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  #91   Spotlight this post!  
Unread 04-15-2012, 03:12 PM
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Re: Intermittent connection on field only

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Originally Posted by rsisk View Post
Was talking with 846 at SVR and they made the comment about the radio increasing power requirement when it started to detect dropped packets. They supposed that was part of their issued with dropped communications. The ncreased power requirement was causing a a marginal compnent (PDB in their case) to fail
It would only get worse with packet loss. TCP is a reliable protocol so it'll keep trying until it times out to deliver the packets you've asked to be sent. So basically if something starts to cause issues it'll try again, causing congestion, then it'll try some more. Eventually it's a storm.

One of the things I suggested to Team 11 was to change the timing behavior of the driver's station TCP stack so that it would either wait longer or give up sooner for a successful delivery. They could also do that on their robot mounted laptop if they were using it. This would help reduce the load on the network but with so little time to test might have cause unpredictable control issues for them. Course in their case the damage to the DC-DC converter could already have been done so it might have helped before that damage happened but in this case possibly not.

A camera using TCP would also set up this situation. It's really not the best protocol for streaming live video content (if you loose live video data...give up and get more). So if the D-Link AP does draw more power when packets are lost then this would be a great way to cause a problem.

I'm gonna leave my questions on the floor for other input:

Did anyone fully load test the D-Link AP power system?

Did anyone measure the D-Link AP power requirements when the robot was running and moving on a competition field (using 2 multimeters, one as a voltmeter and one as an ammeter on MAX/MIN would be a good start...be aware that's not a perfect test)?

Last edited by techhelpbb : 04-15-2012 at 03:19 PM.
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Unread 04-15-2012, 03:17 PM
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Re: Intermittent connection on field only

Expanding on the potential of an increased load on the D-Link power circuit...

We know that teams have had a hard time duplicating this issue at their own facilities. We also know that some events have not had as many reported issues (FiM and MAR district events for example).

Looking at the events where issues have occurred they seem to all be the traditional regional-type event in an arena/larger type venue, perhaps largely taking place in a city. In contrast, smaller events are taking place in high schools and other such venues where the environment is much more controlled.

Are we looking at a situation in which the D-Link AP is exceeding it's published power specifications due to it dealing with "normal" interference from various sources such as campus/venue WiFi, large number of teams with their router on in bridge mode, other devices such as bluetooth? As a result of this increased load are we damaging or pushing the DC-DC converter or PDB out of spec or degrading to out of spec over time? Are we or specific teams (for whatever reason) hitting some issue in the firmware/baseband of the D-Link? I doubt anyone could argue that we aren't exactly using the D-Link in its designed environment...

I'm going to see if I can get one of our DC-DC converters and one of our "not for competition use" PDB and attempt to load them down to their specification and beyond.
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Last edited by Deetman : 04-15-2012 at 03:21 PM.
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Unread 04-15-2012, 03:41 PM
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Re: Intermittent connection on field only

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Originally Posted by techhelpbb View Post
I am confused as to how you arrived at this conclusion that I don't understand what you're trying to communicate.
Two things you said gave me that impression. You challenged the claim that communication can be maintained at a battery voltage of 5 volts, and you responded to a mention of the PDB's boost-regulated 12 volt output with a reference instead to violating the input specification of the 12v-to-5v converter.

I only brought up the low-voltage capabilities of the system because it looked like you said the robot was losing communication at slightly above 9 volts, and that would be a symptom of either a faulty PDB or incorrect wiring.

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It really does not explain why these problems are so hard to troubleshoot off the competition field seemingly regardless of the number of tests run or the equipment.
I haven't had the opportunity to test things using a known-faulty setup, but I have seen hints that the wireless portion of the D-Link quits working if the power drops even a little below 5 volts, while the wired portion continues to function through the sag. If that's indeed the case, then a bad PDB or CPR360 (or incorrect wiring) could result in loss of communication on the field but perfectly good operation in the pit. It's also true that a robot is rarely working as hard when it's up on blocks than when it's trying to turn on a carpeted surface, so a marginal power system is much more likely to reveal itself while the robot is actually running a match.

Quote:
1. If we had the ability to measure the voltage feeding the AP on the robot at all times that would help, I have a circuit that could perform this function, but because it touches those power leads it's probably illegal on the field.
What rule would keep you from doing this on a competition robot?
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Unread 04-15-2012, 03:50 PM
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Re: Intermittent connection on field only

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Originally Posted by Alan Anderson View Post
If communication is lost at 9 volts, something is wrong with the robot.
Well aware of that Alan. I can't speak for others, but low voltage was not a factor for us.
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I'd really like to hear their experiences and what they found out.
See my post in some other related thread, and jteadore's post above.
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Check for metal shavings in your crio bay and ports.
I can't speak for others, but this was not an issue for us, absolutely positively.

As I mentioned in my other post, we are heck-bent on duplicating this at home - after CMP though.
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Unread 04-15-2012, 06:22 PM
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Re: Intermittent connection on field only

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Originally Posted by Alan Anderson View Post
Two things you said gave me that impression. You challenged the claim that communication can be maintained at a battery voltage of 5 volts, and you responded to a mention of the PDB's boost-regulated 12 volt output with a reference instead to violating the input specification of the 12v-to-5v converter.

I only brought up the low-voltage capabilities of the system because it looked like you said the robot was losing communication at slightly above 9 volts, and that would be a symptom of either a faulty PDB or incorrect wiring.
Well the Team 11 robot is >not< loosing communication at slightly above 9 volts norminal on the drivers station. Our robot just isn't a useful system when the driver's station nominally gets that low so it doesn't really matter if you can communicate to a robot that won't perform. Again that voltage was never that low. I respect you and the point you thought you were making so let's move on.

Quote:
I haven't had the opportunity to test things using a known-faulty setup, but I have seen hints that the wireless portion of the D-Link quits working if the power drops even a little below 5 volts, while the wired portion continues to function through the sag. If that's indeed the case, then a bad PDB or CPR360 (or incorrect wiring) could result in loss of communication on the field but perfectly good operation in the pit. It's also true that a robot is rarely working as hard when it's up on blocks than when it's trying to turn on a carpeted surface, so a marginal power system is much more likely to reveal itself while the robot is actually running a match.
Wouldn't be applicable to Team 11. As I've stated we've driven both our robots (we have 2) around on our regulation carperted test field, on other competition fields and other practice fields for full tests of opreration more than 50 times. Sometimes quite aggressively. If the carpet induced load was the prime factor we'd have seen it quite long ago. We did not see this problem before this event and that's a whole lot of hard driving by a wide variety of drivers with a wide variety of experience driving our robots (and cars I hope).

Though I absolutely agree that if the loading of the system were the factor not testing on the regulation surface would be a bad idea. I can assure you, at least with our design on Team 11, it's been tested very well. So this isn't the hidden cause for us and I personally know it's also not the issue for several other effected teams.

Additionally when my oscilloscope was used to test another team's robot at the MAR Mount Olive event they did try loading the wheels while the robot was off the floor along with powering up other devices in different ways. The power from the battery did not sag anywhere into the terrority you're describing from what I was told.

Quote:
What rule would keep you from doing this on a competition robot?
Please see rule R42, part B:

"The wireless bridge power feed must be supplied by the 5V converter (model # TBJ12DK025Z) connected to the marked 12 Vdc supply terminals located at the end of the PD Board (i.e. the terminals located between the indicator LEDs, and not the main WAGO connectors along the sides of the PD Board). No other electrical load can be connected to these terminals (please reference any 2012 Robot Power Distribution Diagram posted on the Kit of Parts site for wireless bridge wiring information."

If you only look at that rule you'd be breaking it if you insert a current sense resistor into the path of the wireless bridge's power or put a high impedance circuit in parallel with it's input. However, I'm aware of this:

Rule R47:

"Custom circuits shall not directly alter the power pathways between the battery, PD Board, speed controllers, relays, motors, or other elements of the Robot control system (including the power pathways to other sensors or circuits). Custom high impedance voltage monitoring or low impedance current monitoring circuitry connected to the Robot’s electrical system is acceptable, if the effect on the Robot outputs is inconsequential."

Problem is, if you're a real stickler it doesn't actually call out the wireless bridge.

If you disagree with my interpretation of this then we are back to my original question as you'd interepret it as an allowed thing to do:

Did anyone measure the D-Link AP power requirements when the robot was running and moving on a competition field (using 2 multimeters, one as a voltmeter and one as an ammeter on MAX/MIN would be a good start...be aware that's not a perfect test)?

So if you think that rule will allow you to measure that information, you can add putting a custom circuit on the D-Link AP power and logging the data (probably into the control system).

Now additionally let me point this out if you create this custom monitoring circuit before build season...like I did...you're dancing with Rule R18 because I don't sell it yet:

"Please note that this means that Fabricated items from Robots entered in previous FIRST competitions may not be used on Robots in the 2012 FRC. Before the formal start of the Robot Build Season, teams are encouraged to think as much as they please about their Robots. They may develop prototypes, create proof-of-concept models, and conduct design exercises. Teams may gather all the raw stock materials and COTS Components they want."

The open source exclusion might not apply because I never fully put up the schematics either:

"Example: A different team develops a similar solution during the fall, and plans to use the developed software on their competition Robot. After completing the software, they post it in a generally accessible public forum and make the code available to all teams. Because they have made their software generally available (per the definition of COTS, it is considered COTS software and they can use it on their Robot)."

Then there's the whole it was built by a mentor not a student that bothers me but isn't against the rules.

If you use commercial multimeters then you avoid this. However, then you have loose test equipment you've put on your robot. Could get it reinspected...but again...had anyone done this? Oh and by the way, the multimeters reading DC aren't the best choice entirely because they will check very infrequently compared to say an oscilloscope so a short surge or drop might slip right past. Can't say how fast the cRIO can monitor that information depends on a lot of factors.

Last edited by techhelpbb : 04-15-2012 at 07:29 PM.
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Unread 04-15-2012, 06:44 PM
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Re: Intermittent connection on field only

Double post (lost Internet access sorry).
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Unread 04-15-2012, 07:43 PM
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Re: Intermittent connection on field only

If you would like to add such a monitoring device, you may be able to get an exception with the consent of the LRI and the FTA. They will need to contact FRC HQ, so ask well in advance.
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Unread 04-15-2012, 08:17 PM
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Re: Intermittent connection on field only

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Originally Posted by EricVanWyk View Post
If you would like to add such a monitoring device, you may be able to get an exception with the consent of the LRI and the FTA. They will need to contact FRC HQ, so ask well in advance.
Thank you. I'm also hoping to get someone's attention at FIRST in the near future to discuss making something like I am describing clearly acceptable in a general sense without the exception.

It might mean I have to make some more and give them away to achieve that but first I need to be clear on the process involved. I'm always happy to help but I'd rather not just blow money and time into the breeze. I have, I hope, already started this process.

Last edited by techhelpbb : 04-15-2012 at 08:21 PM.
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Unread 04-16-2012, 07:10 AM
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Re: Intermittent connection on field only

Guys,
A few thoughts here. The radio boost/buck +12 volt regulator on the PD is capable of a few amps. There is a failure mode on the external 5 volt regulator that effectively turns it into a big resistor making about 7 volts when the battery is at a normal level and then drawing enough current to drag the +12 volt regulator down with varying battery. (I do not have accurate data on this phenomena since a replacement 5 volt regulator fixes the problem.) When connected to a battery instead of the regulated +12 volt output, the failed +5 volt regulator will actually follow the battery voltage when it falls below 7 volts.
The radio is designed to operate at 1.5 amps (less on the newest model) which both the PD and the 5 volt regulator are designed to supply. To my knowledge the bridge does not dynamically adjust power output but does have a power setting in one of the setup screens. (see manual for details) I am under the impression that the return to factory defaults and the WPA encryption routine sets the power output to a normal value. There is a feature of this device that adjusts power delivered to the ethernet ports and that might be where the confusion lies with varying output power. I could not find any reference to RF output power on this device.
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Unread 04-16-2012, 10:09 AM
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Re: Intermittent connection on field only

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Thank you. I'm also hoping to get someone's attention at FIRST in the near future to discuss making something like I am describing clearly acceptable in a general sense without the exception.

It might mean I have to make some more and give them away to achieve that but first I need to be clear on the process involved. I'm always happy to help but I'd rather not just blow money and time into the breeze. I have, I hope, already started this process.
I just wanted to update this topic as I successfully made contact with U.S. FIRST regarding what I was proposing as a 'custom test circuit' and I now have a bearing on how to get it into at least the approved parts.

Basically I need to get a sample as close to production as possible to the US FIRST KOP team before the end of August. They'll check it over a couple of weeks and once it's been rung out along with all the business details (how it's getting made, in what quantity, how can teams get it, what's the cost, etc...) They'll issue an approval if it's warranted to be included in the list of approved hardware they finalize in September.

If somehow it ends up in the KOP I would need to deliver product to them by October for distribution purposes. Otherwise I could sell or give away product without being able to declare it approved by FIRST for competition usage. Obviously the NDA for the approval of the hardware would prohibit any discussion before January of whether it's approved or not.

My appreciation to FIRST for providing me a great place to start working from.

In the mean time I'm considering making a few simple test versions to send out for testing on real fields. Obviously per Eric's post since these aren't approved you'll probably need some approval from US FIRST if you want to try something like this on a live competition field.

Last edited by techhelpbb : 04-16-2012 at 10:16 AM.
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Unread 04-16-2012, 12:14 PM
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Re: Intermittent connection on field only

What is the nominal minimum voltage that can be provided by the DC-DC converter connected to the D-Link AP before things start to become a problem?

Keep in mind that if there's ripple on the DC power supply I need the voltage at the lowest peak of that ripple from the robot 'ground'.

I know it should be 5V, but does anyone know just how far below 5V you can go before you might start having problems?

There must be a window of regulation that is acceptable (for example 4.95V - 5.1V).
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Unread 04-16-2012, 01:44 PM
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Re: Intermittent connection on field only

You know we haven't correlated the possibility of RF pickup on the power wiring to the DAP yet. I haven't thought to check for that but I have seen many robots using a long power cord simply wound up/folded up and secured with a ty wrap. It is possible that large amounts of RF energy are simply walking in on the power wiring. Maybe what we should do is bring a bunch or ferrite chokes with us to St. Louis and give them a try. We should also not rule out intermittant power connectors putting noise on the power input that actually makes it through to the data circuitry.
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Unread 04-16-2012, 01:53 PM
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Re: Intermittent connection on field only

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Originally Posted by techhelpbb View Post
Rule R47:

"Custom circuits shall not directly alter the power pathways between the battery, PD Board, speed controllers, relays, motors, or other elements of the Robot control system (including the power pathways to other sensors or circuits). Custom high impedance voltage monitoring or low impedance current monitoring circuitry connected to the Robotís electrical system is acceptable, if the effect on the Robot outputs is inconsequential."

Problem is, if you're a real stickler it doesn't actually call out the wireless bridge.
Can't answer your other questions unfortunately but I do believe that the wireless radio is included in R47 as it broadly describes the "Robot's electrical system" as the place that these devices may be connected and the previous sentence refers to "other elements of the Robot control system" which would almost certainly include the wireless radio.
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Unread 04-16-2012, 02:09 PM
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Re: Intermittent connection on field only

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Originally Posted by RufflesRidge View Post
Can't answer your other questions unfortunately but I do believe that the wireless radio is included in R47 as it broadly describes the "Robot's electrical system" as the place that these devices may be connected and the previous sentence refers to "other elements of the Robot control system" which would almost certainly include the wireless radio.
I've got a couple of things that I'm trying to finish for Championships. Apparently Team 11 is on the way out there. If I have the time I'll clean up what I have and send it out that way.

I'm a little dubious right now of what I can send out there. I have a circuit I made that can be set with a small handheld setup I made, but you don't really need all that stuff if you just use potentiometers and resistors for setting it up. Even with all those bells and whistles the robot mounted part is tiny and light.

Basically I'm trying to get a grasp on the range of input voltages it needs to accept. If the range is large then I should try the digital setup I made. If it's small then I can probably trim up a few common settings and use that.

If I just stick with working around the 5V supply going into the D-link AP it comes down to just how low can that voltage go before we need to call that a problem. hence my question above. I should think that number is in the tenths or hundreths of 5V.

So if we read this as perfectly acceptable then it comes down to actually doing it during a competition. I basically need to move my butt. Otherwise it'll have to be tested off season on a real competition field (I know it works I just never used it in a competition).

The good news is that this thing is at it's heart a latching analog comparator. So even if noise on the DC power supply reduces the voltage for a split second this will see it (and if not things will need to get expensive to test because that would mean it exceeds the performance of the integrated op-amps I used). At the moment all this thing does is constantly look for the voltage below the setting and if it happens it lights an LED and keeps it that way. Seems utterly trivial but it can do it on the moving robot and much more completely than a DMM.

Last edited by techhelpbb : 04-16-2012 at 02:34 PM.
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Re: Intermittent connection on field only

Quote:
Originally Posted by techhelpbb View Post
What is the nominal minimum voltage that can be provided by the DC-DC converter connected to the D-Link AP before things start to become a problem?
Besides going far enough below 5 volts to cause the bridge to shut down entirely, we don't know what power deviations can cause problems. That's what your proposed datalogger circuit can help us determine.

Quote:
The good news is that this thing is at it's heart a latching analog comparator...
Oh. That's not going to be very useful in characterizing things. It can only give a useful answer if we already know exactly what the question is.

Last edited by Alan Anderson : 04-16-2012 at 03:12 PM.
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