Re: 2015 Beta Testing - The Components are Here.
 

The bus switch that adjusts the signals passed to the FPGA is powered by a supply that is sourced by the buck-boost that powers the controller as a whole. That supply operates down to 4.5 V. That means that if you decide to power your encoder with a supply other than the one provided and the provided supply browns out, the signals will still make their way to the FPGA. As noted earlier, if your sensor depends on pull-up resistors (like limit switches or banner sensors or open-collector output encoders) then you will also need to add pull resistors connected to your external supply. You should be able to test this by either using the new power API to disable the 5 V supply manually or by installing a jumper between 5 V and Ground which puts the supply in protection.

Re: 2015 Beta Testing - The Components are Here.
 

Agreed. That is the next step. Thanks for the thorough description of what is going on. I really appreciate it.

Thanks Joe for describing the signal path to the FPGA, and working on improving the response time.

Hopefully we are all just getting worked up over nothing.

Re: 2015 Beta Testing - The Components are Here.
 

I am an expert in that! :rolleyes:

Re: 2015 Beta Testing - The Components are Here.
 

Does this means that we can use 5v devices (provided they read a 3v3 signal as high) without any risk of damaging the RoboRIO? I'm just thinking about various sensors and custom circuits that were designed for 5v that may perform differently at 3v3. They can probably be re-designed but it would be nice if that wasn't necessary.

Re: 2015 Beta Testing - The Components are Here.
 

yes

Re: 2015 Beta Testing - The Components are Here.
 

I'm looking at the power board/pneumatic bumper, and it seems to me that the pneumatics bumper has a relay/other driver built in to power the compressor. It also is powered from a fuse, which looks like
https://www.eficonnection.com/eficon.../mini_fuse.jpg , which is smaller than the spike fuse, meaning our normal 20 amp resetting breakers won't work here.

How do we replace the 20 amp fuse shown in (http://www.team358.org/files/program...mages/PDP2.jpg) that picture with an auto resetting one?

Re: 2015 Beta Testing - The Components are Here.
 

You don't...

Re: 2015 Beta Testing - The Components are Here.
 

If you use a 20 amp not resetting fuse, as shown in the picture and the robot's battery is a little low, it trips when the compressor starts, leaving your robot without a compressor in the middle of the match. It's happened to me before.

The people who make this know this (as the manual has an exception for this), so either I'm not understanding how this works, or their will be issues with the fuse getting blown during matches. I'm betting that I don't understand how this works, and was wondering if somebody who actually has the part knows how it would work.

Re: 2015 Beta Testing - The Components are Here.
 

Given both the pneumatic module and the power distribution board are connected to the RoboRIO via CAN, there is a possibility that these devices are monitoring the current to prevent fuse blowouts that the comparatively simplistic implementation "on off with a relay" on the old system couldn't compensate for.

Re: 2015 Beta Testing - The Components are Here.
 

To my knowledge - we didn't see any blow fuses during Alpha testing.

The CTRE guys will need to answer this one. I'll fire them an email.

Re: 2015 Beta Testing - The Components are Here.
 

You can get self-resetting circuit breakers in this form factor fairly easily.

Amazon
Grainger

Re: 2015 Beta Testing - The Components are Here.
 

This was exactly our concern when we sat down to wire it up the first time. Fortunately, the PCM is monitoring the current on the compressor and each of the solenoid channels and will disable the channel temporarily if then current is too high. I have not heard of a blown fuse on the PCM yet.

Re: 2015 Beta Testing - The Components are Here.
 

Self-resetting breakers usually do not trip as precisely as fuses. If the downstream circuits really cannot handle >20A, even for a second, you ought to use a fuse.

Re: 2015 Beta Testing - The Components are Here.
 

Fine, but aren't we're talking about an application (powering the compressor) where self resetting circuit breakers have been used successfully for some time?

Re: 2015 Beta Testing - The Components are Here.
 

With different hardware, yes. From what I've been told in the past, Vex (the makers of the spike relay) did specific testing with a circuit breaker to validate it as safe before FIRST allowed it to be used for compressors in the rules. That's the only reason teams were allowed to replace the provided fuse with a breaker for use with compressors.

For FRC usage, breakers, in general, are present to protect the wiring, not the components attached to that wiring. For this 20A fuse, it could protect the PCM from over-current if (for example) something gets shorted out... but my guess would be that the fuse is there to prevent the PDP from burning out by drawing too much current from those outputs. It's probably there to protect against a short much more than to protect downstream circuitry.