COTS Shifter Comparison Question

[asid61]

Originally Posted by Paul T.

whats the point of shifting? your limited to the traction of the wheels, your not going to trip the breaker at any reasonable speed. It'll just slip. (try to stay away from mecanum, they tend to be a disadvantage if any team against you has a decent drive train. you've never seen a mecanum robot on einstein.

+1, although I think the reason no mecanums are on einstein is partially because of their very limited usage and availability. We'll see mecanums on einstein in several years probably with Vex mecanums and other suppliers that might come around.

Anyway, I like the WCP shifters because they are all CNC'd and nice and hold 3 cims without problem. The Vex ballshifters are nice, but to me they don't offer as much the WCP shifters do due to weight and size. However, on a budget I would take Vex every time.
If 192 ever sells their gearboxes I would jump on those like nobody. Those weigh half as much as a WCP equivalent.

[cbale2000]

Originally Posted by TheHolyHades1

1. Does anyone know if more COTS solutions exist? It seems each of the major FRC parts suppliers has their own, and I think we've covered all of the major suppliers.

There are certainly other COTS solutions to two speed gearboxes out there, but none I've ever found that are nearly as well tailored for FIRST applications.

Originally Posted by TheHolyHades1

2. How do the gearboxes compare to each other in terms of durability, ease of use, ease to modify/change gear ratio and motors, shift ability, shift speed, ease to mount, etc? We're a relatively low budget team and currently don't have the budget to do testing with all of the various designs.

We've used Andymark Super Shifters in past years, this year we went with a VexPro 3CIM ball shifter and were very happy with it. We also purchased a pair of 2CIM ball shifters but did not use them.

Here's a few things we observed from our 3CIM Ball shifters (This will probably look pretty similar to Joseph Smith's response above)...

Pros

• Surprisingly lightweight (until you add 3 CIM motors of course)
• Fairly easy to assemble, but not as easy as the 2CIM Ball shifter
• Very durable, we took our shifters apart after our 2nd event to switch ratios, and the gears all looked like new.
• Shifted without issue using the low profile pancake cylinders we got with them.
• Shifting is virtually instantaneous and can (usually) be done while stopped, in addition to while moving.
• Changing gear ratios is really easy if you're not also changing the shift spread since it only requires changing out the 3rd stage.

Cons

• Changing the shift spread requires removing the tiny C-clips for the shifter coupling in order to get the ball gears out which is a HUGE pain. Other than that though the process was fairly simple.
• We ended up having to create custom spacers to be able to face mount the gearbox with the 3rd stage and have it secured in more than 2 spots. Not a big deal but it would have been nice if something were included with the 3rd stage (or could be purchased) to accommodate this.
• Assembly instructions could have been a bit clearer in places

For comparison, here's some things we've found out about Andymark Super Shifters we've used in the past...

Pros

• Easy to mount
• Decent variety of available ratios (though the Sonic Shifter has far more)
• Completely enclosed gears (No external 3rd stage)
• Easy to assemble

Cons

• The servo shifting doesn't work reliably, don't even try.
• Steel gears are heavy, but the lighter aluminum gears don't hold up nearly as well.
• Parts of the assembly seem unnecessarily heavy (The spacer/cover piece in particular).
• More expensive than its VexPro 2 motor counterpart.
• Slightly slower to shift than a ball shifter

And finally, even though we did not use our 2CIM Ball Shifters on our robot, we did note the following:

• They're the cheapest, by far of all the 2-speed gearboxes in common use in FIRST
• They're very easy to assemble (from the time we opened the boxes we had them both assembled in less than 20 minutes).
• They're very, very lightweight.
• They have a very small profile

Beyond that, I would venture to guess their performance characteristics are very similar to the 3CIM ball shifters.

Originally Posted by TheHolyHades1

3. Which one would you recommend (doesn't have to be from the list)?

I've honestly been quite impressed with the VexPro gearboxes this year, I'd personally recommend either of their ball shifters.

Originally Posted by TheHolyHades1

4. Overall opinion on shifters?

Honestly it depends on the game. Some years there have been games that did not require a shifter at all (2009 comes to mind just to name one), but years like this year where you have a wide open field and a need to cross it quickly but also be able to play defense, a shifter is absolutely essential. The exception to this is if you're using a drive system built for maneuverability over pushing power (like using all omni wheels for instance), in that case a simple low reduction single speed would probably work fine.

[TheHolyHades1]

Originally Posted by cbale2000

There are certainly other COTS solutions to two speed gearboxes out there, but none I've ever found that are nearly as well tailored for FIRST applications.



We've used Andymark Super Shifters in past years, this year we went with a VexPro 3CIM ball shifter and were very happy with it. We also purchased a pair of 2CIM ball shifters but did not use them.

Here's a few things we observed from our 3CIM Ball shifters (This will probably look pretty similar to Joseph Smith's response above)...

Pros

• Surprisingly lightweight (until you add 3 CIM motors of course)
• Fairly easy to assemble, but not as easy as the 2CIM Ball shifter
• Very durable, we took our shifters apart after our 2nd event to switch ratios, and the gears all looked like new.
• Shifted without issue using the low profile pancake cylinders we got with them.
• Shifting is virtually instantaneous and can (usually) be done while stopped or moving slow.
• Changing gear ratios is really easy if you're not also changing the shift spread since it only requires changing out the 3rd stage.

...

Thanks for the detailed comparison. One question though; I was under the impression that the shifters can switch while moving (i.e. at the top speed of low gear)? You've said that it can be done while stopped or moving slowly; does this mean that you can't shift at speed?

[cbale2000]

Originally Posted by TheHolyHades1

Thanks for the detailed comparison. One question though; I was under the impression that the shifters can switch while moving (i.e. at the top speed of low gear)? You've said that it can be done while stopped or moving slowly; does this mean that you can't shift at speed?

Sorry, I should have been more clear, as far as I know all shifters can shift at speed, the benefit of the ball shifters that we found is that (in our experience) they can almost always shift while stopped in addition to at speed (think of it as a bonus feature).

This is a result of the difference between a ball shifter and a dog-gear based shifter, a "dog" must be lined up exactly with the holes in the gear in order to shift (and in the case of AM shifters, there isn't a lot of slack in the fit). By comparison, a ball shifter can "roll" into the notches in the ball gears much more easily and at a larger variety of angles relative to the gear, this allows for the shifter to work except in the rare occasion the ball lands on the "flat" between the notches.


Now, in most situations, you wouldn't notice the difference, especially when using pneumatics for shifting, since as soon as you accelerate from stop, the gears will usually engage in less than a second. It can, however, make a difference if for some reason you have an autonomous mode that includes a gear shift in it, especially prior to movement, since if one of the shifters has a longer shift delay than the other it can cause inconsistency in the autonomous.

[TheHolyHades1]

Originally Posted by cbale2000

Sorry, I should have been more clear, as far as I know all shifters can shift at speed, the benefit of the ball shifters that we found is that (in our experience) they can almost always shift while stopped in addition to at speed (think of it as a bonus feature).

This is a result of the difference between a ball shifter and a dog-gear based shifter, a "dog" must be lined up exactly with the holes in the gear in order to shift (and in the case of AM shifters, there isn't a lot of slack in the fit). By comparison, a ball shifter can "roll" into the notches in the ball gears much more easily and at a larger variety of angles relative to the gear, this allows for the shifter to work except in the rare occasion the ball lands on the "flat" between the notches.


Now, in most situations, you wouldn't notice the difference, especially when using pneumatics for shifting, since as soon as you accelerate from stop, the gears will usually engage in less than a second. It can, however, make a difference if for some reason you have an autonomous mode that includes a gear shift in it, especially prior to movement, since if one of the shifters has a longer shift delay than the other it can cause inconsistency in the autonomous.

Gotcha. That makes sense, thank you.

[RonnieS]

Maybe vex pro will come out with a good servo shifting method?

[cbale2000]

Originally Posted by Ronnie314

Maybe vex pro will come out with a good servo shifting method?

Honestly, the ball shifter requires a lot less force to shift than a dog shifter does so it might be plausible, but I still think I'd have to see one working to believe it.

Our team toyed around with the idea of using linear actuators (Electrical solenoid actuators) to shift this year, hoping we could avoid using pneumatics. The idea never got beyond the concept stage (and electrical solenoid actuators that comply with the rules are apparently quite hard to find).