FRC Blogged: - Motor Controllers
 

Found here: http://www.usfirst.org/roboticsprogr.../blog-10-03-12

Re: FRC Blogged: - Motor Controllers
 

I like this new Frank guy. He knows what the people want to hear.

More IFI is best IFI.

Re: FRC Blogged: - Motor Controllers
 

Nothing about the Talon? I hope it becomes FRC legal.

Re: FRC Blogged: - Motor Controllers
 

Teams are Beta Testing it.

Re: FRC Blogged: - Motor Controllers
 

The post mentions a conformal coating - am I right to hope that this would reduce their vulnerability to stray metal shavings?

Re: FRC Blogged: - Motor Controllers
 

What is the benefit of removing the firmware current limit? This seems like great way to blow a lot more Jags.

Re: FRC Blogged: - Motor Controllers
 

Good to hear!

Re: FRC Blogged: - Motor Controllers
 

It did have much tolerance for excursions from the 40 amp limit despite the fact that the hardware was perfectly capable of handling it. This had the nasty consequence of disabling motors mid match and preventing the robot from performing effectively.

Re: FRC Blogged: - Motor Controllers
 

So wouldn't the real solution be to increase the current limit instead of completely disabling it?

Re: FRC Blogged: - Motor Controllers
 

Props to TI for making the transition seamless!

Re: FRC Blogged: - Motor Controllers
 

I'm somewhat worried about this change from a control perspective - last year there were reports of Jaguars losing their state when they lost power, so any CAN configuration commands (PID, voltage ramping, e.g.) had to be re-sent. This will become much more common if overcurrent results in tripping breakers and resetting Jaguars rather than just disabled motors.

I am hoping that this can be solved by enabling the overcurrent protection by default, but allowing it to be disabled via CAN if a team knows what they are doing, or they do not care if the Jaguar resets. This way, if it does reset, the overcurrent protection will be reenabled when it does.

Re: FRC Blogged: - Motor Controllers
 

I assume you are talking about 1718? They are testing the Talon, but not as part of the FIRST sanctioned beta test. The FIRST Beta test hardware has not been announced.

Re: FRC Blogged: - Motor Controllers
 

We are thoroughly testing the firmware changes with some of the most vigorous testing we know (and believe me, the guys we have here have beat up some FRC robots in their day). The software limit was overly conservative protecting FETs that just really didn't need that kind of protection.

We are confident these changes (conformal coating and firmware changes) will make the Jaguar perceived match robustness much higher. The firmware current limit caused Jags to cut power to motors when they just didn't need to.

We have had extensive technical conversations with the engineers responsible for the jaguar development and are confident this is a positive change.

Paul

Re: FRC Blogged: - Motor Controllers
 

There are plenty of teams who know what they are doing and elect to not use the CAN bus, ourselves included. The current limit seemed to be a bit too "safe" and was pretty annoying.

Re: FRC Blogged: - Motor Controllers
 

The real solution would be for teams to stop designing mechanisms that consistently hit the 40A + mark for extended periods -- which means more teams need to do the math.

Re: FRC Blogged: - Motor Controllers
 

I'm so happy right now I could cry.

Re: FRC Blogged: - Motor Controllers
 

It's not possible to guarantee your drivetrain will never, ever in an FRC match draw current that would possibly reset the jaguars.

Due to a shortage in speed controllers, we redid the drive on a practice bot with jags and they tripped all the time. This was the same drivetrain that ran flawlessly all season (2011) in regards to speed controllers.

Re: FRC Blogged: - Motor Controllers
 

Why? All the hardware we're using can handle the current.

Re: FRC Blogged: - Motor Controllers
 

I would argue that you won't see much of a difference. The breakers take WAY longer to trip and that is only when they heat up due to prolonged excessive current. If you're consistently tripping the breakers, I'd say you have bigger problems to worry about than a resetting Jag.

As always, keeping the battery fully charged will minimize the chance of a Jaguar browning out at ~6V. I'm confident that teams using the advanced CAN features also know to check for the "I just powered on" flag so they can reconfigure the reset Jag.

-David

Re: FRC Blogged: - Motor Controllers
 

Yes I was, thanks for the clarification.

Re: FRC Blogged: - Motor Controllers
 

Having a choice between Victors and Jaguars will be fantastic.

I hope all the Victor 884's we bought last year will still be legal.

Re: FRC Blogged: - Motor Controllers
 

That won't be a problem for veteran teams, but I think there will be a good number of teams who try CAN for the first time without considering a Jaguar reset. To be honest, if I had not heard of that issue, I wouldn't have thought of it either last year when I experimented with CAN.

Ideally, a team would manage their own current limiting with CAN, but for many teams, a stall will certainly trip breakers. (although if they trip them while accelerating normally, that is definitely a design problem)

Re: FRC Blogged: - Motor Controllers
 

I really, really can't imagine they'd make them illegal. It would be a huge blow to teams financially without a solid reason of doing so.

Re: FRC Blogged: - Motor Controllers
 

Interesting news, this. I assume Jaguar's and Victor 888's are different animals?

Perhaps IFI used some of the knowledge gained in purchasing the rights to Jaguars to improve the 884's into the 888's.

Would still be nice to have a straight answer from HQ what combination of Victor 883/884/888, Jaguar (Black/Grey), and Talon will be allowed.

The safe assumption is 884's and Black/Grey Jags, but I have a feeling Talon's and 888's will be allowed too, and possibly 884's dropped from the allowed list.

Re: FRC Blogged: - Motor Controllers
 

The blog entry mentions that IFI will be donating Victors to all rookie kits, and will be giving all teams vouchers to be used on their choice of Jaguars or Victors.

Sounds to me like they will be legal...

Re: FRC Blogged: - Motor Controllers
 

So, does this lay to rest the perception that there was bad blood between IFI and FIRST after the FTC split?

Lord, I hope so!

These two groups working together is a powerful thing.

Re: FRC Blogged: - Motor Controllers
 

Awesome news. Way to step up IFI.

-Brando

Re: FRC Blogged: - Motor Controllers
 

His question was probably referring to the fact that IFI has announced the Victor 888.

Re: FRC Blogged: - Motor Controllers
 

Where on earth did you come up with this? Did you actually read Frank's blog post?

Re: FRC Blogged: - Motor Controllers
 

The question is what victors will be donated? They have several to choose from - 883, 884, 885, and the new 888. I'm guessing the 883 and 885 won't be considered (they're more expensive and run at 24V), but from what I understand the 888 is essentially a remade 884 with a linearized output.

Re: FRC Blogged: - Motor Controllers
 

The issue of lifting the current limit doesn't have to come down to whether someone designs a single mechanism that exceeds 40A continuously.

If you place 8-10 of these Jaguars on a robot and occasionally they draw more than 40A from the power system via multiple Jaguars they can collectively draw enough power to adversely effect the robot power.

That's an interaction that is a little more subtle. The larger point of interest for me is whether they upped the wattage of the current sense resistor. In the old beige/gray Jaguars it was possible to heat that component so much it would reflow that resistor and open the circuit which would leave the attached motor dead in the water.

So I'm a bit curious to see how they'll handle that. Maybe they'll increase the wattage of that resistor or decrease it's resistance to handle the higher currents the existing MOSFETs can easily handle. Maybe they'll short it out but then you can't measure current like that.

In any event this action makes good FIRST assurance they'll make sure these are available. That's great because it makes things much more clear for everyone involved. Plus now LinuxBoy's CAN terminators are for an active product with an audience.

Re: FRC Blogged: - Motor Controllers
 

Our 2010 robot Storm was geared to 17 ft/sec and we could hit top speed then we tried to stuff balls into the goals or crash into walls to pick balls up. No matter what we tried we reset those Jags(Can) every match till we replaced the drive controllers with Victors and ran PWM.

The following year our 2Can enable Jags just reset when they felt like it. We switched to PWM Jags and pushed on for the 2011 season. We put a lot of resources behind finding out the problems with the Jags and how we could program to use the Jag like we wanted.

2012 we decided not to lose matches because our jags were resetting so we used Victors.

So the moral of the story is if you want to make it fast run the motor till it almost blows up ::safety::

Re: FRC Blogged: - Motor Controllers
 

You are right to hope. Conformal coating covers the PCB and components insulating it from swarf (debris).

Ideally, you don't put swarf in the motor controller to begin with.. but..

Re: FRC Blogged: - Motor Controllers
 

IFI didn't purchase the rights to Jaguars. TI donated the rights to FIRST, and FIRST contracted IFI to produce them for 2013.

IFI independently improved the 888.

Re: FRC Blogged: - Motor Controllers
 

Has anyone else noticed the Part Number on IFI's Web Site, for the Jag?

Part #: 217-3367

Looks like it should be called the "Hot-Killer-Chicken" (217, 33, and 67)

Interesting.

-Clinton-

Re: FRC Blogged: - Motor Controllers
 

VEX's director of product development, John V-Neun, has a strange sense of humor.

Re: FRC Blogged: - Motor Controllers
 

I like his style and sense of humor.

-Clinton-

Re: FRC Blogged: - Motor Controllers
 

FYP :)

Re: FRC Blogged: - Motor Controllers
 

*cheer* now to wait and see what the official ruling on our new options will be.

Thank you FIRST, TI, and IFI for doing this!

Re: FRC Blogged: - Motor Controllers
 

Although the specifics on motor controllers won't be released in till kickoff (3 months, 1.5 days!) does anyone have comparison data on Talon vs the Victor vs Hot-Killer-Chicken (endorsement of JVN's humor) ? I'm looking ahead to motor controllers for next season and I'm trying to figure out the pros and cons of each for different subsystems.

Re: FRC Blogged: - Motor Controllers
 

(well assuming the continuous current of the talon was taken at 28v it should be good for 140a at 12v. vs the victor which will do 40a at 12v

you could pop the main breaker with a single talon.) ignore, incorrect information

also... THE TALON LOOKS LIKE A VICTOR WITH A HEATSINK!!!1!1!!!

Re: FRC Blogged: - Motor Controllers
 

That is not at all how that math works. An H-bridge's current rating is very nearly flat across its voltage range.

Additionally, the victor will handle more than 40A at 12V.

Re: FRC Blogged: - Motor Controllers
 

i thought it was (voltage1*amps1=total watts=voltage2*amps2)

but seeing as that doesn't apply to h-bridges....

Re: FRC Blogged: - Motor Controllers
 

You were using the voltage delivered to the output (the motor) times the current delivered to the output. The power dissipated in the motor controller is not 28*60=1680 watts. It would fry.

Re: FRC Blogged: - Motor Controllers
 

That formula is close to what you want, but you have it in a form usually used for power conversion.

Total watts is still volts * amps, but you are thinking of the wrong volts. The voltage that matters is the voltage developed across the bridge elements themselves, not the total voltage applied across the entire bridge.

The switching elements (FETs) have a small resistance when they are conducting. The voltage is then the product of the current times that resistance. You end up with Power = (Current)^2 * (Resistance).

This is only dependent on the motor current, and is unrelated to the applied voltage.

There are a few other heating effects related to that applied voltage, but they are largely dominated by the I^2R losses and can be ignored for a first pass glance at the numbers.

Re: FRC Blogged: - Motor Controllers
 

This is a good example of an anecdote that proves my point -- it doesn't even provide evidence that the Jags are inferior to other speed controllers.

If your practice bot weighed as much as your competition bot, and was geared the same way as your competition bot (a la Poofs @ 17-18ft/s), then no wonder you kept tripping it. To me this is either a fundamental misunderstanding of how the Jags worked, or a misunderstanding of how much current your drivetrain actually pulled in 2011. If your requirements were to pull more than 40A for more than the trip time, you shouldn't have ordered the Jags in the first place.

While there isn't enough detail to comment on your 2011 season, it's reasonable to deduce that your drive train in 2011 was geared at least as fast as 2010 due to an open field. If that's the case, then see my comments to Adam. Your last sentence makes me :rolleyes:



I don't foresee the removal of the current protection as a good thing. It, by itself, at least provided a way for my team to realize the 'oops, I forgot to account for that' moments without burning out a motor or a $100 speed controller.

Re: FRC Blogged: - Motor Controllers
 

We fully understand how much current we were drawing; our drivetrains are completely analyzed before we run them, and their top speed, and time to distance match our analysis pretty closely.

For reference, 254 was geared 1-2 fps faster iirc.

This current was not enough to ever even trip the 40 amp breakers; not once on the comp bot or practice bot during season (when it had victors). We've never blown a Victor from overcurrent, we've also never blown a CIM.

We still tripped the Jags routinely when we switched in slower geared gearboxes at a top speed of about 13 fps.

Overcurrent protection would be an awesome feature, if it was tuned to trip at the proper point; it's simply too conservative now.

Re: FRC Blogged: - Motor Controllers
 

I guess we just have different experiences then.

After some tweaking to our code to prevent immediate full-forward to full-reverse changes, we've never tripped our Jags on the field with 145lbs @ < 12ft/s (and the code complexity is in-line with what the Tom posted here, so I bet the driver->bot response time is on-par). From 2006-2009 we consistently had 2-3 Victors fail over the course of 3 competitions each year whereas we only had 1 Jag in 2011 fail (0 in '10/'12).

Granted, we never put those code changes on the Victor-based robots, so maybe that's a differentiator.

Re: FRC Blogged: - Motor Controllers
 

The 40A breakers will let 60A through for up to 47 seconds (or as little as 3.9) [1]. You always design the fuse or breaker to blow before anything else so this should be the limiting factor of the circuit, not the speed controller

We had the same problem and used the same solution, although we implemented it using the limited-acceleration feature built into the Jag (I don't remember it's proper name). We have never blown a victor due to load.

[1] http://www.snapaction.net/pdf/MX5%20Spec%20Sheet.pdf

Re: FRC Blogged: - Motor Controllers
 

I believe Al Skierkiewicz has stated on multiple occasions that the 40a breaker is there to protect the wiring, not the device.

Re: FRC Blogged: - Motor Controllers
 

There are many ways to kill a device other than high load, but the breakers should protect from high load. Not just because it's proper design, but because the FETs can handle it (at least the ones in the Victor, I haven't checked on the FETs in the Jag).

Re: FRC Blogged: - Motor Controllers
 

Man, 47 is everywhere on this website!

Re: FRC Blogged: - Motor Controllers
 

230 is testing the Talon as well. Unofficially, of course.

Re: FRC Blogged: - Motor Controllers
 

Jason,

Good design works from the end device back towards the supply.

1> You start with the expected average current draw od the device, in this case a Jaguar -- 40Amps (note that the Jag can pull much higher loads but that the 'expected load is 40 Amps).

2> You then set the gage of the wire to handle the expected load (10 AWG can handle a ~55Amp average)

3> you then set the breaker to protect that wiring (40 Amp breaker)

I believe the FETs on the Jag are designed for 60 Amps. They can handle a lot more, but that will cause them to heat up. Heat is the primary failure mode with power FETs.

The overcurrent on the Jags was too conservative (~40Amps) since the expected load could jump to ~132 Amps with a stalled CIM. For short periods of time that high current is fine since the Jag (FETs), wire, and breaker can also handle that for the time it takes for the breaker to trip. The real issue comes whenb your pulling a constant 60-80 Amps and it becomes which tripps first, the FETs (dying) or the breaker.

Re: FRC Blogged: - Motor Controllers
 

Correct... Did I say anything to contradict that?

If you're not sure which is going to blow first, the FETs or the breaker, that is an indication of a poorly designed (not necessarily improperly designed) system. There are three solution: decrease the load to what the system can handle (but who's going to give up CIMs), increase the capacity of the FETs (so that the breaker blows before any expensive equipment blows), or decrease the capacity of the breaker (for the same reason).

Re: FRC Blogged: - Motor Controllers
 

This blog really made my day.

I've believed in the Jaguar for the past two years now. It still has its flaws, but like any product, the improvements are an iterative process.

The one thing that was not touched upon in the blog was price. I've got my fingers crossed that the Jaguar will be offered at a similar cost to what FRC teams had in the past.

I'm really excited to hear about both the conformal coating, and the firmware tweaks. Both are weaknesses in the product that we've fought with.

My dream is that one day we see a speed controller that gives us the best of all our current options.

-Conformal coat
-Sealed unit with heatsink
-Linear output
-15kHz response
-Integrated velocity and position PID (with a derivative term that actually works...)
-Velocity PID with feed forward support
-Direct limit switch, potentiometer and encoder inputs
-CAN communications
-status LED that blinks progressively faster as speed increases
-small footprint

The best part is, if this happens, and it's in a package reliable enough to put into an industrial machine, you have a product viable enough to displace industrial motor controllers that cost 4+ times as much.

Re: FRC Blogged: - Motor Controllers
 

The Jaguar is listed at $89 on vexrobotics.com

Re: FRC Blogged: - Motor Controllers
 

As promised, I am rejoicing.

FIRST and IFI both deserve great big shiny gold stars for playing well with others. :D

Re: FRC Blogged: - Motor Controllers
 

Well said, Richard. I totally agree.

Andy B.

Re: FRC Blogged: - Motor Controllers
 

Ether is correct, the breakers have always been sized to protect the wiring. This is an attempt to keep fires to a minimum in the event of catastrophic failure of wiring or devices. When examining the wire tables, the max current specifications for chassis wiring are used. As stated above, the max continuous current for #10 wire 55 amps. So if a chassis part were to fall across the input to a speed controller, the breaker would trip.
Since all of our breakers are capable of passing 600% over current for a few seconds, they are not appropriate devices to use for protecting electronics. In the case of the 40 amp breaker, it will pass sufficient current to damage FETs in any controller under the right conditions. All competitors should remember that all motors draw stall current when current is first applied. A quick check of legal 2012 motors will show that many are rated for more than 40 amps stall.
Jason, there is a fourth way that most teams use without realizing it. That is to add resistance to limit current. Often this comes in the form of extraneous wire length. I have used a term for many years, "wire foot" to demonstrate this concept. At 100 amps, one foot of #10 wire will introduce .001 ohms of resistance and drop 0.1 volts. Other stranded wire sizes per foot are roughly:
#6=0.5 WF
#12=2 WF
#14=4 WF

Re: FRC Blogged: - Motor Controllers
 

Something to think about.

-The Victor has been around for over a decade.
-It has never had internal over current protection and it has not affected it's performance on the field.

With the few failures I have seen most are caused from metal debris shorting the tabs of the H-bridge FET's. Although Internal over current protection would help prevent this, I think an even better approach would be to take measures to prevent the metal debris from entering in the first place.

Another thing to consider is the resistance of the power path feeding the motor controller. Al pointed out the role 10 gauge wire plays in this. Another even bigger player is the resistance of the Wago connectors, the 40 amp breakers, the PD and the internal resistance of the battery. In total you are looking at around ~40 mohms of resistance at 25 degrees C. This number increases significantly as these components heat up. If you have a way to measure internal resistance of your battery try performing the test at the power leads of the motor controller(with the controller out of circuit). You will be surprised at the amount of resistance that is actually present.