New Talon Speed Controller

[theprgramerdude]

Originally Posted by Ether

What test data are you looking at as a basis for that conclusion?

I take back what I said about the driver, as it could also quite easily be the increased switching speed and better MOSFET's, but for maximum power output, the newer controllers can achieve a much higher speed at a given torque than the old Victor 884. This might just be due to the switching issues though that 120 Hz present.

[theprgramerdude]

Additionally, question about the test: Was there time allowed between runs for the motor to cool down to ambient before starting up again? If not, which runs were done "hotter" than others?

[AlexH]

so does anyone know why the heatsink on a talon only touches the cap and not the board?

[mikets]

I've never seen a Talon controller, but are you sure that's a cap not a MOSFET?

[Mike Copioli]

Originally Posted by AlexH

so does anyone know why the heatsink on a talon only touches the cap and not the board?

It touches both.

[Ether]

Originally Posted by theprgramerdude

the newer controllers can achieve a much higher speed at a given torque than the old Victor 884

Nothing I've seen supports the above statement.

What data are you using to draw this conclusion?

[scottandme]

Talons are FRC legal as per the AndyMark email blast.

Seems that they're responding to market pressure ($50 pricing for IFI 888's), and dropped the price to $59.00. Hard to pass up at that price.

http://www.andymark.com/Talon-p/am-2195.htm

[F22Rapture]

Originally Posted by scottandme

Talons are FRC legal as per the AndyMark email blast.

Seems that they're responding to market pressure ($50 pricing for IFI 888's), and dropped the price to $59.00. Hard to pass up at that price.

http://www.andymark.com/Talon-p/am-2195.htm

Wow. That basically makes them an automatic buy for us, unless the price of the Jaguars is also reduced.

[Gary Dillard]

Originally Posted by scottandme

Talons are FRC legal as per the AndyMark email blast.

As I pointed out in another thread, an email from AndyMark doesn't make something FIRST legal; that ruling can only come from an official communication from FIRST. However, the fact that it is in FIRSTChoice appears to make it legal according the the FIRST Blog.

In this case it appears that the net effect is the same, just be careful on jumping to conclusions.

[Tom Line]

They are legal. A couple of phone calls confirmed that. No word confirming it on the 888 yet.

In addition, I just got confirmation that the 888 is legal as well.

Data for the failure amperage has been retracted: it appears we made have had some measurement errors. We'll reupdate after we fry a couple more.

[Ether]

Tom, I think the relevant metric that's missing here is: "how much torque can each motor controller generate (driving a locked-rotor CIM) without popping the breaker".

If we had a locked-rotor-CIM torque vs battery rms current for each controller, I think that would answer the question.

[Jon Stratis]

Looking through everything that's been generated about the different speed controllers, I think we have enough information to come to some general conclusions for each (please note these are my own conclusions, yours may vary):

Victor 884 - It's been the go-to speed controller for many, many years. However, it's failings in linearity and the introduction of the Victor 888 have relegated it to a back shelf. It's still great for applications where fine-tuned speed control (especially slow speed) isn't necessary, if you have some laying around collecting dust.

Victor 888 - A step up from the Victor 884 in linearity. In fact, Ether's graph's put it on par with the other speed controllers, although those from 1718 show that they "over corrected", which could cause a loss in definition at high speeds. More work may need to be done to show which graph is more accurate for FRC uses.

Jaguar - No real surprises here. The Jaguar has maintained its linear response nicely for years. The addition of CAN (and the associated limit/encoder/potentiometer feedback) may make this the ideal speed controller for many teams. The most obvious downside, however, is the larger footprint the Jaguar has, which may also make it less than ideal for many teams. Also note that the Jaguar has a slightly larger deadband than the other controllers.

Talon - The Talon seems to be a great mix of all the others. It provides the small deadband and small size we got from the Victor, and the linear response we got from the Jaguar. The fact that it can be used only with passive cooling and no fan is a great bonus (although I would still put a fan on any used for the drive train or other strenuous applications).

With this combination of speed controllers, it seems that we have one for every situation. I think the difficult part for most teams is going to be finding a noticeable difference between the Victor 888 and the Talon, aside from the passive cooling in the Talon.

[Ether]

Originally Posted by Jon Stratis

...although those from 1718 show that they "over corrected", which could cause a loss in definition at high speeds

Hi Jon, could you please elaborate on the following:

1) what specifically are you referring to: "those from 1718"

2) what do you mean by "over corrected"

3) what do you mean by "a loss of definition"

Thanks.

[Jared Russell]

The AndyMark product page for the Talon (http://www.andymark.com/Talon-p/am-2195.htm) says something interesting:

"Do you want your motor to hold it's position after power is cut?"

How does the Talon provide this? Does it stay in brake mode even after power is removed?

[Jon Stratis]

I'm referring to these images:


from 1718's beta testing: http://www.fightingpi.org/Resources/...12_Day_9.shtml

Basically, the Victor 884 curved away from being linear in one direction, while the 888 seems to curve a little bit away in the other (thus over corrected when adjusting the 888 to be more linear than the 884).

The result would be the exact opposite of the 884 - you would be able to finely tune the speed of your motor at the low end, as each step change in input would be a smaller change in output, but would have worse control at the high end, as the same step size would result in a much larger change in output.

Of note, the data you gathered didn't seem to show this same result, which leads to a question of which data set more accurately reflects real-world usage on a FIRST robot. Only having two data points makes it tough to reach a conclusion on this.