Mounting 2009 Controller and Components

[frank.pendzich]

We just received the prelim kit of parts including the 2009 controller and associated components. The bench test directions specify the mounting of all the components on a peice of plywood or plastic. Is this really necessary. Can it be mounted on a sheet of aluminum instead? We want to mount the components in a sheet alumimun chassis that can be removed from the robot as a single unit to be tested on the bench. Are there rules stating that the controller components must be mounted on a nonconductive base?

[dlavery]

The cRIO has a grounded enclosure. The 2009 rules are not out yet, so no one can say whether it would actually be permitted or not for the competition. Regardless, mounting it on a conductive surface would be a REALLY BAD idea.

-dave



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[Zflash]

You can mount the electronics to aluminum. For protoype purposes and bench top testing wood is just less expensive and faster to work with.

[Joe G.]

We can't know for sure whether it will be a rule or not until kickoff.

However, this kind of rule is a rule for a reason: Its a good idea to have electronics mounted on a non-conductive surface for saftey reasons.

[Pat Fairbank]

I had heard about the cRIO having a grounded enclosure, but, oddly enough, neither I nor a bunch of other people were able to find continuity between any part of the cRIO's chassis and the robot's ground, on Team 1114's beta-test robot. Some people I talked to theorized that this could have something to do with the 12V to 24V conversion circuit - can anyone shed some light on this?

In any case, 1114 had the cRIO mounted (using Velcro), without incident, to an aluminium sheet along with the rest of the control system. It's feasible, but, as Dave indicated, its legality has yet to be disclosed.

[DonRotolo]

Originally Posted by dlavery

The cRIO has a grounded enclosure. .....mounting it on a conductive surface would be a REALLY BAD idea.

Perhaps mounting this to a conductive surface being a bad idea has more to do with electricity than the 2008 rules.

Static electricity impulses are bad for electronics, especially those that come with those yellow static warning labels on them - so touching any part of the metal mounting surface will conduct those pulses into your device - possibly with bad results.

Dynamic electricity (the counterpart to static, I think) flows along conductive surfaces, and if one of those big red cables happens to wear or get cut through, there may be some excitement - and that's meant in a bad way.

I can speculate on the 2009 rules, and electrical components will likely have to be isolated from the robot chassis, so you'd have to get rid f the aluminum anyway...so use the plywood for now and get the lexan for the production 'bot.

Don


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[minisimon]

It's also worth noting that if your chassis is grounded through the cRIO, then any short through the chassis also runs through the cRIO. This might be bad.

With regard to the lack of continuity between ground and the chassis even when the cRIO is mounted to aluminum: could it be because of the paint?

[EricVanWyk]

I can't speak for the 2009 Rules, look to the GDC for that.

What I can say is that regardless of the rules, please do not mount your cRIO or your Camera to a conductive surface. Both have grounded cases, which could provide an unfortunate current path.

I believe the cRIO's coating is non-conductive (NI, could you chime in here?), but I personally would not rely on that. The PD does have a small self-healing PTC in the cRIO's ground return path, so you shouldn't be able to do damage to it. However, it avoids damage by breaking the circuit, which will shut down your robot and possibly create a "match deciding failure".

In either case, connecting your cRIO or Camera to the chassis increases the likelihood of a bad chassis fault. In a properly wired system, two errors must happen before you short your battery through the frame - a positive AND a negative wire must hit the frame. If you don't isolate the cRIO or Camera, only a single positive wire must hit the frame to cause Badness 10k.

[Russ Beavis]

Addendum to Eric's comments -

The PTC in the ground return path for the cRIO's power supply will limit any chassis shorts that are conducted through the cRIO to an amp or 2. Definitely annoying and match-ending but safe.

There is no equivalent protection for shorts to the camera's chassis. I'm not at liberty to speak for the GDC but I'd be very surprised if using a conductive mouting for the camera will be allowed.

The above issues bring up a very important inspection task - WHEN you test for chassis shorts before shipping your robot (wink wink nudge nudge), you WILL detect a chassis short if your cRIO is attached to a conductive surface and bypasses any non-conductive coatings. You WILL detect a chassis short if you conductively-mount your camera. PLEASE fix the camera mounting issue before shipping your robot. Depending on the robot rules, if conductive mounting of the cRIO is allowed, you'll need to disconnect the power cable to cRIO when testing for shorted chassis.

Russ

[EricVanWyk]

Originally Posted by Russ Beavis

The above issues bring up a very important inspection task - WHEN you test for chassis shorts before shipping your robot (wink wink nudge nudge), you WILL detect a chassis short if your cRIO is attached to a conductive surface and bypasses any non-conductive coatings. You WILL detect a chassis short if you conductively-mount your camera. PLEASE fix the camera mounting issue before shipping your robot. Depending on the robot rules, if conductive mounting of the cRIO is allowed, you'll need to disconnect the power cable to cRIO when testing for shorted chassis.

Conductive mounting of the cRIO is not allowed for any teams I mentor.

[Dale]

Besides putting Velcro on the back of the cRIO, has anyone come up with a secure way to mount the cRIO to a control board? It only has theaded holes on one end. I guess Velcro has the benefit of making it possible to quickly change the cRIO from one robot to another but it seems like there should be a better way.

[AdamHeard]

Originally Posted by Dale

Besides putting Velcro on the back of the cRIO, has anyone come up with a secure way to mount the cRIO to a control board? It only has theaded holes on one end. I guess Velcro has the benefit of making it possible to quickly change the cRIO from one robot to another but it seems like there should be a better way.

There are 3 clearance holes in the bottom, the modules may be obstructing the view.