Things that new members need to know about electronics

Our team has a small, in house competition. We divide the team into 4 small teams, and spread the veterans out onto those teams. Then, our mentors give us a game, ususally involving bots only 18x18x12. this teached the new members how to wire, build, and make mistakes. All in all, it's out most educational couple of weeks pre season.

[sanddrag]

I would emphasize good wire routing. The wiring system should somewhat resemble a system of streets and/or freeways (aerial view). Do not make every wire a straight shot between two points, but on the other hand, you usually don't need a 22 inch long wire to connect to a point 5 inches away. You get what I'm saying. Channel your wires neatly. Put them into thoroughfares.

[DonRotolo]

I agree with the Crimping lessons, these are easy to do poorly and that will cause problems.

I also agree with Al about wiring neatness, a rats nest is impossible to troubleshoot, tight wires fail, and sloppy work is inexcusable. Make it look like a work of art.

I would also emphasize battery safety and the need to keep them charged. There are some threads on this from earlier this year that you can search for.

Don

[Al Skierkiewicz]

OK,
I have a list. First and foremost, teach which end is the hot one on a soldering iron. A burn from a hot iron is the gift that keeps on giving and the smell of burning flesh is something you will never forget. Next work on safety using all tools, small hand tools especially. An errant student with a pair of wire strippers can easily take out an eye or other damage when out of control. Learn to gauge the safe distance by extending your arm and seeing if it bumps into anyone or thing. Get used to moving until there is free space around you and you have some experience in using the tools.
Next on the safety list is battery. Most people think that the battery is safe because it is only 12 volts, but the power density is high enough to cause burns and other injuries if misused. No loose chains or dangly bracelets around the robot because of the chance of electrical contact. Batteries are heavy, always use two hands and never, and I mean never lift by the battery cables.
Next on the list is practice, practice, practice. You can't be good at crimping, soldering, wire runs, or layout the first time. Know that a good solid crimp is one that has just enough insulation removed to allow the wire to penetrate into the contact (about 1/4", the width of your little finger nail), and has the right amount of force applied to the tool. Test the connection by pulling and pushing. If the contact moves, crimp it again. A bad crimp will heat up and deliver less power to your motors.
Know the electrical portion of the robot manual by heart. I will test you on it later. The manual, FIRST_Guidelines,_Tips,_&_Good_Practices_Rev_D http://www2.usfirst.org/2006comp/oth...ices_Rev_D.pdf on the First website also has an excellent section on electrical. I didn't write it, but it is an excellent reference.
Just as in most everything, the shortest distance between two points is a straight (or nearly straight line) Centrally locate the battery and the fuse panel. Then move out to the speed controllers and spikes and then finally to the motors. As a rule of thumb, at stall, each foot of a single #10 wire will drop 1/10 of a volt, #12 will drop almost 2/10 and I won't even talk about #14. I like to use the "wire foot" analogy. 1 WF(wire foot)=1 foot of # 10=1/10 volt@100amps. So #6 is .4WF/ft, #12 1.6WF/ft, #14 is 2.5WF/ft. All you have to do then is measure the wire length (don't forget both wires) and calculate for your wire size, then add 2WF for the speed controller and you will know how much voltage you can deliver to a motor. (remember the battery at full charge has an internal resistance of 11WF) Good crimps should have negligible drop but bad crimps can have easily 2WF per crimp or more.
On the fuse panel use the first position for the RC power (on the IFI panel either #1 or #2) to keep the voltage at the highest for this critical component. If the RC is not happy, you don't drive.
Before applying power or even before hooking up the battery, make sure each member of the electrical team has looked over every connection. Make sure hardware is tight and all wires are the correct polarity. Speed controllers get really unhappy when connected backwards or with the wrong polarity and again the RC is the heart of robot, make sure it is correct.
Finally, when you are ready to power the robot, make sure no one turns it on until they are sure no one has a hand inside and the robot will not run off and hurt someone or something. We have the person who is turning the robot ON, shout "clear" to make sure everyone is away from the robot and moving appendages. Keep the wheels off the floor for the first test and during controller calibration.
We use 3M color wire coding tape to mark everything. The breaker, breaker position, wire going to the controller, PWM output on the RC, PWM cable, fan on the controller, the wire going to the motor and the motor with the same color tape. This way if the "red" motor isn't turning and the fan on the "red" controller is turning then we go to the "red" circuit breaker position on the panel and see if the "red" breaker in in place. If the "red" controller is showing no PWM connection, then we follow the "red" PWM cable back to the "red" position on the RC to see if it is connected. Mark wires at both ends. No need for schematics to troubleshoot on the field.
Above all, remember you can ask me anything at anytime. I check here almost everyday, sometimes more often.
Keep safe and have fun.