REV Sparks or Vex Victor 888?

[Abrakadabra]

In 2015, 3467 also went whole hog with the Talon SRX - we used one running the built-in Speed Control mode for each of our four mecanum wheels, and two (1 master, one slave) for driving our elevator with Positional PID. One of our mentors insisted that the built-in PID algorithm could be faster (he was looking more for a motion-control mode), but it all worked well enough with a minimum of muss or fuss.

Plus - One of the often overlooked advantages of CAN control is built-in current sensing on each motor - granted it wasn't really that useful last year (unless maybe when we were building a twelve stack , but in a defense-heavy game, or a game where climbing might be required, being able to monitor current at the individual motor level might help to intelligently avoid those brown-out conditions that we were all worrying about around this time last year.

[Ari423]

Originally Posted by Abrakadabra

Plus - One of the often overlooked advantages of CAN control is built-in current sensing on each motor - granted it wasn't really that useful last year (unless maybe when we were building a twelve stack , but in a defense-heavy game, or a game where climbing might be required, being able to monitor current at the individual motor level might help to intelligently avoid those brown-out conditions that we were all worrying about around this time last year.

Can't you do the same thing with one CAN run from the RoboRIO to the PDP? The CAN line would even have built-in termination at the PDP. No need for fancy CAN motor controllers if all you need is simple voltage control, and you can still have your current monitoring.

[Abrakadabra]

Originally Posted by Ari423

Can't you do the same thing with one CAN run from the RoboRIO to the PDP? The CAN line would even have built-in termination at the PDP. No need for fancy CAN motor controllers if all you need is simple voltage control, and you can still have your current monitoring.

Yes - if all you care about is the overall current draw on the system, the built-in CAN in the Roborio and the PDP is all you need. I was simply pointing out that having intelligence about each current-drawing node might allow you to make intelligent, real-time decisions about which motor(s) to throttle back, depending on the game scenario.

[Ben Wolsieffer]

Originally Posted by Abrakadabra

Yes - if all you care about is the overall current draw on the system, the built-in CAN in the Roborio and the PDP is all you need. I was simply pointing out that having intelligence about each current-drawing node might allow you to make intelligent, real-time decisions about which motor(s) to throttle back, depending on the game scenario.

The PDP allows you to monitor the current draw on each output (not just the total), so you can still achieve current control with PWM.

[Ari423]

Originally Posted by Abrakadabra

Yes - if all you care about is the overall current draw on the system, the built-in CAN in the Roborio and the PDP is all you need. I was simply pointing out that having intelligence about each current-drawing node might allow you to make intelligent, real-time decisions about which motor(s) to throttle back, depending on the game scenario.

Actually with the new PDP you can get current draws for each power output. So as long as each motor controller is wired 1:1 with a power output on the PDP (which it should be according to 2015 rules), you can get the current draw from each motor.

See documentation here: http://www.ctr-electronics.com/contr...ription_tabbed

The Power Distribution Panel (PDP) is the latest DC power interface for competition robotics. The PDP uses CAN to connect directly to the roboRIO and allows for individual current monitoring on each channel.

EDIT: sniped

[Abrakadabra]

Originally Posted by Ari423

Actually with the new PDP you can get current draws for each power output. So as long as each motor controller is wired 1:1 with a power output on the PDP (which it should be according to 2015 rules), you can get the current draw from each motor.

See documentation here: http://www.ctr-electronics.com/contr...ription_tabbed


EDIT: sniped

OK - thanks. I forgot about that feature. But in my defense, it's still CAN that makes it all possible.

As a mentor whose teams have used CAN beginning way back in 2009 when the Jags first came on the scene, I guess I had gotten used to promoting the current sensing feature of the CAN controllers a little too much. In 2012, when the bugs in the CAN stack and the unreliability of the RJ-11 connectors became too much to handle, I was sorry to see that particular feature go. So when CAN looked like it was going to be viable once again last year, I was ready and willing to give it another go, and I, for one, am glad we did.

[ozrien]

I didn't want to distract from the OP but KrazyCarl92's post requires attention.

Originally Posted by KrazyCarl92

I'll bite and share my experience:

I've been a part of a team that has used CAN in 4 seasons. In 3 of those seasons the CAN out right failed at some point and we switched to PWM on at least some of the motors (granted those were all with Jaguars...I have my own opinions on those too).

In 2012, I personally spent over 70 hours ...
And having not used CAN in 2013 and 2014, we were able to get much improved robot performance which I believe ...

Yes Jaguars had problems. That's why we created the Talon SRX (which is CAN and PWM). That's why we took the RJ11 out. That's why we integrated termination. That's why we re-wrote the CAN api on the RIO side [props to the NI team and WPILIB for making that happen].

Originally Posted by KrazyCarl92

In 2015, Team 20 used CAN with Talons relatively successfully. However, there were still quirks with the code which definitely burned lots of time during build season. I wasn't personally coding, but I recall us taking over a week to iron out the code for switching between current setting and position setting modes of CAN motor controller operation.

This was no current-mode last season for Talon SRX. Talon 1.4.crf had duty cycle, closed-loop pos,and closed-loop velocity. Next season of course is a diff story.....
The examples in the Talon SRX Sofware reference manual are meant to save you time. Were they not helpful?

Originally Posted by KrazyCarl92

There was also one practice match where a motor inexplicably drove the opposite direction it should have throughout a match. We were unable to reproduce the issue and it never happened again, but it was very puzzling. Not sure of the cause. Taking advantage of any of the elegance or benefits of CAN does involve added complexity.

You were having this level of trouble and didn't bother to ask for help from the community or email CTRE?
I haven't found any post from your team regarding this issue. And I know you haven't emailed support@crosstheroadelectronics.com (since it goes to me).
Did the programmers look at the Talon SRX Software Reference Manual?
This feedback is so far-removed from literally ALL of the feedback I've gotten from last season I'm not sure where to start.

If ANY TEAM has questions/concerns/problems with ANY CTRE product please please PLEASE leverage our support email. Or look around CD for similar posts or post yourself. Or PM me. But email is best. But don't wait a full season and then post it when it's too late to be beneficial. We want to help you.

Carl, if you email us your team's 2015 code, we will figure it out. I have robots dedicated for exactly that purpose. Please PM me if there is more info that you think would be helpful.

[Jon Stratis]

Originally Posted by Cory

I would not assume that. It has been ages since 884's were provided in the kit, or a "relevant" product, but they have remained legal since teams have stockpiles of them. I would expect 888's to remain the same way.

Just because teams have a bunch doesn't mean FIRST will keep them legal I future years. Just look at BaneBots motors...

The key difference, I think, is in competitive advantage. There really is no advantage to using the older controllers, other than not having to buy new ones. Once there are none left for FIRST choice, though, I do expect them to become illegal within a couple of years - there is a "cost" associated with keeping them, including maintaining WPI lib classes for them and increased inspector training, as newer inspectors down the road may not have any prior experience with the old controllers. As it is, teams have now had two years to switch over, possibly even more down the line, so when they do become illegal I don't think there will be too much complaining.

[Ari423]

Originally Posted by Jon Stratis

Just because teams have a bunch doesn't mean FIRST will keep them legal I future years. Just look at BaneBots motors...

The key difference, I think, is in competitive advantage. There really is no advantage to using the older controllers, other than not having to buy new ones. Once there are none left for FIRST choice, though, I do expect them to become illegal within a couple of years - there is a "cost" associated with keeping them, including maintaining WPI lib classes for them and increased inspector training, as newer inspectors down the road may not have any prior experience with the old controllers. As it is, teams have now had two years to switch over, possibly even more down the line, so when they do become illegal I don't think there will be too much complaining.

We still primarily use Victor 888s to power our robots. We have a ton of them, they are simple and effective to use, and they rarely break if used properly. We plan on continuing to use them into the future until they all break from misuse or they are made illegal. As far as WPILib classes go, I don't believe there is any difference between controlling a Victor 888 and a Spark or Victor SR. I would even be willing to just use the PWM class and manually set values from 0 to 255 if it meant we wouldn't have to spend a ton of money on new speed controllers.

[Cory]

Originally Posted by Jon Stratis

Just because teams have a bunch doesn't mean FIRST will keep them legal I future years. Just look at BaneBots motors,

884's haven't been sold since sometime in 2012, but they remained legal through last season and there's no real reason to expect they won't be legal this year too...so 888's are probably safe for at least 3 more years.

[pilleya]

Originally Posted by Jon Stratis

Just because teams have a bunch doesn't mean FIRST will keep them legal I future years. Just look at BaneBots motors...

With the discontinuation of the Banebots motors( 775 and 550 mainly) there was the potential for a huge power deficit between the motors available to rookie teams and those of veteran teams, especially those holding large stockpiles. There would have been close to a 100 watt power deficit between the BB RS775-18 and the am-9015. This was until VEXPRO released the 775pro, legality is still unknown sadly.

The 888 on the other hand, does not give a major advantage over other currently available FRC controllers. It is still a great controller, and it can cope with serious amp draw.

[GreyingJay]

I've heard people tout the fully-sealed enclosures of the newer controllers as an advantage. Does the "open" nature of the Victor 888 pose a serious disadvantage? Is it highly susceptible to swarf, dust, dirt, etc. blocking the fan or getting into the electronics?

[Greg Needel]

Originally Posted by GreyingJay

I've heard people tout the fully-sealed enclosures of the newer controllers as an advantage. Does the "open" nature of the Victor 888 pose a serious disadvantage? Is it highly susceptible to swarf, dust, dirt, etc. blocking the fan or getting into the electronics?

Yes. The biggest issue with the 884/888 style is how susceptible they are to catching on fire due to metal chips. Under the fan, you have a direct shot down to the PCB and FETS. While the PCB is conformally coated, it doesn't take much of a shaving to short across the leads of a FET. I would be that 75% + of the failures of these style controllers come from metal shaving or chips inside of them. The rest of the failures come from teams wiring them up wrong (either reverse polarity on the input side or power into the motor side).

[Munchskull]

Originally Posted by Munchskull

One thing that people are forgotten to mention is that the spark motor controller is more linear than the victor 888. That means as a PWM signal increases, the motor will increase at a more constant rate if you are using a spark motor controller.

Just to back up my previous statement. The Spark motor controller has very similar specs to the Jaguar motor controller. Both have a switching frequency of 15.625 kHz and switch using synchronous rectification. Knowing that, it is safe to assume that the Spark motor controller would follow the path of the jaguar on the graph bellow.

My source for this graph.

[Jon Stratis]

Important note for anyone that looks at the above graph without following the link - "Victor" refers to the really old 884, which was known to have a very non-linear output. "Talon" refers to the original Talon speed controller, not the newer SRX. None of the current commercially available speed controllers is in that graph.

So, in short, with all these new speed controllers the past year or two, the community needs to do some more testing to come up with similar curves for all of them! While we expect all of the newer speed controllers to be very linear, testing to make sure would be really nice!