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Eagle

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Reply with quote  #1 
We are a Junior High team and no experience programming.  Using  Vex.  That much I know.  Our robot started (at Mall Day) losing connection and we have to bring the remote close to the cortex and wait for it to re-connect.  Any ideas?
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jgraber

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Reply with quote  #2 
Losing connection is not a programming problem, but it is a Vex problem.

Describe in more detail : 
A What does losing connection look like?   
B What color and blink are all the LEDs on Cortex & Joystock ?
C Describe what the robot is doing when you lose connection.
D Does your hub provide Red/Black Power Pole connectors for the battery?
E Whack your robot frame with a hammer,  does the jolt cause losing connection?  
F If you leave the robot on but not moving, and back away with the joystick, what distance do you lose connection,  in that circumstance?

Ideas: 
1 Take away the cell phones from the driver and spotter.
2 If you lose connection when motors are straining, you may be drawing too much power.
3 You can ask to try new Vexnet keys at Game day check-in, see if that helps.
4 You can use a team provided 18" USB extension between Cortex and Vexnet USB key, and put the Vexnet up high in the air like an antenna, and away from your motors and cortex.
5 Don't mount your Cortex and Vexnet key directly under the Arm motor.  Motors and even the motor wires all generate Radio noise,  keep the Cortex away from that.
6 Point the flat side of the Vexnet Joystick key toward the robot; Dont point the shoulder buttons toward the robot.    The radio waves come out the flat side of the key.

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EvansPhysics

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Reply with quote  #3 
While I can't speak to exactly what is causing your issue,  I can say that jgraber has given you pretty good advice.  He helped us trouble shoot the issue last year.  We would have what we thought were connection issues almost every year.  We tried...

  • relocating the cortex away from motors
  • using a USB extender to relocate the VEXnet key
  • "shock mounting" the cortex to reduce vibrations
  • confiscating cell phones
  • programming solutions
  • multiple keys
  • Hub provided channel shunt (the radio dongle)
  • taping keys and battery connectors in place.
  • running tethered
  • and probably a few more

I think (fingers crossed) that we may have solved our problem.  The connection problem was not with VEXnet.  It was with the battery.

We talked to our hub and had the cortex converted to power pole battery connectors.  So far so good, but time will tell.  I've converted the batteries of our own vex kits to work with power pole adapters (for an engineering class) and problems have decreased drastically.  Once BEST season is over, I plan on changing them all over to power pole connectors directly wired to the cortex and completely eliminate the standard connector.

While most of the long list of things we tried did not solve the problem, they did lead to better design practices that I remind the team of each year

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Eagle

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Reply with quote  #4 
We moved our cortex further away from the motor tower and took away the cell phones.  We drove the bot for abut 30 minutes before it started losing connections again.  The lights on the remote and cortex are green when the robot strains to move.  I would think low batteries but we just turn it off, reconnect the signal and then it works again. 

Any other ideas?  We don't think that we have an extension for the antennae was not provided in our hub kit.

We do have a red and black power adapter. 
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jgraber

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Reply with quote  #5 

I moved this thread from Simulink to General, since it is not a Simulink programming specific problem.

Since the USB extender is an allowed/optional RKit component, you can provide your own. 
Part spec'ed is Monoprice #5431 shows 93cents, plus $$$ shipping.

When you turn off and on again to regain connection, what is it you are turning off and on?  Joystick, cortex, both?
Why does the robot ever strain to move?

30 minutes makes it sound like a heat issue. 
Good thing matches are only 3 minutes then.
Does Joystick USB key feel warm?  after 30 minutes does it keep disconnecting often, but not in the first 30 minutes?

One reason I use numbered and lettered lists, is to remind you to address all of them by name/number/letter.
I can ask them one at a time, but it takes longer than the shotgun approach.  
You answered (D), what about A,B,C,E,F?  They are helpful for diagnosis.

Can you be more specific about what the LED on the joystick do when you lose connection? questions (A)(B)
Each LED has a name (Joystick, Robot, Vexnet, Game), 3 colors(red, yellow, green), and 2-3 blink patterns (steady, slowblink, fastblink).

 

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Eagle

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Reply with quote  #6 

A  Losing connection is the wheels do not turn, none of the motors turn but the servo works.  It "inches" but really just mm at a time

B  LEDs are all green

c.  When we lose connection, it just doesn't go forward or backward.   it has green lights but it doesn't work

e.  hammer whack - no workie

f.  We can go quite a way before we lose connection - like maybe 40 feet


We would go buy a USB extender if we had any idea where to do so. 

We are turning on/off the switch on the cortex adn the controller both

It strains to move but just doesn't tunr the wheels

The joystick USB does not feel warm.  THe LED on the cortex seem to. 

Yes, it runs for a while then once it starts messing up, it is frequent. 

The joystick light is solid green, the robot light is a slow blinking green, the VEX NET light is a fast blink.  They are all green

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jgraber

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Reply with quote  #7 
I don't understand your description of E.    I like complete sentences, but it is less important now that....

Good thing you finally answered in sufficient detail.
Your descriptions don't match connection failure,  so a USB extension won't help.
Connection failure looks like this:  the Vexnet light flashes red, then looks like it does when you first turn it on, which is : slow blink green, then fast blink green, then solid green.

Your descriptions match Cortex or MC#29 thermal fuse safety breaker, which greatly increases resistance when it gets hot, and that's why your motors move very slowly.

Since Servos still work, you have connection and Cortex power on at least half your ports.
Tell me about your motor and servo assignment, what functions do they do and what port do they plug into.
The Cortex has one 5A breaker on ports 1-5 and one 5A breaker on ports 6-10.  That's why the default program has one wheel on each side, and one other motor on each side, to balance them out.   Lots of designs drive or move the arm, but not as much both at once.

There are also PTC thermal breakers in the MC#29 motor controllers, so if some of your motors work, but not the hardest working one,  it could be that one.
If there is a direct short across the motor wires, the MC#29 also has a PCB trace that will explode and be permanently broken before the PTC can trigger.
The MC#29 can also have a failure mode where just half the H-bridge is broken, so the motor only works in one direction,  but not the other.

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Terry

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Reply with quote  #8 
Were all 30 minutes of driving with a single battery?  If so, that's impressive!  I'm guessing that after 30 minutes, your battery may be running at partial capacity (even though the voltage will stay close to correct, the current that can be delivered will be less than it should be).  As others have pointed out, connect problems are often a power issue (either directly, or indirectly).  While your Cortex may show nice green lights on the battery, as soon as you put load on it (like driving a motor), the voltage can drop when there is either a bad connection to the cortex, or a mostly discharged battery. 

Swap batteries, check for loose connections at the cortex and do all the stuff Joel suggests (he's a smart guy) 
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EvansPhysics

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Reply with quote  #9 
Well... I spoke too soon.

Our drivers only reported 1 or 2 connection drops while practicing outside of the competition venue (at school, no other robots)
There were a few more drops during practice night at the hub, but not too many.

During the competition... our connection gremlins returned

I would not be exaggerating too much if I said the robot lost connection once per round. (easily more than 50%)
At times it lost connection while sitting in the starting box waiting for the round to start.
Other times, it was while simply driving forward (2 large motors on ports 5 & 6).
We had a driver stall a winch motor while also driving - the nylon cord eventually broke  -  did not lose connection (probably the largest power demand)

There was no consistency to when it failed, so I don't think it was an overheat/overload issue.
The cortex is different than the one we experienced issues with last year.
We switched out VEXnet keys.
The cortex is near 2 servos, but about 8 inches from the closest motor.
The cortex has power pole connectors wired directly to the cortex (no adapter).
Batteries were never used for more than 3 rounds before recharging, and drops occurred on fresh batteries.
tried to cause a disconnect by jolting the cortex/keys - could not

I was not aware of other teams having issues, but it would have been easy to miss.  (The hub did ask for hot-spots to be turned off at one point, so...)


I really think it has to be an interference problem.  I will give the team a brand new cortex for regionals (just in case) and have them test an extension USB, but I don't think we will be able to replicate the game day WiFi conditions very easily... we will have to try... maybe at a basketball game with robots from the engineering class running.

on the bright side... Our veteran drivers were used to the issue and handled it very well... and the taught the new drivers not to panic.  They also designed the gripping manipulators to "lock" into place to resist damage - they never dropped an item when connection was lost.

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jgraber

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Reply with quote  #10 
OK, so EvansPhysics had power issues last year, and fixed those, but still has connection issues this year.
Eagle's rookie team had (my guess) thermal fuse overload, and game last Saturday.
How did it go?

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dannyk

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Reply with quote  #11 
After about 100 problem free practice runs using the exact same setup at school, our team had at least 3 disconnects during the competition. The first time, the cortex would not reconnect at all, although I am not sure what the lights were showing. The keys were replaced and that problem did not recur. The next 2 were brief, lasting only a few seconds and did not require the reconnection/reboot delay that would be expected. There were up to 7 different WIFI hotspots going at the time of the first event where it would not reboot. The last event had no hotspots detectable. There were red lights showing during all events but the exact pattern was not recorded. The robot was doing various maneuvers during the different events.
The most difficult thing for me to understand is why there were no problems for 2 weeks at the school and then problems with almost half the rounds at the hub. They are very careful about securing the battery cable.
The real question is this brief (2-3 second) disconnect that I have not seen before. Is it possible to lose power connection for such a brief period that the cortex does not have to reconnect/reboot in the usual process and just pops back connected instantly.
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jgraber

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Reply with quote  #12 
I tried counting the "?" question marks to make sure I addressed all your questions, but that was unsuccessful, so I'll just have to wing it.
If I assume that 'disconnects' is same as 'events', 
1st time: no reconnect, replace Vexnet keys, all is fine.   There were also 7 wifi hotspots going, and it would not reboot (same as not connect?) 
2nd time: quick reconnect, just a flash of red,  no mention of whether there were wifi hotspots or not.
3rd time: quick reconnect, just a flash of red, and no wifi hotspots were detectable.
    did I get this description right?

Did you come up with any Hypotheses other than H1 about 'no problems for 2 weeks at the school and then problems with almost half the rounds at the hub.'  ?
H1: battery connection .  discounted because intentional checking of battery cable.
H1a: still the battery connection, supported by "robot doing various maneuvers", rather than happens when standing still.
  T1a: do you have white battery connectors, or red/black power poles.  include a picture, or describe in detail.

 my ideas,  do you have any comments or ways to test them?

H2: you practice for 2 weeks at school is on a different floor than hub game day field with more friction
H3: you practice with driver closer to the robot, instead of standing in the driver box.

H4: Far more wifi noise at Game day, than only your robot at practice time. 
   For example, I can hear the clock ticking and the refrigerator running now in a quiet environment, but when I turn on the stereo, the TV, and someone is talking loudly on the phone, the environment is not quiet and so I can't hear the clock ticking.
  T4: Try surrounding your joystick with all the cellphone hotspots you can muster.  If you have other VexNet Cortex systems, turn them all on as well.

Regarding 'real question': What hub competition was this?   Did you qualify for regionals?  what was your high match score?  what was your seeding round cumulative score?
  Did they use "wifi antennas" . aka "game mode dongles" . that you plug into the joystick at each match?
   The default wifi channels for Vexnet Joysticks are 6 or 11,  but using game mode forces channel 1, to keep away from pit testing wifi noise.
Game mode also forces "faster resync" behavior, which would explain faster reconnect.

You can also force connection issues in any environment, by unplug and quickly replug joystick Vexnet key.
You can also force connection issues in any environment, by backing away from robot until it disconnects from distance.  I tried this in the hallway at CoCo BEST, without a Game mode dongle, and there was just one flash of red before resyncing.

I go to 2-4 days of competition a year, and all of them have disconnection events.   
At Texas BEST regional competition, between teams with near perfect scores (600-rescue time points), disconnection during the first 30 seconds can put you behind a similarly perfect team.
 
I counted 9 question marks ("?").

  

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EvansPhysics

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Reply with quote  #13 
purely on anecdotal evidence, I am more convinced that our issues this year are related to WiFi interference.  

our disconnects were shorter duration this year - probably 3-5 seconds on average.  Last year, some of them were quite long.  In fact, the cortex we used last year has not been upgraded to power pole connectors yet and it is easy to force a power disconnect on it.

Talking in more depth with our drivers, they confirm that there was a brief disconnect in most competition rounds... but our hub ran a "Chancellor's Challenge" event after the awards ceremony (College engineering club vs. regional bid winners - 4 rounds) and they do not remember a single connection issue during 4 consecutive rounds (same battery).  As this was after the awards, some teams were clearing out and a large amount of the crowd was also leaving.  There would have been a lot less noise.

FYI... small hub - only 7 teams this year - no game mode dongles
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dannyk

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Reply with quote  #14 
Will try to answer inline

1st time: no reconnect, replace Vexnet keys, all is fine.   There were also 7 wifi hotspots going, and it would not reboot (same as not connect?)
Would not reconnect
2nd time: quick reconnect, just a flash of red,  no mention of whether there were wifi hotspots or not.
Hotspots present
3rd time: quick reconnect, just a flash of red, and no wifi hotspots were detectable.
    did I get this description right?

Did you come up with any Hypotheses other than H1 about 'no problems for 2 weeks at the school and then problems with almost half the rounds at the hub.'  ?
Not any that we could prove
H1: battery connection .  discounted because intentional checking of battery cable.
H1a: still the battery connection, supported by "robot doing various maneuvers", rather than happens when standing still.
  T1a: do you have white battery connectors, or red/black power poles.  include a picture, or describe in detail.
White connectors

 my ideas,  do you have any comments or ways to test them?

H2: you practice for 2 weeks at school is on a different floor than hub game day field with more friction
It was very similar. The only difference was the plywood at the hot zone entrance was thicker at the competition but disconnects did not occur when going over the board.
H3: you practice with driver closer to the robot, instead of standing in the driver box.
Always practice in the driver's box

H4: Far more wifi noise at Game day, than only your robot at practice time. 
   For example, I can hear the clock ticking and the refrigerator running now in a quiet environment, but when I turn on the stereo, the TV, and someone is talking loudly on the phone, the environment is not quiet and so I can't hear the clock ticking.
  T4: Try surrounding your joystick with all the cellphone hotspots you can muster.  If you have other VexNet Cortex systems, turn them all on as well.
Will try

Regarding 'real question': What hub competition was this?   
Cowtown
Did you qualify for regionals? 
Yes
what was your high match score? 
Probably around 475, but we didn't keep a record
what was your seeding round cumulative score?
THey did average scores, was probably around 430, but we didn't record it
  Did they use "wifi antennas" . aka "game mode dongles" . that you plug into the joystick at each match?
No
 Thank you
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jgraber

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Reply with quote  #15 
me: Did you have any other Hypothesis?
you: Not that we could prove.

What about Hypothesis that you couldn't prove? 
The way the Scientific Method works, in my view, is to propose Hypothesis, find tests for them, try the tests, refine etc.
Maybe other people can think of tests to try against your Hypothesis that you didn't think of.

I'm surprised that Cowtown has White connectors.    Surely they at least have White to PowerPole adapters, and tell you not to use the white connector, right?

We will have 'wifi antennas' aka 'game mode dongles' at Best of Texas,  I'll see you there.
Make sure to introduce yourself as "dannyk from the forum".

Did you report your connection problem to Hub people?    Be sure to speak up at regionals about stuff like this.
We had just one team reporting problems, and swapping to the 4th set of Vexnet keys worked for them.

Another Question/Test:  If you back away from the robot until the you get a disconnection,  does it look the same as on the field?
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