IR Beam Breaking Circuit

[Steve Warner]

We are using a Banner sensor on our robot this year and were asked by a KC inspector to add an inline fuse since the wire from the sensor was < #18 on a 20 amp breaker. The use of an inline fuse is probably the smart thing to do but is it required and, if not, is that what most of you are doing anyway?

[MCahoon]

By R47, he could (should) have required you to replace the wire with a 18 AWG wire or larger. You did not specify the wire size you used, but it would be reasonable to use an in-line fuse if the value of the fuse was selected to be appropriate for the wire size, and was chosen to be a "fast blow" type fuse. Situation becomes ambiguous though, unless you can provide documentation about the device and it's load characteristics.

[Alan Anderson]

Originally Posted by Steve Warner

We are using a Banner sensor on our robot this year and were asked by a KC inspector to add an inline fuse since the wire from the sensor was < #18 on a 20 amp breaker.

Originally Posted by MCahoon

By R47, he could (should) have required you to replace the wire with a 18 AWG wire or larger.

When the wire is permanently attached to the sensor, it's not reasonable to require it to be changed.

Our 2009 robot design had a 5A fuse inline with the 12V power to the Banner sensor for exactly the reason the KC inspector gave. (There was a brief moment of contention when one of the inspectors at DC didn't think such fuses were legal, but he was of course unable to come up with any support for that opinion in either the manual or the inspectors' checklist.)

[Al Skierkiewicz]

Although I have tried to get the powers that be to accept the use of 5 amp breakers in the PD, the rules allow you to still use the wiring as attached to the pre-wired sensor. Please read the rules carefully next year in case I succeed.

R46
F. Custom circuits and sensors powered via the cRIO-FRC or the Digital Sidecar are protected by the breaker on the circuit(s) supplying those devices. Power feeds to all other custom circuits must be protected with a dedicated 20-amp circuit breaker on the Power Distribution Board.

As an alternative you could also wire the sensor to a enclosed perf board that contains a wired fuse and allows power wiring to continue to the PD via #18 wire.

[Steve Warner]

Another question here. Can more that one Banner photo sensor be protected by a single 20A fuse? A single #18 wire could be connected to the breaker and then to a smaller fuse. Can the load side of the smaller fuse then be connected to more than one sensor? I don't see where the rules address this unless it's R46 F or G if this would be considered a custom circuit.

[Bongle]

2702 had a moderately unique solution: rather than have the ball break a beam, we mounted both the emitter and sensor on the same chip, and stuck that inside our vacuum cup. When a ball was close, or when a ball was grabbed, it would reflect IR back to the sensor.

This meant we only needed one mounted place, and it meant that we weren't tricked by things like ramps, robots, or chains getting in the way (unless they fully blocked the vacuum cup).

[Al Skierkiewicz]

Originally Posted by Steve Warner

Another question here. Can more that one Banner photo sensor be protected by a single 20A fuse? A single #18 wire could be connected to the breaker and then to a smaller fuse. Can the load side of the smaller fuse then be connected to more than one sensor? I don't see where the rules address this unless it's R46 F or G if this would be considered a custom circuit.

Yes,
Multiple sensors can be powered from a single 20 amp breaker. All other electrical rules apply however, including only one wire per Wago terminal. You can bring the sensors to a common enclosed circuit board (preferred) or you can tie them to a barrier strip or terminal block as long as the connections are insulated. It can be considered a custom circuit and so the stated rules allow you to fuse the power line in the circuit per par G. If you use the circuit board method, a fuse on the board is a good idea. Then you can connect the sensors to the board and use your own connector to wire the outputs to your breakouts.

[Steve Warner]

Thanks Al, I thought that might be the case but I wasn't sure if this would be considered a custom circuit. Very good information.

[Azores]

Rather than using a breakbeam sensor, we rigged up an IR rangefinder instead. The voltage it returns increases as an object moves closer to the rangefinder. So with it mounted in a fixed position in our frame, there's a baseline value that the voltage is steady at when there is no ball in position. When a ball enters the frame perimeter, the voltage spikes up (well alright, it increases by less than half a volt ). So the code just compares the reading every cycle to the reading taken upon initialization and when it increases enough, alerts the driver that a ball is in place through the dashboard (still getting this to work), or allows the bot to know when to kick in autonomous.