SD540 Motor Controller

[techhelpbb]

Originally Posted by talon540

If you are wondering how the SD540's heat up over time, mindsensors and Talon 540 performed a few tests on one of our old robots.

http://www.team540.com/sd540/

That's great! Can we get the drivetrain information that produced those temperatures? Wheels, ratios and motor configurations please. There seems to be a section of your website for it, but that information does not seem to be there.

[philso]

Originally Posted by talon540

If you are wondering how the SD540's heat up over time, mindsensors and Talon 540 performed a few tests on one of our old robots.

http://www.team540.com/sd540/

Do you have any thing to show the test conditions such as ambient temperature, motor current. These have a significant effect on the measured value. Test results are meaningless without knowing the test conditions.

[talon540]

I just realized... I need more caffeine! Apologies for an earlier post, but our robot does NOT use an SD540 for our pneumatics. It was for our lift mechanism.

Man, that's embarrassing. I'll drink some Redbull and be quiet now.

[Chris is me]

Will a firmware upgrade be released to remove the "safety feature" that cuts motor output if the input voltage drops below 9.5 volts? The "feature" is a deal breaker for me, as that is a surprisingly easy condition to reach on an FRC robot.

Also, the spec sheet claims the speed controller operates at voltages as low as 6 volts, but this "safety feature" kicks in long before that, so the spec sheet is wrong.

[sastoller]

Since you guys seem to be SD540 experts in this thread, I was wondering if you could comment on the very high output resistance of the SD540 that was measured by CTR in their tests (surely you've seen the results). The voltage drop (power lost) in the motor controller is drastically worse than the competition? Did you guys make a design choice or tradeoff that resulted in this? Or is it possible that CTR just got a bad (or damaged) SD540?

And I'll also echo Chris's question regarding a FW update to modify the 9.5V brownout feature. Could you make this voltage threshold user adjustable in the future so that users could control which motor controllers shut off first? Would it be possible to add a throttling feature to reduce output to 50% when a certain voltage threshold is reached?

http://www.ctr-electronics.com/downl...er-Testing.pdf

[Andrew Schreiber]

Originally Posted by Chris is me

Will a firmware upgrade be released to remove the "safety feature" that cuts motor output if the input voltage drops below 9.5 volts? The "feature" is a deal breaker for me, as that is a surprisingly easy condition to reach on an FRC robot.

Also, the spec sheet claims the speed controller operates at voltages as low as 6 volts, but this "safety feature" kicks in long before that, so the spec sheet is wrong.

And claiming it's a safety feature makes little sense to me. I can run Victors off a 2S Lipo (7.2-8.4V) and be fine. No safety issue, just the robot only operates at those voltages (say for smaller than FRC robots) but this "feature" makes SD540's worthless in these applications. Despite them appearing to be a better fit because of lower cost. (Performance isn't as critical in this application, cost is more a factor)

[pnitin]

Originally Posted by Chris is me

Will a firmware upgrade be released to remove the "safety feature" that cuts motor output if the input voltage drops below 9.5 volts? The "feature" is a deal breaker for me, as that is a surprisingly easy condition to reach on an FRC robot.

If you are letting down your battery 9.5 V your are basically killing your battery( actually 10.8V that is 1.8V per cell).
Lead-Acid battery will quickly built lead sulfide layers on plates ( no matter what is battery technology and what manufacturer claims)
you are basically screwing up battery and now it will have much high internal resistance so the you will start seeing voltage drop when you try to take out good amount of current.

[notmattlythgoe]

Originally Posted by pnitin

If you are letting down your battery 9.5 V your are basically killing your battery( actually 10.8V that is 1.8V per cell).
Lead-Acid battery will quickly built lead sulfide layers on plates ( no matter what is battery technology and what manufacturer claims)
you are basically screwing up battery and now it will have much high internal resistance so the you will start seeing voltage drop when you try to take out good amount of current.

Don't think I've seen a robot get through a match without dipping that low in their battery voltage.

[Andrew Schreiber]

Originally Posted by notmattlythgoe

Don't think I've seen a robot get through a match without dipping that low in their battery voltage.

Pretty sure I've seen that on a non aggressively geared kitbot that only weighed 80 pounds... Unless the 9.5V limit only kicks in after a period of time in which case I'd like to see that in the documentation (and still complain because my use case for low cost controllers involves lower voltages anyway)

[notmattlythgoe]

Originally Posted by Andrew Schreiber

Pretty sure I've seen that on a non aggressively geared kitbot that only weighed 80 pounds... Unless the 9.5V limit only kicks in after a period of time in which case I'd like to see that in the documentation (and still complain because my use case for low cost controllers involves lower voltages anyway)

I guess a robot that doesn't move would probably keep a pretty high voltage too.

[geezloueez]

Originally Posted by notmattlythgoe

Don't think I've seen a robot get through a match without dipping that low in their battery voltage.

I am a first year mentor for a rookie team. May seem like a dumb question, but I have not been involved first hand in a match yet. What is causing the batteries to drop so low? Are you using old batteries?

[notmattlythgoe]

Originally Posted by geezloueez

I am a first year mentor for a rookie team. May seem like a dumb question, but I have not been involved first hand in a match yet. What is causing the batteries to drop so low? Are you using old batteries?

Running any number of motors at the same time. Compressors running a lot. Pushing matches with other robots. FRC robots can use a lot of power and usually do.

[geezloueez]

Originally Posted by notmattlythgoe

Running any number of motors at the same time. Compressors running a lot. Pushing matches with other robots. FRC robots can use a lot of power and usually do.

What is the lowest you have witnessed in a match?

[asid61]

Originally Posted by pnitin

If you are letting down your battery 9.5 V your are basically killing your battery( actually 10.8V that is 1.8V per cell).
Lead-Acid battery will quickly built lead sulfide layers on plates ( no matter what is battery technology and what manufacturer claims)
you are basically screwing up battery and now it will have much high internal resistance so the you will start seeing voltage drop when you try to take out good amount of current.

Hence why batteries in FRC have such a low lifetime... Interesting tidbit.
We don't use batteries from 2011 or earlier. And we're probably going to start phasing out the 2012 batteries too. They start being unable to hold a significant charge.

[Chris is me]

Originally Posted by pnitin

If you are letting down your battery 9.5 V your are basically killing your battery( actually 10.8V that is 1.8V per cell).
Lead-Acid battery will quickly built lead sulfide layers on plates ( no matter what is battery technology and what manufacturer claims)
you are basically screwing up battery and now it will have much high internal resistance so the you will start seeing voltage drop when you try to take out good amount of current.

Momentary drops to 9.5vs are not at all uncommon in FRC matches, depending on the number of motors on the machine, weight, traction, etc. It might not be great for batteries but I'd rather be able to drive for the rest of the match and potentially shorten a battery's life than not be able to drive to save a couple of bucks later on. Basically, I don't want the products I use to try and protect me from myself.