2015 Beta Testing - The Components are Here.

[AdamHeard]

Originally Posted by FrankJ

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.

If that's the case then I would say no rule covers it, and it is therefore legal.

Any board that interfaced w/ the PWM outputs would be a glorified connector. This is assuming it is all signal pass through, with no active components.

If this is considered illegal, we're entering a realm of craziness by dictating to teams exactly how they are to interface in terms of connectors that have no affect on signal.

[Joe Ross]

Originally Posted by AdamHeard

Have you been happy with the cables from deal extreme?

Yes, no problems. The only negative is you have to remove the shroud around the male pins, but that is very easy.

[Aren Siekmeier]

Originally Posted by Ether

What easy function did you have in mind?

I don't, one would have to find a suitable model, for example one that is consistent with your statement about 60A for a minute vs 1A for an hour.

I'm just saying that once you have such a function, it's just as easy to numerically integrate that as it is the current itself.

[Ether]

Originally Posted by compwiztobe

You could easily integrate a function of current...

Let S be the state-of-charge.

Your statement is equivalent to saying that

dS/dt = f(I)

But how do you know that the rate of change of state-of-charge at a given instant in time depends only on the instantaneous current at that time?

For example, how do you know that dS/dt is a function of I only, and not, say, a function of both I and S: dS/dt = h(I,S) ?

This would make an interesting pre-season project.

[wireties]

Originally Posted by Joe Ross

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.

Strictly speaking, it is not just an MXP board. This will connect to all the digital and analog I/O pins. And FIRST will not allow that without approving the design. Make sense?

[wireties]

Originally Posted by FrankJ

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.

Exactly, but not everything - just the MXP, DIO, AIO, PWM, I2C, RSL, RS232 and relay pins.

If I can get it approved, do you CDers think people might buy it?

TIA

[wireties]

Originally Posted by AdamHeard

If that's the case then I would say no rule covers it, and it is therefore legal.

I hope so! But I'm gonna run it by FIRST to make sure. They want 5 of the boards for some reason - crazy. I'm hoping to get a couple betas to try it and send a single unit to FIRST.

[wireties]

Originally Posted by Joe Ross

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.

That is great news! But I can't get the memories of the old IFI boards out of my head - they were a constant headache. To be honest, my OCD is probably kicking in a bit - the idea of unsecured connectors keeps me up at night (we make navigation equipment for the Navy).

[AdamHeard]

Originally Posted by wireties

I hope so! But I'm gonna run it by FIRST to make sure. They want 5 of the boards for some reason - crazy. I'm hoping to get a couple betas to try it and send a single unit to FIRST.

I must be missing something, where does it say passive connections need to get approved?

If I make a 27" long PWM cable custom, doesn't that therefore need approval?

[wireties]

Originally Posted by AdamHeard

I must be missing something, where does it say passive connections need to get approved?

If I make a 27" long PWM cable custom, doesn't that therefore need approval?

I agree with you - just trying to be thorough. We are thinking that anything not in a MXP form factor will get special attention. Proving that is is passive during inspection would be a big hassle (possibly removing board so inspector can see the solder side etc).

[Caleb Sykes]

Originally Posted by Ether

Let S be the state-of-charge.

Your statement is equivalent to saying that

dS/dt = f(I)

But how do you know that the rate of change of state-of-charge at a given instant in time depends only on the instantaneous current at that time?

For example, how do you know that dS/dt is a function of I only, and not, say, a function of both I and S: dS/dt = h(I,S) ?

This would make an interesting pre-season project.

What is the definition of state of charge?

I know that a "fully charged" battery should have 100% charge, but what is the criterion for a battery to be 0% charged? Would it be a terminal voltage of zero? For a given battery, is S a function of terminal voltage alone?

[Ether]

Originally Posted by inkling16

What is the definition of state of charge?

I will re-direct your question to "timytamy":

Originally Posted by timytamy

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.

[timytamy]

Originally Posted by inkling16

What is the definition of state of charge?

Interesting question, I'm hoping someone more qualified will step in but I'll try anyway.

The easiest answer is that 100% of charge is when 204Wh (12V*17Ah) of energy can be drawn from the battery, and 0% is when 204Wh has been drawn. This of course requires a few assumptions, such as we ignore any aging affects and the battery is able to push reasonably large currents at near 12V (say 10.5V and above).

Maybe a more useful answer is that 100% corresponds to what a useful charger will say is charged, and 0% is the point at which most robots will no longer completely function (ie have difficulty driving/turning). Perhaps you could go one further and say 0% is when non-motor electronics start failing (such as the RoboRIO or the VRM) and have another point, say 10% which is when robots stop turning. ie 0% is when the robot can no longer "idle". This one would require characterising some batteries in that you would need to find an amount of energy that you could draw before reaching this point.

An even simpler answer is that state of charge is just what a battery analyser such as the Battery Beak or the CBA will say. Does anyone know how the Battery Beak works out what it's state of charge is?

Unless we can get an answer on how the CBA/Battery Beak defines state of charge, I'd suggest we go with the 0% - idle, 10% - motors, 100% - off chargers model for this discussion. Of course I'd be happy to be corrected by someone with a better understanding of lead acid batteries.

[Caleb Sykes]

Originally Posted by timytamy

Interesting question, I'm hoping someone more qualified will step in but I'll try anyway.

The easiest answer is that 100% of charge is when 204Wh (12V*17Ah) of energy can be drawn from the battery, and 0% is when 204Wh has been drawn. This of course requires a few assumptions, such as we ignore any aging affects and the battery is able to push reasonably large currents at near 12V (say 10.5V and above).

It seems that you are saying that state of charge has no formal definition, but rather that it is defined uniquely for each system to provide a useful value representing the state of a system. Would you agree with that?

Originally Posted by timytamy

Maybe a more useful answer is that 100% corresponds to what a useful charger will say is charged, and 0% is the point at which most robots will no longer completely function (ie have difficulty driving/turning). Perhaps you could go one further and say 0% is when non-motor electronics start failing (such as the RoboRIO or the VRM) and have another point, say 10% which is when robots stop turning. ie 0% is when the robot can no longer "idle". This one would require characterising some batteries in that you would need to find an amount of energy that you could draw before reaching this point.

If we are defining S for FRC batteries ourselves, then I would suggest the relationship S = Eavailable/Emax where Emax is the difference in energy of the battery between the state that some standard charger says "fully charged" and some standard 0 energy value E0, such as the energy at which non-motor electronics on the robot start to fail. If we just define these two points, the relationship between S and E is linear, but if we also try to define a third point (such as the point at which motors start failing), we will not generally be able to use a linear relationship to describe S in terms of E.

Originally Posted by timytamy

An even simpler answer is that state of charge is just what a battery analyser such as the Battery Beak or the CBA will say. Does anyone know how the Battery Beak works out what it's state of charge is?

Unless we can get an answer on how the CBA/Battery Beak defines state of charge, I'd suggest we go with the 0% - idle, 10% - motors, 100% - off chargers model for this discussion. Of course I'd be happy to be corrected by someone with a better understanding of lead acid batteries.

I too would be interested to learn how the battery beak defines state of charge. If the beak says 78% charged, does that tell me anything quantitative about the battery or does it just mean I should leave it on the charger longer before using it in a match?

[SteveGarward]

Originally Posted by Tom Line

On the roboRIO, loose PWM's are our biggest complaint. We've already resorted to hot glue.

We also had issues with cables coming off easily, both bought pre-made cables, and ones we make ourselves. Older, well used cables were especially an issue.

Originally Posted by kstl99

I was thinking more of a sort of clip that would sit between the device and the board it is mounted on that would bend around and lock the connector in place. The clip part would be like the clip on the digital side car.

We've been working on a part to be 3D printed that would (hopefully) help with cables coming off, and also the large space between the pins. We've just published a blog post about it here. We are still iterating over the design. But, you'll get the idea of where we're headed.