FRC shifting gears

[first_newbie]

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

[arc25565]

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

[R.C.]

Originally Posted by first_newbie

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

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

[asid61]

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

[EricH]

Originally Posted by asid61

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

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...

[jkelleyrtp]

Originally Posted by EricH

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).

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.

[EricH]

Originally Posted by jkelleyrtp

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.

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.

[mrnoble]

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!

[IndySam]

Originally Posted by jkelleyrtp

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.

"It's a cylinder, not a piston"

Brought to you by the IACNAP campaign.

[jkelleyrtp]

Originally Posted by EricH

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.

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.

[IndySam]

Originally Posted by jkelleyrtp

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.

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.

[GeeTwo]

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.

[Lil' Lavery]

Originally Posted by IndySam

"It's a cylinder, not a piston"

Brought to you by the IACNAP campaign.

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.

[Peyton Yeung]

Originally Posted by jkelleyrtp

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.

For video of it in action check this out.

[Tristan Lall]

Originally Posted by EricH

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.

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.)