What do teams use to shift gears on gear boxes. Other motors? pneumatics?
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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
This would be a great question to use the search tool here on cd. There are quite a few threads about this subject.
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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…
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.
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!
“It’s a cylinder, not a piston”
Brought to you by the IACNAP campaign.
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.
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.
While you’re correct that deviceslike theseare pneumatic cylinders, the portion of the cylinder applying a force to shift gears would be a piston. What he said is not incorrect.
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.)
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.
Actually the part applying the force is a rod or shaft. The rod is attached to a piston.
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.
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.”
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.