Victor 888: Upgrade to the Victor 884
 

I was just looking at the VEX site, planning to buy some spare 884's, and I noticed this message on the page:

"A new and improved version of the Victor 884, the Victor 888, will be available Thanksgiving 2012. The Victor 888 will include a linearized output."

http://www.vexrobotics.com/products/...ontroller.html

Anybody have any inside information? Sounds like a nice improvement to the 884's, and removes the need to linearize the output via code.

Maybe wishful thinking, but it would be nice to hear if they are going to be FRC legal for the 2013 game sometime before January 5th.

Re: Victor 888: Upgrade to the Victor 884
 

There is also new the Talon controller from cross road electronics that was talked about at IRI.

Re: Victor 888: Upgrade to the Victor 884
 

Hmmm, wonder if there is a connection there?

A family connection :)

Re: Victor 888: Upgrade to the Victor 884
 

I hope they reduce the price or introduce a cheaper speed controller in the 20Amp range.

I'm tired of paying $90 for a product that was created 10 years ago.

Re: Victor 888: Upgrade to the Victor 884
 

I'm really hoping the talon become legal for use. From the limited time I had looking at it, it seemed a really high quality product.

Re: Victor 888: Upgrade to the Victor 884
 

Our lead Mentor picked up a cut sheet on the Talon at IRI. Info that was listed.
15khz switching frequency, 100 amp max, 60 amp continuous, 800 micro- ohm per leg, lock anti-phase rectification.
The Talon departs from the Victor and Jag by using a heat sink and optional fan.
I would suggest that they not say anything about a fan being optional and just put a fan on it powered all the time. There are some graphs of time, current and temperature. No info on the specifics of the test set up for the graphs. They also show a linear response. IFI has modified the Victor to have a linear response. I understand they are doing it in software. Is the Talon linear because off the 15khz switching frequency? Can the Talon hold up to First abuse? Time will tell. Whats the price? Will the Talon because of the switching frequency have problems with the window motors like the jag? If Cross the road would get some to us we would being willing to beat the hell out of them this fall.

Re: Victor 888: Upgrade to the Victor 884
 

If I remember correctly, there was a number of teams running the Talon motor controller at IRI and it seemed well up to the challenge. Perhaps they can speak up here.

I spent some time at their booth talking to them about it. Besides the linear output another nice feature was a tighter fit on the pwm cable (I saw them lift the controller while it was powered up by the pwn cable)

The heat sink looked nice and seemed to go further with protecting the internals of the unit, and it still retained mounting holes for a standard fan.

Re: Victor 888: Upgrade to the Victor 884
 

Does it also work with CAN?

Re: Victor 888: Upgrade to the Victor 884
 

Negative. At least, I didn't see any CAN ports on the unit at IRI.

Re: Victor 888: Upgrade to the Victor 884
 

If the fan came with the Talon then it's use would be mandated, if FIRST decides to make it legal. Having the fan separate would allow teams to only use the fan when necessary thus allowing for a lighter design. Each fan weighs 16 grams, ten fans = 160 grams or .35 lbs. Teams would now have yet another way to "Trim fat".

The test setup can be found in the user manual.
www.crosstheroadelectronics.com/Talon


Which problem are you referring to?

Re: Victor 888: Upgrade to the Victor 884
 

This version of the Talon does not support CAN.

Re: Victor 888: Upgrade to the Victor 884
 

Re: Victor 888: Upgrade to the Victor 884
 

This would not reduce the cost any significant amount. The only difference between a 20 amp design and a 40 amp design is the choice of FET's. A Fet with a lower continuous drain current would most likely have a higher Rds on(drain source resistance). This would cause more heat rise/power dissipation than a higher current device. The cost to assemble, test and the part count does not change. Your $90 controller would become maybe $85. I think the 5 bucks is worth the extra efficiency and power.

Re: Victor 888: Upgrade to the Victor 884
 

From the posted information:

Any Debris that does enter the housing won't get past the conformal coating that protects the surface mount components.

A conformal coating on the the PCB! Now that's a huge step in the right direction for FRC motor controllers where metal shavings always seem to find their way into motor controllers.

Re: Victor 888: Upgrade to the Victor 884
 

Oh that problem. That was the PTC. We have used Jags on our window motors since 2009 and have never seen a problem like this that was not caused by the PTC. Also I would like to correct some factual errors in that post.

The poster describes the output of the Jag to be switching between +12 and -12 volts. This type of rectification is known as locked anti-phase. Both the Victor and the Jaguar use a type of rectification called sign-magnitude. Although both motor controllers use the same type of rectification the Jaguar Does whats known as synchronous sign-magnitude rectification.

During the off period of the duty cycle the Victor allows the free wheeling current(opposite of the forward current) of the motor to return through the body diode of the FET's. The diode has a forward voltage drop of about 1 volt regardless of the current passing through it. Since Power = I x V if 20 amps of current is passing through the body diode, then the power being dissipated in the FET is 20 watts (1volt x 20 Amps). This causes heat rise and losses to accumulate in the Victor.

The Jaguar does something a little different, during the off period the jaguar switches the opposing low side FET on thus connecting the motor leads together, the freewheeling current is now passing through the drain source junction of the FET's rather than the body diode. Since the FET's have a very low drain source resistance (say 2 mOhms) the power dissipated by the FET's is = to (I*I)*r the power dissipated is .8 watts. What does this mean? Well basically more power is being dissipated in the motor windings instead of the FET's. This is probably what is causing the PTC to over heat and trip. However what it really means is that the window motor is being over driven. Moving it to a Victor allows a slower decay of the free wheeling current thus decreasing the heat dissipated by the motor.

So the problem has nothing to do with the switching frequency and more to do with the type of rectification. I would suspect in this example the Victor was actually providing less power than the Jag possibly due to calibration differences. Both devices use different PWM input values so it is possible that the Victor may not have been delivering full power. Another thing to remember is that at full power both devices are full on so switching has no affect. This could also be a contributing factor since the Victor is not linear, the same PWM value will yield a very different output.