FRC Blog - 2016 Motor Controllers

[Jared Russell]

Originally Posted by Mark McLeod

Everything on FIRST Choice is legal by definition.

So that digital multimeter is a legal robot part!

[notmattlythgoe]

Originally Posted by Jared Russell

So that digital multimeter is a legal robot part!

[Collin Fultz]

Originally Posted by Mark McLeod

Everything on FIRST Choice is legal by definition.

Mark -

I don't know that this is necessarily 100% true.

Going by the 2014 manual (I can't find the 2015 with the site redesign), only the motors listed in Table 4-1 are legal.

So a motor could be in FIRST Choice, but not in that list of motors. That motor could then be used on the robot, just not as a "motor".

-CF

[AllenGregoryIV]

Originally Posted by Jared Russell

So that digital multimeter is a legal robot part!

Seems perfectly legal to me. Not sure what you would use it for but it is legal. Actually it might even be legal as a

"Custom high impedance voltage monitoring or low impedance current monitoring circuitry connected to the ROBOT’S electrical
system is acceptable, if the effect on the ROBOT outputs is inconsequential."

[Mr. B]

I know first hand that this statement is incorrect.
" In the past FIRST Choice components have always been FIRST legal."

[cgmv123]

Originally Posted by Mark McLeod

Everything on FIRST Choice is legal by definition.

Non-legal 2009-2014 control system components were in FIRST Choice last year.

[Mark McLeod]

Originally Posted by Collin Fultz

Mark -

I don't know that this is necessarily 100% true.

Going by the 2014 manual (I can't find the 2015 with the site redesign), only the motors listed in Table 4-1 are legal.

So a motor could be in FIRST Choice, but not in that list of motors. That motor could then be used on the robot, just not as a "motor".

-CF

I concede the point that the manual does rule.
A good instance is the KOP white Clippard tanks that were explicitly called out by the 2015 rules as no longer legal despite having been KOP items.

Although, it does mean we shouldn't take FIRST Choice motors until the season's rules are issued.
I mislead myself thinking of this old Frank quote that admittedly doesn't apply since it is taken way out of the season in which it was Blogged:

- It’s safe to assume that if you see a robot component in FIRST Choice when it opens for “window shopping” on November 12th, it will be legal for teams to use in the 2013 season. Please don’t go all ‘lawyer’ on me with this one. Use good judgment. If you see a plasma cutter available in FIRST Choice, you should not think you’ll be able to put it on your robot. (Spoiler: There will be no plasma cutters available in FIRST Choice).

[Mark McLeod]

Originally Posted by Jared Russell

So that digital multimeter is a legal robot part!

Only putting a battery in it is illegal on a robot

[Thad House]

Originally Posted by Mark McLeod

Only putting a battery in it is illegal on a robot

Actually, if I remember right, COTS devices are allowed to use their internal batteries...

Originally Posted by cgmv123

Non-legal 2009-2014 control system components were in FIRST Choice last year.

There were no rules saying you couldn't use those parts. Just that they couldn't directly control the robot with them. If you wanted to put a cRIO on the bot and use it for camera processing then communicate to the RoboRIO you legally could.

[Monochron]

Originally Posted by Mr. B

Will the PG71 Gearmotors offered on FIRST Choice be Legal? Both have a 775 motor on them

If I remember right, that AndyMark 775 performs very differently from the Banebots 775 anyway.

[cgmv123]

Originally Posted by Thad House

There were no rules saying you couldn't use those parts. Just that they couldn't directly control the robot with them. If you wanted to put a cRIO on the bot and use it for camera processing then communicate to the RoboRIO you legally could.

You could probably have gotten away with a cRIO, but I don't think you could have gotten away with an earlier PDB.

[Michael Corsetto]

Cross The Road Electronics has posted a detailed report of some Motor Controller Output Power Testing they preformed with the four main FRC speed controllers on the market:

• Victor SP
• Talon SRX
• SPARK
• SD540

Link to .pdf document here

Please take note of the test results on page 7. I'm very concerned about the SD540's performance, particularly that the SD540 appears to brown out at 9.5V.

2016 will be the year of the brown out...

-Mike

[Thad House]

Originally Posted by Michael Corsetto

2016 will be the year of the brown out...
-Mike

Programmers better bring their A game this year if teams want any sort of speed with 3 CIMs. Some very intelligent ramping and shifting code is going to be required for all the top teams.

Maybe someone who knows a lot about working with motor controls would be willing to do a white paper or something how how to limit current. Trying to find documentation online on how to do that has been impossible for me.

[Jared Russell]

Originally Posted by Michael Corsetto

Cross The Road Electronics has posted a detailed report of some Motor Controller Output Power Testing they preformed with the four main FRC speed controllers on the market:

• Victor SP
• Talon SRX
• SPARK
• SD540

Link to .pdf document here

Please take note of the test results on page 7. I'm very concerned about the SD540's performance, particularly that the SD540 appears to brown out at 9.5V.

2016 will be the year of the brown out...

-Mike

This is a very interesting study, and props to CTRE in making it easy to reproduce the test.

Assuming the motor controllers are all linear, we can calculate series resistances from the test data. Averaging all non-brownout trials gives me:

R(Victor SP) = 0.0042 ohms
R(Talon SRX) = 0.0050 ohms
R(SPARK) = 0.0075 ohms
R(SD540) = 0.0175 ohms

We can roughly model a stalled CIM as a resistor R(CIM) = 12V/131A = 0.092 ohms.

Now put our stalled CIM in line with each speed controller (so the total resistance is R(CIM) + R(motor controller), the resulting current is calculated by I=V/R, and the resulting stall torque is the ratio of this current to the CIM's nominal stall current of 131A using motors.vex.com data):

Stall torque (Victor SP) = 2.30 N*m. This is 95.6% of the motor spec.
Stall torque (Talon SRX) = 2.29 N*m. This is 94.9% of the motor spec.
Stall torque (SPARK) = 2.23 N*m. This is 92.5% of the motor spec.
Stall torque (SD540) = 2.02 N*m. This is 84.0% of the motor spec.

These are large enough differences from the motor spec (even in the Victor/Talon case) that designers will want to keep these numbers close by when choosing gear ratios.

And of course, keep these numbers in mind when choosing speed controllers this season. In some applications, it won't really matter which one you choose...in others, it most certainly will.

[Jon Stratis]

Originally Posted by cgmv123

You could probably have gotten away with a cRIO, but I don't think you could have gotten away with an earlier PDB.

Well, you could have used that old PDB, powered from a 40A breaker on the new PDP, to power your custom electronics (but not speed controllers, etc). It wouldn't really be worth doing, as there are smaller and cheaper ways to get power to a collection of custom electronics, but it would be legal.