Shifting Gearboxes

[valkyrie2240]

My team is thinking about using shifting gearboxes this coming season. This is the first season we've really deviated from the kit chassis and kit gearboxes. Any advice about shifting gearboxes and/or gearboxes in general?

Shifting is a very powerful tool that is up to driver preference. Personally, I don't run a shifter unless my specific strategy requires a really low gear (~4 ft/s), or a really high gear (~19+ ft/s). A single speed 3-CIM gearbox at ~16 ft/s is my favorite setup to run because most of the time I really don't need shifting, and the extra acceleration and power from the extra motors makes the single speed just as powerful, and mathematically you gain the biggest benefit from the extra motors at that speed.

Just my $0.02.

[Gregor]

Searching around will find you a treasure trove of advantages, but here's a useful thread for disadvantages and look fors when shifting.

http://www.chiefdelphi.com/forums/sh...d.php?t=109959

Pay attention to the date of the thread. This was before teams had ever used ball shifters in an official FRC match, because they had been released after the 2012 season.

While most information in the thread is general and regards shifting in general, some posts are specific to AM super shifters, which where the COTs shifting gearbox of choice at that point in time.

[E Dawg]

We use double solenoids for shifting.

[AdamHeard]

Originally Posted by E Dawg

We use double solenoids for shifting.

Why not use singles? Doubles waste an extra relay output.

[Ether]

Originally Posted by Andrew Lawrence

...and mathematically you gain the biggest benefit from the extra motors at that speed.

Would you please clarify what you meant by that?

[Alan Anderson]

Originally Posted by AdamHeard

Why not use singles? Doubles waste an extra relay output.

Double solenoids let you maintain the gear selection when the robot is disabled. That can be important for autonomous mode, where you can choose in advance which gear to start in and not have a problem with the gear not being engaged at first.

[E Dawg]

Originally Posted by Alan Anderson

Double solenoids let you maintain the gear selection when the robot is disabled. That can be important for autonomous mode, where you can choose in advance which gear to start in and not have a problem with the gear not being engaged at first.

Exactly.

Of course, it works fine with a single solenoid, albeit less efficiently.

[R.C.]

Originally Posted by Alan Anderson

Double solenoids let you maintain the gear selection when the robot is disabled. That can be important for autonomous mode, where you can choose in advance which gear to start in and not have a problem with the gear not being engaged at first.

Why not just pick which way the cylinder defaults to with a single solenoid?

I dont see an advantage for a double solenoid in shifting.

-RC

[Alan Anderson]

Originally Posted by R.C.

Why not just pick which way the cylinder defaults to with a single solenoid?

You mean physically swap the pneumatic tubing if you want to start in the other gear? That'll reverse the gear selection for everything.

[AdamHeard]

Originally Posted by Alan Anderson

You mean physically swap the pneumatic tubing if you want to start in the other gear? That'll reverse the gear selection for everything.

Which you presumably need to do once per season...

[Alan Anderson]

Originally Posted by Alan Anderson

You mean physically swap the pneumatic tubing if you want to start in the other gear? That'll reverse the gear selection for everything.

Originally Posted by AdamHeard

Which you presumably need to do once per season...

Depending on the game, it could make sense to run some autonomous routines in high gear and others in low gear (2007 was one such game). That's swapping defaults potentially once per match. Requiring a physical reconfiguration of the pneumatics also removes the option of selecting the most appropriate routine at the last possible moment, since you don't want to be unplugging the tubing while the system is pressurized.

Another risk of using single solenoids for gear selection is the potential for a brief "disable" in the middle of driving. There are some things you don't want to change state when that happens, and I'd argue that the gear ratio is one of them. Our 2005 robot had a couple of near-tumbles when downshifting because of the high center of mass when carrying a game piece, before the drivers learned not to do that.

[AdamHeard]

Originally Posted by Alan Anderson

Depending on the game, it could make sense to run some autonomous routines in high gear and others in low gear (2007 was one such game). That's swapping defaults potentially once per match. Requiring a physical reconfiguration of the pneumatics also removes the option of selecting the most appropriate routine at the last possible moment, since you don't want to be unplugging the tubing while the system is pressurized.

Another risk of using single solenoids for gear selection is the potential for a brief "disable" in the middle of driving. There are some things you don't want to change state when that happens, and I'd argue that the gear ratio is one of them. Our 2005 robot had a couple of near-tumbles when downshifting because of the high center of mass when carrying a game piece, before the drivers learned not to do that.

Ah, I see your point there.

I'd argue in most games that's not necessary, and the single provides piece of mind in that the driveteam isn't responsible for setting/checking gear before each match.

As for the brief disable, we generally default ours to high gear.

Your comments are valid overall, but in the general case we'd stick with single. I do see the validity of your points now though.

[pmangels17]

We always use a double solenoid, and we also use plumb both shifters to one valve so they throw at the same time. Please remember to USE PNEUMATICS TO SHIFT. Servo shifting is pure garbage and wont work under the the slightest pressure against the side of a dog, such as when pushing.

We usually start in low gear, and use high gear when we want to go really fast.

We have never tried using ball shifters, but since we have familiarity with the dog shifting style used in AndyMark gearboxes, and it has proved reliable so far as a shifting method, that probably won't change. Dog shifting is proven and tested, but ball shifters have been generally well reviewed as well, though they may be harder to implement in a custom gearbox.

Originally Posted by Ether

Would you please clarify what you meant by that?

From JVN's Acceleration calculator, I've found a speed of around 16 ft/s gains the largest time loss to travel a set distance when using 6 motors instead of 4 (Shaves off about a half a second on average). As you get further from 16 ft/s in either direction, the time difference to travel a set distance between 6 motor drives and 4 motor drives gets closer and closer to 0.