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  #46   Spotlight this post!  
Unread 10-27-2017, 09:45 PM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

Quote:
Originally Posted by Chris is me View Post
This is awesome news on both fronts. Looking forward to it, especially the game data API. We will probably be able to get a field clock reading, from the actual field!

The brushless motor is pretty low-power, but that's probably a good way to ease teams into the world of brushless motor control.
Just an FYI, getting the current match timer was already possible in the current API. I believe it has been available since 2011.
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Last edited by dirtbikerxz : 10-27-2017 at 09:49 PM.
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Unread 10-27-2017, 10:28 PM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

Quote:
Originally Posted by dirtbikerxz View Post
Just an FYI, getting the current match timer was already possible in the current API. I believe it has been available since 2011.
It's not the official time, its just a timer that starts when the robot gets enabled for auto.

From the API docs:
Quote:
The FMS does not currently send the official match time to the robots. This returns the time since the enable signal sent from the Driver Station. At the beginning of autonomous, the time is reset to 0.0 seconds. At the beginning of teleop, the time is reset to +15.0 seconds. If the robot is disabled, this returns 0.0 seconds. Warning: This is not an official time (so it cannot be used to argue with referees).
Emphasis mine.
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Unread 10-27-2017, 10:41 PM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

Quote:
Originally Posted by firecrafty View Post
It's not the official time, its just a timer that starts when the robot gets enabled for auto.

From the API docs:


Emphasis mine.
Ahhhh interesting, I stand corrected.
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Unread 10-27-2017, 11:21 PM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

Quote:
Originally Posted by firecrafty View Post
It's not the official time, its just a timer that starts when the robot gets enabled for auto.

From the API docs:
Quote:
The FMS does not currently send the official match time to the robots. This returns the time since the enable signal sent from the Driver Station. At the beginning of autonomous, the time is reset to 0.0 seconds. At the beginning of teleop, the time is reset to +15.0 seconds. If the robot is disabled, this returns 0.0 seconds. Warning: This is not an official time (so it cannot be used to argue with referees).
You're looking at old API documents (although your point is still valid).

Quote:
Return the approximate match time.

The FMS does not send an official match time to the robots, but does send an approximate match time. The value will count down the time remaining in the current period (auto or teleop).

Warning: This is not an official time (so it cannot be used to dispute ref calls or guarantee that a function will trigger before the match ends).

The Practice Match function of the DS approximates the behaviour seen on the field.
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Unread 10-28-2017, 12:01 AM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

Quote:
Game Data API
The other thing that Beta teams will be seeing is a new software API to provide teams with Game Specific data on the field (though it just looks a lot like an empty box until Kickoff). We’re not quite ready to reveal what this will be used for in 2018 (and beyond!), but we do want to share a bit about the implementation for those who may not keep close tabs on the Beta.

Starting this year, WPILib, in all 3 languages, will have APIs to access a Game Specific data string which will contain information sent from the Field Management System to the Robot (via the Driver Station). There will also be a new text box in the Driver Station which will allow teams to simulate this functionality when testing at home. The implementation has been kept as generic as possible to allow for maximum flexibility as we use this new feature in future years.

Keep your eyes peeled after Kickoff for documentation and examples about what will be contained in this Game Specific Data for 2018 and how to parse it in your Robot Code. Until then, let your imagination run wild about what the Field might have to say to your Robot!
I've wanted this for years! That's so exciting, and it's going to make events much more fair and competitive for all teams.
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Unread 10-28-2017, 06:06 AM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

Quote:
Originally Posted by thefro526 View Post
The spec sheet is missing the shaft diameter along with the specifics of the key way, and more importantly, the mounting boss is 1” OD on the DM3012-1063 and .750 OD on the CIM - I wouldn’t say the mounting interfaces are compatable just yet.

The 2” OD bolt circle is likely just a coincidence - if they were trying to match the CIM, they’d have tapped for a #10 - not a #6.

All of that being said, it should be easy enough to make these work in a transmission originally intended for a CIM, drill out the mounting bore to 1” and figure out how to adapt to the shaft (if needed, it would be nice if the shaft is in fact 8mm, [I can’t imagine them key-ing anything smaller] but again it’s not listed) and you’d be good to go. Regarding the mounting screws, there should be 6-32 shoulder screws with a .1875 OD shoulder, but always double check to be sure.
If you go to the Hurst website, you can find the shaft diameter of the other Size 17 motors (which this appears to be). It is .3125", which is very close to the 8mm shaft of a CIM (.315").
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Unread 10-28-2017, 08:44 AM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

I was discussing the "game specific string" with another mentor last evening at cowtown and he had an interesting idea. Think Pacman and the large power up dots and how that temporarily changes game play. Perhaps something similar to that will be included in our game this year.

Steve
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Unread 10-28-2017, 01:22 PM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

Quote:
Originally Posted by Ether View Post
Notice that the "rated" speed, power, and torque do not match the 12V speed vs torque curve in the document.

The 12V curve says the power is 34 Watts and the torque is 27 oz_in at the "rated speed" of 1700 RPM.

The "rated" power of 44 Watts occurs nowhere on the 12V curve.
Yup, been looking at the same thing! (Written before seeing Ether's note above.)

Converting all the numbers at the top to MKS:
Code:
Rated Speed:        178 rad/s
Rated current	   4.00 Amp
Rated power	   44.0 Watt
Rated torque	 0.1412 N-m
No Load Speed	  282.7 rad/s
No load current    0.28 Amp
Peak Torque       .3178 N-m
Peak Current        6.5 Amp
Voltage Constant  37.15 Vs/rad
Torque Constant  0.0371 N-m/A
L-L Resistance     0.67 Ohms
L-L Inductance     0.66 mH@1kHz
Rotor inertia  9.18E-06 N-m/s2
Voltage:           12.0 Volts
The first thing that jumps out at me is "Rated Power" of 44W. If this is indeed at the rated current of 4A and 12V, the motor is about 92% efficient at its rated capacity, which is impressive to the point of being suspect.

Calculating mechanical power instead as rated torque times rated speed, I get 25.1W, or 52% efficiency.

Interestingly, the current and speed curves cross at about 1640 rpm and 3.82A, which is a bit below those ratings on both curves.

Using the free speed numbers and the rated speed, torque, and current, I can extrapolate a stall torque and current of 54 oz-in (0.381 N-m) and 10.8A respectively. Plotting this between the free speed and a bit below the "kink" at 6A, I get the attached graphic; the dashed blue line indicates the rated speed, torque, and current.
Attached Thumbnails
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ID:	22609  
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[Quoting brennonbrimhall]: We design a new robot every year, but we can't forget that we also design a new team every year as folks come and go.

Last edited by GeeTwo : 10-28-2017 at 02:42 PM. Reason: current curve, not torque curve!
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Unread 10-28-2017, 01:57 PM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

Quote:
Originally Posted by Michael Hill View Post
If you go to the Hurst website, you can find the shaft diameter of the other Size 17 motors (which this appears to be). It is .3125", which is very close to the 8mm shaft of a CIM (.315").
Nice find Michael. I checked out the site last night and wasn’t having much luck. That being said - if we do luck out and the shaft is 5/16” OD, then we might get lucky enough to use CIM pinions.

Guess the question now is what size is the key way? It’s been a while but I believe 2mm is nominally 5/64”.
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Unread 10-28-2017, 02:53 PM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

Quote:
Originally Posted by Blog
The other thing that Beta teams will be seeing is a new software API to provide teams with Game Specific data on the field (though it just looks a lot like an empty box until Kickoff). We’re not quite ready to reveal what this will be used for in 2018 (and beyond!), but we do want to share a bit about the implementation for those who may not keep close tabs on the Beta.
I think a lot of the speculation on this has missed the "Game Specific" part of this. While this could be as generic as high goals, low goals, rotors & climbs, it could also be something that doesn't even make sense in any other year. For video games, it could be the location of the magic "power up" mushroom, or a cheat code. I also isn't clear if the same information is available to every team, or even every team on the same alliance. I really expect it to include data which is NOT on the public real time scoreboard.
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[Quoting brennonbrimhall]: We design a new robot every year, but we can't forget that we also design a new team every year as folks come and go.
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Unread 10-28-2017, 04:40 PM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!


GeeTwo has pointed out that the labeling of the torque axis in the datasheet curve is ambiguous.

I will re-digitize the curve based on the assumption that the max torque of the curve is 45 oz_in.
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Unread 10-28-2017, 06:07 PM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

I hope you’re all happy. You’ve ruined Christmas.
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Unread 10-28-2017, 10:40 PM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

Quote:
Originally Posted by Ether View Post

GeeTwo has pointed out that the labeling of the torque axis in the datasheet curve is ambiguous.

I will re-digitize the curve based on the assumption that the max torque of the curve is 45 oz_in.
OK, I re-digitized the curve assuming that the far right edge of the datasheet graph represents 0.35 Nm instead of .4 Nm. This makes the labeling on the datasheet curve torque axis make more sense:

Code:
0, .1,  .1, .2,  .2, .3,  .3, .4   should be:
0, .05, .1, .15, .2, .25, .3, .35
... and it makes the peak torque on the curve match the specified peak torque (45 ounce inches).

Here's the corrected speed and power vs torque curve.

At 1700 RPM the torque is 23.6 oz_in and the power is 29.7 Watts

At 20 oz_in the speed is 1832 RPM and the power is 27.1 Watts

The peak power is about 35 Watts at about 1200 RPM, but you'd never want to design for that operating point due to the sharp drop-off of power and torque below 1200 RPM.

I am guessing that the datasheet speed vs torque curve is actual test data, and that the "rated" spec numbers in the datasheet were somehow mis-calculated.
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Unread 10-29-2017, 01:29 AM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

Quote:
Originally Posted by Ether View Post
The peak power is about 35 Watts
only 35 Watts?

one of my small brushless motors for my RC airplanes is around 280...
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Unread 10-29-2017, 02:25 AM
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Re: FRC Blog - 2018 Beta Teams, Brushless Motors, and More!

That huge drop off in speed AND torque worries me. Could this be caused by it being an unsensored brushless motor? I thought that sensored ones used the commutation detection to get higher torque at low rpms.
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