Power Expander

VEX Robotics Competition Discussion VRC > Turning Point (18/19)
#21

my batteries hardly finish charging before we got to use them so yea… power expander might help us

#22

https://vexforum.com/t/how-to-use-a-power-expander/32774/1

#23

There are three good reasons that immediately come to mind:

  1. An extra ptc means you can divide power better to make it less likely to trip one.
  2. An extra battery means the robot can run with more consistently full batteries, which will help with consistency of performance.
  3. You can take advantage of the extra battery for weight distribution.

If your main battery dies, the power expander won’t do anything. It has to receive a signal coming from the Cortex, which itself is powered off the main battery. However, you could run four motors on the power expander so that the batteries won’t die nearly as quickly. Split the motors wisely. For example, if your drivetrain uses 6 motors, you could put 2 motors on each of the 3 ptc’s (2 on ports 1-5, 2 on ports 6-10, and 2 on the power expander).

#24

One thing that would be useful to ensure consistency with the power expander is using the analog port, a single port on the expander to have maintenance of the voltage. Connect the analog of the power expander to the analog of the brain, and in ROBOTC tell the port that it’s analog in. The voltage of the expander is the AnalogIn value/270, in which you can use that for displaying voltage, as well as have an emergency “Do not move anything” if the robot notices no voltage from the power expander when a match is going so you will make sure that you can plug the power expander in without losing. A simple statement in the beginning of usercontrol as well as autonomous can save your life:


 while(sensorValue[Expander]/270 < 1); //If the power expander is unlplugged or below 1V, don't continue
#25

wait the power expander would need to be programmed? When i looked it up earlier this week, it said it doesnt need programming…

#26

If you are using a power expander, I would suggest using only 4-5 motors on it. Any more than 5 will burn out the PTC relatively easy inside of the expander which is not good. Also, hearing and living through problems with ports 1 and 10, I would suggest distribution similar to this:
2 - Drive Left
3 - Drive Right (2 Motors Y Cabled)
4 - Manipulator (Power Expander)
5 - Manipulator (Y-Cabled, with one going directly to motor and the other going to Expander, which would run a second motor)
6 - Manipulator (Power Expander)
7 - Manipulator (Y-Cabled, with one going directly to motor and the other going to Expander, which would run a second motor)
8 - Drive Right
9 - Drive Left (2 Motors Y Cabled)
EDIT//: The CORTEX has 2 PTC’s, with one PTC at ports 1-5 and the second being at ports 6-10 It is HIGHLY reccomended to have all drivetrain motors be on the CORTEX because it is the most important mechanism on the robot, as well as evenly distributing the sides among the 2 PTC’s to prevent burnout as much as possible.

#27

So we should plug our drive into the PE?

#28

AB,C, and D are spots we can plug motors into right?

#29

I am confusing you, my apologies. The power expander does not need any programming. The power expander has 4 input 3 wire ports and 4 output 3 wire ports, and on the side of that is a 3 wire analog port for voltage monitoring. You run 3 wire extension cords from the CORTEX motor port to the 3 wire input ports on the expander. Across from the 3 wire input ports is 3 wire output ports. You plug the motor and motor controller to the port adjacent to the 3 wire extension that is extended from the CORTEX

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#30

Then the motors we want on the power expander, we will need to run a 3 wire cable from the cortex into the slot beside where the motor is pluged into so that it will run?

#31

@[TVA]Connor right?

#32

Yes. Also

You should never be running the motors on your drivetrain on the expander. If the expander has a time of failure you want to make sure you at least have the capability to drive.

#33

ok, thanks :slight_smile:

#34

Then would it be a good idea to plug the fly wheel into it then? @[TVA]Connor since it is 2 motors and only shoots?

im sure u answered this already but would the power expander also help power the rest of the robot as well as the main battery?

#35

No problem xD
Make sure that you understand what I said anove because it’s really useful to make sure you are using the expander in a consistent manner as well as using it to its fullest extent.

To answer the first question I would actually HIGHLY reccomend having the flywheel be on a separate power supply so the power drain would not affect the performance of the drivetrain, which is on the CORTEX. This also indirectly answers your next question; the power expander does not power the entire robot, only the motors connected to it. The power expander, simply put, blocks out the + and - from the CORTEX and replaces the power to the motors with its own power supply.

#36

Coolio. It should also help with making sure that the flywheel does have enough power to do what it needs to do and not go slow.

#37

Some one, at some point, will forget to plug the power expander in - that is where a program might come in handy. If I’m reading right, @[TVA]Connor, your program would keep the robot from moving if the pe isn’t plugged in - the benefit being that you can then reach into the field and plug it in even while the match is running because your robot hasn’t moved?

#38

Yep! :slight_smile:
It can save your life a great deal of times, especially in elims with BO1.

#39

I put a write up on what the girls did with our power expander here

#40