Wire color...

[fsgond]

Originally Posted by eagle33199

On the contrary Al... we find using two colors to be helpful and to help avoid confusion. If you need to disconnect something at any point from the speed controller, hooking it back up could be confusing if both leads are the same color - potentially hooking it up backwards could be an issue.

IMO (which is not the opinion of the GDC or the inspectors), It's always beneficial to use two colors for motors, and always have them wired to the speed controllers in the same way (red to the M+, black to the M-, for example). This way, you can avoid mistakes a lot easier, and ensure you always hook it up the same way for your programmers (or they'll hate you when they have to change the direction of things in code constantly).

Our policy is to use different connectors on the wires so that there is no way of hooking anything up backwards. This can be a big problem if there are 2 cims in the same gear box that run opposite of each other.

[Jon Stratis]

Originally Posted by fsgond

Our policy is to use different connectors on the wires so that there is no way of hooking anything up backwards. This can be a big problem if there are 2 cims in the same gear box that run opposite of each other.

in that situation (two CIM's that have to always run opposite each other), we would handle it in code, and still have the red lead go to the M+ and the black to the M-. What do you mean by different connectors?

[dtengineering]

We generally use all yellow wires to go from our relays/speed controllers to our motors. I'd say about 50% of inspectors express a concern over this, so we politely point out that the reason we do this is to alert people that we don't know whether the wire is going to be + or - at any given time, and explain how the relay and speed controller work to change direction of the motors.

Usually that satisfies them. They come away knowing a bit more about robots and FRC inspections (many are doing this for the first time and are just trying to be thorough), and we're happy to help educate them about the reasons for our choice. If they still have concerns we advise them to discuss the matter with their lead inspector, check the rule book, and get back to us.

We've never had a problem.

Well, with coloured wires, that is. We used speaker wire once many years ago (only "downstream" of the controls), and the lead inspector did raise a concern that it had a different fire resistance rating for the insulation than did the less flexible automotive/home wiring. It turned out his concerns were based on the fact that he had built speaker wire into the walls of his house and then had a building inspector make him rip it all out.

We pointed out that all of our wires were significantly larger diameters than required by the rules, and that the wires were not buried out of sight in an insulated wall, so the chances of overheating were essentially zero. This was a big deal as the wiring runs were not going to be replaced in less than four to six hours of intensive work, and we needed that time for other issues.

Note that we kept our sarcastic comments about the state residential building code not really applying to robots to ourselves and, while firm with our arguments, went out of our way to be respectful.

Thankfully the lead inspector, with the encouragement of the tournament director, sought a second opinion "from FIRST" on Thursday night. I don't know who they called, but: a) we passed tech WITH the speaker wire and b) we've been very conservative with our wiring choices ever since.

FIRST usually makes the right call, if you give all the volunteers a chance to do so by being polite, listening to what you're being told, and presenting a calm, reasonable explanation of your position.

Jason

[Al Skierkiewicz]

Jason,
It really depends on the speaker wire but what is of prime importance is the ability of the insulation to withstand voltage breakdown. Most wire is capable of withstanding 300 volts which we never achieve. Speaker wire is generally unrated but typical home systems running 100 watts per channel can easily peak over 80 volts P-P so the wire is able to handle that. Building inspectors following most electrical codes expect/demand that any wiring over 25 volts must be in conduit. It is for this reason, that PA amplifiers have a 25 volt output as well as a 70.7 volt output. It doesn't change the fact that higher voltages are present, but make the inspector happy. In many states, conduit is not required in residential installations. Minnesota is one of these and the wire used is a dual insulation type.