Re: SD540 Motor Controller
 

We are planning on implementing CAN on future models. Possibly as a single board swap out kit. The firmware upgrader will actually use I2C that is already implemented for bootloading the device.

Re: SD540 Motor Controller
 

Have you seen the results of our performance tests? Check it out at the link below.

http://www.mindsensors.com/content/7...haracteristics

Re: SD540 Motor Controller
 

It seems to be getting quite hot; I'm not sure I would consider these for my drivetrain.

Re: SD540 Motor Controller
 

This graph doesn't mean anything to most teams.

They need to see it run by a bunch of teams in a bunch of different applications w/o failure before they believe in it.

Re: SD540 Motor Controller
 

Those results show a 50 amp load with the motor mechanically stalled. Even then, after two minutes the controller is under 100 degrees Celsius.

If you typically stall your motors for 5 minutes at 50 amps, then temperature might be of concern.

Re: SD540 Motor Controller
 

The stalling doesn't matter as much as the current; IIRC the heat generated is proportional to current.
I would be worried about getting a burn or burning something at that temperature. Plus, CIMs often run at high currents for the duration of the match; it's certainly possible to average 40-50 amps for a match.

Re: SD540 Motor Controller
 

There's definitely inertia in teams adopting any new item, whether part of the control system, an actuator, or a mechanical system. Our overwhelmingly positive experiences with the Talon SR and Spike (and negative experiences with Victors and even worse with Jaguars) led us to use these two motor controllers/switches exclusively last year. This year, especially as the Talon SR has been discontinued, we do plan some experimentation with the Talon SRX, and some of the new less expensive motor controllers (SPARK and SD540). Over the years as an occasional purchaser for the government, I've learned to take vendors' tests with a big grain of salt. It's rather harsh to say this, but one failure under conditions where we cannot produce calculations that would lead us to expect failure or which may be beyond our reasonable control can put a motor controller on our black list, along with the Jags and Victors. At this point, we keep Vics and Jags around just to give the freshmen a sense of how much things have improved even in recent years; we haven't put either on so much as an off-season project in over two years.

In the interest of total disclosure, I am personally quite harsh on vendors who seriously disappoint me. For example, I haven't had a McDonalds hamburger since my sophomore year in high school (can't you dress a hamburger without including that awful special sauce?), and I haven't bought anything but a few batteries and tires (and those under otherwise desperate situations) from Wal-Mart in over ten years. The traffic from selling groceries drove me 90+% away circa 2003; the way they abandoned New Orleans after Katrina in contradiction of all of their advertising about helping communities after disasters sealed the deal.

This is competing with the spark but, the spark has the advantage of being from a more experienced company, and looking pretty. It looks decent and we will buy one to test but for us staying with talon SRX'es and Sparks or Victor Sp's for this year make sense.

Next year we will see how people feel about these guys and it they work we will use them.

Re: SD540 Motor Controller
 

Honestly I don't have many feelings one way or another about this speed controller (our team uses CAN).
That said, a few things did stick out for me...

• It requires me to have 6-32 screws, and have them at a specific length to mount to anything (Imo, through holes are better, and allow you to avoid hunting for "that one screw").
• The signal input connector seems like an odd choice, and it looks like the kind of thing that PWM cables could fall out of easily, and then, due to lack of labeling, get reconnected incorrectly.
• If you have a bank of controllers, and one of them dies, do you have to replace the whole bank?
• Would be nice if brake/coast could be changed on the fly (we used to do this with victors by connecting a PWM cable where the jumper would go).

Might get one of these to play around with it, but generally we avoid new, un-FRC-proven components the first year they're out (unless there are no alternatives like in 2014).

Re: SD540 Motor Controller
 

To answer your questions:
The mounting screws are included when you purchase the SD540. Also, our case is 3D printed so there are multiple options in the works that do not call for a complete redesign. We plan to release casing options with different mounting options and through holes.

The connector is not only for PWM. Currently it allows for firmware updates, and in the future CAN, encoder connection, and possible I2C. Labels are on the bottom.

If a unit dies on one of the multi-bank options, you only need to replace that unit. A kit will be offered for just such a situation.

Brake/coast can be changed on the fly. There is a dip switch on the bottom that just needs to be flipped. You can also change direction.

Re: SD540 Motor Controller
 

oops. double post.

Re: SD540 Motor Controller
 

It would be best if Mindsensors can present time/temperature charts that show the temperature stabilizing. It would be even better if you can present such charts with different (continuous) loads (10%, 20%, 40%, 60%, 80%, 100%). In FRC, it is rare that a motor controller would be run for the duration of the match at the same current level but these extra load lines can give the users some indication of what kinds of temperatures they can expect by estimating their average current over a short time period. The time/temperature charts will also give some indication of what the short term thermal capacity of the motor controller is; i.e. it may withstand an 80A load for 1 second better than it can withstand a 50A load for 2 minutes or longer). Your chart ends at just past 4 1/2 minutes which is much longer than a standard FRC match. In practice sessions, we have often run our robots continuously for much longer than 4 1/2 minutes, often repeating the most stressful actions. Considering how quickly the temperature is still rising at 270 seconds, I would be concerned that the transistors hit thermal-runaway and self destruct.

It is also of concern to me that your time/temperature chart is reaching almost 100 degrees at 150 seconds and about 125 degrees at 270 seconds, with your initial temperature of 25 degrees. It appears from your photo that these temperatures are measured on the top of the heatsink. If this is true, your transistor junction temperatures (taking into account the thermal impedance through the base plate of the your heatsink and the junction-to-case thermal impedance) will be much higher, possibly leaving you with very little (or no) margin from the maximum operating temperature of your transistors, depending on your device type. These high junction temperatures will lead to reduced life of the transistors. Have you done extended life testing on your motor controllers? Batch-to-batch variations in the transistor characteristics can have a large effect on your temperature performance so a test result showing little or no thermal margin raises red flags in my mind.

Lastly, the high heatsink temperatures are a concern, as Asid has also pointed out. Various safety standards specify different "maximum touch temperatures" but they will all be well below 100 degrees C (UL/IEC 60950-1 specifies a maximum of 75 C). With the thermal mass of your heatsink, temperatures at 100 degrees and above will most likely cause serious burns to anyone touching the heatsink. America has far too many lawyers. Some of them have children on FRC teams. I would not want to see Mindsensors dragged into court and many students be deprived of a great resource.

I am sorry if I am being hard on Mindsensors. They have a pretty good history in educational and hobby robotics where the power levels are low (NXT/EV3, Raspberry Pi, Arduino) and the energy sources have limited capacity (AA's or equivalent). They have now entered an arena where the energy levels are much higher and the hazards and consequences are much more serious. My comments and warnings are based on my experience developing power electronics products for mass production over the last 20+ years.


The heat generated has two components; the switching loss in the output transistors and the conduction loss of the output transistors. The switching loss is roughly proportional to the switching frequency (output frequency) of the controller. The conduction loss is calculated by multiplying the on-resistance of the output MOSFET (at the instantaneous operating current) with the square of the instantaneous output current (P = R x I^2).

I have not seen actual efficiency numbers for any of the motor controllers currently in use or for the new ones from Rev and Mindsensors so it is not clear how people in this thread are saying that the new controllers are more efficient.

Re: SD540 Motor Controller
 

Is there a polarizing feature on this connector? Connectors of this type, with 16 pins generally don't fall out on their own but changing to one with latches would give added security.

How many mating cycles is the connector rated for? It looks like a tin plated type in the photo. One major manufacturer of such connectors, Tyco Electronics, considers 50 cycles a "large number" for their tin plated connectors. This means they will not guarantee "stable electrical contact" after 50 mating cycles.

http://www.te.com/documentation/whit...f/sncomrep.pdf

Re: SD540 Motor Controller
 

This product looks like something that was developed by someone with limited FRC experience. The features being touted as benefits are actually detractors in my mind:

- Lightweight (The difference is negligible in my mind. If we get to the point where we need to save a fraction of a pound, we get out the big drill or hole saw. I also question what was skimped to get the weight loss.)
- Low Cost (REV Spark is $5 cheaper and has fewer issues that I can see. Honestly this controller would have to be under $40 for me to consider buying over the REV.)
- Multi Bank Option (Sure we need a bank of controllers for the drive train, but sometimes they need to be placed creatively to get the rest of the bot to work. I can mount them touching each other just fine by myself without the need for the bank. Also there is no air gap between controllers. I like a small air gap, especially if these are the drive train motors that will producing a good deal of heat.)

Things I like:

1) Well labeled (colored) inputs and outputs

2) Robust screw terminals for a ring type connector or bare wire

Things I dislike:

1) Single 16 pin male connector with no cable retention. It is very easy to plug the PWM into the limit switch pins or vice versa. Do I use a standard PWM connector (3x1) and two 2 pin limit switches connectors? Or do I make my own 16 pin custom connectors? How do these stay in during the season (please no more hot glue)? How do I keep the exposed male pins safe (especially from student hands when they are rooting around in the belly pan)? Also I am not sure why connectors are mounted parallel to the mounting face instead on normal to it (this will increase the part footprint quite a bit when it is used).

2) Brake/Coast & Cal under the mounting face. To me this is inexcusable. If I want to change/control the mode or re-cal a controller I have to demount these (by unscrewing them from the bottom - see #3)?! Why not use the spare 8 pins on the connector for these features?

3) Lack of thru hole mounting. I can't zip tie these down to something temporarily. Grrrrr.

4) Heatsinking. The test data shows a test at 50A continuous and does not reach steady state in the data provided. Not sure why you used 50A and not 60A (since the specs say 60A continuous). We want a controller we can practice with for long sessions, not just one FRC match. Based on your test data it looks like you will hit a steady state temp of 140-150C on the heatsink, curious what junction temp you will hit on active devices. If you are relying on a thermal pad or thermal grease to keep your ICs cool, what happens over a period of time as these degrade? We want to keep these controllers for a few years! Your test needs to be repeated many times at different loading profiles to convince me you have a proper passive thermal cooling design (and at 60A continuous like the spec sheet says). If you can truly run the controller at 60A continuous (and are not just copying the IC's specs) then show multiple 15-20 minute tests of a single controller at 60A.

5) 3D printed case. Other plastic manufacturing methods would make more consistent parts for cheaper and with better properties (at the right manufacturing quantities).

6) No CAN. I don't expect this in a low cost controller, but would love to have it.

As others have noted, these concerns lead me to believe there will be reliability problems when using this controller during FRC season. It is a great prototype, but needs some major packaging rework.

-matto-

Re: SD540 Motor Controller
 

It would be good if Mindsensors could provide temperature test data covering the 2-bank and 4-bank configurations with all inverters in the bank loaded the same way. Because the individual inverters are right next to each other and the heatsinks rely on convection cooling, the heat coming off one heatsink WILL cause the temperature on the adjacent heat sinks to be higher than if there were "ample space" around individual heatsinks. A simple test of this would be to monitor the heatsink temperature of all 4 heatsinks of a 4-bank controller where only one of the middle ones is loaded and the other 3 are not loaded. The two heatsinks on either side of the loaded inverter will be hotter than ambient.

Temperature test data with the controllers mounted in different orientations would also be helpful to the potential users.


Solid wire would be acceptable under the screw head but no one should be using solid wire on a robot. Stranded wire would be risky since it could slip out. Mindsensors can add a clamp plate under the screw head for just pennies to make this safe with bare, stranded wire.



Locating the 16-pin connector and the Brake/Coast & Cal DIP switch to the top surface would increase the footprint of the product. While they are at it, they may as well move the LED's to the top surface so they would not be obscured by the wiring.


The blind, threaded mounting holes on the bottom may be a very bad idea. What happens when a screw that is too long is screwed in till it bottoms out and is continued to be driven in? Will it damage the circuit board? Will it cause a short circuit and possibly a fire? Will it push the heatsink off the top?

Making it mandatory to have access to the back side of the mounting surface severely restricts where these can be mounted and remain serviceable. The mounting holes will have to be drilled pretty accurately or nothing will line up. The low-resource teams who are likely to be attracted to this controller will likely find it hard to do this. Mounting ears that one can match-drill from the front side would have been much better.


If this product does gain wide acceptance, will Mindsensors be able to manufacture them fast enough? The build period for FRC is very short and not receiving their motor controllers in a timely manner would be (near) fatal for any team.


Mindsensors may want to consider dropping the switching frequency to half of what they are using now. It would cut the switching losses in the transistors in half and should reduce the heatsink temperatures very significantly. It is not clear what benefit the 32kHz switching frequency gives. It may also be beneficial to attach a fan like those used to cool the CPU's in a desktop computer. A modest amount of air flow will increase the heat removal capacity of the heatsink by several times.

As it is, the high heatsink temperatures would make me question the service life of the product. Any electrolytic capacitors used in the controller would live a very short life since they are typically rated for operation in an 85 degrees C environment with some available that are rated for 105 (but they are more expensive and probably physically larger). Mindsensors may also want to check the temperature rating of the plastic they are using for the casing since many are only rated for around 90 degrees C.