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  #1  
Old 02-24-2011, 01:18 AM
C@meron C@meron is offline
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Vexnet Keys

As vex has recently moved from the stone age of crystals to super-fancy wifi (!!!!), most people were happy



HOWEVER, there is one problem; the keys often fail and short out



this is rumored to be an electrical problem, and if so, is it dangerous to have anyone touch the robot?



and, furthermore, why does it take so long to connect? sometimes it feels like your robot is having a BSOD



does anyone have a solution to this?

THANK YOU

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  #2  
Old 02-24-2011, 07:37 AM
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lyncas lyncas is offline
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Re: Vexnet Keys

Thanks for providing the daily humor !

We have been using VEX keys & cortex systems for a while. They seem to be fairly robust but sometimes after massive firmware changes in RobotC , we have noticed erratic behavior. We are hoping these are just software programming problems that will go away in due time.
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Old 02-24-2011, 08:40 AM
TPRMentor TPRMentor is offline
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Re: Vexnet Keys

We have been using this system all season, and lately our link is dropping out during matches. The last 3 competitions, we lost link 2 or 3 times in matches, but we havent been able to find the problem or solution. We are going to try a new USB extension cable next. If anyone has any suggestions, they would be appreciated. As a side note, normally the robot just dies and sits for about 20 seconds, then relinks. The last time we lost link, the robot remembered the last command it received and drove backwards into another robot and we could not stop it.
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Old 02-24-2011, 11:52 AM
Chuck_Glick Chuck_Glick is offline
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Re: Vexnet Keys

The biggest culprit we have seen at our events is teams failing to plug in their backup battery or have a charged/new backup battery installed. Most failures are a result of teams pulling too much current and resetting their controller, which can cause a vexnet "failure".

"Remedies"

-Make sure you are not pulling over 4amps per breaker (ports 1-5/6-10; each set has ONE 4amp breaker)

-Use either a NEW backup battery each match OR make sure it has a full CHARGE before each match.

-PLUG IN your backup battery


If none of the above fix your problems, go back and re-flash your cortex AND drive controller(s) with the latest firmware; then re-pair them with each other. This SHOULD fix all issues that you are having and if not contact IFI with a detailed description of your issue and the steps you have taken to fix the problem.


*All of the above have worked for KTOR and our mentored teams. Experiences stem from cortex beta testing as well as numerous events run as tech support.*

-Chuck
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Old 02-24-2011, 12:33 PM
TPRMentor TPRMentor is offline
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Re: Vexnet Keys

Thank You for the information, we normally have a freshly charged backup battery, but have not looked into the amperage we are pulling. We will look into that. Thanks Again.
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Old 02-24-2011, 01:44 PM
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murdomeek murdomeek is offline
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Re: Vexnet Keys

Chuck pretty much summed it up
a tip about back-up batteries:
if they are NOT fully charged and you plug in a low-dead back up battery, then the vexnet will not link AT ALL
(as in you cannot even control the robot)
this has happened to many teams that used the 9v battery last few competitions
the fix for that is of course to unplug the backup batt

long story short: its better to have NO 9v batt then a dead one...
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Old 02-25-2011, 07:43 AM
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Re: Vexnet Keys

Quote:
Originally Posted by TPRMentor View Post
Thank You for the information, we normally have a freshly charged backup battery, but have not looked into the amperage we are pulling. We will look into that. Thanks Again.
Do any teams suggest a clip on Amp-meter to watch current usage ?

Maybe VEX should consider making a current sensor since drawing too much current this year is a big problem with the new motors as well.
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Old 02-25-2011, 01:08 PM
jgraber jgraber is offline
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Re: Vexnet Keys

Quote:
Originally Posted by lyncas View Post
Do any teams suggest a clip on Amp-meter to watch current usage ?

Maybe VEX should consider making a current sensor since drawing too much current this year is a big problem with the new motors as well.
I use a $3 (on sale) DVM from harbor freight, works up to 10A.
Make a Battery extension cable, and put the DVM in series with the positive line.
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Old 02-25-2011, 01:50 PM
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Quazar Quazar is offline
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Re: Vexnet Keys

Quote:
Originally Posted by lyncas View Post
Do any teams suggest a clip on Amp-meter to watch current usage ?
I picked up one of these with my SparkFun Free Day winnings, though I haven't had a chance to play with it yet. My idea was to monitor current load in software and have the robot automatically reduce power when the load exceeds 4A or so.

It would be very cool if IFI came out with a smart power expander or smart motor controller that attached via IC or UART and had an ammeter like this built-in.

Cheers,
- Dean
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Old 03-12-2011, 01:43 AM
bobsalive bobsalive is offline
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Re: Vexnet Keys

After extensive testing by borrowing a lot of vexnet keys from other teams, we found that apparently two of our vexnet keys are duds. They take a long time to connect with any other vexnet key, and then the connection cuts out quickly, with or without backup battery, with or without extension USB cable. Unfortunately it looks like we're going to have to buy two new vexnet keys, which is a problem because they're reasonably expensive and we can't afford them.
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