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Unread 22-02-2014, 07:12
Dan252 Dan252 is offline
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Exclamation 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

Hey, we need your help.

About a day before we bagged and tagged we noticed that the DS lost communication every couple on seconds and everything on the robot flickered (we also heard it because of the solenoids). When we checked for the source of the problem we noticed that the frame of the robot had 12V on it. We checked with a multimeter by putting the (+) on battery + and (-) on the aluminium frame.

We found that the problem root is a BaneBot motor whose common is shorted to its cover (which touches the robot frame). What was weird is that the multimeter showed resistance between the (-) wire and the motor cover only when the motor was at a certain orientation. When I removed the motor to test it alone, not embedded in the system, I did not see any resistance (and I varied it's orientation between each test).

Do you think the motor is really the component that is causing the problem or might there be another cause?

Also, our team had built 2 robots, one for each idea we had (so they are completely different, also their electrical). And in that second robot the multimeter also showed that there is 12V on the frame but on the other hand, communication worked fine and was solid. (So might the problem be in the software?)

Thanks for any help,
Dan #3075
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Unread 22-02-2014, 08:34
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

Based on your description, it sounds like your frame is actually connected to battery negative. The polarity is irrelevant though.

Some RS-775 motors have been known to get internal shorts to the housing. In some cases these connections are intermittent and orientation dependent. I haven't seen this with any of the RS-550 motors with my own eyes, but the designs of the two motors are very similar.

While this condition will cause your robot to fail inspection, I doubt it is the reason for your communication problem. I would check for metallic debris in the Digital Sidecar and perhaps try another ribbon cable. Our Digital Sidecar can attract metal chips from distant planets.

Of course code is a possible culprit, but I'm a hardware guy so...
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Unread 22-02-2014, 08:54
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

Quote:
Originally Posted by electroken View Post
Based on your description, it sounds like your frame is actually connected to battery negative. The polarity is irrelevant though.

Some RS-775 motors have been known to get internal shorts to the housing. In some cases these connections are intermittent and orientation dependent. I haven't seen this with any of the RS-550 motors with my own eyes, but the designs of the two motors are very similar.

While this condition will cause your robot to fail inspection, I doubt it is the reason for your communication problem. I would check for metallic debris in the Digital Sidecar and perhaps try another ribbon cable. Our Digital Sidecar can attract metal chips from distant planets.

Of course code is a possible culprit, but I'm a hardware guy so...
Thank you for your comment. We tried taking out our electrical board (made of poly-carbonate) and disconnect all the motors from the speed controllers and testing it outside the robot where there is surely no short. In this condition everything worked fine and the communication was solid. We didn't change anything in the hardware nor in the software. How can you explain this?
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Unread 22-02-2014, 09:06
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

It might not be the motor's case that's shorted to the power, but the output shaft. When installed on your robot, the rest of the assembly probably has metal that could provide a current path to the frame from there.
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Unread 22-02-2014, 11:42
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

Our team had the same exact issue with the bane bot motors we were using to run our rollers. It turns out there was a bad batch of them last year that all shorted out. Cost us two jags before we figured that out but now we have switched to a cim for the time being because it has the right speed and does not short.
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Unread 22-02-2014, 11:50
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

This is how we fix case short issues with the RS775:

http://www.youtube.com/watch?v=zpxolE76bZw

These motors have cost us failed inspections in the past. Usually the windings short to the armature which grounds to the frame through the bushings at either end or the interface with the output shaft. Your only solution is to get a new one and hope it isn't case shorted or mount them in a plastic to electrically isolate them.
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Unread 22-02-2014, 13:08
NotInControl NotInControl is offline
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

With the motor removed, do you still have a short to the frame?

How is the dlink wired? Is it going to the proper port on the power distro board and through the 12V-5V regulator?

Is the communication intermittant only when the robot is running its motors, or if it is just on, you notice comm dropouts.

Posting your DS logs might help.

Definetly, get the short to frame fixed, because you could potentially be providing 12 volts to other things inadvertly mounted to the frame.

Note, you don't need to worry about resistance or voltage as much as simple continuity. If you have a digital multimeter with continuity mode on it, you can check to see if there is any continuity between the + or negative side of the PD board, and the frame. And you can do all of this without the bot being powered, so you don't need to worry about frying stuff if there are shorts.

You can also do the same thing with the motors you suspect are shorted (checking for continuity between either motor terminal and the motor housing).

Any continuity is an issue and needs to be rectified.


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Last edited by NotInControl : 22-02-2014 at 13:17.
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Unread 22-02-2014, 13:21
Dan252 Dan252 is offline
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

Quote:
Originally Posted by NotInControl View Post
With the motor removed, do you still have a short to the frame?
I don't remember :/ I'll check it first thing tomorrow

Quote:
Originally Posted by NotInControl View Post
How is the dlink wired? Is it going to the proper port on the power distro board and through the 12V-5V regulator?
Yes

Quote:
Originally Posted by NotInControl View Post
Is the communication intermittant only when the robot is running its motors, or if it is just on, you notice comm dropouts.
Only when enabled (even if no motors are actually running). - Which may hint that there is another short somewhere?

Quote:
Originally Posted by NotInControl View Post
Posting your DS logs might help.
Tomorrow i'll be in the workshop and post those.

Thanks for helping
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Unread 22-02-2014, 13:24
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

Quote:
Originally Posted by fox46 View Post
This is how we fix case short issues with the RS775:

http://www.youtube.com/watch?v=zpxolE76bZw

These motors have cost us failed inspections in the past. Usually the windings short to the armature which grounds to the frame through the bushings at either end or the interface with the output shaft. Your only solution is to get a new one and hope it isn't case shorted or mount them in a plastic to electrically isolate them.
LOL, was not expecting this
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Unread 22-02-2014, 14:12
NotInControl NotInControl is offline
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

Quote:
Originally Posted by Dan252 View Post
I don't remember :/ I'll check it first thing tomorrow


Yes


Only when enabled (even if no motors are actually running). - Which may hint that there is another short somewhere?


Tomorrow i'll be in the workshop and post those.

Thanks for helping


Not a problem.... three more question to check once you get back to your robot.

When you have comm issues, are the lights on the dlink do anything (turn off, go red, or are they always blue?

Are you running tethered, AP, or Bridge?

On the driverstaion, are you noticing any errors in the user message box? (watchdog timers etc.)

As for diagnosing your short:
If without the motor connected to the robot, you still have intermittant comms, or a short to the frame.

The fastest way to run through the circuits, is to pull all of the breakers on the power distro board. Also unplug power to your digital side card, analog, and solenoid card. Turn the robot on, and check continuity between the frame and the PD board.

Plug in each breaker one by one and run the check until you find the circuit that is causing the short. After running through the breakers, add power to the analog, digital, and solenoid cards one by one, and perform the continurity checks again.

If you notice the short after plugging in one of the CRIO cards, then that narrows your search down, to the electrical components connected to that card.

If even with all breakers and cards unplugged you still have a short, then only what is still being powered is causing your short. your PD board, CRIO, or Dlink, main breaker etc.

Hope this helps,
Kevin
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[2015 Season] - NE Championship Controls Award, 2nd Blue Banner
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Last edited by NotInControl : 22-02-2014 at 14:17.
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Unread 22-02-2014, 14:44
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

Check w/ an OHMMETER between the hot lead and the case on that banebot motor w/ the sound signal on...Get sound, then that case is certainly grounded.

There has always been a quality control issue w/ those particular motors and we have received many in the past that were brand new and had fine metal debris inside the case that led to case shorts right out of the box. We devised (actually copied from others here and on YouTube, and improved for safety reasons), a way to fix them and actually be able to use them.

It must be done very carefully (w/ 2 people at least...1 manning the switch for a quick emergency shutoff, one working the actual motor fix procedure).

On a plywood board out of a robot on a table or floor...We hooked up a battery to a robot 125 AMP switch to a power board, ran a set of leads (12 gauge wires), from a 20 AMP breaker spot on the power board (w/ the breaker in of course)....Then we attached the ground lead to the ground side of the Banebot motor that we knew was case grounded, put on the face shields, welders jackets and safety glasses.....(Got the 1 man ready to immediately trip the switch and cut off the power real fast should the hot lead decide to weld itself electrically to the case during the "fix" swipe...It never happened in our many attempts, but, it certainly could happen so be very aware of the possibility, and be ready to act fast if it does)...then we quickly swiped the hot lead against the case of the motor. There was an electrical short connection in each case and you could hear an internal "loud pop" (some sounded like gunshots), sound as the debris that had originally made contact inside the motor between the case and windings was removed/dislodged, burned and blown away in each case that we attempted that fix of an actual case grounded motor....we then blew out each motor well w/ compressed air, and then checked each motor again for case ground situation w/ the meter and then operation of the motor.

No more case grounding issues w/ those motors...and each of those motors fixed in that manner worked fine from then on (except the very first one of course, that I took apart and disposed of, to actually find out what was originally wrong w/ those motors in the first place, (which was noted as minor metal debris between very close tolerance areas of case / windings).....We must have received at least 80% of a large number of those purchased in batches a couple of years ago, were received in that case grounded condition, brand new. (Just MFG. quality control issues to be sure).

We fixed many of those that way.....Not the most comfortable or safe fix, but a fix that actually works. (We may have some of the fixed versions brand new w/ leads soldered to them, that we are not using this year, that we bought as spares 2 years ago that our team just may be willing to let go of if interested).
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Unread 22-02-2014, 17:30
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

Quote:
Originally Posted by NotInControl View Post
The fastest way to run through the circuits, is to pull all of the breakers on the power distro board. Also unplug power to your digital side card, analog, and solenoid card. Turn the robot on, and check continuity between the frame and the PD board.
Removing the breakers probably won't work in this situation. The breakers are single-pole on (AFAIK) the high side of the circuit. Since they are reading a delta 12v between battery positive terminal and frame, it means the robot chassis is shorted to battery negative terminal somewhere. If a RS775 is case shorted, removing the breaker won't show the problem.

I would check first to make sure cRIO is isolated, then check to make sure the camera is isolated, then physically disconnect both wires leading to every RS775 (one at a time) from the M+/M- side of the speed controller, then check any custom sensors (such as Sharp IR sensors), as these in that order are the most likely causes of grounded frames.
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Unread 22-02-2014, 17:57
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

Quote:
Originally Posted by artdutra04 View Post
Removing the breakers probably won't work in this situation. The breakers are single-pole on (AFAIK) the high side of the circuit. Since they are reading a delta 12v between battery positive terminal and frame, it means the robot chassis is shorted to battery negative terminal somewhere. If a RS775 is case shorted, removing the breaker won't show the problem.

I would check first to make sure cRIO is isolated, then check to make sure the camera is isolated, then physically disconnect both wires leading to every RS775 (one at a time) from the M+/M- side of the speed controller, then check any custom sensors (such as Sharp IR sensors), as these in that order are the most likely causes of grounded frames.
What can be insulated in the camera? It's case is made of plastic, or you ment it's LEDs?

Anyway, our cRio is insulated and I'll have to wait until the competition day to check how is it without the motors connected.

Thanks
-Dan
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Unread 22-02-2014, 18:11
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

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What can be insulated in the camera? It's case is made of plastic, or you ment it's LEDs?
If you are using an old Axis 206 model camera, then the case is grounded and must be isolated from the robot frame. The mounting bolt will conduct.

If you are using a newer Axis M10 model camera, then the case is isolated and you don't have to worry about that conducting to the robot frame.
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Unread 22-02-2014, 18:13
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Re: 12V Voltage on Robot Frame (Perhaps because of a BaneBot)

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Originally Posted by artdutra04 View Post
I would check first to make sure cRIO is isolated, then check to make sure the camera is isolated, then physically disconnect both wires leading to every RS775 (one at a time) from the M+/M- side of the speed controller, then check any custom sensors (such as Sharp IR sensors), as these in that order are the most likely causes of grounded frames.
This. My team had the same issue during 2012. It was traced back to the C-Rio forming an intermittent connection with our frame. Your symptoms sound very similar to what was happening with our bot.
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