Could a magnetic field around CIMs cause fuses to blow?

[scitobor 617]

Could a magnetic field around CIMs cause fuses to blow?

After testing our drive train for the first time we noticed some strange behavior from one of the CIMs and the Victor controlling it. We are using the gearboxes and the CIMs from the KOP.

When we started testing our motors we noticed that whenever we tried to turn a fuse would blow for one of the motors in the gearbox on the left side of our robot and the right side would begin to struggle. This happend wether the robot was on the ground not. We decided that we should isolate the problem by testing one side of the robot at a time, so we pulled out the fuses for the gearbox on the left side. When we drove the motors on right side we noticed that the cooling fan on the Victor of the motor that had been blowing fuses began to spin, and the Victor's LED came on. This seemed very odd because the cooling fan only came on when we drove the rightside motors. I noticed that the black wire for this "problem motor" was running directly under one of the motors on the rightside. I began to wonder if the magnetic field generated by the aperture of CIM could be powerful enough to induce a current in this cable. If so this would explain where the power was coming from to power the fan on the Victor. Could this also explain why this motor was blowing fuses? Jay(a team mate) and I speculate that the magnetic field around the CIMs could have caused a large amount of resistance in the problem motor's cables whenever we tried to turn. Does this explain our problem? Are we crazy?


P.S. We tried to reproduce the situation and use a multi-meter to measure the voltage produced but failed to get any definative results. I think a science teacher at my school has some sort of meter(EMF meter I think) for measuring the strength of magnetic fields so we should have some measurements by monday. Also here are some pics of our gearboxes and the wiring to them.
Picture of the wiring
Picture of the motors

[jdiwnab]

As clarification of what Scitobor said, the sensor measures the Magnetic Field Strength in guass. This is distance sensitive, but will tell you if there is a strong magnetic field, or even a weak one. I used it on by science project. But it only goes to about 1000 gauss or .1 Tesla or all you tech heads

[Bduggan04]

I would expect behavior like that from a short in the wiring. You could be back-feeding current into the speed controller for the unconnected motor. I have never seen a current like that induced in a wire on a FIRST robot, so before you chase the rabbit with the emf meter, check your wiring. Using the ohm checking capability of a multimeter, check for continuity where there shouldn't be continuity (i.e. motor wires on opposite sides of the drivetrain)

[scitobor 617]

Originally Posted by Bduggan04

I would expect behavior like that from a short in the wiring. You could be back-feeding current into the speed controller for the unconnected motor. I have never seen a current like that induced in a wire on a FIRST robot, so before you chase the rabbit with the emf meter, check your wiring. Using the ohm checking capability of a multimeter, check for continuity where there shouldn't be continuity (i.e. motor wires on opposite sides of the drivetrain)

Backfeed was prevented, we tested the robot while it was off the ground so the left motors were not spinning at all and the fuses to their Victors were removed leaving only one possible power source... we think.

[Bduggan04]

How did you prevent backfeed? I don't think the motor is powering it, I think it's a short. Disconnect the input side and rerun the test, then if it doesn't do anything, disconnect the output side wires and reattach the input side.

Also, I didn't notice the picture before, but you are grounding the electrical system to the frame, something I don't believe you are alowed to do. Disconnect your groundstrap and see if the problem dissappears. The groundstrap could turn a harmless short of one of the terminals into a nightmare.

[Sparks333]

Hmmm... An induction spike through a magnetic field? Interesting thought...

On the whole, I don't think so. It would need a pretty strong field (one I don't think the CIMS can create) to screw with the fuses in the ways you are describing. Theoretically speaking, you could do it, but it seems unlikely at best. Have you tried relocating the victors? That's the only real way to tell.

Sparks

[scitobor 617]

Originally Posted by Bduggan04

How did you prevent backfeed? I don't think the motor is powering it, I think it's a short. Disconnect the input side and rerun the test, then if it doesn't do anything, disconnect the output side wires and reattach the input side.

Also, I didn't notice the picture before, but you are grounding the electrical system to the frame, something I don't believe you are alowed to do. Disconnect your groundstrap and see if the problem dissappears. The groundstrap could turn a harmless short of one of the terminals into a nightmare.

The frame is not being used as a ground, the motor's wire was disconnected and is pointing straight up. Sorry I was not very clear, backfeed was prevented by removing the motor's wires from the Victor. When we did this the Victor no longer came on as it had before. We know the power is not coming from the power supply because if it were it would be getting constant power and not power only when we run the right side motors.

[Bduggan04]

Looking at the picture more, I see another issue. Remove the button heads on the speed controllers. They are too large and several of your connectors are touching the heads or are near to touching the heads. The best solution is to use nylon or some other type of plastic fastners. Check your wiring for shorts, and I believe your issue will be solved.

[jdiwnab]

One theory that we had was that the start current was above the 40A and caused one moter to go, and that forced the other moter to start two moters worth, and that caused it's fuse to go, but it doesn't explain what happened when we isolated the offending victors electronically. And it doesn't happen on both sides. I don't think, I wasn't around for it all.

[scitobor 617]

Originally Posted by Sparks333

Hmmm... An induction spike through a magnetic field? Interesting thought...

On the whole, I don't think so. It would need a pretty strong field (one I don't think the CIMS can create) to screw with the fuses in the ways you are describing. Theoretically speaking, you could do it, but it seems unlikely at best. Have you tried relocating the victors? That's the only real way to tell.

Sparks

We isolated/removed every known power source so I'm not sure what else could have caused the Victor's fan and it's LED to turn on only when we drove the right side. I also felt that the field would be too weak to cause this but we eliminated all known power sources which caused me to come to this conclusion.

Originally Posted by Bduggan04

Looking at the picture more, I see another issue. Remove the button heads on the speed controllers. They are too large and several of your connectors are touching the heads or are near to touching the heads. The best solution is to use nylon or some other type of plastic fastners. Check your wiring for shorts, and I believe your issue will be solved.

While this is true this does not explain how the Victor was being fully power while its fuses were out. Also, the connects on the offending Victor are no where near the screw head.

[jdiwnab]

Originally Posted by Bduggan04

Check your wiring for shorts, and I believe your issue will be solved.

We checked and double checked for shorts, partly because we had trouble getting both sides to run with one joystick drive (but it was becuse IFI Loader was set to the default hex and not the new hex.)

[Yan Wang]

Yes it can. Two years ago, we (ie professionals) welded our frame while the electronics were still mounted. Pretty much everything fried and we lost $1000 replacing the RC, victors, spikes, fuses, etc.

Say no to big EM fields around the FIRST electronics!

[jdiwnab]

Originally Posted by Yan Wang

Yes it can. Two years ago, we (ie professionals) welded our frame while the electronics were still mounted. Pretty much everything fried and we lost $1000 replacing the RC, victors, spikes, fuses, etc.

Say no to big EM fields around the FIRST electronics!

We already had our frame welded, but there arn't any shorts we can find. As I had said, we checked everything twice to find something wrong. We're just stumped.

[Bduggan04]

From experience, problems can often be fixed by fixing seemingly unrelated problems. I would advise that you try the following. It is what I would do if I was there.

Set a multimeter to Ohms

Put one probe on the frame. Use the other probe to check other spots on the robot such as the terminals of speed controllers. They should be isolated, but I suspect they are not.

You should also try removing all of the motors from the output side of the speed controllers and make sure the terminals are not touching the robot. The problem lies on the output side of the victors. This has to be true due to the fact it only happens when you run the motors on one side.

If the problem no longer occurs, connect the motors one by one and look for the problem. You may be able to isolate it.


Another thing you may want to consider is that you could have mixed the motor wires up. The fuses could be blowing because the motors are running in opposite directions in the same gear box.

To test this, remove all of the motor wires but the ones going to one motor. Run it and see which direction the wheels move. Then, disconnect it and run a different motor similarly, if they run the same direction, attach both motors to their speed controllers. Do this for both gear boxes. If one motor in a given gear box runs in a different direction than the other, reverse the polarity or revise the program.

One thing you need to keep in mind is that the victors can be powered through the output side. If you push the robot on the ground, the controller and the victors will all light up because the motors act as generators.

[Bduggan04]

Originally Posted by Yan Wang

Yes it can. Two years ago, we (ie professionals) welded our frame while the electronics were still mounted. Pretty much everything fried and we lost $1000 replacing the RC, victors, spikes, fuses, etc.

Say no to big EM fields around the FIRST electronics!

A welder is a little different than a few camper jack motors.