Jaguar Failure

[billbo911]

Originally Posted by utlinebacker

Luminary Micro is working with Mike to understand the issue he is seeing.

The initial speculation is that the inrush current due to the charging of the big bus capacitor in each Jaguar is causing the bench power supply to glitch causing a power on issue with the microcontroller. If this is indeed the case, it is very unlikely to affect battery operated systems.

More data will be generated when Mike has an opportunity to conduct further experiments in the team's shop. I'll respond back to the forum once I learn more.

By the way, I just updated the Jaguar microsite with the special Jaguar reorder link for FRC teams (through Digi-Key), a link to our technical support page, and a link to Luminary Micro's main webpage.

Regards,
Scott

Scott,

Thanks for the update. And, thanks for the new links.

From what I have read thus far, I was not aware that the system Mike was demoing was powered by a bench supply. This information is really good to know. If in fact, powering the systems this way is not a good idea, then that information will be really good get out. Although, that info was already put out with regard to the early shipment systems. So.... maybe it now has a two fold reason. Stay tuned and we will find out.

[Russ Beavis]

Powering ANY motor drives from a bench supply can be problematic. The most common problem is the need to absorb regeneration energy as a spinning motor (and its load) are commanded to stop/reverse.

Many power supplies do an excellent job of providing overvoltage protection on their outputs and will not tolerate current being forced into their outputs. As a result, the power supply bus for the motor drive can jump to a super high voltage when a motor tries to regenerate. This high voltage often results in a silent death.

This is the reason why special power supplies and shunt loads are used to power motion control systems.

I'd encourage everyone to ALWAYS use a battery to power their motor drives to avoid this particular issue.

Russ

[Paul Copioli]

Scott,

Thanks for your very proactive and quick response.


Russ,

I witnessed the test and one thing to note is that there were no motors or load hooked up to the controllers and the power source was a very high end, very clean power supply (gotta love local sponsors). The scary thing for us non-electrical guys is that both the Jags and Victors were hooked up and the Victors did not lock up. We are doing more testing tomorrow on our 2008 robot and battery power so we will have more data.

Stay tuned,
Paul

[Russ Beavis]

So much for my motor regeneration hypothesis...

It's still a good warning to teams, though - using a typical lab-type power supply (eg switching supply with lots of overcurrent/voltage protection) to drive a motion control system WILL help to kill nearly any motor drive that you use. You should either use a battery to power the system, use a shunt load or use a really simple linear supply or similar that can "absorb" any regeneration currents.

Here's an example of a shunt load. This is NOT a good example for a FIRST application (wrong voltages) -
http://www.animatics.com/catalog_pdf/48-49.pdf

Russ

[Al Skierkiewicz]

One thing to remember with bench supplies feeding motors is that the supply needs to be able to function with the stall current of the motor. CIM motors have a stall current of 129 amps, something too high for most common 25 amp bench supplies to handle. Many, regulated supplies will go into current limit or will trip off during that kind of load.
Switching power supplies may also radiate high frequency energy that could interfere with the operation of digital devices if some preventive measures are not taken. That is why all computers use extensive LC filtering on power supplies and peripherals.

[utlinebacker]

Following up here to hopefully close the loop:

Team 217 (Thunder Chickens) has indicated to us that they performed the same test again, only this time using a battery instead of a power supply... and they were not able to reproduce the problem. Therefore, the power supply seems to be the cause of the problem.

Thanks for your patience.

Merry Christmas / Happy Holidays / Happy New Year!!

Regards,
Scott

[GBIT]

All I have to say is that reading that whole thread scared me then that last post was like a Christmas present...

Thanks so much to everyone for all the work...