Linear Actuators

[Julian Gabriel]

I have noticed a lot of discussion and I personally have had a number of discussions on other options for pneumatics. Often times it seems to me it would be beneficial to avoid the extra weight with a compressor, air tanks, and other peripherals on a robot when something could be done with a linear actuator.

The largest thing that comes up is that they are slow, but they are accurate. I find them to be an interesting component that FIRST should allow in next years game as an option for teams who want to go without pneumatics, or for other types of systems.

I know there are converters that could turn a regular motor into a linear actuator, and there are other work around solutions, but do you think FIRST should allow a dedicated linear actuator to be used during the 2015 season? Would your team find it useful? What would you use it for?

[Jon Stratis]

The term "Linear Actuator" is a little vague... there are many types of linear actuators. All the term means is that it's something that creates motion in a straight line. It's something teams do quite frequently with cams or winches. Most commonly available linear actuators are really just motors connected to a lead screw... they would require some disassembly and replacement of the motor, but could be made to work.

I would guess, however, that you're thinking more along the lines of an electric solenoid actuator, which have been legal for a couple of years.

Electrical solenoid actuators, no greater than 1 in. stroke and rated electrical input power no greater than 10 watts (W) continuous duty at 12 volts (VDC)

If you had a specific product to link to, you could probably get better discussion over what you want to discuss.

[Julian Gabriel]

Originally Posted by Jon Stratis

The term "Linear Actuator" is a little vague... there are many types of linear actuators. All the term means is that it's something that creates motion in a straight line. It's something teams do quite frequently with cams or winches. Most commonly available linear actuators are really just motors connected to a lead screw... they would require some disassembly and replacement of the motor, but could be made to work.

I would guess, however, that you're thinking more along the lines of an electric solenoid actuator, which have been legal for a couple of years.



If you had a specific product to link to, you could probably get better discussion over what you want to discuss.

Sorry for not being specific. I had been talking about electric lead screw acutators. Here's a quick example of the kind that I am thinking of.
http://www.bosch-ibusiness.com/boaae...%20Spindle/357
When talking about changing angles on our robot from 2013 this came up as an option. It would be able to change the position of the heavy shooter while being very precise. Also, it could have pulled shooter springs on a 2014 robot to varying tensions and differant shots. Do you think it could come in handy in similar ways in the future of First?

[Jon Stratis]

All that is is a motor attached to a gear box. The form of the motor for that particular product doesn't easily match anything that's legal, but I'm sure with a little searching you could find one that utilizes a 500-series motor and swap out the motor for an RS-550. Doing so would make it perfectly legal, similar to all of the teams over the years that have taken a shop vac, swapped out the motor, and used it as a suction device on their robots. The only thing that makes it illegal is the model of motor that's attached to it.

[adciv]

I think it woudl be useful. I've seen some teams try to use them before I told them it wasn't a legal motor. I think the easiest thing (for now) would be a piece of hardware that mounts to a standard CIM or banebot motor. Provide built in limit switches to attach to the control system/motor controller and you're all set.

[pfreivald]

They've been legal for a long time, and they're not hard to build or use. They are, however, slow as death.

We sped ours up from this initial test, and it was still far too slow, and we'd have been better off going with pneumatics.... The fine adjustment ability was really cool (and led to the first successful autonomous scoring our team had ever done--and it was killer consistent), but massive overkill for the game.

https://www.youtube.com/watch?v=gTLMkUmhU2Y

[JohnFogarty]

I think an allowed COTS Linear actuator (or one we get in the KOP) would be very good for teams as they could use them to expand designs a little. (Expand designs they wouldn't have thought of otherwise.)

Of course there can still be custom options that are better for achieving a particular design goal, but something like those motors would not be a bad thing.

More than likely if a game called for fine angle adjustment like 2013 did I would consider a linear actuator in a design like that. The fine angle adjustment of my shooter would allow me more versatility in shooting positions around the pyramid. Granted it was proven that such angular adjustment was not needed to be successful, my former team attempted to use a custom 2 bar linkage for angle adjustment and it didn't quite work, or package as well as I wish it would have.

[pfreivald]

Originally Posted by JohnFogarty

I think an allowed COTS Linear actuator (or one we get in the KOP) would be very good for teams as they could use them to expand designs a little. (Expand designs they wouldn't have thought of otherwise.)

We've gotten multiple-start screws and nuts in the kit for years and years.

[JohnFogarty]

Originally Posted by pfreivald

We've gotten multiple-start screws and nuts in the kit for years and years.

You might be remembering some kit in the past. I know that my old team had some lying around, but I'm not going to look up the kits that I got when I was on 1102. Since my rookie season mentoring 4901 has ended I can soundly say, since I took part in receiving the kit this year, that the 2014 KOP did not have one.

Source: http://www.usfirst.org/roboticsprogr...c/kit-of-parts

http://www.usfirst.org/sites/default...e_2014.1.7.pdf

http://www.usfirst.org/sites/default...e_2014.1.4.pdf

[JALV]

Here's a differant question: Do we like the user interface of this new completed assembly better than having to put the motor, gear box and lead screw together seperatly?

I think that the motors in the included link are well packaged and could be easier and quicker to include in a robot design than to put the whole system together as a custom set up. This could open the door for newer teams to use a linear acuator that wouldn't have considared it before.

[AllenGregoryIV]

Originally Posted by JohnFogarty

You might be remembering some kit in the past. I know that my old team had some lying around, but I'm not going to look up the kits that I got when I was on 1102. Since my rookie season mentoring 4901 has ended I can soundly say, since I took part in receiving the kit this year, that the 2014 KOP did not have one.

Source: http://www.usfirst.org/roboticsprogr...c/kit-of-parts

http://www.usfirst.org/sites/default...e_2014.1.7.pdf

http://www.usfirst.org/sites/default...e_2014.1.4.pdf

They moved to FIRST Choice, I think we got 4 or 5 of them this season.

[JohnFogarty]

Originally Posted by AllenGregoryIV

They moved to FIRST Choice, I think we got 4 or 5 of them this season.

Ah. That would be it.

http://firstchoicebyandymark.com/en/fc14-095

Still, the point remains. I think some teams would benefit from a complete module as opposed to a lead screw kit.

[pfreivald]

Originally Posted by JohnFogarty

Still, the point remains. I think some teams would benefit from a complete module as opposed to a lead screw kit.

I think more teams would benefit from a lead screw and nut and having to figure out just how they're going to make their own module!

[Michael Hill]

FYI, you are allowed to use electric solenoids <= 1" stroke

[Jon Stratis]

I think those teams that would most benefit from having a module provided are those who don't have the resources to create it from the individual parts. Lets also keep in mind that a single module won't fit all uses - you have questions of speed, force, and distance to take into consideration... those variables are going to be very specific to the application at hand, and could easily drive those teams with abundant resources to create their own.

So why don't we see more of them? For one, there are design tradeoffs with going with this approach over other options. Which option is best entirely depends on the weight the team gives to the tradeoffs. But perhaps more importantly, there is probably a lack of inspiration towards this mechanism. We are all familiar with springs and motors, wheels and pulleys, grabbers and elevators. But you don't really see or interact with lead screws very often, and it's not something that's already prevalent in FRC... all that combines to make it something that doesn't really come to mind when designing a robot. I know the only times my team has talked about it was many years ago when we prototyped a scissors lift, driven by a lead screw, and when we got a box of them donated (by a wife who wanted them out of her garage, I think... I'm not sure if she even told her husband she was donating his gearboxes!). It's just something that hasn't come up in discussion, and something we don't have much experience with. For that reason, having one in hand in the KoP may provide the inspiration for a team to go in a new direction.