Re: FRC Blog - 2016 Motor Controllers
 

Linked here.

Re: FRC Blog - 2016 Motor Controllers
 

A sales pitch is a broad term. I am guessing that your thinking of an elevator pitch or any other short form pitch. I was thinking more of the full blown sales presentation, where you have all the details on the table to discuss.

I agree to your point, a pitch without addressing supply chain and donations would make a poor pitch.

Re: FRC Blog - 2016 Motor Controllers
 

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

Re: FRC Blog - 2016 Motor Controllers
 

Everything on FIRST Choice is legal by definition. (or maybe not :-) the season rules, rule )
The 775 motors on the PG71's are not Banebot motors which are the only ones that have been discontinued and thus made illegal.

Re: FRC Blog - 2016 Motor Controllers
 

The blog post said that the Banebots 775 would not be legal. It did not comment on the illegality of the AndyMark 775. In the past FIRST Choice components have always been FIRST legal.

Re: FRC Blog - 2016 Motor Controllers
 

So that digital multimeter is a legal robot part! :)

Re: FRC Blog - 2016 Motor Controllers
 

Re: FRC Blog - 2016 Motor Controllers
 

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

Re: FRC Blog - 2016 Motor Controllers
 

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

Re: FRC Blog - 2016 Motor Controllers
 

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

Re: FRC Blog - 2016 Motor Controllers
 

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

Re: FRC Blog - 2016 Motor Controllers
 

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:

Re: FRC Blog - 2016 Motor Controllers
 

Only putting a battery in it is illegal on a robot :)

Re: FRC Blog - 2016 Motor Controllers
 

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

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.

Re: FRC Blog - 2016 Motor Controllers
 

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

Re: FRC Blog - 2016 Motor Controllers
 

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

Re: FRC Blog - 2016 Motor Controllers
 

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

Re: FRC Blog - 2016 Motor Controllers
 

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.

Re: FRC Blog - 2016 Motor Controllers
 

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.

Re: FRC Blog - 2016 Motor Controllers
 

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.

Re: FRC Blog - 2016 Motor Controllers
 

With everything I've been reading about brown outs, I think we're just going to go back to the tried and true '4 CIMs on your drive' depending on the game. It just isn't worth the risk of being dead on the field in a match.

Re: FRC Blog - 2016 Motor Controllers
 

Great paper! I found the read very interesting, with very informative, useful results to help teams pick the right motor controller.

A great addition to this experiment would also have been to include temperature measurements on the motor controllers after 30 seconds, 1 minute etc. I would also love to see results for the older Talon SR and JAG motor controllers since many teams still use these. One final addition would be to test several motor controllers of the same type to get an idea of the variation between controllers (is it 1% or 10% variation between controllers of the same type?).

My big takeaway from all this is that the SD540 is unnacceptable for use in FRC robots due to the brown-out issue. In addition, with it's high output resistance, it would no doubt, would get very, very warm in a stall condition. You can estimate the power that is turned into heat in the output devices of the SD540 to be nearly 50 Watts in the resistive load test 3, at 11.20 volts. With a CIM motor, the SD540 would be dissipating ~100 watts of energy as heat. I wonder how long it takes to melt (can someone test and post pictures please)?

It looks like the SPARK is a very good controller, for the price. It performs nearly as well as the two pricier alternatives. The downside for the SPARK is the form-factor.

Re: FRC Blog - 2016 Motor Controllers
 

Very interesting, although it would be nice if someone could do these tests with multiple of each controller (in case of either defective units or just generally varying units). In particular, I wouldn't want to judge the SD540 too much without confirming the results on multiple units.

Re: FRC Blog - 2016 Motor Controllers
 

It would be awesome if the Talon SRX gets a firmware update that lets it do this (current limiting). It can already do ramping.

Re: FRC Blog - 2016 Motor Controllers
 

Yup Yup.

I'd love this for FRC, and a few non-FRC applications I use Talons for.

Re: FRC Blog - 2016 Motor Controllers
 

A continuous sensor option would be nice too. Similar to the continuous sensor option in the WPILib PID Controllers.

Re: FRC Blog - 2016 Motor Controllers
 

Even if its not built in, since we can access all the current and speed data, wouldn't we be able to do this on the RoboRIO? It wouldn't be anywhere close to as fast of a loop, but it should be good enough, right?

Re: FRC Blog - 2016 Motor Controllers
 

I haven't spent nearly enough time trying to track down the correct way to do this, but I would love to know what it is.

Re: FRC Blog - 2016 Motor Controllers
 

Hopefully someone knows the answer to this.

If you're just running 4 Talon SRXs on the CANbus, nothing else and you're in a separate thread running your drive, what's the fastest you can run that loop and still get a fresh current measurement over CAN for each one?

Same question, but w/ PWM speed controllers and reading current over PDP?

Re: FRC Blog - 2016 Motor Controllers
 

I know that the PDP only reads new currents every 25ms, or at least it was last season. Don't know if that changed. In addition, PWM updates at max every 5ms, so you couldn't go any faster then that even if you had a faster sensor.

The default status update period for Talons is 10ms. However I know that you can set it even faster. I bet you could do 5ms easily, and could probably push about every 2ms if you are careful with your CAN usage.

I would bet that is plenty fast enough, as your mechanical system probably won't react much quicker then that.

Re: FRC Blog - 2016 Motor Controllers
 

sastoller : I think you need to brush up your Knowledge of "Switch Mode Operation" You cannot calculate the resistance just like R= V/I, in today's switching technology used everywhere. If you apply your theory to your cell phone charger your charger should be dissipating ridiculously large amount (120V-5V) * 1amp = 115W (120V input, 5 V output and 1 amp current) but is is not doing that. All it means is that it is not 100% ON but around 95% ON.

Re: FRC Blog - 2016 Motor Controllers
 

Mike,

It is not brownout it is Seafty Feature, documents above says lockout due to Seafty feature,
I agree with this if you are going down to 8.2 V ( or even 10V ) you are seriously killing your battery.
Lead Acid battery do not like deep discharge, no matter what manufacturers say(deep discharge or what not), but they will not be same again if you discharge them down to 10.8V (1.8V per cell)