I have a few questions about the electrical systems for the robot. I’ve been looking all over FIRST’s website for the rules with no luck and I’d like to get this all squared away before kickoff.
Can we use a multiple wire cable with connectors on both ends(Ex. D-Sub) to connect say multiple encoders on a shooter down to the control board. Instead of having to run those tinyyyyyy little wires down through a bundle. Any ideas or examples of what you all have used in the past that is legal?
What are the rules of busing? With the motor controllers, can you run one wire from the GND plug of a single PWM output to more than one GND pin of a VEX Victor 884 or 888 motor controller. Looking in the schematic for the Digital Sidecar all the third pins are connected to ground on each plug. Would FIRST accept that?
I’m sure I’ll have more questions as they pop up but those have been the two bothering me recently.
To speculate on what is and is not legal for 2014 BEFORE the rules come out is pointless.
That being said: Once the rules DO come out (Saturday), READ THEM because they will answer ALL your questions.
Asking on CD “if something is legal” is also pointless: We are not the GDC, what we say has no value at competition. If the rules really don’t answer your question (read them again!), then your lead mentor can submit a question to the GDC via the FIRST website.
THAT being said: Wire things as shown in the diagram. You won’t save anything by daisy-chaining grounds, and you WILL increase (electrical) noise, complexity and reduce reliability and repairability. Bundling wires is OK, as is the use of connectors. YMMV depending on the rules though…
In the past, we have used ethernet cables to run the wiring for sensors and pneumatics. This has been legal in the past and it is much cleaner than running 8 small wires. 1 larger cable does the job.
You can also use a CAT5 coupler to make detachment of your wiring very simple. For example, if you had an arm on your robot and wanted to be able to easily remove or replace it, placing a CAT5 coupler near the joint or detachment point would allow you to take it off by removing 1 clipped ethernet connector rather than multiple tiny cables.
You can review last year’s rules here: http://www3.usfirst.org/roboticsprograms/frc/2013-competition-manual-and-related-documents
However, as Don said, you will still need to read the 2014 rules after kickoff, to see if there are any changes.
Thats a big 10-4 thank ya thank ya
Any multi-conductor cable has been legal in the past for sensor wiring provided that no power is supplied in the cable. If you are powering sensors, then the appropriate electrical rules for power wiring will apply. Usually #22 or #24 wire would be sufficient.
It is unwise to “common” PWM signals anywhere beyond the DSC. The generated noise and subsequent issues with driving your controllers makes this bad practice. (Look up ‘ground loops’ for general discussion) The PWM input of a speed controller is opto-isolated and by definition is supplying switched current to drive the isolator. The power supply and board layout of the DSC is designed with that in mind.
As mentioned for pneumatic valve input, multi-conductor cable has also been legal in the past, however, the length of your connection should be considered when choosing conductor size. Significant loss can build across a long, small gauge, cable making valve action unreliable.