FRC shifting gears

[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.

[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.

[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.)

[brianbond]

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

[Alan Anderson]

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.

[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.

[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.

[MrBasse]

Originally Posted by Lil' Lavery

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.

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.

[IndySam]

Originally Posted by Lil' Lavery

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.

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