Victor reversed wiring...

[Al Skierkiewicz]

Fox,
Unfortunately the answer is NO, there is nothing in the way of backward protection. The FETs have a diode that is across the terminals that results from the manufacturing process. If you look at the spec sheet you can see the diode and the direction in which it conducts. The four legs of the "H" bridge do conduct as a full wave bridge and provide power of the correct polarity at a reduced voltage backwards to the power rails of the controller. These diodes do have a forward voltage drop though, so the conducted voltage isn't quite what you would think. Remember that when the controllers are powered correctly, and a 'coast' condition is commanded, all of the FETs are off and current only flows through the diodes (the same is true for pushing with power off). When a 'brake' is commanded both low side legs of the controller are turned 'on' resulting in a short across the motor but no power being delivered to the controller internals and no current flowing through the diodes. In the case of the power leads being attached to the output terminals, we don't know if they were wired in a normal polarity. In any case, considerable current may flow through the controller restricted only by the breaker feeding the device. Depending on the duration (or repeated attempts to determine the cause) significant damage to the device might be the result. Magic smoke is almost always the result.

[pfreivald]

Originally Posted by Al Skierkiewicz

Depending on the duration (or repeated attempts to determine the cause) significant damage to the device might be the result. Magic smoke is almost always the result.

The fun part about this is that robots get pushed around all the time... on the field, by other robots. I have found thus far that, while there is no good reason that I know of for this to be true, Victors used on the drive train tend to hold up well, while Jaguars used on the drive train need to be treated as consumables on a yearly basis (or so).

That's entirely anecdotal, mind.

[MrBasse]

If the wires were truley just connected and then powered up on the motor side they should actually be fine as long as no commands for driving were sent to the controller. Not saying there isn't any chance that damage occured but without activating the speed controller, there should be no real concern. Our lead mentor uses Victors frequently and his response to this situation was to shrug his shoulders and say "it's fine"

[fox46]

Al- I've never seen the schematic and doubt that I could fully interpret it if I did so I'll concede there is no specific engineered protection in the design. That being said, I still believe there is an inherent tolerance to this condition in the design of the controllers, whether intended by the designer or not.

I would run them during testing and so long as everything works fine, run them in competition. Just be weary that if you begin to have trouble at the competition that there is a possibility it is due to a damaged controller.

[Al Skierkiewicz]

Fox et al,
It is my firm belief that if you want to play on Einstein, you must have good engineering practice. That being said you believe what experience tells you and don't leave anything to chance. You don't wait for a failure to occur, you anticipate and replace when needed. It is for this reason we solder our crimp connections, keep spares handy and plan for easy replacement of everything in the field. Murphy is alive and well, why encourage him?

[EricVanWyk]

Originally Posted by Al Skierkiewicz

It is my firm belief that if you want to play on Einstein, you must have good engineering practice.

It seems like we've been answering the "good enough" question a lot lately. I think it is the difference between a robot that is able to compete, and a robot that is able to be competitive. A team might be able to limp by on partially broken hardware, but they have to be willing to accept that the cost is measured in lost matches spent dead in the water, and time spent debugging systems with multiple active failure modes.

So fox, please feel free to make that value judgement for your own team, but please hesitate to make it for other teams without making them fully aware of the risks they are assuming. Covering the real risks and real costs does them a disservice.

[fox46]

Well I know none of my teams can afford to go out and buy a brand new fleet of speed controllers, let alone in the last week of build.

Everyone has different definitions of good engineering practice. I detest the "replace and toss it" mentality. I would argue that "Test and replace if necessary" is an excellent engineering practice and is that which is respected far more often in the real world. In today's society, everyone is too ready to throw out an otherwise perfectly good component in favor of something that is *new*. I personally have a big problem with this kind of "disposable" thinking.

Should they replace them? Sure- if they are worried, have the money and time- might as well.

Is replacement definitively the *one and only right* thing to do? No.

[Al Skierkiewicz]

Originally Posted by fox46

Everyone has different definitions of good engineering practice. I detest the "replace and toss it" mentality. I would argue that "Test and replace if necessary" is an excellent engineering practice and is that which is respected far more often in the real world.

Fox,
I work for a TV station in the third market of the US. I would be fired for taking that attitude. Failure of a component that was thought to be suspect that results in a loss of air time is unforgivable in my line of work. We recently replaced a $35K output tube on the transmitter for fear it would cause a loss of air time based on a several factors it exhibited in operation. One of which is a nearly two day replacement time window. While the tube tested fine, there was enough doubt in it's continued operation that the decision to replace was made.

Mark,
Good luck!

[fox46]

So fox, please feel free to make that value judgement for your own team, but please hesitate to make it for other teams without making them fully aware of the risks they are assuming. Covering the real risks and real costs does them a disservice.

I have not made any judgments for anyone. If you look to someone on the internet to tell you how to run your team then that's your own problem. This is the internet- My posts and any other posts on this and any other forum should be taken as nothing more than personal opinion. To take for fact the statements of someone you have never met and have no indication as to their experience or creditability is a very risky business.

When I post to this forum I don't expect anyone to take what I have to say as fact. It is their responsibility to determine how much or how little of my or anyone else's advice they decide to follow.

This Thread has covered all of the risks and gambles associated with this issue. Presenting an alternate solution is by no means a disservice.

[fox46]

based on a several factors it exhibited in operation. One of which is a nearly two day replacement time window. While the tube tested fine, there was enough doubt in it's continued operation that the decision to replace was made.

And these controllers have exhibited none - nor any signs of damage....

Anyway, I'm done here. I can't even keep up with the pace of these posts so I guess 3647 better do as told by Chief Delphi and replace all their victors.

[fox46]

We will be running the victors as is for now, but have a full replacement set coming in before competition.

Good call-

Please let us all know how long they last before they fail.

[Joe Ross]

Originally Posted by fox46

When I post to this forum I don't expect anyone to take what I have to say as fact. It is their responsibility to determine how much or how little of my or anyone else's advice they decide to follow.

Realize that many high school students haven't yet discovered this level of discernment. I'd rather not be the person who helps them figure that out the hard way.

[Al Skierkiewicz]

Fox and Mark,
I am sorry that I have pushed this subject with you. It is not my intent to insist that the devices be changed and I hope you are not taking it that way. There is no hard and fast rule that I am quoting on this subject that requires you to change anything. It is certainly possible that these devices will never fail and I hope they never do. I fear I was responding as if the discussion turned away from Victors to true engineering practice and that was the view from which my last posts were written, as strictly an opinion. I am sorry if my posts were perceived as an attack. I most certainly did not intend that when I responded.

[Kevin Sevcik]

I'm going to second that the Victors probably aren't too badly hurt by this, depending on how long the were run like this. If the motor wasn't under load, it was mostly running at the free-speed current of a couple of amps. I don't have a schematic for the Vics, but everyone thinks Jags are wimpier, so I'll start there...

One of the FETs has a 4mOhms on resistance, so it'd be dissipating about 1.6W under normal conditions. The diode has a 1.0V drop, so it could handle 1.6A and generate the same thermal load. Which means you could run 3.2A backwards through the Jag and it'd be about the same as a 40A load normally. So I think the vics would be relatively fine if you hooked them up backwards and didn't try to run them, provided your motor wasn't under a significant load.

EDIT:That said, Eric and Al are right that it's no longer an entirely trustworthy part once you've taken it out of spec in some fashion. If I were a cash-strapped team I'd use it and try to be prepared for it failing on me. If I had the opportunity to replace it, I'd permanently brand it questionable and slap it on the practice bot.

[Shaun Coon]

i did this with 2 BLACK JAGS this year and they work on and off so we arent using them ny more. THEY are now very prone to act up so keep your eve on them .