and it's easy for small strands (''whiskers'') of stranded wire to accidentally make contact creating a short circuit.  The robot pit crew must inspect these connections regularly during competition.
 
 == Voltage Regulation ==
-[[Image(http://cdn3.volusion.com/vyfsn.knvgw/v/vspfiles/photos/am-2857-2.jpg?1442240393, 25%)]] The voltage regulator module (VR or VRM) contains circuitry that takes the battery voltage (which varies according to how much current is being drawn at any given moment) and generates well controlled 12V and 5V outputs.  These outputs are used to power sensitive electronic devices such as computers and radios whose voltage must remain stable at all times.  The regulator uses a SEPIC switching circuit to step up the voltage if it is below the target (5v or 12v) and step down the voltage if it is above the target.  The step up/down function takes place so quickly that any variations in the battery voltage are not seen by the output device.
+[[Image(http://cdn3.volusion.com/vyfsn.knvgw/v/vspfiles/photos/am-2857-2.jpg?1442240393, 15%)]] Many devices on the robot require voltage other than the 12v supplied by the battery and/or must not be exposed to the voltage fluctuations that occur when the battery is placed under heavy load.  The voltage regulator module (VR or VRM) contains circuitry that takes the battery voltage (which varies according to how much current is being drawn at any given moment) and generates well controlled 12V and 5V outputs.  These outputs are used to power sensitive electronic devices such as computers and radios whose voltage must remain stable at all times.  The regulator uses a [https://en.wikipedia.org/wiki/Single-ended_primary-inductor_converter SEPIC] switching circuit to step up the voltage if it is below the target (5v or 12v) and step down the voltage if it is above the target.  The step up/down function takes place so quickly that any variations in the battery voltage are not seen by the output device.
 
 == Motor Controllers ==
-[[Image(https://www.vexrobotics.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/2/1/217-4358-on-talon.jpg,25%,left)]] Motor controllers allow the robot computer to control the speed and direction of each motor.  There are several popular models including:
+[[Image(https://www.vexrobotics.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/2/1/217-4358-on-talon.jpg,15%,left)]] Motor controllers allow the robot computer to control the speed and direction of each motor.  There are several popular models including:
 
  * [http://www.andymark.com/Talon-SRX-p/am-2854.htm Talon SRX] intelligent, CAN or PWM ($90)