Victor 884 won't go forward

[Andy Baker]

Originally Posted by Manoel

Again, I'm open to suggestions.

I second the notion of replacing FETS. We have done this and resurrected a few Victors (all 883s).

But... that seems to not be your problem. The Victors up here in North America work well. Yours give you problems. Since you are located in the southern hemisphere, maybe you should mount them upside down.

Hey, you said you were open for suggestions.



Andy B.

[Joe Johnson]

I am looking at a Victor with exactly the same problem you describe.

We were noodling around driving things we probably should be driving with a Victor (I am ashamed to say I was using it a load for a charge circuit for batteries -- Not exactly the design usage) something when pop and no more reverse.

Anyway, it is hard, but not impossible to fry an entire leg a Victor's H bridge*.

Joe J.

*Actually, it is quite easy to toast the MOSFETS in a typical H-bridge (I have a PILE of those next to the bad Victor). It is a tribute to Tony & Bob & the rest of the IFI Gang that they have wrapped these fragile jewels in such a way as to make it quite difficult for us to destroy.

[Matt Krass]

My team has a Victor with the same failure characteristics also, but we've determined the cause to be driving the motor the victor was connected to manually.

In Atlanta,, a student got metal shavings in one of our Victors for the drive, and it blew out next power up. We were left with 3 functioning and a few minutes until our next match. So we decided to go from 4-motor/2-wheel to 2-motor/2-wheel. But in our rush we only disconnected the PWMs to the corresponding Victor on the other side of the drive. After the match that Victor failed to work. We think it's because the disconnected motor was manually spun by transmission (it was geared to a working CIM) and the reverse current flow blew out the forward half of the H-bridge. It's the only logical problem we can find, and seeing as how 2 motors geared together was considerably more popular this year, combined with loose PWM cables, that could explain the apparent rise in Victor failures.

I think.

[sanddrag]

We've pushed our robot on the ground and spun the motors sometimes generating enough current and voltage to make all the lights come on and the fans spin. So, I know the electronics can tolerate a little bit of this. But a whole matches worth I guess not.

So my two questions:
Is is really bad to backdrive motors in turning them into generators in the FRC electrical system and why?
How long can you do this for without causing any damage?

[sciguy125]

Originally Posted by sanddrag

Is is really bad to backdrive motors in turning them into generators in the FRC electrical system and why?
How long can you do this for without causing any damage?

You know, I've actually been trying to figure out why backdriving the motors generates current to turn the system on. I haven't been able to figure it out though. The MOSFETs have diodes, but they're reverse biased, so any current going through them would be in the wrong direction. The other thing is that at some point, the power has to get to the RC to turn it on.

But to answer your second question, we had someone pushing it through a parking lot one time. By the time it got to it's storage location, it had turned itself on. The backup battery was maintaining the RC. It also smelled funny, like burning electronics. But, it still worked fine. I wouldn't advise doing it though.

[Joe Johnson]

Originally Posted by sciguy125

...The MOSFETs have diodes, but they're reverse biased, so any current going through them would be in the wrong direction. ...

But there are 4 of them in an H configuration. These 4 diodes end up working like a rectifier bridge; no mater which way the motors generate electricity, the diodes funnel + voltage to the +batt and the - voltage to the -batt (a.k.a. ground).

This is why the lights come on no matter which way you turn the wheels.

Joe J.

[KenWittlief]

when you spin a motor (backdrive it) it acts like a generator. We use to demo this with the globe motors and the old rotating lights - hooking them together, turning the globe motor with a wrench and the rotating light would lightup and spin

during an event when you let off the joystick, the motors back-feed, and depending on whether you have your victors set to coast or brake, the counter-EMF (generated voltage) from the motors will either be shorted through the victors to act like a brake, or it will be left open circuit and the bot will coast to a stop.

I dont think you can blow out your victors this way unless you were pushing the bot really fast, and the motors were generating a voltage above the Victors rated MAX voltage spec.

[Matt Krass]

Originally Posted by KenWittlief

when you spin a motor (backdrive it) it acts like a generator. We use to demo this with the globe motors and the old rotating lights - hooking them together, turning the globe motor with a wrench and the rotating light would lightup and spin

during an event when you let off the joystick, the motors back-feed, and depending on whether you have your victors set to coast or brake, the counter-EMF (generated voltage) from the motors will either be shorted through the victors to act like a brake, or it will be left open circuit and the bot will coast to a stop.

I dont think you can blow out your victors this way unless you were pushing the bot really fast, and the motors were generating a voltage above the Victors rated MAX voltage spec.

Well they were being spun at the same speeds as the CIM motors running at 12VDC and driving the bot, considerably more power then you can do by hand, and more or less continuously for 1:30 to 2:00 minutes....So it's pretty rough on the circuits. That and we did it four matches in a row

[JVN]

This may be a silly question:
Have you tried contacting the official Innovation First technical support?

There is an entire forum at www.ifirobotics.com with this purpose in mind.

If nothing else, you will get some feedback from the engineers who actually designed the Victor, as well as those who do a functionality QC check on every product IFI ships.

They may have something for you.

John

[Rickertsen2]

Originally Posted by KenWittlief

when you spin a motor (backdrive it) it acts like a generator. We use to demo this with the globe motors and the old rotating lights - hooking them together, turning the globe motor with a wrench and the rotating light would lightup and spin

during an event when you let off the joystick, the motors back-feed, and depending on whether you have your victors set to coast or brake, the counter-EMF (generated voltage) from the motors will either be shorted through the victors to act like a brake, or it will be left open circuit and the bot will coast to a stop.

I dont think you can blow out your victors this way unless you were pushing the bot really fast, and the motors were generating a voltage above the Victors rated MAX voltage spec.

Reminds me of the day a couple years ago when we were dusting off our robot with compressed air and we realized that when spun by compressed air, the large kit fan produced enough voltage and current to power up the robot(but not to move anything other than pneumatics). I would not recommend doing this as very high voltages can be produced this way. The lil fans also make a whizzing noise when you blow air over them.... until they promptly die....

[CJO]

Are you exactly positive what version of the Victor you have? Because they also make a couple of versions which are designed to power rotating objects, and only have a single direction of output.

http://www.ifirobotics.com/victor-sc...r-robots.shtml

[greencactus3]

Originally Posted by CJO

Are you exactly positive what version of the Victor you have? Because they also make a couple of versions which are designed to power rotating objects, and only have a single direction of output.

http://www.ifirobotics.com/victor-sc...r-robots.shtml

unless they specifically bought those they shouldnt have any of those. as they arent in the kit. and didnt he say they had it mounted on the robot and was working till theybackdrove it for a while because they didnt have time to unplug it? or was that a nother person?

[Al Skierkiewicz]

Manoel,
It is possible for you to have checked all the FETs good and still have a problem in reverse. I did come across a few Victors at inspections and other times that did not take the calibration the first or even second time. However in you case since you stated that the LED was coming on in the correct position of the drive , I suspect that the driver for the FETs may be bad. Generally, the FETs short when defective. During operation if no drive is applied and the brake jumper is in the "coast" mode, all FETs are off. If you set the jumper to brake does the Victor actually brake? If so, all the FETs in the low side (that's 6 for those who are counting.) are good. If you do calibration with joysticks and the LEDs go full green and full red, I would contact IFI about repairs. I am sure they would like to find out what died as much as I would.
For the rest of you, the motors back driving a voltage into the robot was covered in another discussion some time ago. Search the archives or I will when I get a chance.