[Mike Copioli]

Originally Posted by Darkknight512

Just had a jag blow today, looks like the same problem from the picture. We are a rookie team, a little behind havent cut a single peice of metal except the original frame but when that happend the electronics board was not even assembled yet.

There are several possible causes for the failures occurring with the Gray Jags. The obvious afore mentioned causes are a result of conductive particulate (metal shavings) entering the housing and shorting across one or more legs of the H-bridge. This is an issue with both the Jags and the Victors. The Victors however have additional protection from this debris in the form of conformal coating. While this conformal coating protects the device at the surface component level it provides little or no protection to the FETs that make up the H-Bridge. This is unavoidable in both brands of speed controller and the major contributer to failures. These failures can be prevented by adopting practices and mounting techniques that reduce the risk of foreign body intrusion.

Other failures that I have observed can be attributed to ESD. There are a couple key elements to switching the H-bridge circuitry safely. The switch must occur in a way that prevents the high side of the bridge from saturating (switching on) while the low side of the bridge is saturated. This would cause what is called shoot-through and is basically a direct short between battery positive and battery negative through two legs of the bridge. This switch timing is controlled by a microprocessor inside the device. While the timing of the switch is most likely not the cause of the shoot-through, the driver circuitry that allows the NFETs to switch the positive side of the bridge failing is. This device is called a charge pump and what it does is very simple. A charge pump takes an input voltage and steps it up to a higher voltage. This higher voltage is what drives the gates of the High side NFETs. Why am I explaining all of this? very simple. One should understand how the device works in order to understand how it fails. After examining several Jags that have failed I have made a few discoveries, first and foremost the charge pump chip that is used in the gray Jags appears to be sensitive to ESD. In a one instance the chip had a hole blown through it. This happened shortly after a lightning bolt jumped from the bot to a desk. A charge pump chip that fails to do its job and or latches up can and does cause shoot-through. A second discovery revealed that the fans used in the gray Jags do not tolerate shock and vibration very well. Two of our failures are attributed to the struts breaking off of the fans after traveling over the bumps a couple of times. A loud rattling sound soon followed. In all cases the devices were free from debris and foreign body invasion. Many of these issues claim to be resolved in the Black Jaguar. Some of the changes that I have noted between the black Jaguar and the Gray are increased input voltage range, more ESD protection, and 4 less FETs (one per leg). The FETS used in the black Jags also have a higher continuous Drain current rating. This year our team is using Black Jags primarily due to these hardware changes. We have used the Victors in years past but made the switch to the Jags because of the legality of CAN in this years competition. Most of the failures can be repaired if you know what you are doing and have the ability to solder and remove surface mount and through hole components. I am not sure how legal this is but we are only using the gray Jags for the practice bot so it is irrelevant to us.