Update tech-tips.rst (#293)

* Update tech-tips.rst

Author: texasdiaz

docs/source/tech_tips/tech-tips.rst

@@ -14,6 +14,61 @@ Just click to expand the Tech Tip you'd like to read.
 .. dropdown:: Week of 06/24/2024 "Calculating Motor and Servo Power"
    :open: 
 
+   .. _servopowerinjectors:
+
+   This week’s Tech Tip of the Week is intended to be a short treatise on Servo 
+   Power Injectors. Servo Power Injectors have been used in FIRST Tech Challenge
+   for several years now, but do you really understand what they are and how they 
+   work? What is a Servo Power Injector and how might servos behave differently 
+   when used with one?
+
+   A servo connection is a 3-wire combination that combines power, ground, and 
+   a signal. The actual command signal for the servo travels on the signal wire, 
+   and the power used to power the servo travels on the other two wires. A servo 
+   power injector is a device that removes the power provided by the servo controller 
+   (REV Control Hub or REV Expansion Hub for FTC) and provides a new, usually higher 
+   wattage power source. Both the REV Servo Power Module and Studica Servo Power Block 
+   replace the 5V/10W power provided by the REV Control/Expansion Hubs with a 6V power 
+   source with a higher maximum wattage. 
+
+   So what does higher voltage do for a servo? Servos operate on a power range; the 
+   more power they get, the faster and stronger they can become, up to a certain limit. 
+   Servos operating at 5V get a noticeable boost in speed and output power when used 
+   at 6V. The same servos may seem superhuman at higher voltages!
+
+   The downside of servo power injectors is that teams are now responsible for 
+   managing their own power usage. On the REV Control Hub, for instance, each servo 
+   port pair is limited in how much power it can draw (at least there’s a limit on 
+   how long it can draw high loads). When using a servo power injector, the pool of 
+   power for a servo is much larger and less restricted since it pulls its power 
+   directly from the robot battery - using power injectors means you could consume 
+   all of the power on the robot just from the servos alone! This will result in the 
+   robot power system browning out (resulting in loss of communications or loss of 
+   power to the control system) or even blowing the 20A battery fuse.
+
+   Using a servo power injector can also expose different behaviors in servos that 
+   were not present when using the REV Control/Expansion Hub directly. The biggest 
+   behavior is the “Lost Signal” behavior. When an OpMode ends, the REV 
+   Control/Expansion hubs stop the signal and also cut power to the servo ports - 
+   this leads to the servos “going limp” as they lose power. With a servo power 
+   injector, the servos never lose power, and so “lost signal” behaviors will often 
+   then take over which may cause the servo to move to a “default” position (which 
+   is virtually never advantageous for robots but definitely advantageous for R/C 
+   planes for example). The Axon MAX+ servo and several higher-power HiTec servos 
+   have this behavior, the Axon MAX+ behavior is at least configurable with a servo 
+   programmer.
+
+   Finally, when using a servo power injector it’s of VITAL importance that you 
+   cover unused ports with tape or other debris-limiting measures to protect the 
+   ports. It’s very easy to get metal swarf in open servo ports, and that metal 
+   can short out the power output pins - especially lower-cost power injectors 
+   cannot tell when they’re being used, or don’t have protections against short 
+   circuits, but they still have all output pins powered. This can quickly turn 
+   your servo power injector into an expensive paperweight when the power 
+   regulator overloads and burns out. 
+
+.. dropdown:: Week of 06/24/2024 "Calculating Motor and Servo Power"
+
    .. _calculatepower:
 
    In this Tech Tip of the Week we’ll be exploring mechanical and electrical