FRC Blog - 2016 Motor Controllers

[Joe Johnson]

Originally Posted by AdamHeard

That's assuming you trust the banebots power rating. Many people suspect they were over rated performance wise.

I have designed a ton of applications with those 775 motors using the specs published by Banebots (Scorpion, Overclock's robot from last year, had 14 of those bad dads on her), I have never had a case where I said to myself, "those specs are messed up!" When we design our lift to raise 6 totes at 2ft per second, the lift raised 6 totes at 2ft per second.

Of course there is variation from motor to motor but nothing out of the normal manufacturing tolerances (typical for this style of motor is +/-15%).

If you knew what your were doing, those motors were amazing. More power than a Mini-CIM at less that half the weight and volume.

I will serious miss those motors.

Dr. Joe J.

[AdamHeard]

Originally Posted by Joe Johnson

I have designed a ton of applications with those 775 motors using the specs published by Banebots (Scorpion, Overclock's robot from last year, had 14 of those bad dads on her), I have never had a case where I said to myself, "those specs are messed up!" When we design our lift to raise 6 totes at 2ft per second, the lift raised 6 totes at 2ft per second.

Of course there is variation from motor to motor but nothing out of the normal manufacturing tolerances (typical for this style of motor is +/-15%).

If you knew what your were doing, those motors were amazing. More power than a Mini-CIM at less that half the weight and volume.

I will serious miss those motors.

Dr. Joe J.

The 550 is where I noticed performance differences. We never ran the 775s on anything critical so I'm unsure on them.

[Ari423]

I'm confused what the point of designing a motor controller for 60 amp continuous is if the largest breaker we are allowed to use is 40 amps. I understand the higher peak, but the I was under the impression that breakers would snap once you get above 40 amps for more than a few milliseconds. It would make sense if these were already being produced and are just now being approved for FRC, but the blog post makes it sound like they were developed specifically for FRC teams.

[Mike Marandola]

I guess that explains why there were so many 775s, 550s, and P60s available in FIRST Choice this year.

[Thad House]

Originally Posted by AdamHeard

The 550 is where I noticed performance differences. We never ran the 775s on anything critical so I'm unsure on them.

We've used lots of 775s and they were always fairly close to what we had calculated them to be. What made that motor so great was it was an 18v motor so it ran super cool even at stall because it was only 12v. That motor surely will be missed by many teams.

[AllenGregoryIV]

Originally Posted by Ari423

I'm confused what the point of designing a motor controller for 60 amp continuous is if the largest breaker we are allowed to use is 40 amps. I understand the higher peak, but the I was under the impression that breakers would snap once you get above 40 amps for more than a few milliseconds. It would make sense if these were already being produced and are just now being approved for FRC, but the blog post makes it sound like they were developed specifically for FRC teams.

Your millisecond estimate is the part that is incorrect. Here is the data sheet for the 40 amp snap action breaker. They can sometimes hold 200% over the rating for a maximum of almost 4 secs.

The current ratings on these types of breakers tell you when they won't trip, not when they will trip.

[Jared Russell]

Banebots 775s have always matched the advertised specs for us (modulo case shorting issues in 2011).

Banebots 550s have always provided substantially less torque than advertised for us.

[Aren Siekmeier]

Originally Posted by Ari423

I'm confused what the point of designing a motor controller for 60 amp continuous is if the largest breaker we are allowed to use is 40 amps. I understand the higher peak, but the I was under the impression that breakers would snap once you get above 40 amps for more than a few milliseconds. It would make sense if these were already being produced and are just now being approved for FRC, but the blog post makes it sound like they were developed specifically for FRC teams.

Check out the spec sheet for the 40A breakers in the kit. They can sustain 200% of their rating (80A) for over a second before tripping, and often do when the robot is accelerating. Edit: Allen got me

Originally Posted by Thad House

Yes they are, however they are nowhere close to the power provided by the banebot motors. The 9015 is 179W vs 253W, and the AM 775 is only 150W vs 273W. So there are similar size motors, but nowhere near similar power. That means if you want more then 250W in a motor you either need to double up motors, or go to a CIM, where there just sometimes isn't space.

Which is the Andymark 775 that's rated at 150W? I only see the 9015 (~179W) and the motors used in PG gearboxes, which are closer to 40W.

[cgmv123]

Originally Posted by Ari423

I'm confused what the point of designing a motor controller for 60 amp continuous is if the largest breaker we are allowed to use is 40 amps. I understand the higher peak, but the I was under the impression that breakers would snap once you get above 40 amps for more than a few milliseconds. It would make sense if these were already being produced and are just now being approved for FRC, but the blog post makes it sound like they were developed specifically for FRC teams.

Breakers exist to protect the wiring, not the device. Breakers can and will pass current in excess of the rated current. If you draw 80 amps, the 40 amp breakers used by FRC will not trip before 1 second passes.

For what it's worth, the Victor 888, Victor SP, Talon SR and Talon SRX are all also rated for 60A continuous. If I remember correctly, most of the components in the Talon SR are rated for 100 amps continuous. I think it's good that a device designed for use by high schoolers is rated for more than the expected conditions.

[Greg Needel]

Originally Posted by Ari423

I'm confused what the point of designing a motor controller for 60 amp continuous is if the largest breaker we are allowed to use is 40 amps. I understand the higher peak, but the I was under the impression that breakers would snap once you get above 40 amps for more than a few milliseconds. It would make sense if these were already being produced and are just now being approved for FRC, but the blog post makes it sound like they were developed specifically for FRC teams.

When someone wants to design a motor controller for FRC, FIRST will provide you a document with their required specifications. One of those requirements is 60 amp continuous operation.

While this may seem like over kill when you do have a 40amp breaker, a factor of safety is a very common thing for equipment like this. It is easy to under estimate the power of 40 amps because we are around it so much on robots but this amount of power density can be extremely dangerous if not done correctly. Back in the "old days" it was not uncommon to see a robot fire or two at a regional event.

We test our controllers to failure at 100amps, to make sure they are as solid and reliable as possible for teams.

[Scott Kozutsky]

Is anyone else excited about the new speed controllers? They're $45 and $50 respectively. This is an awesome thing for the vast majority of teams as it means you can execute your plans and make mistakes for cheaper. I'm still waiting for $20 speed controllers for the automotive motors. It's also really nice that teams can use the older motor controllers for the same reason.

[Knufire]

So many new motor controllers but no new relays?

[cgmv123]

Originally Posted by Knufire

So many new motor controllers but no new relays?

What do we need relays for anymore? (Note that Spikes are discontinued.) The pneumatic compressor runs through the PCM, and if you absolutely need relay-type control for something, programming a speed controller act like a relay is trivial.

[notmattlythgoe]

Originally Posted by cgmv123

What do we need relays for anymore? (Note that Spikes are discontinued.) The pneumatic compressor runs through the PCM, and if you absolutely need relay-type control for something, programming a speed controller act like a relay is trivial.

That, and there are only 4 relay ports on the rio now.

[Taylor]

Originally Posted by cgmv123

What do we need relays for anymore? (Note that Spikes are discontinued.) The pneumatic compressor runs through the PCM, and if you absolutely need relay-type control for something, programming a speed controller act like a relay is trivial.

Spikes are $10 cheaper than the least expensive motor controller, and most veteran teams have bunches of them.