Interesting Vexpro Victor 888 failure.

This past season we purchased 4 Vexpro Victor 888s during build season. They all worked flawlessly up until CalGames. At some point, at least one of them failed, but in a peculiar way.

When the joystick is in the middle position, there is no output from the Victor, as would be expected. Then once you move the stick forward to about 10%, the Victor outputs to the motor approx. 10v. As you continue to advance the stick, the voltage to the motor increases fairly linearly until full power is achieved.
When the joystick is pulled in the reverse direction, the Victor continues to output 0v to the motor and there is a clicking sound from the Victor and the status LED on it blinks in sync with the sound. The frequency of the clicks is about 3 Hz.

We thought that the calibration of the Victor might have somehow become corrupted, so we recalibrated it. There was no change in the behavior of the Victor after calibration.

Disassembling the Victor showed no signs of component failure. There was no burnt smell at all. We found no debris inside that might be shorting anything out either. We don’t believe any of the FETs are shorted, otherwise the motor would be receiving power at all times. It sounds more like the FET drive controller is toasted.

Has anyone else ever seen behavior like this?

PS, If Vexpro would like this one back to diagnose it, just ask.

These might be unrelated, but simple troubleshooting steps to eliminate other causes: Have you tried changing controllers? Have you checked the code for changes or gone to a simple code driving only motor controller? Has the electrical wiring been checked?

Just want to make sure, you’re 100% certain that you have a good battery on the robot? Low battery voltage can make the controllers to odd things…

We have a couple new controllers on order.

We actually did quite a bit of testing and troubleshooting while we were at CalGames. In fact, we ended up calling in a replacement in the elimination matches because of the difficulties and time it would take to replace it. We definitely narrowed it down to the Victor. It is on a “Y” PWM cable with the second motor on that side of the drive. When we pulled the PWM from the bad Victor once we were back in the shop, the other Victor on that side ran normally. This shows that the code was correct and had not changed. All testing in the shop was with a fresh battery.

I’m fairly certain the Victor is toast. Just it’s odd behavior alone is indicative of internal problems with the Victor.

Did you try pulling the PWM from the “good” Victor on that side to see if the “bad” one ran normally?

Could the clicking sound you heard come from the breaker powering the victor? Based on “clicking+LED blinking in sync”, it could very easily indicate some type of short circuit that’s tripping the breaker when you put the victor in reverse. Have you tried running the victor (both forwards and reverse) with no output attached?

Definitely sounds like it could be caused an intermittent short circuit caused by a voltage spike. Maybe a partial internal failure in one of the solid state components.

No, honestly I can say we did not try that.

After seeing the behavior, we put a meter on the output to verify what was being sent to the motors. One had normal 0v to ~12v output based on the joystick’s position and the other jumped from 0v to 10v then progressed to ~12v with the joystick.
These same results were also seen when the motor was removed and the output of the bad Victor was read open circuit.

Now that I think of it, it would be quite possible that if one of the FETs in the H bridge were shorted, this behavior would be exhibited.
In one direction, the shorted FET would not conduct until it’s paired FET turned on. At this point it would cause lots more current to flow than normal, but the paired FET would still regulate. The current wouldn’t trip the breaker because the motor would be limiting the current.
In the opposite direction, it would be shorting out half of the opposing FETs and could easily trip the breaker.

Sounds to me like you may have help explain it Jon!!!

I think you are correct. There is every indication that one of the FETs in the H bridge is shorted as Jon pointed out above. Since it is not switching it will produce non-linear results in one direction and then produce a short to the high side FET leg when commanded to the other direction. It is unlikely the Victor is making the clicking sound, it is the breaker feeding the Victor as indicated by the LED flashing. However, the shorted FET may be making some noise when voltage is supplied. This is highly unusual but possible.

Anyone who experiences a failure with a VEXpro product (or any IFI or VEX product for that matter) should immediately contact our tech support folks. They’ll help you diagnose what’s going on, and make things right.

If the Victor is truly damaged, they’ll get you replacement hardware ASAP.

When you call in, you get much better service than when you just post on Chief Delphi. :slight_smile:

Thanks John, we will be calling in on Monday. BTW, we already ordered 2 more 888s. One as a replacement, one as a spare.

I posted here because I felt we must be outside of any warranty. We have used these in three competitions so far and they have worked perfectly until now.

Partially unrelated, but last season for our shooter motors, we kept shorting out our BAG motors, and, in tern, kept damaging the victors. Does anyone know what could be going on? Could it be because the shooter motor runs at 100% throttle for a minute at a time. Also, why aren’t there any slits and fins built into these motors for cooling themselves down?

Need more information.

Wheels: how many, what diameter, what kind.

Motor(s): how many

Gearbox: what gear ratio

Drive: direct, chain, or belt. sprocket and/or pulley ratios.

At full speed, what was the actual (measured) RPM?