2015 Beta Testing - The Components are Here.

[Ether]

Originally Posted by FrankJ

It is a measure of the battery to pass current, not necessarily the number of electrons in the battery.

@Frank: You seem to be implying that the number of electrons in the battery changes as the battery supplies current. Was that your intent?

[Ether]

Originally Posted by Mark McLeod

The PWM signals are always 5v max.

What about the output impedance of the PWM 5v? Has anyone measured that? Or, is it specified somewhere?

Also, has anyone collected millamps vs voltage drop data across the input of the new motor controllers?

[Aren Siekmeier]

Originally Posted by Mark McLeod

The 3.3v/5v internal jumper only affects the DIO power output.
The PWM signals are always 5v max.
The PWM power is always 6v. The motor controllers have this line disconnected, so power on it doesn't affect them.

I was wondering today about how exactly all the signals are pulled up/down.

I've seen in the myRIO docs that all the DIO pins are pulled up to 3.3V with a 40k (or 2k for the shared I²C pins).

Are the main PWM pins pulled down to ground like they were 09-14? How strong/weak is the pull down?

And most importantly, if main PWMs are pulled down and all DIOs are pulled up, what is the roboRIO doing with the shared PWM pins on the MXP breakout?

[FrankJ]

Originally Posted by Ether

@Frank: You seem to be implying that the number of electrons in the battery changes as the battery supplies current. Was that your intent?

I was being a little bit tongue & cheek since the number of electrons in the battery really doesn't change with the state charge or current. It mostly related to the number of protons in the battery.

My real point was internal resistance is really a measure of the batteries ability to supply current under particular set of conditions. It says nothing about the actual efficiency of the chemical reactions going on in the battery. Others, who know a lot more than I do about batteries, have posted in effect that the amount of useful energy in the battery changes with the current or power. That matches my experience.

[controls weenie]

It appears that the MXP interface on the new RoboRio is only redundant connections from the outer edge RoboRIO connectors. If they are redundant, then why would anyone use this interface?

Thanks

[Mark McLeod]

They are not redundant, they are additional.

[Greg McKaskle]

It appears that the MXP interface ...

What lead you to that conclusion?

The MXP adds to the outer-edge I/O. Internally, there are two MXP buses, one is exposed via the MXP connector and the other was used to construct the outer-edge connectors.

If some of the documentation is misleading, please point it out.

Greg McKaskle

[Ether]

Originally Posted by Ether

Using a simple model of the battery as a fixed internal resistance of 0.011 ohms in series with a constant 12.7v voltage source...

I was hoping someone well-versed in lead-acid battery chemistry and thermodynamics would please comment on whether or not computing I²R losses with the above model is a useful (i.e. approximately correct) way to illustrate the observed phenomenon that energy delivery efficiency is substantially reduced at higher power levels.

[Caleb Sykes]

Originally Posted by Ether

I was hoping someone well-versed in lead-acid battery chemistry and thermodynamics would please comment on whether or not computing I²R losses with the above model is a useful (i.e. approximately correct) way to illustrate the observed phenomenon that energy delivery efficiency is substantially reduced at higher power levels.

I'm hoping this as well.

[controls weenie]

Here is my justification for assuming the MXP pins are redundant. Maybe I should use a better explanation instead of the word redundant.

How many ways are there to access I2C SDA? We can use the MXP pin 34 and the outer area of the RoboRIO connector labeled I2C SDA. Are these the traces the same? Are there really two independent I2C interfaces?

Where is the signal DIO0-9 accessed? MXP contains DIO0-9. There are also DIO0-9 on the outer edge of the RoboRIO. Are there two separate DIO0 signals? A and B ?

Greg mentioned that these are different buses. Does that mean the processor/FPGA can really control two I2C interfaces at the same time? I am not sure what he means by different buses. I thought two separate buses means that the FPGA controls the I2C-A and I2C-B independently.

Maybe some pins are redundant () and some are extra.

Sorry for the confusion.
Thanks

[SteveGarward]

As it says on the specs here:

I2C: 2 channels (1 dedicated, 1 shared)
<many other similar examples>

So 1 channel is available on the roboRIO, and is a dedicated I2C bus. There is also another on the MXP, which is a separate bus, but it's pins may be used as Digital I/O instead, if you want to. Not D I/O and I2C at the same time. But, there are two I2C channels.

The MXP is an expansion port, not just a move-all-the-onboard-IO-somewhere-else port.

[controls weenie]

>> It appears that the MXP interface ...

OK. I understand, now. The MXP is a powerful interface. Our team should be able to come up with many uses for this interface.

Thanks for clearing up my confusion.

[Mark McLeod]

Here's a photo of both SPI interfaces in use at the same time to duplicate devices that have identical SPI address. They worked fine without conflicts.

We did the same thing with the I2C ports, but I only have a photo of one port in use.

[controls weenie]

>> Has anyone put the PWM signals on an o'scope?

I had a buddy measure the PWM 6V line from the RoboRIO (Our team does not have RoboRIO and it was 5.7 volts with a fresh 12V battery. Does this concern anyone for driving several servo motors? What would happen to the 6V line if there are 6 servos running at the same time?

I measured 6.0V on the older cRio. Is there a current limit on the output of each of these RoboRIO PWM 6V (5.7V ) pins? I wanted to make sure I get all the power I need for driving several servos at the same time.

Thanks,

[Ether]

Originally Posted by Ether

What about the output impedance of the PWM 5v? Has anyone measured that? Or, is it specified somewhere?

Also, has anyone collected millamps vs voltage drop data across the input of the new motor controllers?

Alternatively, have any of the beta testers experimented with driving multiple (two or even more) motor controllers with one PWM.