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Unread 04-03-2018, 11:49 AM
Brhea Brhea is offline
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Problem with REV Robotics Magnetic Switch

Has anyone had any issues with the Rev magnetic limit switch?
http://www.revrobotics.com/rev-31-1462/

We mounted one of these on the bottom of our elevator and connected it to the RoboRio to reset the encoder on our elevator motor. This established a zero at the bottom of travel on the lift. However, at least 2 times during a competition the Rio detected that the switch was on when the elevator was not near the switch. (the magnet part was mounted on the elevator). This zero'ed the encoder and made the Rio think that the zero was at about 3 feet. We disabled this in our code. However, we put added the switch to correct for another problem where our chain that drove the lift skipped a tooth.

I suspect that electrical noise on the wires may have caused the problem. Does anyone use filtering with these switches?

The switched seemed to operate fine when tested and the problem was only seen a couple of times before we disabled the switch in our code.
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Unread 04-03-2018, 12:08 PM
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Re: Problem with REV Robotics Magnetic Switch

Quote:
Originally Posted by Brhea View Post
Has anyone had any issues with the Rev magnetic limit switch?
http://www.revrobotics.com/rev-31-1462/

We mounted one of these on the bottom of our elevator and connected it to the RoboRio to reset the encoder on our elevator motor. This established a zero at the bottom of travel on the lift. However, at least 2 times during a competition the Rio detected that the switch was on when the elevator was not near the switch. (the magnet part was mounted on the elevator). This zero'ed the encoder and made the Rio think that the zero was at about 3 feet. We disabled this in our code. However, we put added the switch to correct for another problem where our chain that drove the lift skipped a tooth.

I suspect that electrical noise on the wires may have caused the problem. Does anyone use filtering with these switches?

The switched seemed to operate fine when tested and the problem was only seen a couple of times before we disabled the switch in our code.
Spurious noise on the signal line might cause this, and a .1uf cap may help. That being said, usually false triggers on a mag switch is caused by a nearby magnetic field like those generated by motors. Are there and motors near the switch?
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Unread 04-03-2018, 01:54 PM
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Re: Problem with REV Robotics Magnetic Switch

I would suspect a stray magnetic field triggered the sensor. There are three hall sensors inside the case, so that it can detect a magnet on 3 sides of the sensor.

In addition to Daniel's question about the sensor's proximity to motors, how long are your signal wires? Would you be able to post a picture of the sensor in your mechanism?

Feel free to send us an email at support@revrobotics.com if you would like.

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Unread 04-06-2018, 06:04 AM
Brhea Brhea is offline
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Re: Problem with REV Robotics Magnetic Switch

It will be a few days or a couple of weeks before I see our robot again. I'll take a couple of pictures then and post.

I think there is an RS775 motor that is at least 4 to 6 " away.
The wiring is probably 12-18" long max.

This was a very spurious problem. It happened at least once and at max twice. When it happens it causes major problems.
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Unread 05-21-2018, 10:10 AM
Brhea Brhea is offline
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Re: Problem with REV Robotics Magnetic Switch

I finally made it back to our school for this year's wrap up meeting and I took a picture of the installation of the switch (see attached jpg). There are not any motors nearby and the cable does not route near any motor controllers or power cables.

I also inspected the RoboRio for any metal shavings that may have been in the DIO bus that could have shorted the pins and pulled the input voltage down. There were none.
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