Re: 2015 Beta Testing - The Components are Here.
 

Tom, can I ask what your team is doing that is resulting in loose PWM cables? Do you do any sort of cable management or strain relief with zip ties? Could you post some pictures of your setup?

I ask as a fellow beta team. We haven't seen any issues yet and I'm just trying to figure out if it is something we need to be looking at more in depth than we are. I'm not saying the RoboRIO is perfect on this... I think there is a crap ton of wasted space between the pins where something could have been placed to help with strain relief but that being said, we haven't seen any issues with loose cables yet.

We're off to Rumble in the Roads to compete with the beta robot next week so I'm eager to see if this comes up on the field.

Re: 2015 Beta Testing - The Components are Here.
 

Would someone be able to confirm whether or not the VRM/PCM/RoboRIO ports have current monitoring? ie Do the three ports along the bottom of the PDP have current monitoring like the rest of the panel?

Also it would be good to know a little more detail about said current monitoring, things like resolution, accuracy, sample rate etc. Would someone be able to comment?

It would be interesting if the current measurement was good enough to integrate and sum the currents to be able to have a proper measure of battery charge, although this relies on accuratly knowing the state of charge at the beginning of the match.

Re: 2015 Beta Testing - The Components are Here.
 

The PDP does not monitor those dedicated power outputs directly.
The PDP does monitor:

• The current outputs of each (16) of the high power draw wago connectors
• Short circuits detected on each of the (16) wago connectors
• The incoming battery voltage
• The internal PDP temperature
• Any over-temperature fault

The PCM monitors compressor current, and faults for shorts and compressor over-current.

Resolution of the current monitoring is displayed to two decimal places, but we haven't independently verified the accuracy yet.
Haven't seen any specs for the sample rate or other internal details. Probably because the documents are still being written.

Re: 2015 Beta Testing - The Components are Here.
 

The integral of 60 amps for 2 minutes would be the same as 2 amps for one hour. Would the effect on battery charge be the same?

Re: 2015 Beta Testing - The Components are Here.
 

As far as coulomb counting goes, I would think so, but for it to be useful, you'd really have to know the state of charge of the battery before it was put into the robot, which is a non-trivial task.

Re: 2015 Beta Testing - The Components are Here.
 

I'd recommend looking at a battery data sheet before trying this, even if you know that a battery is fully charged.

Re: 2015 Beta Testing - The Components are Here.
 

At 60 amps you would get more losses through heat/resistance (P = I^2*R), including losses to the internal resistance of the battery? However the PDP will only let us get a measurement on the power being used by the robot, not the losses of the battery's internal resistance and it's cabling. ie the charge will be the same iff heat losses are zero. Whether this will be anything more than negligable however, I don't know.

Is it possible to get a good idea of the battery's initial condition from measuring it's voltage and internal resistance? If not what other information would you need? I know the battery beak does this and gives a percentage, but how accurate is this? Potentially you could have a system where you plug in a battery, measure it's characteristics before the match start and then do the intergral throughout the match to get the state of charge. This assumes that the power draw by the RoboRIO/PCM/VRM can be assumed constant or estimated accurately.

Finally what would you use this for? I'm not sure but it's 1am here and I'm bored and speculative :)

Re: 2015 Beta Testing - The Components are Here.
 

What (I think) Ether is trying to say is that the result of drawing 300 amps for 1 second and drawing 1 amp for 300 seconds will be equal to the same charge, but the effect on the battery's state of charge will be drastically different.

That said, it would be pretty cool to see how much power the robot uses over the course of an entire match.

Re: 2015 Beta Testing - The Components are Here.
 

Who says you're integrating current? You could easily integrate a function of current to get a much better model of battery state. But this requires a theoretical model.

However, the sampling rate will introduce some pretty significant integral error that stacks up over time.

Re: 2015 Beta Testing - The Components are Here.
 

We are laying out a board to pass all the signals to latching connectors. It will be completely passive but FIRST will still have to approve it - not sure if we can get it done in time. We are thinking of adding a second active circuit using common Arduino components, maybe a nav6 or something similar.

Re: 2015 Beta Testing - The Components are Here.
 

What easy function did you have in mind?

Re: 2015 Beta Testing - The Components are Here.
 

We just ran through 2 days of competition with the roboRIO, and did not have a single loose PWM cable. We did not do any type of cable retention or strain relief. I have not looked at which cables we specifically used, but our stock of PWM cables are a mixture of AndyMark, IFI, locally sourced servo cables, and cables ordered from deal extreme.

Re: 2015 Beta Testing - The Components are Here.
 

I'm not sure I understand this statement. FIRST does not need to approve a passive MXP board by the November deadline. It will be approved at inspection, when you prove to the inspector that it is passive.

Re: 2015 Beta Testing - The Components are Here.
 

Have you been happy with the cables from deal extreme?

Re: 2015 Beta Testing - The Components are Here.
 

Maybe he is talking about the PWM connectors not on the MPX plug. The preliminary rule on the blog does not cover the non-MPX pins. Picky distinction I know, but I have seen worse.