Linear Servo Actuator Legality

[graywhaler]

We're looking for a linear actuator to use and found these: Firgelli Technologies L16 Actuator 50mm 63:1 6V RC Control. They are motor driven linear servo actuator. Looking at R29, I think they will be allowed as a PWM COTS Servo. While they have a greater stroke than 1", they are not solenoid driven, so I think they are not prohibited. Any help would be greatly appreciated!

[Mark McLeod]

They look like a COTS servo (R29).
They run solely off of PWM (R54, R68).
They pull less power (650ma) than the PWM outputs can provide (2.2A) - (Blue box under R29)

I suggest bringing a spec sheet with you to show the robot inspectors.
CD opinions are not binding at competition.

[rich2202]

IMHO:

"Solenoid Actuator" - linear motion. Subject to 1" stroke maximum

PWM COTS Servos - Circular motion.

If I read the specs right, the Firgelli Technologies L16 Actuator 50mm 63:1 6V RC Control has a stroke of 98mm, or 3.85 inches, well beyond the 1" stroke maximum for solenoid actuators in R29.

[Sparky3D]

Originally Posted by Mark McLeod

They look like a COTS servo (R29).

Um, those don't look like any servo I've ever seen. They look like a small, dc motor powered linear actuator (the description even states they run off of a PMDC motor). Unless the motor in them is in the approved motor list, or you replace it with an approved motor; you will likely have a long conversation with your inspector about them. But as Mark said, opinions on CD are unofficial.

[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.

[Kevin Sevcik]

Originally Posted by Sparky3D

Um, those don't look like any servo I've ever seen. They look like a small, dc motor powered linear actuator (the description even states they run off of a PMDC motor). Unless the motor in them is in the approved motor list, or you replace it with an approved motor; you will likely have a long conversation with your inspector about them. But as Mark said, opinions on CD are unofficial.

You do realize that the "servo" you're more familiar with is a small DC motor powered rotational actuator with an integral controller that uses a PWM signal. The only difference I can see here is that these are linear actuators and they're not exclusively called "servos". Firgelli's L12 series apparently is called a micro linear servo. Would that make you happy?

Anyways, Q&A this immediately and we'll see how nit-picky the GDC is or isn't this week.

EDIT:
http://store.firgelli.com/RC_linear_servos_s/1853.htm

The L12-R, L16-R and PQ12-R series of linear servos for RC operate as a direct replacements for standard analog rotary servos. They use the same standard 3 wire connector, ground, power and signal. Firgelli Technologies has 18 models of affordable receiver ready RC linear servos to help you move your RC project!

These linear servos are approved by First Tech Challenge and are compatible with their allowed servo controllers
Part of a FIRST Team? Contact us about available discounts!

Looks like they're "servo" enough for FTC. Wonder if they're "servo" enough for FRC?

[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.