Chief Delphi - paper: New Control Functions

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Chief Delphi (http://www.chiefdelphi.com/forums/index.php)

- Extra Discussion (http://www.chiefdelphi.com/forums/forumdisplay.php?f=68)

- - paper: New Control Functions - Drive System Testing (http://www.chiefdelphi.com/forums/showthread.php?t=131593)

magnets

18-12-2014 15:18

Re: paper: New Control Functions - Drive System Testing

Toward the end of our match, we get the battery voltage down to 6.5V easily during normal driving. This will affect us.

Perhaps there could be an option to disable this "feature". I understand that it's there for a reason, but I'm comfortable cutting it a little closer.

Arpan

18-12-2014 15:24

Re: paper: New Control Functions - Drive System Testing

As a related question (I was never electrically closely involved) - could you regulate the 12V power being fed to the roborio?

cgmv123

18-12-2014 15:29

Re: paper: New Control Functions - Drive System Testing

Quote:

Originally Posted by Ether (Post 1414960)

How would that be implemented with a CAN connection without affecting other non-motor CAN devices?

(I could guess, but if anyone knows where this is documented would you please post a link)

CAN Speed Controllers need an enable 'flag' to be sent out over CAN before they output anything. That enable 'flag' (or lack thereof) presumably wouldn't affect devices that it doesn't need to.

Quote:

Originally Posted by Arpan (Post 1414994)

As a related question (I was never electrically closely involved) - could you regulate the 12V power being fed to the roborio?

The VRM does have enough capacity to run the RoboRIO, but that configuration will most likely not be legal for competition.

Thad House

18-12-2014 17:56

Re: paper: New Control Functions - Drive System Testing

Quote:

Originally Posted by Alan Anderson (Post 1414961)

Consider this an opportunity to do dynamic power management. You can monitor battery voltage and motor currents, and you should be able to come up with a way to keep the voltage from sagging low enough to trigger the automatic brownout.

Is there a way to calculate how much current it would take in total to drop battery voltage to a certain level? It seems like there should be, but I don't know where to start.

AdamHeard

18-12-2014 18:14

Re: paper: New Control Functions - Drive System Testing

Quote:

Originally Posted by Thad House (Post 1415031)

Is there a way to calculate how much current it would take in total to drop battery voltage to a certain level? It seems like there should be, but I don't know where to start.

You'd have to know the batteries current nominal voltage (no load), the batteries resistance (which will change some over the match), and the current current draw.

I imagine you could BS this enough to get a decent cutoff that is somewhat conservative.

Ether

18-12-2014 19:41

Re: paper: New Control Functions - Drive System Testing

Quote:

Originally Posted by cgmv123 (Post 1414995)

CAN Speed Controllers need an enable 'flag' to be sent out over CAN before they output anything.

so connect the dots. how does that relate to the original question.

and where is it documented.

Mark McLeod

18-12-2014 20:53

Re: paper: New Control Functions - Drive System Testing

Staged Brown Out when the battery voltage drops too low proceeds through the following stages:

Stage 1: 6.5-7.3v -PWM/CAN motor controllers/Relay outputs are cutoff, 6v power rail drops out
- Driver Station displays “Voltage Brownout”
- Servo power lost
- Disable pulse sent to CAN motor controllers, turning them off.
- Can result in robot stutter as motors pull the voltage low, get cut off, voltage rebounds, motors immediately pull voltage low again

Stage 2: 4.5-6.4v - , GPI outputs go High, 5v/3.3v power rails drop out
- Sensor brownout occurs, e.g., encoders!
- Stage 2 persists until battery voltage recovers to 7.5v

Stage 3:<4.5v - roboRIO drops out
- <3.5v the VRM/DLink drops out

Arpan

18-12-2014 21:01

Re: paper: New Control Functions - Drive System Testing

Quote:

Originally Posted by Mark McLeod (Post 1415090)

That slide posted earlier from Behind The Lines was inadvertently incorrect as it was taken from an early sketch of the notes we were developing for the show.

Here are the latest notes:

Staged Brown Out when the battery voltage drops too low proceeds through the following stages:

Stage 1: 6.5-7.3v -PWM/CAN motor controllers/Relay outputs are cutoff, 6v power rail drops out
- Driver Station displays “Voltage Brownout”
- Servo power lost
- Disable pulse sent to PWM and CAN motor controllers, turning them off.
- Can result in robot stutter as motors pull the voltage low, get cut off, voltage rebounds, motors immediately pull voltage low again

Stage 2: 4.5-6.4v - , GPI outputs go High, 5v/3.3v power rails drop out
- Sensor brownout occurs, e.g., encoders!
- Stage 2 persists until battery voltage recovers to 7.5v

Stage 3:<4.5v - roboRIO drops out
- <3.5v the VRM/DLink drops out

I'm really not certain why this was done; we regularly pull our batteries below 7 volts in normal operation. Why is there no regulated supply to the roborio? Is there a technical hurdle to accomplish this?

AustinSchuh

18-12-2014 21:14

Re: paper: New Control Functions - Drive System Testing

Quote:

Originally Posted by Ether (Post 1415068)

so connect the dots. how does that relate to the original question.

and where is it documented.

Not sure where it is documented (Q/A on the beta forums is the closest that I know of), but there is an explicit pulse/message sent out over PWM and CAN to disable all controllers as soon as the system enters the brownout state. The goal of this (whether you agree with it or not) is to save the rest of the system from browning out.

Ether

19-12-2014 00:02

Re: paper: New Control Functions - Drive System Testing

Quote:

Originally Posted by AustinSchuh (Post 1415100)

..there is an explicit pulse/message sent out over ... CAN to disable all controllers as soon as the system enters the brownout state.

that's the opposite of what cgmv123 posted:

Quote:

Originally Posted by cgmv123 (Post 1414995)

CAN Speed Controllers need an enable 'flag' to be sent out over CAN before they output anything.

AustinSchuh

19-12-2014 01:48

Re: paper: New Control Functions - Drive System Testing

Quote:

Originally Posted by Ether (Post 1415124)

that's the opposite of what cgmv123 posted:

I'm quoting what I was told by the engineer who implemented the brownout procedure when I asked for the gory details. Not sure where cgmv123 got his info. There should be some sort of heart beat on the bus in addition, but I don't have any hard information about how that works.

RufflesRidge

19-12-2014 08:20

Re: paper: New Control Functions - Drive System Testing

It doesn't describe the implementation to the detail Ether is asking about, but page 7 of the roboRIO user manual describes the brownout: https://decibel.ni.com/content/servl...r%20Manual.pdf

Alan Anderson

19-12-2014 09:46

Re: paper: New Control Functions - Drive System Testing

Quote:

Originally Posted by Arpan (Post 1415096)

There is a regulated roboRIO supply. It's built in to the roboRIO. It functions properly until battery voltage drops below 4.5 volts.

MrForbes

19-12-2014 10:13

Re: paper: New Control Functions - Drive System Testing

The new "low battery" indicator....a jerking robot. Wonder how long it will take teams (who don't read Technical Paper threads on CD) to figure this out? :o

Monochron

19-12-2014 11:12

Re: paper: New Control Functions - Drive System Testing

Quote:

Originally Posted by MrForbes (Post 1415187)

The new "low battery" indicator....a jerking robot. Wonder how long it will take teams (who don't read Technical Paper threads on CD) to figure this out? :o

Hopefully they will read teh RoboRio documentation and learn about it . . . but we'll see if they do. Though even that seems to not match what teams are reporting. Especially with CAN brownout as far as I can tell.

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