Re: reverse-voltage protection
 

How about a partial solution?

Earlier I mentioned putting a diode in front of the 5v and 3.3v linear regulators. This would protect everything except the power MOSFETs and the electrolytic capacitor. The only impact on performance would be a higher minimum voltage.

Say a Jaguar with such protection had reversed voltage. Let's take a look at what it would take to fix it:
The power MOSFETs (FDP8441) can be bought for less than $3 apiece at Digikey.
The electrolytic capacitor is an inexpensive and easily available part.

Both the capacitor and the MOSFETs can be hand soldered by someone with reasonable experience.
Thus, the Jaguar can be fixed by an end user for less than $30.


Does anyone have a better solution?

Re: reverse-voltage protection
 

Bot,
This is a very costly lesson, lucky you only lost two Jaguars and not the PD and other stuff. This suggestion should go in another thread as well but check and recheck before applying power. There is a lot of ways to do this. Get a red sharpie and mark the battery positive terminal. Red to Red to Red gets the right polarity to the robot. Check every battery with a voltmeter before connecting to the robot. The Anderson plugs actually have a big "+" marked on the connector body. Don't trust that the person who assembled the connector pushed the correct wire into the body. Most voltmeters have a polarity sign in the display, even my $3 flea market pocket voltmeter has one. Check the battery before connecting, then before any breakers are added to the PD, check the voltage again with a battery connected. Check every battery you own the same way. Then add breakers after you have checked the wiring from each breaker to it's destination. Have someone (usually two or three) check you. Then when all agree, power the system.
Here's a couple of hints that are common problems...
1. Whiskers at the termination point. A stray strand of wire, in a connector, touching an adjacent wire in a connector (PD to Crio and sidecar power). This is easily handled by not stripping the wire too long. Twist the wires before insertion. If there is any copper showing when you are done, hold the wire in one hand and pull down on the insulation towards the connector with your other hand. The insulation will stretch and cover the exposed copper.
2. Use heatshrink to cover up exposed wiring. It is cheap and fun to use.
3. Insulate the battery terminals when you are finished terminating the power wiring. The battery is capable of 600+ amps when fully charged. It won't kill you but it can cause a halacious fire in the right setting.
4. Use the "tug" test on crimped terminals. Pull on the terminal with all your might, it should not pull off and it should not move. A ratchet crimper will cure most of these problems and costs about $50.
5. Tie down all wiring near the termination (PD, connector, speed controller, Spike, motor, etc.) The robot moves, sometimes violently, so don't depend on the terminal or connector to take care of itself.
6. Inspect every connection after every match. Use your eyes, ears and nose.

Re: reverse-voltage protection
 

Al,

FIRST didn't put out a 'Best Practices' Manual last year; it was a great document, especially for rookie teams. If they don't do it again this year, I suggest a compilation of 'Best of CD' to be made available. While rookies do need to learn how to search CD, I think a compilation would be a good resource for them.

Re: reverse-voltage protection
 

Jon,
That document never made it to published status last year. I am pushing for a re-release this year. Yes it is a good document that rookies need.
It can be found here...
http://www.usfirst.org/uploadedFiles...%20Rev%20A.pdf

Re: reverse-voltage protection
 

Did someone learn a valuable lesson that day? If so, it's worth a couple of Jaguars.

Try that with a $250,000 device and see how long you remain employed.

Re: reverse-voltage protection
 

This is interesting. My sophomore year I made the same mistake of hooking it up backwards, and what happened to us was that the battery simply turned into a short since the PD Board acted as a reverse battery protector. Wires were fried before we stopped it, but that was all. How did you manage to even run any components with a reversed battery?

Re: reverse-voltage protection
 

I don't know the specifics, because i wasn't at the robot at the time. I just know that we damaged at least 2 jaguars.

As Kamocat has said, if the processor and other stuff was protected from reverse voltage it might have saved our jaguars. I do agree that protecting the entire jaguar would could be cost prohibitive.