our robot has a voltage induction problem in the robot chassis. I know it is induced current because I did a test by connecting a resistor to the negative terminal and to the chassis, then the unwanted voltage disappeared. I’m afraid because if I’m not mistaken, the judges measure the voltage in the robot .
Can i put a resistor in the negative terminal and in the chassis? Or you guys have another idea ?
Hope this clears is up:
I was once told by an inspector that there’s usually small amounts of current running through the frame. As long as it’s not significant amounts of voltage, it should be fine.
Unplug everything and run continuity checks. Inspectors will use a similar method, and just having a resistor won’t be enough.
- unplug everything from the PDP/PDH. Check continuity between terminals of PDP/PDH and frame.
- one item at a time, plug items back in and check continuity. First item that beeps, trace that circuit to find the short and eliminate it.
- repeat until no more continuity, then check resistance as the manual says.
Oh, and if you have Spark Flex that were not sent out just now, follow instructions and request your replacements. That’s likely your problem.
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You are not understanding. It is not a short, i checked that. Its because the negative wire is building a capacitance whith the robot frame. That means that there is no wire conectes direclty to the robot frame.
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Inspectors measure the resistance between the frame and both the positive and negative terminals. The resistance must be above a threshold which is apparently now 1200 ohms. It previously needed to be in the megaohms range.
Now, if you truly have an induced potential it will not show up when the inspector tests the resistance because it would only exist when a motor controller or something else is producing an AC current near the frame.
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Not necessarly AC. The inductance in this case works the same way as a capacitor. So with only the terminals of the baterry on my PDH.
I checked that with a eletrical engineer.
But my fear is of the inspector sees the voltage, because it doesnt have continuity, so there is no resistance to measure. But there is voltage
As long as no electrical devices or wires are touching the frame, you should be fine. There will always be voltage on the frame.
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The robot rules measure the resistance from the chassis to either the + or - poles of the electrical system with no battery connected. The resistance must not be more than 1200 ohms. If you’re robot passes that test, the frame is sufficiently isolated. If not, fix it. Voltage is never measured to chassis as part of the inspection.
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I’ve inspected two robots at competitions that failed to have an isolated frame. First off, measure the resistance - if not “off scale high” (eg infinite or isolated) there is a resistance number that you are allowed to have. It changed last year, but I don’t have the number in front of me. (And haven’t looked to see if it’s the same this year yet.)
I will say that both LRIs I reported to instructed me to stay with the robot until fixed and the robot could not attend practice matches, even scheduled ones, as this was a safety issue for the field volunteers and crews.
There is excellent troubleshooting steps above (isolate everything, add/test one at a time), and I strongly encourage you to use them. Some culprits I’ve seen - LED strips against the aluminum frame may only be isolated by the double-sided adhesive. I’ve seen motor/electrical wires rub against the frame and get small nicks. I’ve also seen fasteners over tightened on motors causing conductivity.
While inspectors will allow robots with sufficiently high resistance but not fully isolated to pass, I personally would encourage you to completely find any isolation issues now. It’s a great learning experience and you may expose other issues that would more negatively effect your team and experience at an event later on.
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The allowed resistance is [edit] 120 ohms [/] for this year. I see that maybe once/twice a season. Usually pretty easy to find the reason. Most read open circuit.
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On rare occasions, I’ve seen Neo motors short a winding to the case. Banebots 775 motors were also notorious for this. Start unplugging things until the problem goes away so you can figure out where it is.
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Wait, where did you get 1200Ω? Last year it was 120, and the manual (R611 blue box) seems to still reflect that. That’s all I have to go off of since from what I know the RI training isn’t open yet, but maybe I’m out of the loop 
It’s 120.
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All the inspectors will look at is resistance, not voltage. What is the resistance between your frame and the positive/negative terminals of the robot-side Anderson connector?
Keep in mind that a short to the frame can happen on either the positive or negative sides. So reading 0V doesn’t tell you in there is a short to the negative (ground) side. Additionally, keep in mind that there is no “universal” ground reference point. A voltage measurement is simple a measurement of the difference in voltage between two points. Without having a common reference point between the two (typically ground), that is a floating voltage that can read different every time you try to measure it, and is meaningless.
Attaching a resistor between your frame and the electrical system’s negative terminal is specifically against the rules.
Are you sure it’s not static electricity?
My bad. its what is I get from trying to read a PDF on my phone. At 120 ohms you will be able to measure voltage from the frame to the battery. Even use the frame as a wire. But the rules only require an resistance check. An RI should only recommend (not require) the reason for the low resistance, <120 ohm, be corrected.
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In 2012 when the inspector measured the resistance on or bot it kept changing, which turned out to be a couple open backed sensors which effectively formed a capacitor with the frame. We had an unfun teardown before we figured that out.
We’ve previously had the 775 motor issue as well and also an air compressor with an inetrnal negative short to its frame.
Induced voltage requires a changing magnetic field (i.e. AC current). The PDH does have internal electronics but I would be surprised if this would gererate enough of a magnetic field to induce an easily measurable voltage.
Is the voltage you are measuring AC or DC?
it acts exactly like a capacitance voltage, when i put a 1k arduino resistor on a random non used positive terminal of the PDH to the frame, the voltage was almost gone. i tested the resistance of the frame with the poles and it did’nt appear to be conected to the frame