SD540 Motor Controller

[AllenGregoryIV]

Originally Posted by Cory

Just out of curiosity, are you affiliated with mindsensors.com in any way?

If you are affiliated with mindsensors, it seems slightly disingenuous to refer to yourself/your team as a third party without a stake in the game. This is especially true when it comes to endorsement of a new product that serves a critical role and has no competition heritage.

I am in no way accusing you of not doing due diligence or appropriate testing, or questioning your results, but I think it's important for teams to know whether testimony they are basing their purchasing decisions on is coming from an end user or essentially from the inventor(s)/vendor.

This controller is designed jointly with Team 540 students and manufactured in Richmond, VA with the help of local FIRST students. Source: http://www.mindsensors.com/frc/135-m...roller-for-frc

Their team helped to design them and from that seems like they help build them as well.

[techhelpbb]

Originally Posted by Cory

Just out of curiosity, are you affiliated with mindsensors.com in any way?

If you are affiliated with mindsensors, it seems slightly disingenuous to refer to yourself/your team as a third party without a stake in the game. This is especially true when it comes to endorsement of a new product that serves a critical role and has no competition heritage.

I am in no way accusing you of not doing due diligence or appropriate testing, or questioning your results, but I think it's important for teams to know whether testimony they are basing their purchasing decisions on is coming from an end user or essentially from the inventor(s)/vendor.

Just to share - I have nothing to do with MindSensors or their team.
I merely like the idea of competition for the pricing of FRC motor controls.
It's easy to go back through my post history to show that I have built other controls in the past and expressed public interest in the matter on this forum.

To be fair I also bought 2 Sparks as well.
This is not a Team 11 thing either.
It's just little old me being curious.
I have my own parts to build FRC robots so I don't have to impact Team 11 or 193 operations to do this.
I also have my own machine tools.

At the moment I am planning on doing the temperature and current measurements with an Arduino based data logger but I have more development boards than I care to discuss so I could do this with something more powerful. I will likely use a Dallas 18B20 for the temperature measurement with it installed in a steel cartridge in direct contact with the ESC heatsink and a either a TI or Maxim chip for the current measurement using a current sense resistor of a value I will disclose. It's likely the current sense resistor will be less than 1mOhm right now. I need to disclose that because it has a slight impact on the motor circuit.

[philso]

Originally Posted by techhelpbb

Just to share - I have nothing to do with MindSensors or their team.
I merely like the idea of competition for the pricing of FRC motor controls.
It's easy to go back through my post history to show that I have built other controls in the past and expressed public interest in the matter on this forum.

To be fair I also bought 2 Sparks as well.
This is not a Team 11 thing either.
It's just little old me being curious.
I have my own parts to build FRC robots so I don't have to impact Team 11 or 193 operations to do this.
I also have my own machine tools.

At the moment I am planning on doing the temperature and current measurements with an Arduino based data logger but I have more development boards than I care to discuss so I could do this with something more powerful. I will likely use a Dallas 18B20 for the temperature measurement with it installed in a steel cartridge in direct contact with the ESC heatsink and a either a TI or Maxim chip for the current measurement using a current sense resistor of a value I will disclose. It's likely the current sense resistor will be less than 1mOhm right now. I need to disclose that because it has a slight impact on the motor circuit.

Is it too much to ask if one of the Talon SRX's or Victor SP's to act as a point of reference?

As long as the temperature data is measured at the same output current, the value of the current sense resistor does not matter. The losses in the controller are related to the characteristics of the switch devices used (MOSFETS?), how they are driven by the circuitry in the controller, the switching frequency and the output current. As a user, one would only have control over the output current.

[techhelpbb]

Originally Posted by philso

Is it too much to ask if one of the Talon SRX's or Victor SP's to act as a point of reference?

As long as the temperature data is measured at the same output current, the value of the current sense resistor does not matter. The losses in the controller are related to the characteristics of the switch devices used (MOSFETS?), how they are driven by the circuitry in the controller, the switching frequency and the output current. As a user, one would only have control over the output current.

I don't have either to use as a reference currently.
AndyMark is sold out of the Victor SP.
I can get it here:
http://www.robotmarketplace.com/prod...-VICTORSP.html

At some point I have to point out that the more parts I have to accumulate on short notice the higher the unplanned cost to me of this exercise. I don't really need these chassis until well after build season outside of this. However I will entertain this because I probably will buy at least 2 of the Victor SP sooner or later. I do have the older gray Jaguar, black Jaguar, Victor 888 , Victor 884 and Talon SR (not the SRX).

Here are the constraints of doing this with a proper Arduino and the hardware I have planned:

1. The DS18B20 has variable bit resolution measurement. The more resolution the longer the readings take. I intend to run it at the fastest of 9bit resolution at 0.5C resolution. This means I need to wait likely more than 75ms to get a temperature from it. After issuing the request it can be configured to be non-blocking so I can go off and do other things then check back for the reading.

2. I will likely use either the A/D of the Arduino which for the Mega2560 is 16 channel analog muxed 10bit or something like the MCP3008/MCP3208 like that found on the Propeller ASC+ from Parallax. With the current sense resistors as I plan them this should give me something around a 0.1A resolution for the current. I would figure these are not super high-end A/D so some error is to be expected but most of the error I hope will cancel by being consistent across all measurements. The current sense resistors are high enough wattage that a complete stall shouldn't cause them to fail but likely will rail the current reading. I am going to assume we won't be trying to run the motors consistently at 95A or more.

3. The AdaFruit Data Logging shield provides a DS1307 RTC and access to SD card storage. I can also go down the route of this: https://www.parallax.com/product/27937

Since the current PDP model can only report current as fast as 25ms over the CAN bus connection to the RoboRIO, the only part of this I think is a bit slow is the DS18B20. No matter how fast my CPU/MCU that 75ms is pretty slow but thermally the heatsink mass is not so small that I think we need to be all that fast reading temperature.

4. My initial thought is to store the 2 temperatures and the 2 currents packed.
9 bits (temp) + 9 bits (temp) + 10 bits (current) + 10 bits (current) = 38 bits
Stored as 4 bytes and some bytes for any time stamps.
A trivial amount of code can unpack that and dump it into Excel.

[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/

[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

[pnitin]

Originally Posted by 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...please)?<br />

All FRC the controller on market use synchronous rectification,
they are not linear converter, so what is mentioned above is incorrect.
for example, consider your cellphone charger 115V In 5V Out @ 1A current,.
According to your theory it should dissipate 110W and should melt, but it does not. It dissipate much low power since it uses switching topology.

[Daniel_LaFleur]

Originally Posted by pnitin

All FRC the controller on market use synchronous rectification,
they are not linear converter, so what is mentioned above is incorrect.
for example, consider your cellphone charger 115V In 5V Out @ 1A current,.
According to your theory it should dissipate 110W and should melt, but it does not. It dissipate much low power since it uses switching topology.

Incorrect.

The output is 5VDC@1A not the input. The input is closer to 115VAC@0.05A or ~6Watts (assuming 1W inefficiency which is actually high).

In a phone charger (or most other chargers/USB power supply sources) you have a AC to DC converter (most likely a bridge rectifier). Then you have a buck converter (probably a transformer) and a switcher boost (High speed MosFET, inductor, and shottkey diode).

[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.