Victor Burnouts

[Mark McLeod]

This year for the first time we had recurring problems blowing victors.

The (6) FETs on one direction of the “H” would all burn out for some reason. Luckily no underlying damage was done, so it was only a matter of replacing 90 cent FETs, but we haven’t come up with a definitive reason for the failure.

The obvious suspects are metal chips, but the victors seemed to be clean when they are pulled apart.



Any of you have unusual victor issues this year, or have other interesting theories on blowouts?

[Matt Attallah]

When do they blow for you? What where you doing when they failed? High amperage draw or just some 'fun driving' out-n-about with the robot...

I don't think we had any problems....

[Mark McLeod]

Originally Posted by Matt Attallah

When do they blow for you? What where you doing when they failed? High amperage draw or just some 'fun driving' out-n-about with the robot....

Oddly enough nothing in particular. One on our wench blew as we were doing a systems check before it went into the crate on the ship date and pulling the wench cable out by hand. Luckily, only one blew during actual competition, so that one on a drill was probably stressed, but not unusually so. It wasn't during a pushing match.

We didn't have any problems with victors we'd rebuilt, so I suppose it could have been a bad batch. I found it interesting that all the FETs would be burned out, but that may have been because we weren't noticing when just one FET went and only recognized it when power to a motor was gone completely after the remaining FETs were overloaded.

[Al Skierkiewicz]

Were you powering the fans and were they running at the time of failure? What exactly was the failure? Did the FETs short or open? Did the circuit breakers click prior to the failure?

[Ryan M.]

We had at least two Victors fail on us. We had a few extras and didn't have time to mess around with figuring out what was wrong, but, yes, we did have problems with them...

[aaronbr28040]

My team had no problems with the Victors this year. We have run the robot even harder than we did at competition once we got it back. Today we ran it for almost 2 hours straight with breaks every once in a while, pushing objects around, showing off, etc. and we still havent had any problems..........even after carrying me around. I do know that we check to make sure our fans are running before we start up the bot for an event but they have been fine. I still havent had a Victor die on me (883's or 884's) though i have melted the pwm cables going to them .
-Aaron
[edit] Also what type of drive system are you running? Are the Victors dealing with high current loads often? [/edit]

[Mike Hendricks]

We had no problems with the victors (or fuses) at all this year. On the other hand, our driving was done with 2 drills, the bosch gearbox and a 2wd setup - According to what I've been told, that setup puts a fraction of the strain 4wd and 6wd bots on the motors. We ran the same 2 motors for almost our entire build season, the sacramento regionals (9 seeding rounds, and a few quarterfinals), and the practice day at atlanta. We saw the bot was moving slower than usual, and the driver said it was reacting slower. We had 4 extra drills in boxes, and they didnt take too long to swap.

We had spare victors ready to go, because we were told (and read on CD) about the magic smoke. Hopefully innovationfirst doesnt change them for the 2005 season .. and we can use the spares if we need to

[Mark McLeod]

Originally Posted by Al Skierkiewicz

Were you powering the fans and were they running at the time of failure? What exactly was the failure? Did the FETs short or open? Did the circuit breakers click prior to the failure?

Fans were always powered, we've had no circuit breaker's popping.
I believe the FETs opened, but I'll have to verify and get back on that.

[fred]

We had a lot of problems with them at Chesapeake I believe. Twice I think, we extensively went back over the code and wiring and then it was like "Maybe we should try a different speed controller." and the new one worked. I dunno if we ever figured out what it was though. Too busy trying to get the robot ready.

[Shu Song]

our fan blow on us once. It was very mysterious. We were testing out a camera on the robot by driving around just the day before. when we came in the next day, the fan just wouldn't work. Nothing serious, just replaced it, but its very puzzling.

[copperhead47]

Originally Posted by fred

We had a lot of problems with them at Chesapeake I believe. Twice I think, we extensively went back over the code and wiring and then it was like "Maybe we should try a different speed controller." and the new one worked. I dunno if we ever figured out what it was though. Too busy trying to get the robot ready.

hey fred- its always good to have a trouble shooting list (for everyone not just fred) so that you can check for the simple stuff first then progress from one to the next and narrow it down to what you think it is and keep testing testing testing. and yes replacing the SC is the obvious one but we had a wire slip 1/2 way out of its contact and we had no idea why the SC kept cutting out and shuddering plus getting very hot. so another step i have for you is to check your contacts!!! among other things- but ill leave it to you to create your own list- trust me its different for all of us

[copperhead47]

ok- time to make myself sound like a noob- whats an FET? ive been in FIRST for 3 years and im a senior and ive seen some pretty crazy electronics systems. for instance- 357 has a self designed omni drive that is some of the best engineering i've ever seen. but part of that engineering was to tear a huge hole in the RC and add their own circuit of an original design into the system. pure genius. I digress, if anone could help me with my question(s) that would be great

[Al Skierkiewicz]

FET stand for Field Effect Transistor. More accurately the Victors use Power MOSFETs or Metal Oxide Semiconductor Field Effect Transistors. The nature of these little beasties is a micro amount of drive current, fast on and off times, very low "on" resistance and the ability to leap tall buildings in a single bound! Effectively they act like a bidirectional switch that is controlled by voltage and can deliver 64 amps at less than .012 ohms between two current carrying pins. (i.e. source to drain resistance) So with three FETs in parallel for each leg, the entire package drops as much voltage as 4 feet of #10 wire (that's two conductors, one red and one black)

[Al Skierkiewicz]

Originally Posted by Mark McLeod

Fans were always powered, we've had no circuit breaker's popping.
I believe the FETs opened, but I'll have to verify and get back on that.

Were the cases damaged? i.e. blown off or burned. Simple electrical failure of some of the FETs without case damage, may indicate a static problem. Were the same FETs involved in all cases with the same motor? That might be an indication of a bad brush assy. or a bad drive part in one direction.

[Mark McLeod]

Originally Posted by Al Skierkiewicz

Were the cases damaged? i.e. blown off or burned. Simple electrical failure of some of the FETs without case damage, may indicate a static problem. Were the same FETs involved in all cases with the same motor? That might be an indication of a bad brush assy. or a bad drive part in one direction.

No case damage at all. All damage was limited to the FETs alone. The underlying substrate was unaffected.
It almost always involved different motors/speed controllers each time it happened (globe, drill, CIM). We never had a problem with a rebuilt Victor, and we didn't replace any of the motors this year. By Nationals all Victor problems had gone away, but we'd replaced/rebuilt a half dozen by then.

Static is a possibility.
Any ideas on tests we can run in the off-season? I'd like to make it into a research project for the students, but I don't want to risk expensive mistakes.