Victor failure question--Can power from motors cause them?

[Kit Gerhart]

Our 2006 robot which we now use for demos and practice has 4 failed Victors, all of them powering the drive CIM motors. Three of the blown Victors have output in one direction only, and one has no output at all. The lights on all of them respond normally to PWM inputs.

Here's my question. Is there any possibility that power from motors acting as generators when pushing a robot can blow up a Victor? It's possible that these failures were caused by metal chips, "abusive" driving, or other things, but it is very unusual to have four failed Victors on the same robot. Of course, we don't know when each of the Victors failed, because in the robot's post-competition life, we might not know if we were running on one motor per side.

[RyanN]

I think it is entirely possible for a Victor to fail when pushing it. Although unlikely, it can, and has happened (to me). It is also common for Victors to stop working in one direction. Our 2005 robot had a Victor that was only working one way and it would go reverse crookedly because we had a 4 motor design. You may want to blow out the robot with air before you replace the Victors.

[billbo911]

Kit,

Both possibilities can cause this. But most likely it was because of metal chips, or static.
We have a T-Shirt Launcher on one of our old robots. Loading the PVC barrel with a shirt generates a large static charge. We had blown Victors on two different occasions until we placed a discharge chain on the frame. That chain drags around on the ground all the time and discharges any static before it can build up.
With the chain in place, we have pushed the bot hundreds of times without problems.

BTW, there are several discussions about the topic of blowing Victors by pushing a robot. Use the Search tool to find out more about this subject.

[AdamHeard]

I seem to remember a long thread on this from 1-2 years ago. I tried to find it by searching but can't.

If I recall correctly, Al S (sorry, can't spell that from memory) from 111 said it shouldn't be a problem.

From personal experience, we pushed our 05-07 robots all the time (especially the '06 that was cartless half the time) and never had a victor failure during the season (had a short after, unrelated though).

[Al Skierkiewicz]

Kit,
Anything is possible but extremely unlikely in this configuarion. Each of the FETs have diodes across the terminals (drain and source) to prevent backfeeding voltages from damaging the FET. These diodes are capable of 34 amps each. The FETs are also rated for a 30 volt breakdown so with two strings in series, the theoretical breakdown is 60 volts and currents of 102 amps. Since the Chalupas are 12 volt motors and you can't push them to top speed, it is unlikely that the motor is capable of making more than 5 or 6 volts. If you conceptulize the layout of the H bridge inside the Victor, the protection diodes form a diode bridge which then supplies current through the diodes to the power input terminals.
I always suspect metal shavings in Victor failures as you may remember from the Technokats robot in Houston 2003. Even small dust particles from rubbing metal parts will build up a layer of conductive material over time. The humidity of southern Florida may also pose a threat for condensation within the Victor. Best bet is to wait for 15-30 minutes after taking the robot out of doors to apply power.

[Kit Gerhart]

Thanks for the replies. For a start, I think we need to be more careful when drilling and filing. Also, thanks, Al, for mentioning the possibility of condensation. That could happen, since we often take our machines outdoors from air conditioned spaces to run them.

[popo308]

We would always backpower are victors on are 06' bot and i don't believe we ever had one fail. So i would have to agree with Al that it is unlikely

P.S. also thanks again Al for bringing up the issue of condensation of using your robot outside i will have to keep that in mind