Reading Battery Voltage

[implosionprez]

Our team put a jumper across the analog breakout, to get the battery voltage reading, just like last year. Is there something else or something different that has to be done, besides putting the jumper on, to get the classmate to recieve a battery voltage reading from the robot?

[jee7s]

Two thoughts:

1. Are you are supplying power to the analog breakout? If that wago connector isn't hooked up, the battery voltage feedback won't work.

2. Are you sure you have your battery jumper in the right place? There are two possible ways to get the jumper on there. One way will give you battery voltage, the other won't.

An easy way to check this is to use a multimeter to measure the voltage between the jumped pins and ground. If you get something close to battery voltage, you're good. If not, check your connections.

[implosionprez]

What do you mean between the jumped pins and ground? I've got the jumped pins alright, but where do I put the multimeter for ground?

[jee7s]

Ground can be found in many places on the robot.

The easiest (most obvious) is the black terminal of the power distribution board or the black side of the battery. Also, you can use the ground terminals on the analog breakout, or any of the number of ground pins on a digital sidecar (properly wired, of course).

Aside from that, I'm pretty sure the cRIO chassis will work, or a black terminal on a Jaguar, or the black terminal on a spike.

Like I said...many places. Just make sure you're using a multimeter in voltage mode, with the probes plugged into the voltage pins. You don't want to short anything out by accident.

[michael714]

Check out the manual at:
http://www.usfirst.org/uploadedFiles...rol_System.pdf

It explains how you have to run 12v to the analog breakout in addition to putting the jumper on in the correct position.

[Al Skierkiewicz]

Guys,
There is no 'ground' on the robot. There is only power supply common. The power common is connected at the negative battery input terminal on the PD. This is the same point as the case of the Crio, the negative lead of everything powered by the PD, and the case of previous years cameras. None of these items should be electrically tied to the frame of the robot. That means at minimum the Crio and last year's camera must be insulated from the frame of the robot.

[Matt Krass]

Originally Posted by jee7s

Aside from that, I'm pretty sure the cRIO chassis will work, or a black motor terminal on a Jaguar, or the black terminal on a spike.

The black motor terminal of the Jaguar is not a valid common node, it can be connected to both the positive or negative or neither depending on what the Jaguar is doing and how it is configured.

The black power input to the Jaguar (directly across) should be acceptable to use though, at least as far as multimeter probes go.

[jee7s]

Originally Posted by Matt Krass

The black motor terminal of the Jaguar is not a valid common node, it can be connected to both the positive or negative or neither depending on what the Jaguar is doing and how it is configured.

The black power input to the Jaguar (directly across) should be acceptable to use though, at least as far as multimeter probes go.

I don't have one in front of me right now, but I seem to recall that the inputs to a Jaguar use red and black screws and the outputs are colored green and white. The "black" terminal I was referring to was the input side of the Jaguar.

And, Al's right, there's no "ground" in the most literal sense on the robot. My use of "ground" could have probably been better worded as the EE colloquial "virtual ground" (i.e. the node of the circuit from which voltage is measured) or as "common". The chassis being electrically isolated (therefore there is no ground) is an important and sometimes overlooked detail in the FRC.

[Matt Krass]

Originally Posted by jee7s

I don't have one in front of me right now, but I seem to recall that the inputs to a Jaguar use red and black screws and the outputs are colored green and white. The "black" terminal I was referring to was the input side of the Jaguar.

And, Al's right, there's no "ground" in the most literal sense on the robot. My use of "ground" could have probably been better worded as the EE colloquial "virtual ground" (i.e. the node of the circuit from which voltage is measured) or as "common". The chassis being electrically isolated (therefore there is no ground) is an important and sometimes overlooked detail in the FRC.

Ah, that makes sense. I tend to kind of associate black to common in my head (which always seems to make for a bad day when I have to change a switch or light socket) so between that and you saying motor terminal, I misunderstood a bit.

The robot being isolated has lead to some interesting hilarity when abruptly grounded by a serial cable in the past, on the IFI control system. We had an amusing set of circumstances that truly and completely isolated the robot on a work table, and just unfortunate luck of having lots of little charges brought to it. By the time we grounded that sucker, it was.... not fun.