FRC shifting gears
 

What do teams use to shift gears on gear boxes. Other motors? pneumatics?

Re: FRC shifting gears
 

Our team uses pancake Pneumatic cylinders from vex pro. They work quite well, allowing the robot to shift fast and reliably but require a pneumatic system. They can be found here: http://www.vexrobotics.com/217-2778.html

Re: FRC shifting gears
 

This would be a great question to use the search tool here on cd. There are quite a few threads about this subject.

Re: FRC shifting gears
 

Pneumatic cylinders usually, and in the old days I believe servos were more common than they are now.

Re: FRC shifting gears
 

Other way around, actually. FRC-legal servos are WEAK. I'd tell you young'uns when my team tried that, but I'd feel really old... and we went with pneumatics because of the servo response (and AM had a handy conversion kit for their Gen2 Shifter).

Did you know that before 2005, every team got two shifting gearboxes in the KOP?*

The thing is that most shifting gearboxes take force to shift. Servos have a hard time providing enough force to actually shift. Ball-shifters, I think are the exception for that, and a 3-speed ballshifter could really use a servo's "infinite" positioning, but as a general rule a short-throw small-bore cylinder per gearbox (and per gear change in the gearbox) say about a 1" throw 3/4" diameter unit in the old days, is by far preferable. Pancake cylinders are more common now because they're smaller, lighter, and don't take as much air. Servos are sluggish, and tend to need to be ganged together to shift. Ain't worth it.

You could also use an electrical solenoid actuator, but the power limits on those are even more restrictive than on servos.


*Two drill motor transmissions, to go with the drill motors generally used for drive. Shifting took a little machining, creativity, and luck during matches, but it was present. Before my time the full drill was included...

Re: FRC shifting gears
 

What kind of force is needed? I saw a supershifter demo with a servo that put out around 9 lbs but it was no where near as snappy as the pistons.

Re: FRC shifting gears
 

9 lbf is not a legal FRC servo. Unless it's insanely slow... servos are only 4W in FRC, and I find it very difficult to comprehend a 9 lb force out of a 4W servo. Also, factor in the load of a moving drivetrain.

60 psi on a 3/4" diameter cross-section seems to do the trick nicely.

Re: FRC shifting gears
 

I just want to say how glad I am that First Newbie has been asking these questions. You'll go far by approaching problems this way. Way to go!

Re: FRC shifting gears
 

"It's a cylinder, not a piston"

Brought to you by the IACNAP campaign.

Re: FRC shifting gears
 

Here is the shifter in question: http://www.andymark.com/product-p/am-2297.htm

Doesn't look like people like it very much, and I don't see a power rating on it.

Re: FRC shifting gears
 

If you call the good folks at AndyMark they will recommend you shift with air. FIRST legal servos (as of previous years rules) will have great difficulty shifting under load. I have seen teams use window motors to shift successfully but nothing beats the instant snap of a 3/4" cylinder.

You can get a lot of shifts out of a couple filled tanks.

Re: FRC shifting gears
 

Most commonly pneumatics, though a few use servos, especially if the robot will not have any other pneumatic systems. AndyMark and VexPro shifters have pneumatic parts or kits referenced from their web pages, and AM also has servo kits. Due to the limits of servos allowed by recent FRC rules, servos do not provide as much force or speed in shifting, making pneumatics the favored method.

Re: FRC shifting gears
 

While you're correct that devices like these are pneumatic cylinders, the portion of the cylinder applying a force to shift gears would be a piston. What he said is not incorrect.

Re: FRC shifting gears
 

For video of it in action check this out.

Re: FRC shifting gears
 

They're not even 4 W. (Servo manufacturers who publish ratings based on free speed × stall torque are falsifying or don't understand the power output of a DC brush motor.)

Re: FRC shifting gears
 

Just because he isn't incorrect doesn't mean that he's right. This is a great opportunity to stress the proper terminology for the assembly, and not use the term for a single component within.

Just like I don't claim to drive my engine up to the store... truck is a lot more appropriate.

Re: FRC shifting gears
 

Actually the part applying the force is a rod or shaft. The rod is attached to a piston.

Re: FRC shifting gears
 

With the update to the servo rules this season, is there any change in the viability of using a servo to shift? Thinking of using a SonicShifter as a winch with about 20 lbs of force from surgical tubing when retracted. Don't know if it would be possible to shift with a 10-12W servo in that case.

Would appreciate help. Thanks.

P.S. For those unaware, servos are now limited to the current put out by the 6V rail on the RoboRio instead of a strict Watt requirement as in previous years.

Re: FRC shifting gears
 

This "IACNAP Campaign" is pretty annoying.

Linguistically, language evolves and usage is king, so what you want words to mean (and/or what you were taught that they mean, and/or what they originally meant (assuming you can even chase down the etymology to verify)) has no bearing whatsoever on what they currently mean. There is value in specificity, but there's also value in not "correcting" people when they're using terminology understood by everyone in the conversation.

To whit, McMaster-Carr redirects searches for "pneumatic pistons" to their catalog page for "pneumatic cylinders."

Re: FRC shifting gears
 

I believe I saw in the Q&A that automotive motors like window motors but more importantly door lock actuators are legal. A door lock actuator could be a dandy device for shifting.

Re: FRC shifting gears
 

Couldn't be said the part applying the force is the air? :) Clearly you don't have a force until you start having a differential pressure.

Re: FRC shifting gears
 

That is because McMaster-Carr is more interested in selling stuff that what you call it. They should get an award for the best web based catalog ever.

Or the difference between an engineer and smart engineer.

Re: FRC shifting gears
 

The piston rod is transferring force from the piston head to the shifting mechanism.

Re: FRC shifting gears
 

I like that the actuation is linear in door lock motors but from the specs that I've seen (hard to find specs on them for some reason) it looks like they won't be enough. Maybe I haven't looked hard enough but the most I've found was capable of 8lbs of force... :/

Re: FRC shifting gears
 

8 pounds is quite a bit of force. I'll bet it's good enough as long as you weren't shifting under full load. If your robot didn't have a pneumatics system for other things, it would be a shame to pay that pneumatics weight tax just for those little cylinders.

This one does 10 pounds.

Re: FRC shifting gears
 

By the way, here's the Q&A that makes door lock actuators legal for the first time ever:

642 Q. Does an actuator with an included motor sold as a "door lock actuator" meet the definition of "Select Automotive Motors" per R29 (sample: http://www.amazon.com/dp/B0088YE6YQ/)?

A. Yes. As per the answer to Q626 , the intent of "Select Automotive Motors" is to limit the selection criteria of automotive motors to those specifically listed in the parenthesis that immediately follows. "Door" motors are listed, and a motor sold as a "Door Lock Actuator" does fall under that category.

Re: FRC shifting gears
 

Our team chose to use servos with the Andymark sonic shifters however now we are looking into using pneumatic cylinders, however we'd also like to avoid adding another system if possible. Has anyone successfully or otherwise used door lock actuators such as this to shift?

Re: FRC shifting gears
 

Hands down pneumatics, you can not beat the snappy action of a pneumatic cylinder in this application.

Re: FRC shifting gears
 

This might be the first year such automotive "door motor" devices are legal. You're breaking new ground here. I think it's a great idea, and if you make it work well you'll probably want to talk to AndyMark about how you mounted things.

I second the pancake pneumatic cylinder from Vexpro. We use it with the 2 CIM ball shifter and it works great.

Re: FRC shifting gears
 

Has anyone ever attempted to use multiple servos to actuate a single shifter? Seems like it would be the logical thing to try given the option to use unlimited numbers of servos and their relative low weight (especially when considering the weight of adding an entire pneumatics system for a single function).

That said, that door lock actuator is intriguing as well. My team is planing on using pneumatics for actuating our ball shifters this year, but those actuators might be something worth trying out too.