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Unread 21-04-2011, 22:49
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Robot losing and regaining drive power

During our regional competition we would lose control of the robot, but then after a few seconds we would regain control although it would start a bit sluggish. Now it appeared that it never happened while tethered, but we did not run enough while tethered to be sure.
We would also have matches where we would not see this problem at all, and there was not any noticeable correlation between the matches we did not have the problem versus where we did have the problem.
We aren't necessarily sure what was causing the problem, but it looked like some sort of power loss to me.

As the "coach" who went up with the drivers, I was watching the voltage value on the classmate when we had the problem. There would be no change in voltage when power was applied and there was no movement, but the moment the robot moved the voltage would drop from about 12.5ish to 11.75ish. The voltage, when the robot was functioning normally appeared to be in a range from 11.8 through 12.2.

Any input as to what could be going on with the robot would be appreciated!
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Unread 21-04-2011, 22:58
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Re: Robot losing and regaining drive power

According to my drive captain, if the battery voltage drops below 12 while the robot is working, the robot should continue to work fine. If the battery is less than 12 before a match, that is when you should start thinking about charging your battery.

However, it may not be a battery problem, as our team has experienced random communication losses where the robot "controlled" itself for half or a whole match, and we were also unable to replicate the error while tethered.

Fortunately, we never lost communication again. I suggest examining your PWM or CAN cables, as they may have become loose during a match. If you cannot find the problem, I suggest crossing your fingers and hoping it never shows up again .
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Unread 21-04-2011, 23:07
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Re: Robot losing and regaining drive power

Only a few seconds?
Not the cRio rebooting (would take like 40 seconds to regain control)
Not the radio rebooting (would take at least a minute and a half)

Could be:
Breakers tripping - Reset would be almost instantaneous for the first few trips because as soon as it trips, the load goes away.
Jaguars resetting - These are really annoying - The Jaguars can fault out for any number of reasons, resulting in loss of that motor for 3 seconds.

If you have a 4-motor drivetrain, loosing one motor could overtax the other and cause it to trip as well. If you have a 2-motor drivetrain, the problem is probably that it is geared too high and the continuous driving current is too much.

The battery voltage has to go down to 5.5 for the cRio to cut outputs. You say it only dropped to ~11 volts while driving? I've seen ours drop as low as 8 volts in normal driving during practice, lower when pushing.

Possible code issues::
If your code takes a long time to execute a cycle, it is possible you are just on the threshold of tripping the watchpuppies. If you trip them, you will loose control, and if you are close to tripping them, driver response will be poor. Look for sources of slow-ness in the thread which handles the drivetrain (such as camera tasks or wait statements). IF it's in teleop, there should be no wait statements or loops.
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Unread 21-04-2011, 23:38
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Re: Robot losing and regaining drive power

Possible comm issues:
Make sure your radio gets power from the right place, it doesn't come from the regular 12v blocks, but instead uses CRIO power with a funny adapter, which is nicely regulated

Make sure the ethernet cable on the field plugs all the way into the driver station. On our laptop, the clicky mechanism is borked, so the ethernet plug is never securely fastened. We bend it funny and brace it against other parts of the driver station to ensure it stays in.
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Unread 21-04-2011, 23:43
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Re: Robot losing and regaining drive power

Sounds a lot like the jaguars faulting out. Likely with an overcurrent fault. Under a constant, slight overload, the jags will fault out before the breaker trips. They'll blink for a few seconds, then start working again. If you have a 4 motor drivetrain, one might be faulting first, then the other. So they'll come back in the same fashion, and you'll end up with half power for a bit, then full power. This could also happen with 2 motor drive. 2 motor skid steer with a side dead can often feel like a merely underpowered, sluggish robot.

So your best bet for checking this is to buy or borrow a clamp on ammeter and measure the current drawn by your drive when running. If a single CIM is pulling more that 20 amps just driving around, then you've got a binding problem or a gearing problem.
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Unread 21-04-2011, 23:44
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Re: Robot losing and regaining drive power

Oh, I forgot to add the robot works perfectly when driving backwards, it only has trouble going forwards and turning.
We can try to go forward, have it not work and then go back for a second, and it again wont respond when trying to go forward.
The length of the stops were also random, it seemed to range from about 2 seconds to 8 seconds.

Thanks for the quick replies. I was fairly certain it wasn't the battery, I just wanted to provide as much information as possible. Thanks for confirming my suspicions.

In terms of code, we took out all loops and waits in teleop before this problem even happened! Those were taken out before the drivers really started to practice. At competition we removed any sensor data (we had the line sensors getting values, and encoders still running in teleop) because another team mentioned that they had a similar problem when they had their sensors (a much larger number than us) running in teleop. At camera code has been removed from teleop because we have no camera's. At the moment, we only have joystick values being fed to a "reverse drive toggle" vi which goes to the motors. Another joystick value going to the motor of an arm. And several buttons: one is used for enabling our compressor (we have an off board compressor but it is required to be run by the program), another is used to deploy pistons. There are also various indicators (for the labview front panel) to get the button and joystick values, but there were even more during practice and there were no problems.

Those reasons along with the fact that we are fine going backwards makes me believe it is not a code issue. And the backwards part makes me think its not a communication problem either.

We use a 2-motor drivetrain. I have been thinking that it may be something with the gearing, but we were running perfectly fine at our school during practice. The carpeting that we had was very similar to the one we used at competition, though the one at competition felt more "padded" or "softer".

Hopefully we can take a look at the breakers and jaguars after we uncrate wednesday. That three second break for the jaguars sounds like it is the closest thing.
If it is the breakers, would that get the robot to stop for 8 seconds?
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Unread 22-04-2011, 00:21
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Re: Robot losing and regaining drive power

Ohhhh. Directional problems are my favorite. It tends to focus you problems into specific areas. For instance, electrical problems with the jags... one of your jags might be dead in one direction. Toss your robot on blocks to get the wheels off the floor and make sure the wheels move in the directions you're expecting.

Second, are you running 4 or 6 wheels? Are you driving all the wheels? You might want to check your chains for proper tension and alignment. Misaligned chain can be really funny and work well in one direction and really poorly in the other direction. And it'll be different under load vs. not. So run the wheels by hand with the robot off, and see if you're getting funny catches in one direction or another.
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Unread 22-04-2011, 07:50
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Re: Robot losing and regaining drive power

PSH,
Just to add to Kevin's response, problems with going forward and not backward can also be mechanical in nature. Do you have slack in your drive chains and is the slack enough to throw a link into an adjacent mechanical frame member? If so, that would explain backing up and then having a problem again in forward. Losing power in turns is an age old problem with tank drives and high friction wheels. It is why most teams either use omni wheels or drop center drives to overcome the side loading of the wheels in turns. For reference...

Less than one second (stutter) is branch circuit breakers tripping usually with buzzing sound from robot
Less than one second with all lights blinking off is a faulty main breaker usually follows a robot collision or other mechanical event
3.5 second with power is Jag reset from over current/under voltage fault
20-40 seconds is Crio reset usually due to battery brownout
52 seconds is DAP-1522 reset usually due to battery brownout
Disabled for the remainder of the match with power, could be a failure of the Crio and DAP connecting once reboot occurs
Disabled for the remainder of the match with no power showing, is main breaker trip (highly unlikely)
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Unread 24-04-2011, 13:49
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Re: Robot losing and regaining drive power

Quote:
Originally Posted by Al Skierkiewicz View Post
3.5 second with power is Jag reset from over current/under voltage fault
Sounds like the issue is over current faults when trying to drive forward with 2 motor drive. I have a few more notes to add on the Jag fault logic. 3 sec is the default wait time on a fault (over current/under voltage/over temp). The Jag doesn't actually reset it just waits (with flashing light indicator red on Black Jag, multicolor flashing on Grey Jag) hoping that the issue (motor stall) will resolve and it can continue normal operation.

If you happen to be using CAN, you can set the wait down to half a sec using ConfigFaultTime() (thats C++, I assume there is a LV equivalent). Also with CAN you can monitor your current in the code. Unfortunately, it doesn't sound like you are using CAN. Reducing the wait time probably wouldn't solve the problem any faster since it sounds like you are having multiple faults in a row (2 - 8sec as you said).

Does it go forward fine under no load (on the cart or blocks)? If it doesn't then it is probably an over current fault. As Al & Kevin said the it is likely that some mechanical issue the drive has more resistance going forward. It is unlikely, but also possible, that one Jag has something wrong with the circuitry in one direction (such as the Gray Jags that would only run one direction because the U6 gate driver failed). You could swap the output wires and see if it has a problem going backwards to test for this.
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Unread 24-04-2011, 17:01
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Re: Robot losing and regaining drive power

Until the post about the directional data, this sounded much like my post here.. http://www.chiefdelphi.com/forums/sh...ad.php?t=94497

Could be digital sidecard power short.. with the directional data, I would agree with checking the jags individually. We have had 3 jags fail this year in one direction. The error indication on the jag is a flashing red led, that can easily be mistaken for the normal, jag running backwards proportional flashing red. I know you said when the robot forward, but many times robot forward, is jags reverse.

We have 2 motors per side on a 6 wheel tank drive, and when we lost one jag on a side, the drivers really didn't notice it, but autonomous did. Also in the semi finals at MSC, we lost a drive chain, the drivers did not notice it until we were off the field, and only when battery hold down bungee was cut by the chain saw..
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Unread 24-04-2011, 17:12
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Re: Robot losing and regaining drive power

Make sure your driver station is properly updated. We had a similar problem at WPI where we would seemingly "lose power" for about a second every 5-10 seconds or so. After spending hours looking for shorts, checking breakers, and reloading code, we re-installed the DS update and never had the problem again.

Best of luck.
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Unread 24-04-2011, 18:20
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Re: Robot losing and regaining drive power

Good news! My new clamp ammeter has been delivered in time to break it in at Champs. Hunt me down in Curie in 57's pit on Weds evening and I'll give you a 10 min diagnosis with it. Just make sure you bot's ready to go and drive around, we're all gonna be busy weds night.
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Unread 24-04-2011, 19:22
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Re: Robot losing and regaining drive power

We experienced a similar issue at Waterloo, when ever there was load on the motors even load from driving straight, the jaguars would have a vbus error. They were reporting 6 volts input and at 6 volts they shut off as a safety feature. Even though the input voltage was more like 8 or 9 volts (the battery was fully charged) for whatever reason. After the 3.5 seconds, they would shut off again. Our current draw was well within spec. A Texas Instruments employee who works with the jagurs helped us diagnose the issue and after a hour or so of head scratching, recommended we use victors. We were using a 4 motor drive train, 2 motors /cimple box with 3 wheels per side.
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Unread 24-04-2011, 19:51
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Re: Robot losing and regaining drive power

I guess I'll start with the post right after mine. Thanks to everyone again for your help!
When the robot is on blocks/lifted up we don't see any of problems at all. Every time we were about to leave the pits we would check movement forward, backwards, right and left. There was not a single time when the movement in the wrong direction.

We have 6 wheels. There are two lager wheels and the are in the middle of each side. These are the only wheels being driven by the motors. I do remember we checked the wheels by hand a couple of times, but I will make sure we check again Wednesday.

I will make sure we check the drive train and make sure something hasn't come loose. We haven't really worked much on the drive train after the first two or three weeks of the build season. It does seem possible, but the reason we didn't think it was something like a drive chain was because we didn't need to wiggle the robot to get it to move. Simply holding the joystick forward would eventually lead to the robot moving again.
Also, I'm not sure if that makes a difference for the turning problems but we are using arcade drive not tank.
Thanks for the information Al, if it keeps happening I'll make sure to watch the time more closely just to make sure I'm not dramatically over/under estimating.

So would that mean that a mechanical or electrical problem would be causing the jags to stall and its not specifically the jags? And we are not using CAN but I agree with your analysis that it would most likely not make a difference.
Would a circuitry problem with one jag cause there to be problems for the other jag? If there is some movement from a specific side when the robot is not "responding" it is only at the very moment the joystick is pushed forward. Most of the "driveless state" the robot is stationary and it does not appear to be attempting to move (not fully sure).

How can we check if the problem is a digitical sidecard power short? And if it is for directional data, would we still see the problems moving forward?
I do believe that forward is the jags in reverse, so it is possible what you're saying is absolutely correct. So if the jag is having this problem moving in the reverse direction, how would we know that it is having a fault? I know it does not do this without load, which from the previous posts seems to show that it isn't a problem with the/a jag going in a specific direction.

We updated our driver station software at competition. We had been running fine with the old one, and one of our allies did have a problem with their driverstation so I have seen it for people before. But there was an error given on the driver station window whenever their robot froze. We didn't see anything like that.

That sounds fantastic Kevin, once we get our robot ready to go I'll be sure to come find you!

Thanks again everyone! I'll let you know after Nationals if we figure it out.
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Unread 24-04-2011, 21:20
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Re: Robot losing and regaining drive power

Quote:
Originally Posted by PSHRobotics View Post
Would a circuitry problem with one jag cause there to be problems for the other jag? If there is some movement from a specific side when the robot is not "responding" it is only at the very moment the joystick is pushed forward. Most of the "driveless state" the robot is stationary and it does not appear to be attempting to move (not fully sure).
Can you explain the second bit a little more? I'm not sure I'm understanding it correctly. Are you saying that when you had the problem, it would happen as soon as you start moving that side?

There's specific wiring problems that could affect both jags. Anything affecting the digital sidecar would affect all jags, servos, and digital IOs. Anything that affected the main voltage of the robot would also do it. Basically, that kind of wiring problem would most likely affect all the motors on your robot, a symptom you haven't mention yet.

Other wiring faults that could be causing this are simple ground faults if one of you output terminals is connected to the frame of the robot, weird problems become possible. If that's happened at two different jags, then weird things are likely. The potential is short circuit currents flowing through the robot frame under certain conditions.

Something else I'm considering is some sort of weedy/questionable connection on the power side of your jaguar. If it occasionally wiggles loose(r) then large current draws would drop the input voltage below the minimum volts the jaguar's looking for, which would cause a fault. But that's likely to be a bidirectional problem, so probably not as likely here.
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