Linear Servo Actuator Legality

[Retired Starman]

These are called "Linear Actuator", not "Servo" by the manufacturer, and that is what they look like to me. The fact that they run off a pwm voltage doesn't make them a servo.

I think you might want to do an official FIRST Q & A to get a legal opinion on these before making a critical design decision where your robot depends on one of these to work.

[engunneer]

wow, that's a tough one. as an RI, I'd bring this directly to the LRI at my event. I wouldn't call this a solenoid actuator,since it's not a moving rod in a magnetic coil, which is the typical solenoid (the type limited to 1" travel).

The question comes down to this being a "PWM COTS servo". Knowing full well that past rules don't apply, i do take guidance on them for predicting the GDC response. For reference 2012 and 2014 both discussed

COTS servos with a maximum power rating of 4W each at 6VDC
Per the Servo Industry,
Servo Max Power Rating = (Stall Torque) X (No Load Speed)

This is 100% a Q&A needed question. I suspect/predict that these are not considered PWM COTS Servos, but it's worth asking.

[gpetilli]

Originally Posted by engunneer

wow, that's a tough one. as an RI, I'd bring this directly to the LRI at my event. I wouldn't call this a solenoid actuator,since it's not a moving rod in a magnetic coil, which is the typical solenoid (the type limited to 1" travel).

The question comes down to this being a "PWM COTS servo". Knowing full well that past rules don't apply, i do take guidance on them for predicting the GDC response. For reference 2012 and 2014 both discussed

This is 100% a Q&A needed question. I suspect/predict that these are not considered PWM COTS Servos, but it's worth asking.

I respectfully disagree. It clearly is not a solenoid, so that thread is completely irrelevant. It is very much like the "DART" but that is legal with legal CIM motors. The rules in general attempt to limit output power for safety concerns. This year they seem to have gone from "4W" to warn of the roboRIO practical limit of 12.4W total for all PWM servos (blue box R29). Since the output power is safely limited by the PWM power of the roboRIO, I personally would rule it legal - obviously would need approval from my LRI.

They did ask the GDC question and got the response "In general, if a part is sold by a VENDOR as a "servo" it should be regarded a servo for the purposes of assessing rules compliance." From the VENDOR "The L12-R series of linear servos operate as a direct replacement for standard rotary servos. They use the same standard 3 wire connector, ground power and control." Legal.

[engunneer]

I hadn't noticed this one in my Q&A reading - better read more closely.

I'm not sure what you are disagreeing with. I said it wasn't a solenoid, and I said it was a close call and needed a Q&A to get it right. My suspicion turned out to be wrong, and I was really on the edge. I though they might change the wording to try to define a servo, which would be hard. The ruling as given in Q&A actually does a good job of not trying to over-define things, it just wasn't what I was expecting.

[Jon Stratis]

The key with something like this is to bring the manufacturer/vendor paperwork which clearly identifies the part as a servo. You do that, and the LRI should then accept that it's a servo and apply appropriate rules to it from that point forward.

[gpetilli]

Originally Posted by engunneer

I'm not sure what you are disagreeing with. I said it wasn't a solenoid, and I said it was a close call and needed a Q&A to get it right.

I'm sorry, the not a solenoid comment was aimed at a previous poster that seemed to imply all linear actuators are solenoids.

Nearly everywhere in the rules, when they talk about servos they also mention PWM and powered by the roboRIO. I think most LRI will rule it legal, but absolutely bring datasheets; always good to make the inspector's job easier.