Electrically Isolating Electrical Components

[DavidB]

I was wondering what they mean in the following:

<R41> All wiring and electrical devices, including all control system components, shall be electrically isolated from the ROBOT frame. The ROBOT frame must not be used to carry electrical current (e.g. this is necessary due to polarity reversals that occur under certain operating conditions such as during motor direction reversals).

The chassis for the cRIO Mobile Device Controller and the supplied camera have grounded enclosures. Under this rule (and for their protection), it is REQUIRED that they be electrically isolated from the ROBOT frame when installed on the ROBOT.

Basically On our robot we have a drive train and then we have metal plates attached to the where we are Mounting our electronics. From my understanding the rule is referring to using your robot chassis as ground.
So basically I'm wondering if what we are doing is allowed (Having electronics mounted on a metal plate attached to the drive train). Also what do they mean by the ground enclosures for the cRio and Camera?

Thank you for any help you can provide,
DavidB

[Vikesrock]

Chassis grounded means that the device's enclosure is connected to it's electrical ground.

To isolate the cRIO from the robot chassis means that no conducting material (ie metal) can touch both the cRIO and the robot chassis. There are a few ways this can be accomplished.

If you are already set on using metal plates to mount your electronics to then the easiest way to accomplish isolation is to use nylon bolts, nuts and washers to mount the cRIO. Place nylon washers between the bottom of the cRIO and the metal plate to isolate the cRIO chassis itself. The nylon bolts are necessary to prevent the fastener from being a conductor between the robot chassis and cRIO chassis.

Another method would be to mount the cRIO to a non-conductive material such as lexan.

[Al Skierkiewicz]

David,
Lexan or other insulating material can be used between the Crio and the camera to block them from contact with the robot frame. Please be advised that the camera screws, on the back of the camera, stick out just enough to contact any metal behind the camera (the camera mount kit with servos). The method inspectors use to check isolated electrical systems is to first disconnect and/or remove the battery. Then, using a VOM or DMM. check for resistance between the robot frame and both the negative and positive terminals on the PD. Any reading less than 100,000 ohms indicates you have a sneak path that needs to be corrected. You are probably asking yourself why on this rule about now. If two robots come in contact somehow and one of them should contact part of the other robots electrical system, current would flow through the robot frames and the common connections of parts on the robot. Although highly unlikely, a contact of this type may cause a main breaker trip, or a trip of the PD protection breakers for the Crio and other interfaces. We want everyone to play an entire match so this small addition prevents any action that would result in a robot being disabled. In past years, the most often frame fault has been caused by improper insulation under the KOP sensors, e.g. the gear tooth sensor. All teams should make this simple check during build and often during competition.

[EricVanWyk]

A more likely incident involves a single point shorting - for example, a wire coming loose and contacting the frame. If you are in compliance, this won't cause any damage and you can fix it after the match.

If your frame is not isolated, this single point fault will instead become a match deciding failure.

For example, assume you grounded the frame through the cRIO and the stray wire is positive. Your battery is now shorted through the cRIO frame, which will force the PD to cut power to the cRIO. Instead of having a single wire to fix at the end of the match, you will also need to fix having a trailer full of orbit balls.

If you manage to short through the camera, it is possible that you will permanently damage the PD and/or the camera.

Check early, check often.

[MrForbes]

Originally Posted by Al Skierkiewicz

.....using a VOM or DMM. check for resistance between the robot frame and both the negative and positive terminals on the PD...... All teams should make this simple check during build and often during competition.

We always have trouble getting a reading on our ohm meter when we try to measure the resistance between electrical parts, and the chassis.

darn wood chassis....

[yodameister]

This is one of the reasons we are using a fiberglass chassis. Fiberglass is a great insulator and it is transparent to radio waves, so there should be no conflict with wireless transmissions as well. Thank you Creative Pultrusions for the sponsorship!

[DavidB]

Okay thank you for the replies. I isolated the cRio buy placing a sheet of lexan underneath and by attaching it with nylon nuts and bolts, so the cRio has no contact with the frame at all. I will do the same to the camera when we set it up.

[Paul11]

We always use polycarbonate (Lexan) for the ENTIRE board and have yet to have a grounding issue.